[ffmpeg.git] / doc / filters.texi

@chapter Filtering Introduction
@c man begin FILTERING INTRODUCTION

Filtering in FFmpeg is enabled through the libavfilter library.

In libavfilter, a filter can have multiple inputs and multiple
outputs.
To illustrate the sorts of things that are possible, we consider the
following filtergraph.

@example
input --> split ---------------------> overlay --> output
            |                             ^
            |                             |
            +-----> crop --> vflip -------+
@end example

This filtergraph splits the input stream in two streams, sends one
stream through the crop filter and the vflip filter before merging it
back with the other stream by overlaying it on top. You can use the
following command to achieve this:

@example
ffmpeg -i INPUT -vf "split [main][tmp]; [tmp] crop=iw:ih/2:0:0, vflip [flip]; [main][flip] overlay=0:H/2" OUTPUT
@end example

The result will be that in output the top half of the video is mirrored
onto the bottom half.

Filters in the same linear chain are separated by commas, and distinct
linear chains of filters are separated by semicolons. In our example,
@var{crop,vflip} are in one linear chain, @var{split} and
@var{overlay} are separately in another. The points where the linear
chains join are labelled by names enclosed in square brackets. In the
example, the split filter generates two outputs that are associated to
the labels @var{[main]} and @var{[tmp]}.

The stream sent to the second output of @var{split}, labelled as
@var{[tmp]}, is processed through the @var{crop} filter, which crops
away the lower half part of the video, and then vertically flipped. The
@var{overlay} filter takes in input the first unchanged output of the
split filter (which was labelled as @var{[main]}), and overlay on its
lower half the output generated by the @var{crop,vflip} filterchain.

Some filters take in input a list of parameters: they are specified
after the filter name and an equal sign, and are separated from each other
by a colon.

There exist so-called @var{source filters} that do not have an
audio/video input, and @var{sink filters} that will not have audio/video
output.

@c man end FILTERING INTRODUCTION

@chapter graph2dot
@c man begin GRAPH2DOT

The @file{graph2dot} program included in the FFmpeg @file{tools}
directory can be used to parse a filtergraph description and issue a
corresponding textual representation in the dot language.

Invoke the command:
@example
graph2dot -h
@end example

to see how to use @file{graph2dot}.

You can then pass the dot description to the @file{dot} program (from
the graphviz suite of programs) and obtain a graphical representation
of the filtergraph.

For example the sequence of commands:
@example
echo @var{GRAPH_DESCRIPTION} | \
tools/graph2dot -o graph.tmp && \
dot -Tpng graph.tmp -o graph.png && \
display graph.png
@end example

can be used to create and display an image representing the graph
described by the @var{GRAPH_DESCRIPTION} string. Note that this string must be
a complete self-contained graph, with its inputs and outputs explicitly defined.
For example if your command line is of the form:
@example
ffmpeg -i infile -vf scale=640:360 outfile
@end example
your @var{GRAPH_DESCRIPTION} string will need to be of the form:
@example
nullsrc,scale=640:360,nullsink
@end example
you may also need to set the @var{nullsrc} parameters and add a @var{format}
filter in order to simulate a specific input file.

@c man end GRAPH2DOT

@chapter Filtergraph description
@c man begin FILTERGRAPH DESCRIPTION

A filtergraph is a directed graph of connected filters. It can contain
cycles, and there can be multiple links between a pair of
filters. Each link has one input pad on one side connecting it to one
filter from which it takes its input, and one output pad on the other
side connecting it to the one filter accepting its output.

Each filter in a filtergraph is an instance of a filter class
registered in the application, which defines the features and the
number of input and output pads of the filter.

A filter with no input pads is called a "source", a filter with no
output pads is called a "sink".

@anchor{Filtergraph syntax}
@section Filtergraph syntax

A filtergraph can be represented using a textual representation, which is
recognized by the @option{-filter}/@option{-vf} and @option{-filter_complex}
options in @command{ffmpeg} and @option{-vf} in @command{ffplay}, and by the
@code{avfilter_graph_parse()}/@code{avfilter_graph_parse2()} function defined in
@file{libavfilter/avfilter.h}.

A filterchain consists of a sequence of connected filters, each one
connected to the previous one in the sequence. A filterchain is
represented by a list of ","-separated filter descriptions.

A filtergraph consists of a sequence of filterchains. A sequence of
filterchains is represented by a list of ";"-separated filterchain
descriptions.

A filter is represented by a string of the form:
[@var{in_link_1}]...[@var{in_link_N}]@var{filter_name}=@var{arguments}[@var{out_link_1}]...[@var{out_link_M}]

@var{filter_name} is the name of the filter class of which the
described filter is an instance of, and has to be the name of one of
the filter classes registered in the program.
The name of the filter class is optionally followed by a string
"=@var{arguments}".

@var{arguments} is a string which contains the parameters used to
initialize the filter instance. It may have one of the following forms:
@itemize

@item
A ':'-separated list of @var{key=value} pairs.

@item
A ':'-separated list of @var{value}. In this case, the keys are assumed to be
the option names in the order they are declared. E.g. the @code{fade} filter
declares three options in this order -- @option{type}, @option{start_frame} and
@option{nb_frames}. Then the parameter list @var{in:0:30} means that the value
@var{in} is assigned to the option @option{type}, @var{0} to
@option{start_frame} and @var{30} to @option{nb_frames}.

@item
A ':'-separated list of mixed direct @var{value} and long @var{key=value}
pairs. The direct @var{value} must precede the @var{key=value} pairs, and
follow the same constraints order of the previous point. The following
@var{key=value} pairs can be set in any preferred order.

@end itemize

If the option value itself is a list of items (e.g. the @code{format} filter
takes a list of pixel formats), the items in the list are usually separated by
'|'.

The list of arguments can be quoted using the character "'" as initial
and ending mark, and the character '\' for escaping the characters
within the quoted text; otherwise the argument string is considered
terminated when the next special character (belonging to the set
"[]=;,") is encountered.

The name and arguments of the filter are optionally preceded and
followed by a list of link labels.
A link label allows to name a link and associate it to a filter output
or input pad. The preceding labels @var{in_link_1}
... @var{in_link_N}, are associated to the filter input pads,
the following labels @var{out_link_1} ... @var{out_link_M}, are
associated to the output pads.

When two link labels with the same name are found in the
filtergraph, a link between the corresponding input and output pad is
created.

If an output pad is not labelled, it is linked by default to the first
unlabelled input pad of the next filter in the filterchain.
For example in the filterchain:
@example
nullsrc, split[L1], [L2]overlay, nullsink
@end example
the split filter instance has two output pads, and the overlay filter
instance two input pads. The first output pad of split is labelled
"L1", the first input pad of overlay is labelled "L2", and the second
output pad of split is linked to the second input pad of overlay,
which are both unlabelled.

In a complete filterchain all the unlabelled filter input and output
pads must be connected. A filtergraph is considered valid if all the
filter input and output pads of all the filterchains are connected.

Libavfilter will automatically insert scale filters where format
conversion is required. It is possible to specify swscale flags
for those automatically inserted scalers by prepending
@code{sws_flags=@var{flags};}
to the filtergraph description.

Follows a BNF description for the filtergraph syntax:
@example
@var{NAME}             ::= sequence of alphanumeric characters and '_'
@var{LINKLABEL}        ::= "[" @var{NAME} "]"
@var{LINKLABELS}       ::= @var{LINKLABEL} [@var{LINKLABELS}]
@var{FILTER_ARGUMENTS} ::= sequence of chars (eventually quoted)
@var{FILTER}           ::= [@var{LINKLABELS}] @var{NAME} ["=" @var{FILTER_ARGUMENTS}] [@var{LINKLABELS}]
@var{FILTERCHAIN}      ::= @var{FILTER} [,@var{FILTERCHAIN}]
@var{FILTERGRAPH}      ::= [sws_flags=@var{flags};] @var{FILTERCHAIN} [;@var{FILTERGRAPH}]
@end example

@section Notes on filtergraph escaping

Some filter arguments require the use of special characters, typically
@code{:} to separate key=value pairs in a named options list. In this
case the user should perform a first level escaping when specifying
the filter arguments. For example, consider the following literal
string to be embedded in the @ref{drawtext} filter arguments:
@example
this is a 'string': may contain one, or more, special characters
@end example

Since @code{:} is special for the filter arguments syntax, it needs to
be escaped, so you get:
@example
text=this is a \'string\'\: may contain one, or more, special characters
@end example

A second level of escaping is required when embedding the filter
arguments in a filtergraph description, in order to escape all the
filtergraph special characters. Thus the example above becomes:
@example
drawtext=text=this is a \\\'string\\\'\\: may contain one\, or more\, special characters
@end example

Finally an additional level of escaping may be needed when writing the
filtergraph description in a shell command, which depends on the
escaping rules of the adopted shell. For example, assuming that
@code{\} is special and needs to be escaped with another @code{\}, the
previous string will finally result in:
@example
-vf "drawtext=text=this is a \\\\\\'string\\\\\\'\\\\: may contain one\\, or more\\, special characters"
@end example

Sometimes, it might be more convenient to employ quoting in place of
escaping. For example the string:
@example
Caesar: tu quoque, Brute, fili mi
@end example

Can be quoted in the filter arguments as:
@example
text='Caesar: tu quoque, Brute, fili mi'
@end example

And finally inserted in a filtergraph like:
@example
drawtext=text=\'Caesar: tu quoque\, Brute\, fili mi\'
@end example

See the ``Quoting and escaping'' section in the ffmpeg-utils manual
for more information about the escaping and quoting rules adopted by
FFmpeg.

@chapter Timeline editing

Some filters support a generic @option{enable} option. For the filters
supporting timeline editing, this option can be set to an expression which is
evaluated before sending a frame to the filter. If the evaluation is non-zero,
the filter will be enabled, otherwise the frame will be sent unchanged to the
next filter in the filtergraph.

The expression accepts the following values:
@table @samp
@item t
timestamp expressed in seconds, NAN if the input timestamp is unknown

@item n
sequential number of the input frame, starting from 0

@item pos
the position in the file of the input frame, NAN if unknown
@end table

Additionally, these filters support an @option{enable} command that can be used
to re-define the expression.

Like any other filtering option, the @option{enable} option follows the same
rules.

For example, to enable a blur filter (@ref{smartblur}) from 10 seconds to 3
minutes, and a @ref{curves} filter starting at 3 seconds:
@example
smartblur = enable='between(t,10,3*60)',
curves    = enable='gte(t,3)' : preset=cross_process
@end example

@c man end FILTERGRAPH DESCRIPTION

@chapter Audio Filters
@c man begin AUDIO FILTERS

When you configure your FFmpeg build, you can disable any of the
existing filters using @code{--disable-filters}.
The configure output will show the audio filters included in your
build.

Below is a description of the currently available audio filters.

@section aconvert

Convert the input audio format to the specified formats.

@emph{This filter is deprecated. Use @ref{aformat} instead.}

The filter accepts a string of the form:
"@var{sample_format}:@var{channel_layout}".

@var{sample_format} specifies the sample format, and can be a string or the
corresponding numeric value defined in @file{libavutil/samplefmt.h}. Use 'p'
suffix for a planar sample format.

@var{channel_layout} specifies the channel layout, and can be a string
or the corresponding number value defined in @file{libavutil/channel_layout.h}.

The special parameter "auto", signifies that the filter will
automatically select the output format depending on the output filter.

@subsection Examples

@itemize
@item
Convert input to float, planar, stereo:
@example
aconvert=fltp:stereo
@end example

@item
Convert input to unsigned 8-bit, automatically select out channel layout:
@example
aconvert=u8:auto
@end example
@end itemize

@section afade

Apply fade-in/out effect to input audio.

A description of the accepted parameters follows.

@table @option
@item type, t
Specify the effect type, can be either @code{in} for fade-in, or
@code{out} for a fade-out effect. Default is @code{in}.

@item start_sample, ss
Specify the number of the start sample for starting to apply the fade
effect. Default is 0.

@item nb_samples, ns
Specify the number of samples for which the fade effect has to last. At
the end of the fade-in effect the output audio will have the same
volume as the input audio, at the end of the fade-out transition
the output audio will be silence. Default is 44100.

@item start_time, st
Specify time for starting to apply the fade effect. Default is 0.
The accepted syntax is:
@example
[-]HH[:MM[:SS[.m...]]]
[-]S+[.m...]
@end example
See also the function @code{av_parse_time()}.
If set this option is used instead of @var{start_sample} one.

@item duration, d
Specify the duration for which the fade effect has to last. Default is 0.
The accepted syntax is:
@example
[-]HH[:MM[:SS[.m...]]]
[-]S+[.m...]
@end example
See also the function @code{av_parse_time()}.
At the end of the fade-in effect the output audio will have the same
volume as the input audio, at the end of the fade-out transition
the output audio will be silence.
If set this option is used instead of @var{nb_samples} one.

@item curve
Set curve for fade transition.

It accepts the following values:
@table @option
@item tri
select triangular, linear slope (default)
@item qsin
select quarter of sine wave
@item hsin
select half of sine wave
@item esin
select exponential sine wave
@item log
select logarithmic
@item par
select inverted parabola
@item qua
select quadratic
@item cub
select cubic
@item squ
select square root
@item cbr
select cubic root
@end table
@end table

@subsection Examples

@itemize
@item
Fade in first 15 seconds of audio:
@example
afade=t=in:ss=0:d=15
@end example

@item
Fade out last 25 seconds of a 900 seconds audio:
@example
afade=t=out:st=875:d=25
@end example
@end itemize

@anchor{aformat}
@section aformat

Set output format constraints for the input audio. The framework will
negotiate the most appropriate format to minimize conversions.

The filter accepts the following named parameters:
@table @option

@item sample_fmts
A '|'-separated list of requested sample formats.

@item sample_rates
A '|'-separated list of requested sample rates.

@item channel_layouts
A '|'-separated list of requested channel layouts.

@end table

If a parameter is omitted, all values are allowed.

For example to force the output to either unsigned 8-bit or signed 16-bit stereo:
@example
aformat=sample_fmts=u8|s16:channel_layouts=stereo
@end example

@section allpass

Apply a two-pole all-pass filter with central frequency (in Hz)
@var{frequency}, and filter-width @var{width}.
An all-pass filter changes the audio's frequency to phase relationship
without changing its frequency to amplitude relationship.

The filter accepts the following options:

@table @option
@item frequency, f
Set frequency in Hz.

@item width_type
Set method to specify band-width of filter.
@table @option
@item h
Hz
@item q
Q-Factor
@item o
octave
@item s
slope
@end table

@item width, w
Specify the band-width of a filter in width_type units.
@end table

@section amerge

Merge two or more audio streams into a single multi-channel stream.

The filter accepts the following options:

@table @option

@item inputs
Set the number of inputs. Default is 2.

@end table

If the channel layouts of the inputs are disjoint, and therefore compatible,
the channel layout of the output will be set accordingly and the channels
will be reordered as necessary. If the channel layouts of the inputs are not
disjoint, the output will have all the channels of the first input then all
the channels of the second input, in that order, and the channel layout of
the output will be the default value corresponding to the total number of
channels.

For example, if the first input is in 2.1 (FL+FR+LF) and the second input
is FC+BL+BR, then the output will be in 5.1, with the channels in the
following order: a1, a2, b1, a3, b2, b3 (a1 is the first channel of the
first input, b1 is the first channel of the second input).

On the other hand, if both input are in stereo, the output channels will be
in the default order: a1, a2, b1, b2, and the channel layout will be
arbitrarily set to 4.0, which may or may not be the expected value.

All inputs must have the same sample rate, and format.

If inputs do not have the same duration, the output will stop with the
shortest.

@subsection Examples

@itemize
@item
Merge two mono files into a stereo stream:
@example
amovie=left.wav [l] ; amovie=right.mp3 [r] ; [l] [r] amerge
@end example

@item
Multiple merges assuming 1 video stream and 6 audio streams in @file{input.mkv}:
@example
ffmpeg -i input.mkv -filter_complex "[0:1][0:2][0:3][0:4][0:5][0:6] amerge=inputs=6" -c:a pcm_s16le output.mkv
@end example
@end itemize

@section amix

Mixes multiple audio inputs into a single output.

For example
@example
ffmpeg -i INPUT1 -i INPUT2 -i INPUT3 -filter_complex amix=inputs=3:duration=first:dropout_transition=3 OUTPUT
@end example
will mix 3 input audio streams to a single output with the same duration as the
first input and a dropout transition time of 3 seconds.

The filter accepts the following named parameters:
@table @option

@item inputs
Number of inputs. If unspecified, it defaults to 2.

@item duration
How to determine the end-of-stream.
@table @option

@item longest
Duration of longest input. (default)

@item shortest
Duration of shortest input.

@item first
Duration of first input.

@end table

@item dropout_transition
Transition time, in seconds, for volume renormalization when an input
stream ends. The default value is 2 seconds.

@end table

@section anull

Pass the audio source unchanged to the output.

@section apad

Pad the end of a audio stream with silence, this can be used together with
-shortest to extend audio streams to the same length as the video stream.

@section aphaser
Add a phasing effect to the input audio.

A phaser filter creates series of peaks and troughs in the frequency spectrum.
The position of the peaks and troughs are modulated so that they vary over time, creating a sweeping effect.

A description of the accepted parameters follows.

@table @option
@item in_gain
Set input gain. Default is 0.4.

@item out_gain
Set output gain. Default is 0.74

@item delay
Set delay in milliseconds. Default is 3.0.

@item decay
Set decay. Default is 0.4.

@item speed
Set modulation speed in Hz. Default is 0.5.

@item type
Set modulation type. Default is triangular.

It accepts the following values:
@table @samp
@item triangular, t
@item sinusoidal, s
@end table
@end table

@anchor{aresample}
@section aresample

Resample the input audio to the specified parameters, using the
libswresample library. If none are specified then the filter will
automatically convert between its input and output.

This filter is also able to stretch/squeeze the audio data to make it match
the timestamps or to inject silence / cut out audio to make it match the
timestamps, do a combination of both or do neither.

The filter accepts the syntax
[@var{sample_rate}:]@var{resampler_options}, where @var{sample_rate}
expresses a sample rate and @var{resampler_options} is a list of
@var{key}=@var{value} pairs, separated by ":". See the
ffmpeg-resampler manual for the complete list of supported options.

@subsection Examples

@itemize
@item
Resample the input audio to 44100Hz:
@example
aresample=44100
@end example

@item
Stretch/squeeze samples to the given timestamps, with a maximum of 1000
samples per second compensation:
@example
aresample=async=1000
@end example
@end itemize

@section asetnsamples

Set the number of samples per each output audio frame.

The last output packet may contain a different number of samples, as
the filter will flush all the remaining samples when the input audio
signal its end.

The filter accepts the following options:

@table @option

@item nb_out_samples, n
Set the number of frames per each output audio frame. The number is
intended as the number of samples @emph{per each channel}.
Default value is 1024.

@item pad, p
If set to 1, the filter will pad the last audio frame with zeroes, so
that the last frame will contain the same number of samples as the
previous ones. Default value is 1.
@end table

For example, to set the number of per-frame samples to 1234 and
disable padding for the last frame, use:
@example
asetnsamples=n=1234:p=0
@end example

@section asetrate

Set the sample rate without altering the PCM data.
This will result in a change of speed and pitch.

The filter accepts the following options:

@table @option
@item sample_rate, r
Set the output sample rate. Default is 44100 Hz.
@end table

@section ashowinfo

Show a line containing various information for each input audio frame.
The input audio is not modified.

The shown line contains a sequence of key/value pairs of the form
@var{key}:@var{value}.

A description of each shown parameter follows:

@table @option
@item n
sequential number of the input frame, starting from 0

@item pts
Presentation timestamp of the input frame, in time base units; the time base
depends on the filter input pad, and is usually 1/@var{sample_rate}.

@item pts_time
presentation timestamp of the input frame in seconds

@item pos
position of the frame in the input stream, -1 if this information in
unavailable and/or meaningless (for example in case of synthetic audio)

@item fmt
sample format

@item chlayout
channel layout

@item rate
sample rate for the audio frame

@item nb_samples
number of samples (per channel) in the frame

@item checksum
Adler-32 checksum (printed in hexadecimal) of the audio data. For planar audio
the data is treated as if all the planes were concatenated.

@item plane_checksums
A list of Adler-32 checksums for each data plane.
@end table

@section astats

Display time domain statistical information about the audio channels.
Statistics are calculated and displayed for each audio channel and,
where applicable, an overall figure is also given.

The filter accepts the following option:
@table @option
@item length
Short window length in seconds, used for peak and trough RMS measurement.
Default is @code{0.05} (50 miliseconds). Allowed range is @code{[0.1 - 10]}.
@end table

A description of each shown parameter follows:

@table @option
@item DC offset
Mean amplitude displacement from zero.

@item Min level
Minimal sample level.

@item Max level
Maximal sample level.

@item Peak level dB
@item RMS level dB
Standard peak and RMS level measured in dBFS.

@item RMS peak dB
@item RMS trough dB
Peak and trough values for RMS level measured over a short window.

@item Crest factor
Standard ratio of peak to RMS level (note: not in dB).

@item Flat factor
Flatness (i.e. consecutive samples with the same value) of the signal at its peak levels
(i.e. either @var{Min level} or @var{Max level}).

@item Peak count
Number of occasions (not the number of samples) that the signal attained either
@var{Min level} or @var{Max level}.
@end table

@section astreamsync

Forward two audio streams and control the order the buffers are forwarded.

The filter accepts the following options:

@table @option
@item expr, e
Set the expression deciding which stream should be
forwarded next: if the result is negative, the first stream is forwarded; if
the result is positive or zero, the second stream is forwarded. It can use
the following variables:

@table @var
@item b1 b2
number of buffers forwarded so far on each stream
@item s1 s2
number of samples forwarded so far on each stream
@item t1 t2
current timestamp of each stream
@end table

The default value is @code{t1-t2}, which means to always forward the stream
that has a smaller timestamp.
@end table

@subsection Examples

Stress-test @code{amerge} by randomly sending buffers on the wrong
input, while avoiding too much of a desynchronization:
@example
amovie=file.ogg [a] ; amovie=file.mp3 [b] ;
[a] [b] astreamsync=(2*random(1))-1+tanh(5*(t1-t2)) [a2] [b2] ;
[a2] [b2] amerge
@end example

@section asyncts

Synchronize audio data with timestamps by squeezing/stretching it and/or
dropping samples/adding silence when needed.

This filter is not built by default, please use @ref{aresample} to do squeezing/stretching.

The filter accepts the following named parameters:
@table @option

@item compensate
Enable stretching/squeezing the data to make it match the timestamps. Disabled
by default. When disabled, time gaps are covered with silence.

@item min_delta
Minimum difference between timestamps and audio data (in seconds) to trigger
adding/dropping samples. Default value is 0.1. If you get non-perfect sync with
this filter, try setting this parameter to 0.

@item max_comp
Maximum compensation in samples per second. Relevant only with compensate=1.
Default value 500.

@item first_pts
Assume the first pts should be this value. The time base is 1 / sample rate.
This allows for padding/trimming at the start of stream. By default, no
assumption is made about the first frame's expected pts, so no padding or
trimming is done. For example, this could be set to 0 to pad the beginning with
silence if an audio stream starts after the video stream or to trim any samples
with a negative pts due to encoder delay.

@end table

@section atempo

Adjust audio tempo.

The filter accepts exactly one parameter, the audio tempo. If not
specified then the filter will assume nominal 1.0 tempo. Tempo must
be in the [0.5, 2.0] range.

@subsection Examples

@itemize
@item
Slow down audio to 80% tempo:
@example
atempo=0.8
@end example

@item
To speed up audio to 125% tempo:
@example
atempo=1.25
@end example
@end itemize

@section atrim

Trim the input so that the output contains one continuous subpart of the input.

This filter accepts the following options:
@table @option
@item start
Timestamp (in seconds) of the start of the kept section. I.e. the audio sample
with the timestamp @var{start} will be the first sample in the output.

@item end
Timestamp (in seconds) of the first audio sample that will be dropped. I.e. the
audio sample immediately preceding the one with the timestamp @var{end} will be
the last sample in the output.

@item start_pts
Same as @var{start}, except this option sets the start timestamp in samples
instead of seconds.

@item end_pts
Same as @var{end}, except this option sets the end timestamp in samples instead
of seconds.

@item duration
Maximum duration of the output in seconds.

@item start_sample
Number of the first sample that should be passed to output.

@item end_sample
Number of the first sample that should be dropped.
@end table

Note that the first two sets of the start/end options and the @option{duration}
option look at the frame timestamp, while the _sample options simply count the
samples that pass through the filter. So start/end_pts and start/end_sample will
give different results when the timestamps are wrong, inexact or do not start at
zero. Also note that this filter does not modify the timestamps. If you wish
that the output timestamps start at zero, insert the asetpts filter after the
atrim filter.

If multiple start or end options are set, this filter tries to be greedy and
keep all samples that match at least one of the specified constraints. To keep
only the part that matches all the constraints at once, chain multiple atrim
filters.

The defaults are such that all the input is kept. So it is possible to set e.g.
just the end values to keep everything before the specified time.

Examples:
@itemize
@item
drop everything except the second minute of input
@example
ffmpeg -i INPUT -af atrim=60:120
@end example

@item
keep only the first 1000 samples
@example
ffmpeg -i INPUT -af atrim=end_sample=1000
@end example

@end itemize

@section bandpass

Apply a two-pole Butterworth band-pass filter with central
frequency @var{frequency}, and (3dB-point) band-width width.
The @var{csg} option selects a constant skirt gain (peak gain = Q)
instead of the default: constant 0dB peak gain.
The filter roll off at 6dB per octave (20dB per decade).

The filter accepts the following options:

@table @option
@item frequency, f
Set the filter's central frequency. Default is @code{3000}.

@item csg
Constant skirt gain if set to 1. Defaults to 0.

@item width_type
Set method to specify band-width of filter.
@table @option
@item h
Hz
@item q
Q-Factor
@item o
octave
@item s
slope
@end table

@item width, w
Specify the band-width of a filter in width_type units.
@end table

@section bandreject

Apply a two-pole Butterworth band-reject filter with central
frequency @var{frequency}, and (3dB-point) band-width @var{width}.
The filter roll off at 6dB per octave (20dB per decade).

The filter accepts the following options:

@table @option
@item frequency, f
Set the filter's central frequency. Default is @code{3000}.

@item width_type
Set method to specify band-width of filter.
@table @option
@item h
Hz
@item q
Q-Factor
@item o
octave
@item s
slope
@end table

@item width, w
Specify the band-width of a filter in width_type units.
@end table

@section bass

Boost or cut the bass (lower) frequencies of the audio using a two-pole
shelving filter with a response similar to that of a standard
hi-fi's tone-controls. This is also known as shelving equalisation (EQ).

The filter accepts the following options:

@table @option
@item gain, g
Give the gain at 0 Hz. Its useful range is about -20
(for a large cut) to +20 (for a large boost).
Beware of clipping when using a positive gain.

@item frequency, f
Set the filter's central frequency and so can be used
to extend or reduce the frequency range to be boosted or cut.
The default value is @code{100} Hz.

@item width_type
Set method to specify band-width of filter.
@table @option
@item h
Hz
@item q
Q-Factor
@item o
octave
@item s
slope
@end table

@item width, w
Determine how steep is the filter's shelf transition.
@end table

@section biquad

Apply a biquad IIR filter with the given coefficients.
Where @var{b0}, @var{b1}, @var{b2} and @var{a0}, @var{a1}, @var{a2}
are the numerator and denominator coefficients respectively.

@section channelmap

Remap input channels to new locations.

This filter accepts the following named parameters:
@table @option
@item channel_layout
Channel layout of the output stream.

@item map
Map channels from input to output. The argument is a '|'-separated list of
mappings, each in the @code{@var{in_channel}-@var{out_channel}} or
@var{in_channel} form. @var{in_channel} can be either the name of the input
channel (e.g. FL for front left) or its index in the input channel layout.
@var{out_channel} is the name of the output channel or its index in the output
channel layout. If @var{out_channel} is not given then it is implicitly an
index, starting with zero and increasing by one for each mapping.
@end table

If no mapping is present, the filter will implicitly map input channels to
output channels preserving index.

For example, assuming a 5.1+downmix input MOV file
@example
ffmpeg -i in.mov -filter 'channelmap=map=DL-FL|DR-FR' out.wav
@end example
will create an output WAV file tagged as stereo from the downmix channels of
the input.

To fix a 5.1 WAV improperly encoded in AAC's native channel order
@example
ffmpeg -i in.wav -filter 'channelmap=1|2|0|5|3|4:channel_layout=5.1' out.wav
@end example

@section channelsplit

Split each channel in input audio stream into a separate output stream.

This filter accepts the following named parameters:
@table @option
@item channel_layout
Channel layout of the input stream. Default is "stereo".
@end table

For example, assuming a stereo input MP3 file
@example
ffmpeg -i in.mp3 -filter_complex channelsplit out.mkv
@end example
will create an output Matroska file with two audio streams, one containing only
the left channel and the other the right channel.

To split a 5.1 WAV file into per-channel files
@example
ffmpeg -i in.wav -filter_complex
'channelsplit=channel_layout=5.1[FL][FR][FC][LFE][SL][SR]'
-map '[FL]' front_left.wav -map '[FR]' front_right.wav -map '[FC]'
front_center.wav -map '[LFE]' lfe.wav -map '[SL]' side_left.wav -map '[SR]'
side_right.wav
@end example

@section earwax

Make audio easier to listen to on headphones.

This filter adds `cues' to 44.1kHz stereo (i.e. audio CD format) audio
so that when listened to on headphones the stereo image is moved from
inside your head (standard for headphones) to outside and in front of
the listener (standard for speakers).

Ported from SoX.

@section equalizer

Apply a two-pole peaking equalisation (EQ) filter. With this
filter, the signal-level at and around a selected frequency can
be increased or decreased, whilst (unlike bandpass and bandreject
filters) that at all other frequencies is unchanged.

In order to produce complex equalisation curves, this filter can
be given several times, each with a different central frequency.

The filter accepts the following options:

@table @option
@item frequency, f
Set the filter's central frequency in Hz.

@item width_type
Set method to specify band-width of filter.
@table @option
@item h
Hz
@item q
Q-Factor
@item o
octave
@item s
slope
@end table

@item width, w
Specify the band-width of a filter in width_type units.

@item gain, g
Set the required gain or attenuation in dB.
Beware of clipping when using a positive gain.
@end table

@section highpass

Apply a high-pass filter with 3dB point frequency.
The filter can be either single-pole, or double-pole (the default).
The filter roll off at 6dB per pole per octave (20dB per pole per decade).

The filter accepts the following options:

@table @option
@item frequency, f
Set frequency in Hz. Default is 3000.

@item poles, p
Set number of poles. Default is 2.

@item width_type
Set method to specify band-width of filter.
@table @option
@item h
Hz
@item q
Q-Factor
@item o
octave
@item s
slope
@end table

@item width, w
Specify the band-width of a filter in width_type units.
Applies only to double-pole filter.
The default is 0.707q and gives a Butterworth response.
@end table

@section join

Join multiple input streams into one multi-channel stream.

The filter accepts the following named parameters:
@table @option

@item inputs
Number of input streams. Defaults to 2.

@item channel_layout
Desired output channel layout. Defaults to stereo.

@item map
Map channels from inputs to output. The argument is a '|'-separated list of
mappings, each in the @code{@var{input_idx}.@var{in_channel}-@var{out_channel}}
form. @var{input_idx} is the 0-based index of the input stream. @var{in_channel}
can be either the name of the input channel (e.g. FL for front left) or its
index in the specified input stream. @var{out_channel} is the name of the output
channel.
@end table

The filter will attempt to guess the mappings when those are not specified
explicitly. It does so by first trying to find an unused matching input channel
and if that fails it picks the first unused input channel.

E.g. to join 3 inputs (with properly set channel layouts)
@example
ffmpeg -i INPUT1 -i INPUT2 -i INPUT3 -filter_complex join=inputs=3 OUTPUT
@end example

To build a 5.1 output from 6 single-channel streams:
@example
ffmpeg -i fl -i fr -i fc -i sl -i sr -i lfe -filter_complex
'join=inputs=6:channel_layout=5.1:map=0.0-FL|1.0-FR|2.0-FC|3.0-SL|4.0-SR|5.0-LFE'
out
@end example

@section lowpass

Apply a low-pass filter with 3dB point frequency.
The filter can be either single-pole or double-pole (the default).
The filter roll off at 6dB per pole per octave (20dB per pole per decade).

The filter accepts the following options:

@table @option
@item frequency, f
Set frequency in Hz. Default is 500.

@item poles, p
Set number of poles. Default is 2.

@item width_type
Set method to specify band-width of filter.
@table @option
@item h
Hz
@item q
Q-Factor
@item o
octave
@item s
slope
@end table

@item width, w
Specify the band-width of a filter in width_type units.
Applies only to double-pole filter.
The default is 0.707q and gives a Butterworth response.
@end table

@section pan

Mix channels with specific gain levels. The filter accepts the output
channel layout followed by a set of channels definitions.

This filter is also designed to remap efficiently the channels of an audio
stream.

The filter accepts parameters of the form:
"@var{l}:@var{outdef}:@var{outdef}:..."

@table @option
@item l
output channel layout or number of channels

@item outdef
output channel specification, of the form:
"@var{out_name}=[@var{gain}*]@var{in_name}[+[@var{gain}*]@var{in_name}...]"

@item out_name
output channel to define, either a channel name (FL, FR, etc.) or a channel
number (c0, c1, etc.)

@item gain
multiplicative coefficient for the channel, 1 leaving the volume unchanged

@item in_name
input channel to use, see out_name for details; it is not possible to mix
named and numbered input channels
@end table

If the `=' in a channel specification is replaced by `<', then the gains for
that specification will be renormalized so that the total is 1, thus
avoiding clipping noise.

@subsection Mixing examples

For example, if you want to down-mix from stereo to mono, but with a bigger
factor for the left channel:
@example
pan=1:c0=0.9*c0+0.1*c1
@end example

A customized down-mix to stereo that works automatically for 3-, 4-, 5- and
7-channels surround:
@example
pan=stereo: FL < FL + 0.5*FC + 0.6*BL + 0.6*SL : FR < FR + 0.5*FC + 0.6*BR + 0.6*SR
@end example

Note that @command{ffmpeg} integrates a default down-mix (and up-mix) system
that should be preferred (see "-ac" option) unless you have very specific
needs.

@subsection Remapping examples

The channel remapping will be effective if, and only if:

@itemize
@item gain coefficients are zeroes or ones,
@item only one input per channel output,
@end itemize

If all these conditions are satisfied, the filter will notify the user ("Pure
channel mapping detected"), and use an optimized and lossless method to do the
remapping.

For example, if you have a 5.1 source and want a stereo audio stream by
dropping the extra channels:
@example
pan="stereo: c0=FL : c1=FR"
@end example

Given the same source, you can also switch front left and front right channels
and keep the input channel layout:
@example
pan="5.1: c0=c1 : c1=c0 : c2=c2 : c3=c3 : c4=c4 : c5=c5"
@end example

If the input is a stereo audio stream, you can mute the front left channel (and
still keep the stereo channel layout) with:
@example
pan="stereo:c1=c1"
@end example

Still with a stereo audio stream input, you can copy the right channel in both
front left and right:
@example
pan="stereo: c0=FR : c1=FR"
@end example

@section resample

Convert the audio sample format, sample rate and channel layout. This filter is
not meant to be used directly.

@section silencedetect

Detect silence in an audio stream.

This filter logs a message when it detects that the input audio volume is less
or equal to a noise tolerance value for a duration greater or equal to the
minimum detected noise duration.

The printed times and duration are expressed in seconds.

The filter accepts the following options:

@table @option
@item duration, d
Set silence duration until notification (default is 2 seconds).

@item noise, n
Set noise tolerance. Can be specified in dB (in case "dB" is appended to the
specified value) or amplitude ratio. Default is -60dB, or 0.001.
@end table

@subsection Examples

@itemize
@item
Detect 5 seconds of silence with -50dB noise tolerance:
@example
silencedetect=n=-50dB:d=5
@end example

@item
Complete example with @command{ffmpeg} to detect silence with 0.0001 noise
tolerance in @file{silence.mp3}:
@example
ffmpeg -i silence.mp3 -af silencedetect=noise=0.0001 -f null -
@end example
@end itemize

@section treble

Boost or cut treble (upper) frequencies of the audio using a two-pole
shelving filter with a response similar to that of a standard
hi-fi's tone-controls. This is also known as shelving equalisation (EQ).

The filter accepts the following options:

@table @option
@item gain, g
Give the gain at whichever is the lower of ~22 kHz and the
Nyquist frequency. Its useful range is about -20 (for a large cut)
to +20 (for a large boost). Beware of clipping when using a positive gain.

@item frequency, f
Set the filter's central frequency and so can be used
to extend or reduce the frequency range to be boosted or cut.
The default value is @code{3000} Hz.

@item width_type
Set method to specify band-width of filter.
@table @option
@item h
Hz
@item q
Q-Factor
@item o
octave
@item s
slope
@end table

@item width, w
Determine how steep is the filter's shelf transition.
@end table

@section volume

Adjust the input audio volume.

The filter accepts the following options:

@table @option

@item volume
Expresses how the audio volume will be increased or decreased.

Output values are clipped to the maximum value.

The output audio volume is given by the relation:
@example
@var{output_volume} = @var{volume} * @var{input_volume}
@end example

Default value for @var{volume} is 1.0.

@item precision
Set the mathematical precision.

This determines which input sample formats will be allowed, which affects the
precision of the volume scaling.

@table @option
@item fixed
8-bit fixed-point; limits input sample format to U8, S16, and S32.
@item float
32-bit floating-point; limits input sample format to FLT. (default)
@item double
64-bit floating-point; limits input sample format to DBL.
@end table
@end table

@subsection Examples

@itemize
@item
Halve the input audio volume:
@example
volume=volume=0.5
volume=volume=1/2
volume=volume=-6.0206dB
@end example

In all the above example the named key for @option{volume} can be
omitted, for example like in:
@example
volume=0.5
@end example

@item
Increase input audio power by 6 decibels using fixed-point precision:
@example
volume=volume=6dB:precision=fixed
@end example
@end itemize

@section volumedetect

Detect the volume of the input video.

The filter has no parameters. The input is not modified. Statistics about
the volume will be printed in the log when the input stream end is reached.

In particular it will show the mean volume (root mean square), maximum
volume (on a per-sample basis), and the beginning of an histogram of the
registered volume values (from the maximum value to a cumulated 1/1000 of
the samples).

All volumes are in decibels relative to the maximum PCM value.

@subsection Examples

Here is an excerpt of the output:
@example
[Parsed_volumedetect_0 @ 0xa23120] mean_volume: -27 dB
[Parsed_volumedetect_0 @ 0xa23120] max_volume: -4 dB
[Parsed_volumedetect_0 @ 0xa23120] histogram_4db: 6
[Parsed_volumedetect_0 @ 0xa23120] histogram_5db: 62
[Parsed_volumedetect_0 @ 0xa23120] histogram_6db: 286
[Parsed_volumedetect_0 @ 0xa23120] histogram_7db: 1042
[Parsed_volumedetect_0 @ 0xa23120] histogram_8db: 2551
[Parsed_volumedetect_0 @ 0xa23120] histogram_9db: 4609
[Parsed_volumedetect_0 @ 0xa23120] histogram_10db: 8409
@end example

It means that:
@itemize
@item
The mean square energy is approximately -27 dB, or 10^-2.7.
@item
The largest sample is at -4 dB, or more precisely between -4 dB and -5 dB.
@item
There are 6 samples at -4 dB, 62 at -5 dB, 286 at -6 dB, etc.
@end itemize

In other words, raising the volume by +4 dB does not cause any clipping,
raising it by +5 dB causes clipping for 6 samples, etc.

@c man end AUDIO FILTERS

@chapter Audio Sources
@c man begin AUDIO SOURCES

Below is a description of the currently available audio sources.

@section abuffer

Buffer audio frames, and make them available to the filter chain.

This source is mainly intended for a programmatic use, in particular
through the interface defined in @file{libavfilter/asrc_abuffer.h}.

It accepts the following named parameters:

@table @option

@item time_base
Timebase which will be used for timestamps of submitted frames. It must be
either a floating-point number or in @var{numerator}/@var{denominator} form.

@item sample_rate
The sample rate of the incoming audio buffers.

@item sample_fmt
The sample format of the incoming audio buffers.
Either a sample format name or its corresponging integer representation from
the enum AVSampleFormat in @file{libavutil/samplefmt.h}

@item channel_layout
The channel layout of the incoming audio buffers.
Either a channel layout name from channel_layout_map in
@file{libavutil/channel_layout.c} or its corresponding integer representation
from the AV_CH_LAYOUT_* macros in @file{libavutil/channel_layout.h}

@item channels
The number of channels of the incoming audio buffers.
If both @var{channels} and @var{channel_layout} are specified, then they
must be consistent.

@end table

@subsection Examples

@example
abuffer=sample_rate=44100:sample_fmt=s16p:channel_layout=stereo
@end example

will instruct the source to accept planar 16bit signed stereo at 44100Hz.
Since the sample format with name "s16p" corresponds to the number
6 and the "stereo" channel layout corresponds to the value 0x3, this is
equivalent to:
@example
abuffer=sample_rate=44100:sample_fmt=6:channel_layout=0x3
@end example

@section aevalsrc

Generate an audio signal specified by an expression.

This source accepts in input one or more expressions (one for each
channel), which are evaluated and used to generate a corresponding
audio signal.

This source accepts the following options:

@table @option
@item exprs
Set the '|'-separated expressions list for each separate channel. In case the
@option{channel_layout} option is not specified, the selected channel layout
depends on the number of provided expressions.

@item channel_layout, c
Set the channel layout. The number of channels in the specified layout
must be equal to the number of specified expressions.

@item duration, d
Set the minimum duration of the sourced audio. See the function
@code{av_parse_time()} for the accepted format.
Note that the resulting duration may be greater than the specified
duration, as the generated audio is always cut at the end of a
complete frame.

If not specified, or the expressed duration is negative, the audio is
supposed to be generated forever.

@item nb_samples, n
Set the number of samples per channel per each output frame,
default to 1024.

@item sample_rate, s
Specify the sample rate, default to 44100.
@end table

Each expression in @var{exprs} can contain the following constants:

@table @option
@item n
number of the evaluated sample, starting from 0

@item t
time of the evaluated sample expressed in seconds, starting from 0

@item s
sample rate

@end table

@subsection Examples

@itemize
@item
Generate silence:
@example
aevalsrc=0
@end example

@item
Generate a sin signal with frequency of 440 Hz, set sample rate to
8000 Hz:
@example
aevalsrc="sin(440*2*PI*t):s=8000"
@end example

@item
Generate a two channels signal, specify the channel layout (Front
Center + Back Center) explicitly:
@example
aevalsrc="sin(420*2*PI*t)|cos(430*2*PI*t):c=FC|BC"
@end example

@item
Generate white noise:
@example
aevalsrc="-2+random(0)"
@end example

@item
Generate an amplitude modulated signal:
@example
aevalsrc="sin(10*2*PI*t)*sin(880*2*PI*t)"
@end example

@item
Generate 2.5 Hz binaural beats on a 360 Hz carrier:
@example
aevalsrc="0.1*sin(2*PI*(360-2.5/2)*t) | 0.1*sin(2*PI*(360+2.5/2)*t)"
@end example

@end itemize

@section anullsrc

Null audio source, return unprocessed audio frames. It is mainly useful
as a template and to be employed in analysis / debugging tools, or as
the source for filters which ignore the input data (for example the sox
synth filter).

This source accepts the following options:

@table @option

@item channel_layout, cl

Specify the channel layout, and can be either an integer or a string
representing a channel layout. The default value of @var{channel_layout}
is "stereo".

Check the channel_layout_map definition in
@file{libavutil/channel_layout.c} for the mapping between strings and
channel layout values.

@item sample_rate, r
Specify the sample rate, and defaults to 44100.

@item nb_samples, n
Set the number of samples per requested frames.

@end table

@subsection Examples

@itemize
@item
Set the sample rate to 48000 Hz and the channel layout to AV_CH_LAYOUT_MONO.
@example
anullsrc=r=48000:cl=4
@end example

@item
Do the same operation with a more obvious syntax:
@example
anullsrc=r=48000:cl=mono
@end example
@end itemize

All the parameters need to be explicitly defined.

@section flite

Synthesize a voice utterance using the libflite library.

To enable compilation of this filter you need to configure FFmpeg with
@code{--enable-libflite}.

Note that the flite library is not thread-safe.

The filter accepts the following options:

@table @option

@item list_voices
If set to 1, list the names of the available voices and exit
immediately. Default value is 0.

@item nb_samples, n
Set the maximum number of samples per frame. Default value is 512.

@item textfile
Set the filename containing the text to speak.

@item text
Set the text to speak.

@item voice, v
Set the voice to use for the speech synthesis. Default value is
@code{kal}. See also the @var{list_voices} option.
@end table

@subsection Examples

@itemize
@item
Read from file @file{speech.txt}, and synthetize the text using the
standard flite voice:
@example
flite=textfile=speech.txt
@end example

@item
Read the specified text selecting the @code{slt} voice:
@example
flite=text='So fare thee well, poor devil of a Sub-Sub, whose commentator I am':voice=slt
@end example

@item
Input text to ffmpeg:
@example
ffmpeg -f lavfi -i flite=text='So fare thee well, poor devil of a Sub-Sub, whose commentator I am':voice=slt
@end example

@item
Make @file{ffplay} speak the specified text, using @code{flite} and
the @code{lavfi} device:
@example
ffplay -f lavfi flite=text='No more be grieved for which that thou hast done.'
@end example
@end itemize

For more information about libflite, check:
@url{http://www.speech.cs.cmu.edu/flite/}

@section sine

Generate an audio signal made of a sine wave with amplitude 1/8.

The audio signal is bit-exact.

The filter accepts the following options:

@table @option

@item frequency, f
Set the carrier frequency. Default is 440 Hz.

@item beep_factor, b
Enable a periodic beep every second with frequency @var{beep_factor} times
the carrier frequency. Default is 0, meaning the beep is disabled.

@item sample_rate, s
Specify the sample rate, default is 44100.

@item duration, d
Specify the duration of the generated audio stream.

@item samples_per_frame
Set the number of samples per output frame, default is 1024.
@end table

@subsection Examples

@itemize

@item
Generate a simple 440 Hz sine wave:
@example
sine
@end example

@item
Generate a 220 Hz sine wave with a 880 Hz beep each second, for 5 seconds:
@example
sine=220:4:d=5
sine=f=220:b=4:d=5
sine=frequency=220:beep_factor=4:duration=5
@end example

@end itemize

@c man end AUDIO SOURCES

@chapter Audio Sinks
@c man begin AUDIO SINKS

Below is a description of the currently available audio sinks.

@section abuffersink

Buffer audio frames, and make them available to the end of filter chain.

This sink is mainly intended for programmatic use, in particular
through the interface defined in @file{libavfilter/buffersink.h}
or the options system.

It accepts a pointer to an AVABufferSinkContext structure, which
defines the incoming buffers' formats, to be passed as the opaque
parameter to @code{avfilter_init_filter} for initialization.

@section anullsink

Null audio sink, do absolutely nothing with the input audio. It is
mainly useful as a template and to be employed in analysis / debugging
tools.

@c man end AUDIO SINKS

@chapter Video Filters
@c man begin VIDEO FILTERS

When you configure your FFmpeg build, you can disable any of the
existing filters using @code{--disable-filters}.
The configure output will show the video filters included in your
build.

Below is a description of the currently available video filters.

@section alphaextract

Extract the alpha component from the input as a grayscale video. This
is especially useful with the @var{alphamerge} filter.

@section alphamerge

Add or replace the alpha component of the primary input with the
grayscale value of a second input. This is intended for use with
@var{alphaextract} to allow the transmission or storage of frame
sequences that have alpha in a format that doesn't support an alpha
channel.

For example, to reconstruct full frames from a normal YUV-encoded video
and a separate video created with @var{alphaextract}, you might use:
@example
movie=in_alpha.mkv [alpha]; [in][alpha] alphamerge [out]
@end example

Since this filter is designed for reconstruction, it operates on frame
sequences without considering timestamps, and terminates when either
input reaches end of stream. This will cause problems if your encoding
pipeline drops frames. If you're trying to apply an image as an
overlay to a video stream, consider the @var{overlay} filter instead.

@section ass

Same as the @ref{subtitles} filter, except that it doesn't require libavcodec
and libavformat to work. On the other hand, it is limited to ASS (Advanced
Substation Alpha) subtitles files.

@section bbox

Compute the bounding box for the non-black pixels in the input frame
luminance plane.

This filter computes the bounding box containing all the pixels with a
luminance value greater than the minimum allowed value.
The parameters describing the bounding box are printed on the filter
log.

@section blackdetect

Detect video intervals that are (almost) completely black. Can be
useful to detect chapter transitions, commercials, or invalid
recordings. Output lines contains the time for the start, end and
duration of the detected black interval expressed in seconds.

In order to display the output lines, you need to set the loglevel at
least to the AV_LOG_INFO value.

The filter accepts the following options:

@table @option
@item black_min_duration, d
Set the minimum detected black duration expressed in seconds. It must
be a non-negative floating point number.

Default value is 2.0.

@item picture_black_ratio_th, pic_th
Set the threshold for considering a picture "black".
Express the minimum value for the ratio:
@example
@var{nb_black_pixels} / @var{nb_pixels}
@end example

for which a picture is considered black.
Default value is 0.98.

@item pixel_black_th, pix_th
Set the threshold for considering a pixel "black".

The threshold expresses the maximum pixel luminance value for which a
pixel is considered "black". The provided value is scaled according to
the following equation:
@example
@var{absolute_threshold} = @var{luminance_minimum_value} + @var{pixel_black_th} * @var{luminance_range_size}
@end example

@var{luminance_range_size} and @var{luminance_minimum_value} depend on
the input video format, the range is [0-255] for YUV full-range
formats and [16-235] for YUV non full-range formats.

Default value is 0.10.
@end table

The following example sets the maximum pixel threshold to the minimum
value, and detects only black intervals of 2 or more seconds:
@example
blackdetect=d=2:pix_th=0.00
@end example

@section blackframe

Detect frames that are (almost) completely black. Can be useful to
detect chapter transitions or commercials. Output lines consist of
the frame number of the detected frame, the percentage of blackness,
the position in the file if known or -1 and the timestamp in seconds.

In order to display the output lines, you need to set the loglevel at
least to the AV_LOG_INFO value.

The filter accepts the following options:

@table @option

@item amount
Set the percentage of the pixels that have to be below the threshold, defaults
to @code{98}.

@item threshold, thresh
Set the threshold below which a pixel value is considered black, defaults to
@code{32}.

@end table

@section blend

Blend two video frames into each other.

It takes two input streams and outputs one stream, the first input is the
"top" layer and second input is "bottom" layer.
Output terminates when shortest input terminates.

A description of the accepted options follows.

@table @option
@item c0_mode
@item c1_mode
@item c2_mode
@item c3_mode
@item all_mode
Set blend mode for specific pixel component or all pixel components in case
of @var{all_mode}. Default value is @code{normal}.

Available values for component modes are:
@table @samp
@item addition
@item and
@item average
@item burn
@item darken
@item difference
@item divide
@item dodge
@item exclusion
@item hardlight
@item lighten
@item multiply
@item negation
@item normal
@item or
@item overlay
@item phoenix
@item pinlight
@item reflect
@item screen
@item softlight
@item subtract
@item vividlight
@item xor
@end table

@item c0_opacity
@item c1_opacity
@item c2_opacity
@item c3_opacity
@item all_opacity
Set blend opacity for specific pixel component or all pixel components in case
of @var{all_opacity}. Only used in combination with pixel component blend modes.

@item c0_expr
@item c1_expr
@item c2_expr
@item c3_expr
@item all_expr
Set blend expression for specific pixel component or all pixel components in case
of @var{all_expr}. Note that related mode options will be ignored if those are set.

The expressions can use the following variables:

@table @option
@item N
The sequential number of the filtered frame, starting from @code{0}.

@item X
@item Y
the coordinates of the current sample

@item W
@item H
the width and height of currently filtered plane

@item SW
@item SH
Width and height scale depending on the currently filtered plane. It is the
ratio between the corresponding luma plane number of pixels and the current
plane ones. E.g. for YUV4:2:0 the values are @code{1,1} for the luma plane, and
@code{0.5,0.5} for chroma planes.

@item T
Time of the current frame, expressed in seconds.

@item TOP, A
Value of pixel component at current location for first video frame (top layer).

@item BOTTOM, B
Value of pixel component at current location for second video frame (bottom layer).
@end table
@end table

@subsection Examples

@itemize
@item
Apply transition from bottom layer to top layer in first 10 seconds:
@example
blend=all_expr='A*(if(gte(T,10),1,T/10))+B*(1-(if(gte(T,10),1,T/10)))'
@end example

@item
Apply 1x1 checkerboard effect:
@example
blend=all_expr='if(eq(mod(X,2),mod(Y,2)),A,B)'
@end example
@end itemize

@section boxblur

Apply boxblur algorithm to the input video.

The filter accepts the following options:

@table @option

@item luma_radius, lr
@item luma_power, lp
@item chroma_radius, cr
@item chroma_power, cp
@item alpha_radius, ar
@item alpha_power, ap

@end table

A description of the accepted options follows.

@table @option
@item luma_radius, lr
@item chroma_radius, cr
@item alpha_radius, ar
Set an expression for the box radius in pixels used for blurring the
corresponding input plane.

The radius value must be a non-negative number, and must not be
greater than the value of the expression @code{min(w,h)/2} for the
luma and alpha planes, and of @code{min(cw,ch)/2} for the chroma
planes.

Default value for @option{luma_radius} is "2". If not specified,
@option{chroma_radius} and @option{alpha_radius} default to the
corresponding value set for @option{luma_radius}.

The expressions can contain the following constants:
@table @option
@item w
@item h
the input width and height in pixels

@item cw
@item ch
the input chroma image width and height in pixels

@item hsub
@item vsub
horizontal and vertical chroma subsample values. For example for the
pixel format "yuv422p" @var{hsub} is 2 and @var{vsub} is 1.
@end table

@item luma_power, lp
@item chroma_power, cp
@item alpha_power, ap
Specify how many times the boxblur filter is applied to the
corresponding plane.

Default value for @option{luma_power} is 2. If not specified,
@option{chroma_power} and @option{alpha_power} default to the
corresponding value set for @option{luma_power}.

A value of 0 will disable the effect.
@end table

@subsection Examples

@itemize
@item
Apply a boxblur filter with luma, chroma, and alpha radius
set to 2:
@example
boxblur=luma_radius=2:luma_power=1
boxblur=2:1
@end example

@item
Set luma radius to 2, alpha and chroma radius to 0:
@example
boxblur=2:1:cr=0:ar=0
@end example

@item
Set luma and chroma radius to a fraction of the video dimension:
@example
boxblur=luma_radius=min(h\,w)/10:luma_power=1:chroma_radius=min(cw\,ch)/10:chroma_power=1
@end example
@end itemize

@section colorbalance
Modify intensity of primary colors (red, green and blue) of input frames.

The filter allows an input frame to be adjusted in the shadows, midtones or highlights
regions for the red-cyan, green-magenta or blue-yellow balance.

A positive adjustment value shifts the balance towards the primary color, a negative
value towards the complementary color.

The filter accepts the following options:

@table @option
@item rs
@item gs
@item bs
Adjust red, green and blue shadows (darkest pixels).

@item rm
@item gm
@item bm
Adjust red, green and blue midtones (medium pixels).

@item rh
@item gh
@item bh
Adjust red, green and blue highlights (brightest pixels).

Allowed ranges for options are @code{[-1.0, 1.0]}. Defaults are @code{0}.
@end table

@subsection Examples

@itemize
@item
Add red color cast to shadows:
@example
colorbalance=rs=.3
@end example
@end itemize

@section colorchannelmixer

Adjust video input frames by re-mixing color channels.

This filter modifies a color channel by adding the values associated to
the other channels of the same pixels. For example if the value to
modify is red, the output value will be:
@example
@var{red}=@var{red}*@var{rr} + @var{blue}*@var{rb} + @var{green}*@var{rg} + @var{alpha}*@var{ra}
@end example

The filter accepts the following options:

@table @option
@item rr
@item rg
@item rb
@item ra
Adjust contribution of input red, green, blue and alpha channels for output red channel.
Default is @code{1} for @var{rr}, and @code{0} for @var{rg}, @var{rb} and @var{ra}.

@item gr
@item gg
@item gb
@item ga
Adjust contribution of input red, green, blue and alpha channels for output green channel.
Default is @code{1} for @var{gg}, and @code{0} for @var{gr}, @var{gb} and @var{ga}.

@item br
@item bg
@item bb
@item ba
Adjust contribution of input red, green, blue and alpha channels for output blue channel.
Default is @code{1} for @var{bb}, and @code{0} for @var{br}, @var{bg} and @var{ba}.

@item ar
@item ag
@item ab
@item aa
Adjust contribution of input red, green, blue and alpha channels for output alpha channel.
Default is @code{1} for @var{aa}, and @code{0} for @var{ar}, @var{ag} and @var{ab}.

Allowed ranges for options are @code{[-2.0, 2.0]}.
@end table

@subsection Examples

@itemize
@item
Convert source to grayscale:
@example
colorchannelmixer=.3:.4:.3:0:.3:.4:.3:0:.3:.4:.3
@end example
@end itemize

@section colormatrix

Convert color matrix.

The filter accepts the following options:

@table @option
@item src
@item dst
Specify the source and destination color matrix. Both values must be
specified.

The accepted values are:
@table @samp
@item bt709
BT.709

@item bt601
BT.601

@item smpte240m
SMPTE-240M

@item fcc
FCC
@end table
@end table

For example to convert from BT.601 to SMPTE-240M, use the command:
@example
colormatrix=bt601:smpte240m
@end example

@section copy

Copy the input source unchanged to the output. Mainly useful for
testing purposes.

@section crop

Crop the input video to given dimensions.

The filter accepts the following options:

@table @option
@item w, out_w
Width of the output video. It defaults to @code{iw}.
This expression is evaluated only once during the filter
configuration.

@item h, out_h
Height of the output video. It defaults to @code{ih}.
This expression is evaluated only once during the filter
configuration.

@item x
Horizontal position, in the input video, of the left edge of the output video.
It defaults to @code{(in_w-out_w)/2}.
This expression is evaluated per-frame.

@item y
Vertical position, in the input video, of the top edge of the output video.
It defaults to @code{(in_h-out_h)/2}.
This expression is evaluated per-frame.

@item keep_aspect
If set to 1 will force the output display aspect ratio
to be the same of the input, by changing the output sample aspect
ratio. It defaults to 0.
@end table

The @var{out_w}, @var{out_h}, @var{x}, @var{y} parameters are
expressions containing the following constants:

@table @option
@item x
@item y
the computed values for @var{x} and @var{y}. They are evaluated for
each new frame.

@item in_w
@item in_h
the input width and height

@item iw
@item ih
same as @var{in_w} and @var{in_h}

@item out_w
@item out_h
the output (cropped) width and height

@item ow
@item oh
same as @var{out_w} and @var{out_h}

@item a
same as @var{iw} / @var{ih}

@item sar
input sample aspect ratio

@item dar
input display aspect ratio, it is the same as (@var{iw} / @var{ih}) * @var{sar}

@item hsub
@item vsub
horizontal and vertical chroma subsample values. For example for the
pixel format "yuv422p" @var{hsub} is 2 and @var{vsub} is 1.

@item n
the number of input frame, starting from 0

@item pos
the position in the file of the input frame, NAN if unknown

@item t
timestamp expressed in seconds, NAN if the input timestamp is unknown

@end table

The expression for @var{out_w} may depend on the value of @var{out_h},
and the expression for @var{out_h} may depend on @var{out_w}, but they
cannot depend on @var{x} and @var{y}, as @var{x} and @var{y} are
evaluated after @var{out_w} and @var{out_h}.

The @var{x} and @var{y} parameters specify the expressions for the
position of the top-left corner of the output (non-cropped) area. They
are evaluated for each frame. If the evaluated value is not valid, it
is approximated to the nearest valid value.

The expression for @var{x} may depend on @var{y}, and the expression
for @var{y} may depend on @var{x}.

@subsection Examples

@itemize
@item
Crop area with size 100x100 at position (12,34).
@example
crop=100:100:12:34
@end example

Using named options, the example above becomes:
@example
crop=w=100:h=100:x=12:y=34
@end example

@item
Crop the central input area with size 100x100:
@example
crop=100:100
@end example

@item
Crop the central input area with size 2/3 of the input video:
@example
crop=2/3*in_w:2/3*in_h
@end example

@item
Crop the input video central square:
@example
crop=out_w=in_h
crop=in_h
@end example

@item
Delimit the rectangle with the top-left corner placed at position
100:100 and the right-bottom corner corresponding to the right-bottom
corner of the input image:
@example
crop=in_w-100:in_h-100:100:100
@end example

@item
Crop 10 pixels from the left and right borders, and 20 pixels from
the top and bottom borders
@example
crop=in_w-2*10:in_h-2*20
@end example

@item
Keep only the bottom right quarter of the input image:
@example
crop=in_w/2:in_h/2:in_w/2:in_h/2
@end example

@item
Crop height for getting Greek harmony:
@example
crop=in_w:1/PHI*in_w
@end example

@item
Appply trembling effect:
@example
crop=in_w/2:in_h/2:(in_w-out_w)/2+((in_w-out_w)/2)*sin(n/10):(in_h-out_h)/2 +((in_h-out_h)/2)*sin(n/7)
@end example

@item
Apply erratic camera effect depending on timestamp:
@example
crop=in_w/2:in_h/2:(in_w-out_w)/2+((in_w-out_w)/2)*sin(t*10):(in_h-out_h)/2 +((in_h-out_h)/2)*sin(t*13)"
@end example

@item
Set x depending on the value of y:
@example
crop=in_w/2:in_h/2:y:10+10*sin(n/10)
@end example
@end itemize

@section cropdetect

Auto-detect crop size.

Calculate necessary cropping parameters and prints the recommended
parameters through the logging system. The detected dimensions
correspond to the non-black area of the input video.

The filter accepts the following options:

@table @option

@item limit
Set higher black value threshold, which can be optionally specified
from nothing (0) to everything (255). An intensity value greater
to the set value is considered non-black. Default value is 24.

@item round
Set the value for which the width/height should be divisible by. The
offset is automatically adjusted to center the video. Use 2 to get
only even dimensions (needed for 4:2:2 video). 16 is best when
encoding to most video codecs. Default value is 16.

@item reset_count, reset
Set the counter that determines after how many frames cropdetect will
reset the previously detected largest video area and start over to
detect the current optimal crop area. Default value is 0.

This can be useful when channel logos distort the video area. 0
indicates never reset and return the largest area encountered during
playback.
@end table

@anchor{curves}
@section curves

Apply color adjustments using curves.

This filter is similar to the Adobe Photoshop and GIMP curves tools. Each
component (red, green and blue) has its values defined by @var{N} key points
tied from each other using a smooth curve. The x-axis represents the pixel
values from the input frame, and the y-axis the new pixel values to be set for
the output frame.

By default, a component curve is defined by the two points @var{(0;0)} and
@var{(1;1)}. This creates a straight line where each original pixel value is
"adjusted" to its own value, which means no change to the image.

The filter allows you to redefine these two points and add some more. A new
curve (using a natural cubic spline interpolation) will be define to pass
smoothly through all these new coordinates. The new defined points needs to be
strictly increasing over the x-axis, and their @var{x} and @var{y} values must
be in the @var{[0;1]} interval.  If the computed curves happened to go outside
the vector spaces, the values will be clipped accordingly.

If there is no key point defined in @code{x=0}, the filter will automatically
insert a @var{(0;0)} point. In the same way, if there is no key point defined
in @code{x=1}, the filter will automatically insert a @var{(1;1)} point.

The filter accepts the following options:

@table @option
@item preset
Select one of the available color presets. This option can be used in addition
to the @option{r}, @option{g}, @option{b} parameters; in this case, the later
options takes priority on the preset values.
Available presets are:
@table @samp
@item none
@item color_negative
@item cross_process
@item darker
@item increase_contrast
@item lighter
@item linear_contrast
@item medium_contrast
@item negative
@item strong_contrast
@item vintage
@end table
Default is @code{none}.
@item master, m
Set the master key points. These points will define a second pass mapping. It
is sometimes called a "luminance" or "value" mapping. It can be used with
@option{r}, @option{g}, @option{b} or @option{all} since it acts like a
post-processing LUT.
@item red, r
Set the key points for the red component.
@item green, g
Set the key points for the green component.
@item blue, b
Set the key points for the blue component.
@item all
Set the key points for all components (not including master).
Can be used in addition to the other key points component
options. In this case, the unset component(s) will fallback on this
@option{all} setting.
@item psfile
Specify a Photoshop curves file (@code{.asv}) to import the settings from.
@end table

To avoid some filtergraph syntax conflicts, each key points list need to be
defined using the following syntax: @code{x0/y0 x1/y1 x2/y2 ...}.

@subsection Examples

@itemize
@item
Increase slightly the middle level of blue:
@example
curves=blue='0.5/0.58'
@end example

@item
Vintage effect:
@example
curves=r='0/0.11 .42/.51 1/0.95':g='0.50/0.48':b='0/0.22 .49/.44 1/0.8'
@end example
Here we obtain the following coordinates for each components:
@table @var
@item red
@code{(0;0.11) (0.42;0.51) (1;0.95)}
@item green
@code{(0;0) (0.50;0.48) (1;1)}
@item blue
@code{(0;0.22) (0.49;0.44) (1;0.80)}
@end table

@item
The previous example can also be achieved with the associated built-in preset:
@example
curves=preset=vintage
@end example

@item
Or simply:
@example
curves=vintage
@end example

@item
Use a Photoshop preset and redefine the points of the green component:
@example
curves=psfile='MyCurvesPresets/purple.asv':green='0.45/0.53'
@end example
@end itemize

@section dctdnoiz

Denoise frames using 2D DCT (frequency domain filtering).

This filter is not designed for real time and can be extremely slow.

The filter accepts the following options:

@table @option
@item sigma, s
Set the noise sigma constant.

This @var{sigma} defines a hard threshold of @code{3 * sigma}; every DCT
coefficient (absolute value) below this threshold with be dropped.

If you need a more advanced filtering, see @option{expr}.

Default is @code{0}.

@item overlap
Set number overlapping pixels for each block. Each block is of size
@code{16x16}. Since the filter can be slow, you may want to reduce this value,
at the cost of a less effective filter and the risk of various artefacts.

If the overlapping value doesn't allow to process the whole input width or
height, a warning will be displayed and according borders won't be denoised.

Default value is @code{15}.

@item expr, e
Set the coefficient factor expression.

For each coefficient of a DCT block, this expression will be evaluated as a
multiplier value for the coefficient.

If this is option is set, the @option{sigma} option will be ignored.

The absolute value of the coefficient can be accessed through the @var{c}
variable.
@end table

@subsection Examples

Apply a denoise with a @option{sigma} of @code{4.5}:
@example
dctdnoiz=4.5
@end example

The same operation can be achieved using the expression system:
@example
dctdnoiz=e='gte(c, 4.5*3)'
@end example

@anchor{decimate}
@section decimate

Drop duplicated frames at regular intervals.

The filter accepts the following options:

@table @option
@item cycle
Set the number of frames from which one will be dropped. Setting this to
@var{N} means one frame in every batch of @var{N} frames will be dropped.
Default is @code{5}.

@item dupthresh
Set the threshold for duplicate detection. If the difference metric for a frame
is less than or equal to this value, then it is declared as duplicate. Default
is @code{1.1}

@item scthresh
Set scene change threshold. Default is @code{15}.

@item blockx
@item blocky
Set the size of the x and y-axis blocks used during metric calculations.
Larger blocks give better noise suppression, but also give worse detection of
small movements. Must be a power of two. Default is @code{32}.

@item ppsrc
Mark main input as a pre-processed input and activate clean source input
stream. This allows the input to be pre-processed with various filters to help
the metrics calculation while keeping the frame selection lossless. When set to
@code{1}, the first stream is for the pre-processed input, and the second
stream is the clean source from where the kept frames are chosen. Default is
@code{0}.

@item chroma
Set whether or not chroma is considered in the metric calculations. Default is
@code{1}.
@end table

@section delogo

Suppress a TV station logo by a simple interpolation of the surrounding
pixels. Just set a rectangle covering the logo and watch it disappear
(and sometimes something even uglier appear - your mileage may vary).

This filter accepts the following options:
@table @option

@item x
@item y
Specify the top left corner coordinates of the logo. They must be
specified.

@item w
@item h
Specify the width and height of the logo to clear. They must be
specified.

@item band, t
Specify the thickness of the fuzzy edge of the rectangle (added to
@var{w} and @var{h}). The default value is 4.

@item show
When set to 1, a green rectangle is drawn on the screen to simplify
finding the right @var{x}, @var{y}, @var{w}, @var{h} parameters, and
@var{band} is set to 4. The default value is 0.

@end table

@subsection Examples

@itemize
@item
Set a rectangle covering the area with top left corner coordinates 0,0
and size 100x77, setting a band of size 10:
@example
delogo=x=0:y=0:w=100:h=77:band=10
@end example

@end itemize

@section deshake

Attempt to fix small changes in horizontal and/or vertical shift. This
filter helps remove camera shake from hand-holding a camera, bumping a
tripod, moving on a vehicle, etc.

The filter accepts the following options:

@table @option

@item x
@item y
@item w
@item h
Specify a rectangular area where to limit the search for motion
vectors.
If desired the search for motion vectors can be limited to a
rectangular area of the frame defined by its top left corner, width
and height. These parameters have the same meaning as the drawbox
filter which can be used to visualise the position of the bounding
box.

This is useful when simultaneous movement of subjects within the frame
might be confused for camera motion by the motion vector search.

If any or all of @var{x}, @var{y}, @var{w} and @var{h} are set to -1
then the full frame is used. This allows later options to be set
without specifying the bounding box for the motion vector search.

Default - search the whole frame.

@item rx
@item ry
Specify the maximum extent of movement in x and y directions in the
range 0-64 pixels. Default 16.

@item edge
Specify how to generate pixels to fill blanks at the edge of the
frame. Available values are:
@table @samp
@item blank, 0
Fill zeroes at blank locations
@item original, 1
Original image at blank locations
@item clamp, 2
Extruded edge value at blank locations
@item mirror, 3
Mirrored edge at blank locations
@end table
Default value is @samp{mirror}.

@item blocksize
Specify the blocksize to use for motion search. Range 4-128 pixels,
default 8.

@item contrast
Specify the contrast threshold for blocks. Only blocks with more than
the specified contrast (difference between darkest and lightest
pixels) will be considered. Range 1-255, default 125.

@item search
Specify the search strategy. Available values are:
@table @samp
@item exhaustive, 0
Set exhaustive search
@item less, 1
Set less exhaustive search.
@end table
Default value is @samp{exhaustive}.

@item filename
If set then a detailed log of the motion search is written to the
specified file.

@item opencl
If set to 1, specify using OpenCL capabilities, only available if
FFmpeg was configured with @code{--enable-opencl}. Default value is 0.

@end table

@section drawbox

Draw a colored box on the input image.

This filter accepts the following options:

@table @option
@item x
@item y
Specify the top left corner coordinates of the box. Default to 0.

@item width, w
@item height, h
Specify the width and height of the box, if 0 they are interpreted as
the input width and height. Default to 0.

@item color, c
Specify the color of the box to write, it can be the name of a color
(case insensitive match) or a 0xRRGGBB[AA] sequence. If the special
value @code{invert} is used, the box edge color is the same as the
video with inverted luma.

@item thickness, t
Set the thickness of the box edge. Default value is @code{4}.
@end table

@subsection Examples

@itemize
@item
Draw a black box around the edge of the input image:
@example
drawbox
@end example

@item
Draw a box with color red and an opacity of 50%:
@example
drawbox=10:20:200:60:red@@0.5
@end example

The previous example can be specified as:
@example
drawbox=x=10:y=20:w=200:h=60:color=red@@0.5
@end example

@item
Fill the box with pink color:
@example
drawbox=x=10:y=10:w=100:h=100:color=pink@@0.5:t=max
@end example
@end itemize

@section drawgrid

Draw a grid on the input image.

This filter accepts the following options:

@table @option
@item x
@item y
Specify the coordinates of some point of grid intersection (meant to configure offset). Both default to 0.

@item width, w
@item height, h
Specify the width and height of the grid cell, if 0 they are interpreted as the
input width and height, respectively, minus @code{thickness}, so image gets
framed. Default to 0.

@item color, c
Specify the color of the grid, it can be the name of a color
(case insensitive match) or a 0xRRGGBB[AA] sequence. If the special
value @code{invert} is used, the grid color is the same as the
video with inverted luma.
Note that you can append opacity value (in range of 0.0 - 1.0)
to color name after @@ sign.

@item thickness, t
Set the thickness of the grid line. Default value is @code{1}.
@end table

@subsection Examples

@itemize
@item
Draw a grid with cell 100x100 pixels, thickness 2 pixels, with color red and an opacity of 50%:
@example
drawgrid=width=100:height=100:thickness=2:color=red@@0.5
@end example
@end itemize

@anchor{drawtext}
@section drawtext

Draw text string or text from specified file on top of video using the
libfreetype library.

To enable compilation of this filter you need to configure FFmpeg with
@code{--enable-libfreetype}.

@subsection Syntax

The description of the accepted parameters follows.

@table @option

@item box
Used to draw a box around text using background color.
Value should be either 1 (enable) or 0 (disable).
The default value of @var{box} is 0.

@item boxcolor
The color to be used for drawing box around text.
Either a string (e.g. "yellow") or in 0xRRGGBB[AA] format
(e.g. "0xff00ff"), possibly followed by an alpha specifier.
The default value of @var{boxcolor} is "white".

@item draw
Set an expression which specifies if the text should be drawn. If the
expression evaluates to 0, the text is not drawn. This is useful for
specifying that the text should be drawn only when specific conditions
are met.

Default value is "1".

See below for the list of accepted constants and functions.

@item expansion
Select how the @var{text} is expanded. Can be either @code{none},
@code{strftime} (deprecated) or
@code{normal} (default). See the @ref{drawtext_expansion, Text expansion} section
below for details.

@item fix_bounds
If true, check and fix text coords to avoid clipping.

@item fontcolor
The color to be used for drawing fonts.
Either a string (e.g. "red") or in 0xRRGGBB[AA] format
(e.g. "0xff000033"), possibly followed by an alpha specifier.
The default value of @var{fontcolor} is "black".

@item fontfile
The font file to be used for drawing text. Path must be included.
This parameter is mandatory.

@item fontsize
The font size to be used for drawing text.
The default value of @var{fontsize} is 16.

@item ft_load_flags
Flags to be used for loading the fonts.

The flags map the corresponding flags supported by libfreetype, and are
a combination of the following values:
@table @var
@item default
@item no_scale
@item no_hinting
@item render
@item no_bitmap
@item vertical_layout
@item force_autohint
@item crop_bitmap
@item pedantic
@item ignore_global_advance_width
@item no_recurse
@item ignore_transform
@item monochrome
@item linear_design
@item no_autohint
@end table

Default value is "render".

For more information consult the documentation for the FT_LOAD_*
libfreetype flags.

@item shadowcolor
The color to be used for drawing a shadow behind the drawn text.  It
can be a color name (e.g. "yellow") or a string in the 0xRRGGBB[AA]
form (e.g. "0xff00ff"), possibly followed by an alpha specifier.
The default value of @var{shadowcolor} is "black".

@item shadowx
@item shadowy
The x and y offsets for the text shadow position with respect to the
position of the text. They can be either positive or negative
values. Default value for both is "0".

@item tabsize
The size in number of spaces to use for rendering the tab.
Default value is 4.

@item timecode
Set the initial timecode representation in "hh:mm:ss[:;.]ff"
format. It can be used with or without text parameter. @var{timecode_rate}
option must be specified.

@item timecode_rate, rate, r
Set the timecode frame rate (timecode only).

@item text
The text string to be drawn. The text must be a sequence of UTF-8
encoded characters.
This parameter is mandatory if no file is specified with the parameter
@var{textfile}.

@item textfile
A text file containing text to be drawn. The text must be a sequence
of UTF-8 encoded characters.

This parameter is mandatory if no text string is specified with the
parameter @var{text}.

If both @var{text} and @var{textfile} are specified, an error is thrown.

@item reload
If set to 1, the @var{textfile} will be reloaded before each frame.
Be sure to update it atomically, or it may be read partially, or even fail.

@item x
@item y
The expressions which specify the offsets where text will be drawn
within the video frame. They are relative to the top/left border of the
output image.

The default value of @var{x} and @var{y} is "0".

See below for the list of accepted constants and functions.
@end table

The parameters for @var{x} and @var{y} are expressions containing the
following constants and functions:

@table @option
@item dar
input display aspect ratio, it is the same as (@var{w} / @var{h}) * @var{sar}

@item hsub
@item vsub
horizontal and vertical chroma subsample values. For example for the
pixel format "yuv422p" @var{hsub} is 2 and @var{vsub} is 1.

@item line_h, lh
the height of each text line

@item main_h, h, H
the input height

@item main_w, w, W
the input width

@item max_glyph_a, ascent
the maximum distance from the baseline to the highest/upper grid
coordinate used to place a glyph outline point, for all the rendered
glyphs.
It is a positive value, due to the grid's orientation with the Y axis
upwards.

@item max_glyph_d, descent
the maximum distance from the baseline to the lowest grid coordinate
used to place a glyph outline point, for all the rendered glyphs.
This is a negative value, due to the grid's orientation, with the Y axis
upwards.

@item max_glyph_h
maximum glyph height, that is the maximum height for all the glyphs
contained in the rendered text, it is equivalent to @var{ascent} -
@var{descent}.

@item max_glyph_w
maximum glyph width, that is the maximum width for all the glyphs
contained in the rendered text

@item n
the number of input frame, starting from 0

@item rand(min, max)
return a random number included between @var{min} and @var{max}

@item sar
input sample aspect ratio

@item t
timestamp expressed in seconds, NAN if the input timestamp is unknown

@item text_h, th
the height of the rendered text

@item text_w, tw
the width of the rendered text

@item x
@item y
the x and y offset coordinates where the text is drawn.

These parameters allow the @var{x} and @var{y} expressions to refer
each other, so you can for example specify @code{y=x/dar}.
@end table

If libavfilter was built with @code{--enable-fontconfig}, then
@option{fontfile} can be a fontconfig pattern or omitted.

@anchor{drawtext_expansion}
@subsection Text expansion

If @option{expansion} is set to @code{strftime},
the filter recognizes strftime() sequences in the provided text and
expands them accordingly. Check the documentation of strftime(). This
feature is deprecated.

If @option{expansion} is set to @code{none}, the text is printed verbatim.

If @option{expansion} is set to @code{normal} (which is the default),
the following expansion mechanism is used.

The backslash character '\', followed by any character, always expands to
the second character.

Sequence of the form @code{%@{...@}} are expanded. The text between the
braces is a function name, possibly followed by arguments separated by ':'.
If the arguments contain special characters or delimiters (':' or '@}'),
they should be escaped.

Note that they probably must also be escaped as the value for the
@option{text} option in the filter argument string and as the filter
argument in the filtergraph description, and possibly also for the shell,
that makes up to four levels of escaping; using a text file avoids these
problems.

The following functions are available:

@table @command

@item expr, e
The expression evaluation result.

It must take one argument specifying the expression to be evaluated,
which accepts the same constants and functions as the @var{x} and
@var{y} values. Note that not all constants should be used, for
example the text size is not known when evaluating the expression, so
the constants @var{text_w} and @var{text_h} will have an undefined
value.

@item gmtime
The time at which the filter is running, expressed in UTC.
It can accept an argument: a strftime() format string.

@item localtime
The time at which the filter is running, expressed in the local time zone.
It can accept an argument: a strftime() format string.

@item n, frame_num
The frame number, starting from 0.

@item pict_type
A 1 character description of the current picture type.

@item pts
The timestamp of the current frame, in seconds, with microsecond accuracy.

@end table

@subsection Examples

@itemize
@item
Draw "Test Text" with font FreeSerif, using the default values for the
optional parameters.

@example
drawtext="fontfile=/usr/share/fonts/truetype/freefont/FreeSerif.ttf: text='Test Text'"
@end example

@item
Draw 'Test Text' with font FreeSerif of size 24 at position x=100
and y=50 (counting from the top-left corner of the screen), text is
yellow with a red box around it. Both the text and the box have an
opacity of 20%.

@example
drawtext="fontfile=/usr/share/fonts/truetype/freefont/FreeSerif.ttf: text='Test Text':\
          x=100: y=50: fontsize=24: fontcolor=yellow@@0.2: box=1: boxcolor=red@@0.2"
@end example

Note that the double quotes are not necessary if spaces are not used
within the parameter list.

@item
Show the text at the center of the video frame:
@example
drawtext="fontsize=30:fontfile=FreeSerif.ttf:text='hello world':x=(w-text_w)/2:y=(h-text_h-line_h)/2"
@end example

@item
Show a text line sliding from right to left in the last row of the video
frame. The file @file{LONG_LINE} is assumed to contain a single line
with no newlines.
@example
drawtext="fontsize=15:fontfile=FreeSerif.ttf:text=LONG_LINE:y=h-line_h:x=-50*t"
@end example

@item
Show the content of file @file{CREDITS} off the bottom of the frame and scroll up.
@example
drawtext="fontsize=20:fontfile=FreeSerif.ttf:textfile=CREDITS:y=h-20*t"
@end example

@item
Draw a single green letter "g", at the center of the input video.
The glyph baseline is placed at half screen height.
@example
drawtext="fontsize=60:fontfile=FreeSerif.ttf:fontcolor=green:text=g:x=(w-max_glyph_w)/2:y=h/2-ascent"
@end example

@item
Show text for 1 second every 3 seconds:
@example
drawtext="fontfile=FreeSerif.ttf:fontcolor=white:x=100:y=x/dar:draw=lt(mod(t\,3)\,1):text='blink'"
@end example

@item
Use fontconfig to set the font. Note that the colons need to be escaped.
@example
drawtext='fontfile=Linux Libertine O-40\:style=Semibold:text=FFmpeg'
@end example

@item
Print the date of a real-time encoding (see strftime(3)):
@example
drawtext='fontfile=FreeSans.ttf:text=%@{localtime:%a %b %d %Y@}'
@end example

@end itemize

For more information about libfreetype, check:
@url{http://www.freetype.org/}.

For more information about fontconfig, check:
@url{http://freedesktop.org/software/fontconfig/fontconfig-user.html}.

@section edgedetect

Detect and draw edges. The filter uses the Canny Edge Detection algorithm.

The filter accepts the following options:

@table @option
@item low
@item high
Set low and high threshold values used by the Canny thresholding
algorithm.

The high threshold selects the "strong" edge pixels, which are then
connected through 8-connectivity with the "weak" edge pixels selected
by the low threshold.

@var{low} and @var{high} threshold values must be choosen in the range
[0,1], and @var{low} should be lesser or equal to @var{high}.

Default value for @var{low} is @code{20/255}, and default value for @var{high}
is @code{50/255}.
@end table

Example:
@example
edgedetect=low=0.1:high=0.4
@end example

@section extractplanes

Extract color channel components from input video stream into
separate grayscale video streams.

The filter accepts the following option:

@table @option
@item planes
Set plane(s) to extract.

Available values for planes are:
@table @samp
@item y
@item u
@item v
@item a
@item r
@item g
@item b
@end table

Choosing planes not available in the input will result in an error.
That means you cannot select @code{r}, @code{g}, @code{b} planes
with @code{y}, @code{u}, @code{v} planes at same time.
@end table

@subsection Examples

@itemize
@item
Extract luma, u and v color channel component from input video frame
into 3 grayscale outputs:
@example
ffmpeg -i video.avi -filter_complex 'extractplanes=y+u+v[y][u][v]' -map '[y]' y.avi -map '[u]' u.avi -map '[v]' v.avi
@end example
@end itemize

@section fade

Apply fade-in/out effect to input video.

This filter accepts the following options:

@table @option
@item type, t
The effect type -- can be either "in" for fade-in, or "out" for a fade-out
effect.
Default is @code{in}.

@item start_frame, s
Specify the number of the start frame for starting to apply the fade
effect. Default is 0.

@item nb_frames, n
The number of frames for which the fade effect has to last. At the end of the
fade-in effect the output video will have the same intensity as the input video,
at the end of the fade-out transition the output video will be completely black.
Default is 25.

@item alpha
If set to 1, fade only alpha channel, if one exists on the input.
Default value is 0.

@item start_time, st
Specify the timestamp (in seconds) of the frame to start to apply the fade
effect. If both start_frame and start_time are specified, the fade will start at
whichever comes last.  Default is 0.

@item duration, d
The number of seconds for which the fade effect has to last. At the end of the
fade-in effect the output video will have the same intensity as the input video,
at the end of the fade-out transition the output video will be completely black.
If both duration and nb_frames are specified, duration is used. Default is 0.
@end table

@subsection Examples

@itemize
@item
Fade in first 30 frames of video:
@example
fade=in:0:30
@end example

The command above is equivalent to:
@example
fade=t=in:s=0:n=30
@end example

@item
Fade out last 45 frames of a 200-frame video:
@example
fade=out:155:45
fade=type=out:start_frame=155:nb_frames=45
@end example

@item
Fade in first 25 frames and fade out last 25 frames of a 1000-frame video:
@example
fade=in:0:25, fade=out:975:25
@end example

@item
Make first 5 frames black, then fade in from frame 5-24:
@example
fade=in:5:20
@end example

@item
Fade in alpha over first 25 frames of video:
@example
fade=in:0:25:alpha=1
@end example

@item
Make first 5.5 seconds black, then fade in for 0.5 seconds:
@example
fade=t=in:st=5.5:d=0.5
@end example

@end itemize

@section field

Extract a single field from an interlaced image using stride
arithmetic to avoid wasting CPU time. The output frames are marked as
non-interlaced.

The filter accepts the following options:

@table @option
@item type
Specify whether to extract the top (if the value is @code{0} or
@code{top}) or the bottom field (if the value is @code{1} or
@code{bottom}).
@end table

@section fieldmatch

Field matching filter for inverse telecine. It is meant to reconstruct the
progressive frames from a telecined stream. The filter does not drop duplicated
frames, so to achieve a complete inverse telecine @code{fieldmatch} needs to be
followed by a decimation filter such as @ref{decimate} in the filtergraph.

The separation of the field matching and the decimation is notably motivated by
the possibility of inserting a de-interlacing filter fallback between the two.
If the source has mixed telecined and real interlaced content,
@code{fieldmatch} will not be able to match fields for the interlaced parts.
But these remaining combed frames will be marked as interlaced, and thus can be
de-interlaced by a later filter such as @ref{yadif} before decimation.

In addition to the various configuration options, @code{fieldmatch} can take an
optional second stream, activated through the @option{ppsrc} option. If
enabled, the frames reconstruction will be based on the fields and frames from
this second stream. This allows the first input to be pre-processed in order to
help the various algorithms of the filter, while keeping the output lossless
(assuming the fields are matched properly). Typically, a field-aware denoiser,
or brightness/contrast adjustments can help.

Note that this filter uses the same algorithms as TIVTC/TFM (AviSynth project)
and VIVTC/VFM (VapourSynth project). The later is a light clone of TFM from
which @code{fieldmatch} is based on. While the semantic and usage are very
close, some behaviour and options names can differ.

The filter accepts the following options:

@table @option
@item order
Specify the assumed field order of the input stream. Available values are:

@table @samp
@item auto
Auto detect parity (use FFmpeg's internal parity value).
@item bff
Assume bottom field first.
@item tff
Assume top field first.
@end table

Note that it is sometimes recommended not to trust the parity announced by the
stream.

Default value is @var{auto}.

@item mode
Set the matching mode or strategy to use. @option{pc} mode is the safest in the
sense that it wont risk creating jerkiness due to duplicate frames when
possible, but if there are bad edits or blended fields it will end up
outputting combed frames when a good match might actually exist. On the other
hand, @option{pcn_ub} mode is the most risky in terms of creating jerkiness,
but will almost always find a good frame if there is one. The other values are
all somewhere in between @option{pc} and @option{pcn_ub} in terms of risking
jerkiness and creating duplicate frames versus finding good matches in sections
with bad edits, orphaned fields, blended fields, etc.

More details about p/c/n/u/b are available in @ref{p/c/n/u/b meaning} section.

Available values are:

@table @samp
@item pc
2-way matching (p/c)
@item pc_n
2-way matching, and trying 3rd match if still combed (p/c + n)
@item pc_u
2-way matching, and trying 3rd match (same order) if still combed (p/c + u)
@item pc_n_ub
2-way matching, trying 3rd match if still combed, and trying 4th/5th matches if
still combed (p/c + n + u/b)
@item pcn
3-way matching (p/c/n)
@item pcn_ub
3-way matching, and trying 4th/5th matches if all 3 of the original matches are
detected as combed (p/c/n + u/b)
@end table

The parenthesis at the end indicate the matches that would be used for that
mode assuming @option{order}=@var{tff} (and @option{field} on @var{auto} or
@var{top}).

In terms of speed @option{pc} mode is by far the fastest and @option{pcn_ub} is
the slowest.

Default value is @var{pc_n}.

@item ppsrc
Mark the main input stream as a pre-processed input, and enable the secondary
input stream as the clean source to pick the fields from. See the filter
introduction for more details. It is similar to the @option{clip2} feature from
VFM/TFM.

Default value is @code{0} (disabled).

@item field
Set the field to match from. It is recommended to set this to the same value as
@option{order} unless you experience matching failures with that setting. In
certain circumstances changing the field that is used to match from can have a
large impact on matching performance. Available values are:

@table @samp
@item auto
Automatic (same value as @option{order}).
@item bottom
Match from the bottom field.
@item top
Match from the top field.
@end table

Default value is @var{auto}.

@item mchroma
Set whether or not chroma is included during the match comparisons. In most
cases it is recommended to leave this enabled. You should set this to @code{0}
only if your clip has bad chroma problems such as heavy rainbowing or other
artifacts. Setting this to @code{0} could also be used to speed things up at
the cost of some accuracy.

Default value is @code{1}.

@item y0
@item y1
These define an exclusion band which excludes the lines between @option{y0} and
@option{y1} from being included in the field matching decision. An exclusion
band can be used to ignore subtitles, a logo, or other things that may
interfere with the matching. @option{y0} sets the starting scan line and
@option{y1} sets the ending line; all lines in between @option{y0} and
@option{y1} (including @option{y0} and @option{y1}) will be ignored. Setting
@option{y0} and @option{y1} to the same value will disable the feature.
@option{y0} and @option{y1} defaults to @code{0}.

@item scthresh
Set the scene change detection threshold as a percentage of maximum change on
the luma plane. Good values are in the @code{[8.0, 14.0]} range. Scene change
detection is only relevant in case @option{combmatch}=@var{sc}.  The range for
@option{scthresh} is @code{[0.0, 100.0]}.

Default value is @code{12.0}.

@item combmatch
When @option{combatch} is not @var{none}, @code{fieldmatch} will take into
account the combed scores of matches when deciding what match to use as the
final match. Available values are:

@table @samp
@item none
No final matching based on combed scores.
@item sc
Combed scores are only used when a scene change is detected.
@item full
Use combed scores all the time.
@end table

Default is @var{sc}.

@item combdbg
Force @code{fieldmatch} to calculate the combed metrics for certain matches and
print them. This setting is known as @option{micout} in TFM/VFM vocabulary.
Available values are:

@table @samp
@item none
No forced calculation.
@item pcn
Force p/c/n calculations.
@item pcnub
Force p/c/n/u/b calculations.
@end table

Default value is @var{none}.

@item cthresh
This is the area combing threshold used for combed frame detection. This
essentially controls how "strong" or "visible" combing must be to be detected.
Larger values mean combing must be more visible and smaller values mean combing
can be less visible or strong and still be detected. Valid settings are from
@code{-1} (every pixel will be detected as combed) to @code{255} (no pixel will
be detected as combed). This is basically a pixel difference value. A good
range is @code{[8, 12]}.

Default value is @code{9}.

@item chroma
Sets whether or not chroma is considered in the combed frame decision.  Only
disable this if your source has chroma problems (rainbowing, etc.) that are
causing problems for the combed frame detection with chroma enabled. Actually,
using @option{chroma}=@var{0} is usually more reliable, except for the case
where there is chroma only combing in the source.

Default value is @code{0}.

@item blockx
@item blocky
Respectively set the x-axis and y-axis size of the window used during combed
frame detection. This has to do with the size of the area in which
@option{combpel} pixels are required to be detected as combed for a frame to be
declared combed. See the @option{combpel} parameter description for more info.
Possible values are any number that is a power of 2 starting at 4 and going up
to 512.

Default value is @code{16}.

@item combpel
The number of combed pixels inside any of the @option{blocky} by
@option{blockx} size blocks on the frame for the frame to be detected as
combed. While @option{cthresh} controls how "visible" the combing must be, this
setting controls "how much" combing there must be in any localized area (a
window defined by the @option{blockx} and @option{blocky} settings) on the
frame. Minimum value is @code{0} and maximum is @code{blocky x blockx} (at
which point no frames will ever be detected as combed). This setting is known
as @option{MI} in TFM/VFM vocabulary.

Default value is @code{80}.
@end table

@anchor{p/c/n/u/b meaning}
@subsection p/c/n/u/b meaning

@subsubsection p/c/n

We assume the following telecined stream:

@example
Top fields:     1 2 2 3 4
Bottom fields:  1 2 3 4 4
@end example

The numbers correspond to the progressive frame the fields relate to. Here, the
first two frames are progressive, the 3rd and 4th are combed, and so on.

When @code{fieldmatch} is configured to run a matching from bottom
(@option{field}=@var{bottom}) this is how this input stream get transformed:

@example
Input stream:
                T     1 2 2 3 4
                B     1 2 3 4 4   <-- matching reference

Matches:              c c n n c

Output stream:
                T     1 2 3 4 4
                B     1 2 3 4 4
@end example

As a result of the field matching, we can see that some frames get duplicated.
To perform a complete inverse telecine, you need to rely on a decimation filter
after this operation. See for instance the @ref{decimate} filter.

The same operation now matching from top fields (@option{field}=@var{top})
looks like this:

@example
Input stream:
                T     1 2 2 3 4   <-- matching reference
                B     1 2 3 4 4

Matches:              c c p p c

Output stream:
                T     1 2 2 3 4
                B     1 2 2 3 4
@end example

In these examples, we can see what @var{p}, @var{c} and @var{n} mean;
basically, they refer to the frame and field of the opposite parity:

@itemize
@item @var{p} matches the field of the opposite parity in the previous frame
@item @var{c} matches the field of the opposite parity in the current frame
@item @var{n} matches the field of the opposite parity in the next frame
@end itemize

@subsubsection u/b

The @var{u} and @var{b} matching are a bit special in the sense that they match
from the opposite parity flag. In the following examples, we assume that we are
currently matching the 2nd frame (Top:2, bottom:2). According to the match, a
'x' is placed above and below each matched fields.

With bottom matching (@option{field}=@var{bottom}):
@example
Match:           c         p           n          b          u

                 x       x               x        x          x
  Top          1 2 2     1 2 2       1 2 2      1 2 2      1 2 2
  Bottom       1 2 3     1 2 3       1 2 3      1 2 3      1 2 3
                 x         x           x        x              x

Output frames:
                 2          1          2          2          2
                 2          2          2          1          3
@end example

With top matching (@option{field}=@var{top}):
@example
Match:           c         p           n          b          u

                 x         x           x        x              x
  Top          1 2 2     1 2 2       1 2 2      1 2 2      1 2 2
  Bottom       1 2 3     1 2 3       1 2 3      1 2 3      1 2 3
                 x       x               x        x          x

Output frames:
                 2          2          2          1          2
                 2          1          3          2          2
@end example

@subsection Examples

Simple IVTC of a top field first telecined stream:
@example
fieldmatch=order=tff:combmatch=none, decimate
@end example

Advanced IVTC, with fallback on @ref{yadif} for still combed frames:
@example
fieldmatch=order=tff:combmatch=full, yadif=deint=interlaced, decimate
@end example

@section fieldorder

Transform the field order of the input video.

This filter accepts the following options:

@table @option

@item order
Output field order. Valid values are @var{tff} for top field first or @var{bff}
for bottom field first.
@end table

Default value is @samp{tff}.

Transformation is achieved by shifting the picture content up or down
by one line, and filling the remaining line with appropriate picture content.
This method is consistent with most broadcast field order converters.

If the input video is not flagged as being interlaced, or it is already
flagged as being of the required output field order then this filter does
not alter the incoming video.

This filter is very useful when converting to or from PAL DV material,
which is bottom field first.

For example:
@example
ffmpeg -i in.vob -vf "fieldorder=bff" out.dv
@end example

@section fifo

Buffer input images and send them when they are requested.

This filter is mainly useful when auto-inserted by the libavfilter
framework.

The filter does not take parameters.

@anchor{format}
@section format

Convert the input video to one of the specified pixel formats.
Libavfilter will try to pick one that is supported for the input to
the next filter.

This filter accepts the following parameters:
@table @option

@item pix_fmts
A '|'-separated list of pixel format names, for example
"pix_fmts=yuv420p|monow|rgb24".

@end table

@subsection Examples

@itemize
@item
Convert the input video to the format @var{yuv420p}
@example
format=pix_fmts=yuv420p
@end example

Convert the input video to any of the formats in the list
@example
format=pix_fmts=yuv420p|yuv444p|yuv410p
@end example
@end itemize

@section fps

Convert the video to specified constant frame rate by duplicating or dropping
frames as necessary.

This filter accepts the following named parameters:
@table @option

@item fps
Desired output frame rate. The default is @code{25}.

@item round
Rounding method.

Possible values are:
@table @option
@item zero
zero round towards 0
@item inf
round away from 0
@item down
round towards -infinity
@item up
round towards +infinity
@item near
round to nearest
@end table
The default is @code{near}.

@end table

Alternatively, the options can be specified as a flat string:
@var{fps}[:@var{round}].

See also the @ref{setpts} filter.

@subsection Examples

@itemize
@item
A typical usage in order to set the fps to 25:
@example
fps=fps=25
@end example

@item
Sets the fps to 24, using abbreviation and rounding method to round to nearest:
@example
fps=fps=film:round=near
@end example
@end itemize

@section framestep

Select one frame every N-th frame.

This filter accepts the following option:
@table @option
@item step
Select frame after every @code{step} frames.
Allowed values are positive integers higher than 0. Default value is @code{1}.
@end table

@anchor{frei0r}
@section frei0r

Apply a frei0r effect to the input video.

To enable compilation of this filter you need to install the frei0r
header and configure FFmpeg with @code{--enable-frei0r}.

This filter accepts the following options:

@table @option

@item filter_name
The name to the frei0r effect to load. If the environment variable
@env{FREI0R_PATH} is defined, the frei0r effect is searched in each one of the
directories specified by the colon separated list in @env{FREIOR_PATH},
otherwise in the standard frei0r paths, which are in this order:
@file{HOME/.frei0r-1/lib/}, @file{/usr/local/lib/frei0r-1/},
@file{/usr/lib/frei0r-1/}.

@item filter_params
A '|'-separated list of parameters to pass to the frei0r effect.

@end table

A frei0r effect parameter can be a boolean (whose values are specified
with "y" and "n"), a double, a color (specified by the syntax
@var{R}/@var{G}/@var{B}, @var{R}, @var{G}, and @var{B} being float
numbers from 0.0 to 1.0) or by an @code{av_parse_color()} color
description), a position (specified by the syntax @var{X}/@var{Y},
@var{X} and @var{Y} being float numbers) and a string.

The number and kind of parameters depend on the loaded effect. If an
effect parameter is not specified the default value is set.

@subsection Examples

@itemize
@item
Apply the distort0r effect, set the first two double parameters:
@example
frei0r=filter_name=distort0r:filter_params=0.5|0.01
@end example

@item
Apply the colordistance effect, take a color as first parameter:
@example
frei0r=colordistance:0.2/0.3/0.4
frei0r=colordistance:violet
frei0r=colordistance:0x112233
@end example

@item
Apply the perspective effect, specify the top left and top right image
positions:
@example
frei0r=perspective:0.2/0.2|0.8/0.2
@end example
@end itemize

For more information see:
@url{http://frei0r.dyne.org}

@section geq

The filter accepts the following options:

@table @option
@item lum_expr
Set the luminance expression.
@item cb_expr
Set the chrominance blue expression.
@item cr_expr
Set the chrominance red expression.
@item alpha_expr
Set the alpha expression.
@item r
Set the red expression.
@item g
Set the green expression.
@item b
Set the blue expression.
@end table

The colorspace is selected according to the specified options. If
one of the @option{lum_expr}, @option{cb_expr}, or @option{cr_expr}
options is specified, the filter will automatically select a YCbCr
colorspace. If one of the @option{r}, @option{g}, or @option{b}
options is specified, it will select an RGB colorspace.

If one of the chrominance expression is not defined, it falls back on the other
one. If no alpha expression is specified it will evaluate to opaque value.
If none of chrominance expressions are specified, they will evaluate
to the luminance expression.

The expressions can use the following variables and functions:

@table @option
@item N
The sequential number of the filtered frame, starting from @code{0}.

@item X
@item Y
The coordinates of the current sample.

@item W
@item H
The width and height of the image.

@item SW
@item SH
Width and height scale depending on the currently filtered plane. It is the
ratio between the corresponding luma plane number of pixels and the current
plane ones. E.g. for YUV4:2:0 the values are @code{1,1} for the luma plane, and
@code{0.5,0.5} for chroma planes.

@item T
Time of the current frame, expressed in seconds.

@item p(x, y)
Return the value of the pixel at location (@var{x},@var{y}) of the current
plane.

@item lum(x, y)
Return the value of the pixel at location (@var{x},@var{y}) of the luminance
plane.

@item cb(x, y)
Return the value of the pixel at location (@var{x},@var{y}) of the
blue-difference chroma plane. Return 0 if there is no such plane.

@item cr(x, y)
Return the value of the pixel at location (@var{x},@var{y}) of the
red-difference chroma plane. Return 0 if there is no such plane.

@item r(x, y)
@item g(x, y)
@item b(x, y)
Return the value of the pixel at location (@var{x},@var{y}) of the
red/green/blue component. Return 0 if there is no such component.

@item alpha(x, y)
Return the value of the pixel at location (@var{x},@var{y}) of the alpha
plane. Return 0 if there is no such plane.
@end table

For functions, if @var{x} and @var{y} are outside the area, the value will be
automatically clipped to the closer edge.

@subsection Examples

@itemize
@item
Flip the image horizontally:
@example
geq=p(W-X\,Y)
@end example

@item
Generate a bidimensional sine wave, with angle @code{PI/3} and a
wavelength of 100 pixels:
@example
geq=128 + 100*sin(2*(PI/100)*(cos(PI/3)*(X-50*T) + sin(PI/3)*Y)):128:128
@end example

@item
Generate a fancy enigmatic moving light:
@example
nullsrc=s=256x256,geq=random(1)/hypot(X-cos(N*0.07)*W/2-W/2\,Y-sin(N*0.09)*H/2-H/2)^2*1000000*sin(N*0.02):128:128
@end example

@item
Generate a quick emboss effect:
@example
format=gray,geq=lum_expr='(p(X,Y)+(256-p(X-4,Y-4)))/2'
@end example

@item
Modify RGB components depending on pixel position:
@example
geq=r='X/W*r(X,Y)':g='(1-X/W)*g(X,Y)':b='(H-Y)/H*b(X,Y)'
@end example
@end itemize

@section gradfun

Fix the banding artifacts that are sometimes introduced into nearly flat
regions by truncation to 8bit color depth.
Interpolate the gradients that should go where the bands are, and
dither them.

This filter is designed for playback only.  Do not use it prior to
lossy compression, because compression tends to lose the dither and
bring back the bands.

This filter accepts the following options:

@table @option

@item strength
The maximum amount by which the filter will change any one pixel. Also the
threshold for detecting nearly flat regions. Acceptable values range from .51 to
64, default value is 1.2, out-of-range values will be clipped to the valid
range.

@item radius
The neighborhood to fit the gradient to. A larger radius makes for smoother
gradients, but also prevents the filter from modifying the pixels near detailed
regions. Acceptable values are 8-32, default value is 16, out-of-range values
will be clipped to the valid range.

@end table

Alternatively, the options can be specified as a flat string:
@var{strength}[:@var{radius}]

@subsection Examples

@itemize
@item
Apply the filter with a @code{3.5} strength and radius of @code{8}:
@example
gradfun=3.5:8
@end example

@item
Specify radius, omitting the strength (which will fall-back to the default
value):
@example
gradfun=radius=8
@end example

@end itemize

@section hflip

Flip the input video horizontally.

For example to horizontally flip the input video with @command{ffmpeg}:
@example
ffmpeg -i in.avi -vf "hflip" out.avi
@end example

@section histeq
This filter applies a global color histogram equalization on a
per-frame basis.

It can be used to correct video that has a compressed range of pixel
intensities.  The filter redistributes the pixel intensities to
equalize their distribution across the intensity range. It may be
viewed as an "automatically adjusting contrast filter". This filter is
useful only for correcting degraded or poorly captured source
video.

The filter accepts the following options:

@table @option
@item strength
Determine the amount of equalization to be applied.  As the strength
is reduced, the distribution of pixel intensities more-and-more
approaches that of the input frame. The value must be a float number
in the range [0,1] and defaults to 0.200.

@item intensity
Set the maximum intensity that can generated and scale the output
values appropriately.  The strength should be set as desired and then
the intensity can be limited if needed to avoid washing-out. The value
must be a float number in the range [0,1] and defaults to 0.210.

@item antibanding
Set the antibanding level. If enabled the filter will randomly vary
the luminance of output pixels by a small amount to avoid banding of
the histogram. Possible values are @code{none}, @code{weak} or
@code{strong}. It defaults to @code{none}.
@end table

@section histogram

Compute and draw a color distribution histogram for the input video.

The computed histogram is a representation of distribution of color components
in an image.

The filter accepts the following options:

@table @option
@item mode
Set histogram mode.

It accepts the following values:
@table @samp
@item levels
standard histogram that display color components distribution in an image.
Displays color graph for each color component. Shows distribution
of the Y, U, V, A or G, B, R components, depending on input format,
in current frame. Bellow each graph is color component scale meter.

@item color
chroma values in vectorscope, if brighter more such chroma values are
distributed in an image.
Displays chroma values (U/V color placement) in two dimensional graph
(which is called a vectorscope). It can be used to read of the hue and
saturation of the current frame. At a same time it is a histogram.
The whiter a pixel in the vectorscope, the more pixels of the input frame
correspond to that pixel (that is the more pixels have this chroma value).
The V component is displayed on the horizontal (X) axis, with the leftmost
side being V = 0 and the rightmost side being V = 255.
The U component is displayed on the vertical (Y) axis, with the top
representing U = 0 and the bottom representing U = 255.

The position of a white pixel in the graph corresponds to the chroma value
of a pixel of the input clip. So the graph can be used to read of the
hue (color flavor) and the saturation (the dominance of the hue in the color).
As the hue of a color changes, it moves around the square. At the center of
the square, the saturation is zero, which means that the corresponding pixel
has no color. If you increase the amount of a specific color, while leaving
the other colors unchanged, the saturation increases, and you move towards
the edge of the square.

@item color2
chroma values in vectorscope, similar as @code{color} but actual chroma values
are displayed.

@item waveform
per row/column color component graph. In row mode graph in the left side represents
color component value 0 and right side represents value = 255. In column mode top
side represents color component value = 0 and bottom side represents value = 255.
@end table
Default value is @code{levels}.

@item level_height
Set height of level in @code{levels}. Default value is @code{200}.
Allowed range is [50, 2048].

@item scale_height
Set height of color scale in @code{levels}. Default value is @code{12}.
Allowed range is [0, 40].

@item step
Set step for @code{waveform} mode. Smaller values are useful to find out how much
of same luminance values across input rows/columns are distributed.
Default value is @code{10}. Allowed range is [1, 255].

@item waveform_mode
Set mode for @code{waveform}. Can be either @code{row}, or @code{column}.
Default is @code{row}.

@item display_mode
Set display mode for @code{waveform} and @code{levels}.
It accepts the following values:
@table @samp
@item parade
Display separate graph for the color components side by side in
@code{row} waveform mode or one below other in @code{column} waveform mode
for @code{waveform} histogram mode. For @code{levels} histogram mode
per color component graphs are placed one bellow other.

This display mode in @code{waveform} histogram mode makes it easy to spot
color casts in the highlights and shadows of an image, by comparing the
contours of the top and the bottom of each waveform.
Since whites, grays, and blacks are characterized by
exactly equal amounts of red, green, and blue, neutral areas of the
picture should display three waveforms of roughly equal width/height.
If not, the correction is easy to make by making adjustments to level the
three waveforms.

@item overlay
Presents information that's identical to that in the @code{parade}, except
that the graphs representing color components are superimposed directly
over one another.

This display mode in @code{waveform} histogram mode can make it easier to spot
the relative differences or similarities in overlapping areas of the color
components that are supposed to be identical, such as neutral whites, grays,
or blacks.
@end table
Default is @code{parade}.

@item levels_mode
Set mode for @code{levels}. Can be either @code{linear}, or @code{logarithmic}.
Default is @code{linear}.
@end table

@subsection Examples

@itemize

@item
Calculate and draw histogram:
@example
ffplay -i input -vf histogram
@end example

@end itemize

@anchor{hqdn3d}
@section hqdn3d

High precision/quality 3d denoise filter. This filter aims to reduce
image noise producing smooth images and making still images really
still. It should enhance compressibility.

It accepts the following optional parameters:

@table @option
@item luma_spatial
a non-negative float number which specifies spatial luma strength,
defaults to 4.0

@item chroma_spatial
a non-negative float number which specifies spatial chroma strength,
defaults to 3.0*@var{luma_spatial}/4.0

@item luma_tmp
a float number which specifies luma temporal strength, defaults to
6.0*@var{luma_spatial}/4.0

@item chroma_tmp
a float number which specifies chroma temporal strength, defaults to
@var{luma_tmp}*@var{chroma_spatial}/@var{luma_spatial}
@end table

@section hue

Modify the hue and/or the saturation of the input.

This filter accepts the following options:

@table @option
@item h
Specify the hue angle as a number of degrees. It accepts an expression,
and defaults to "0".

@item s
Specify the saturation in the [-10,10] range. It accepts an expression and
defaults to "1".

@item H
Specify the hue angle as a number of radians. It accepts an
expression, and defaults to "0".
@end table

@option{h} and @option{H} are mutually exclusive, and can't be
specified at the same time.

The @option{h}, @option{H} and @option{s} option values are
expressions containing the following constants:

@table @option
@item n
frame count of the input frame starting from 0

@item pts
presentation timestamp of the input frame expressed in time base units

@item r
frame rate of the input video, NAN if the input frame rate is unknown

@item t
timestamp expressed in seconds, NAN if the input timestamp is unknown

@item tb
time base of the input video
@end table

@subsection Examples

@itemize
@item
Set the hue to 90 degrees and the saturation to 1.0:
@example
hue=h=90:s=1
@end example

@item
Same command but expressing the hue in radians:
@example
hue=H=PI/2:s=1
@end example

@item
Rotate hue and make the saturation swing between 0
and 2 over a period of 1 second:
@example
hue="H=2*PI*t: s=sin(2*PI*t)+1"
@end example

@item
Apply a 3 seconds saturation fade-in effect starting at 0:
@example
hue="s=min(t/3\,1)"
@end example

The general fade-in expression can be written as:
@example
hue="s=min(0\, max((t-START)/DURATION\, 1))"
@end example

@item
Apply a 3 seconds saturation fade-out effect starting at 5 seconds:
@example
hue="s=max(0\, min(1\, (8-t)/3))"
@end example

The general fade-out expression can be written as:
@example
hue="s=max(0\, min(1\, (START+DURATION-t)/DURATION))"
@end example

@end itemize

@subsection Commands

This filter supports the following commands:
@table @option
@item s
@item h
@item H
Modify the hue and/or the saturation of the input video.
The command accepts the same syntax of the corresponding option.

If the specified expression is not valid, it is kept at its current
value.
@end table

@section idet

Detect video interlacing type.

This filter tries to detect if the input is interlaced or progressive,
top or bottom field first.

The filter accepts the following options:

@table @option
@item intl_thres
Set interlacing threshold.
@item prog_thres
Set progressive threshold.
@end table

@section il

Deinterleave or interleave fields.

This filter allows to process interlaced images fields without
deinterlacing them. Deinterleaving splits the input frame into 2
fields (so called half pictures). Odd lines are moved to the top
half of the output image, even lines to the bottom half.
You can process (filter) them independently and then re-interleave them.

The filter accepts the following options:

@table @option
@item luma_mode, l
@item chroma_mode, s
@item alpha_mode, a
Available values for @var{luma_mode}, @var{chroma_mode} and
@var{alpha_mode} are:

@table @samp
@item none
Do nothing.

@item deinterleave, d
Deinterleave fields, placing one above the other.

@item interleave, i
Interleave fields. Reverse the effect of deinterleaving.
@end table
Default value is @code{none}.

@item luma_swap, ls
@item chroma_swap, cs
@item alpha_swap, as
Swap luma/chroma/alpha fields. Exchange even & odd lines. Default value is @code{0}.
@end table

@section interlace

Simple interlacing filter from progressive contents. This interleaves upper (or
lower) lines from odd frames with lower (or upper) lines from even frames,
halving the frame rate and preserving image height.

@example
   Original        Original             New Frame
   Frame 'j'      Frame 'j+1'             (tff)
  ==========      ===========       ==================
    Line 0  -------------------->    Frame 'j' Line 0
    Line 1          Line 1  ---->   Frame 'j+1' Line 1
    Line 2 --------------------->    Frame 'j' Line 2
    Line 3          Line 3  ---->   Frame 'j+1' Line 3
     ...             ...                   ...
New Frame + 1 will be generated by Frame 'j+2' and Frame 'j+3' and so on
@end example

It accepts the following optional parameters:

@table @option
@item scan
determines whether the interlaced frame is taken from the even (tff - default)
or odd (bff) lines of the progressive frame.

@item lowpass
Enable (default) or disable the vertical lowpass filter to avoid twitter
interlacing and reduce moire patterns.
@end table

@section kerndeint

Deinterlace input video by applying Donald Graft's adaptive kernel
deinterling. Work on interlaced parts of a video to produce
progressive frames.

The description of the accepted parameters follows.

@table @option
@item thresh
Set the threshold which affects the filter's tolerance when
determining if a pixel line must be processed. It must be an integer
in the range [0,255] and defaults to 10. A value of 0 will result in
applying the process on every pixels.

@item map
Paint pixels exceeding the threshold value to white if set to 1.
Default is 0.

@item order
Set the fields order. Swap fields if set to 1, leave fields alone if
0. Default is 0.

@item sharp
Enable additional sharpening if set to 1. Default is 0.

@item twoway
Enable twoway sharpening if set to 1. Default is 0.
@end table

@subsection Examples

@itemize
@item
Apply default values:
@example
kerndeint=thresh=10:map=0:order=0:sharp=0:twoway=0
@end example

@item
Enable additional sharpening:
@example
kerndeint=sharp=1
@end example

@item
Paint processed pixels in white:
@example
kerndeint=map=1
@end example
@end itemize

@section lut, lutrgb, lutyuv

Compute a look-up table for binding each pixel component input value
to an output value, and apply it to input video.

@var{lutyuv} applies a lookup table to a YUV input video, @var{lutrgb}
to an RGB input video.

These filters accept the following options:
@table @option
@item c0
set first pixel component expression
@item c1
set second pixel component expression
@item c2
set third pixel component expression
@item c3
set fourth pixel component expression, corresponds to the alpha component

@item r
set red component expression
@item g
set green component expression
@item b
set blue component expression
@item a
alpha component expression

@item y
set Y/luminance component expression
@item u
set U/Cb component expression
@item v
set V/Cr component expression
@end table

Each of them specifies the expression to use for computing the lookup table for
the corresponding pixel component values.

The exact component associated to each of the @var{c*} options depends on the
format in input.

The @var{lut} filter requires either YUV or RGB pixel formats in input,
@var{lutrgb} requires RGB pixel formats in input, and @var{lutyuv} requires YUV.

The expressions can contain the following constants and functions:

@table @option
@item w
@item h
the input width and height

@item val
input value for the pixel component

@item clipval
the input value clipped in the @var{minval}-@var{maxval} range

@item maxval
maximum value for the pixel component

@item minval
minimum value for the pixel component

@item negval
the negated value for the pixel component value clipped in the
@var{minval}-@var{maxval} range , it corresponds to the expression
"maxval-clipval+minval"

@item clip(val)
the computed value in @var{val} clipped in the
@var{minval}-@var{maxval} range

@item gammaval(gamma)
the computed gamma correction value of the pixel component value
clipped in the @var{minval}-@var{maxval} range, corresponds to the
expression
"pow((clipval-minval)/(maxval-minval)\,@var{gamma})*(maxval-minval)+minval"

@end table

All expressions default to "val".

@subsection Examples

@itemize
@item
Negate input video:
@example
lutrgb="r=maxval+minval-val:g=maxval+minval-val:b=maxval+minval-val"
lutyuv="y=maxval+minval-val:u=maxval+minval-val:v=maxval+minval-val"
@end example

The above is the same as:
@example
lutrgb="r=negval:g=negval:b=negval"
lutyuv="y=negval:u=negval:v=negval"
@end example

@item
Negate luminance:
@example
lutyuv=y=negval
@end example

@item
Remove chroma components, turns the video into a graytone image:
@example
lutyuv="u=128:v=128"
@end example

@item
Apply a luma burning effect:
@example
lutyuv="y=2*val"
@end example

@item
Remove green and blue components:
@example
lutrgb="g=0:b=0"
@end example

@item
Set a constant alpha channel value on input:
@example
format=rgba,lutrgb=a="maxval-minval/2"
@end example

@item
Correct luminance gamma by a 0.5 factor:
@example
lutyuv=y=gammaval(0.5)
@end example

@item
Discard least significant bits of luma:
@example
lutyuv=y='bitand(val, 128+64+32)'
@end example
@end itemize

@section mp

Apply an MPlayer filter to the input video.

This filter provides a wrapper around most of the filters of
MPlayer/MEncoder.

This wrapper is considered experimental. Some of the wrapped filters
may not work properly and we may drop support for them, as they will
be implemented natively into FFmpeg. Thus you should avoid
depending on them when writing portable scripts.

The filters accepts the parameters:
@var{filter_name}[:=]@var{filter_params}

@var{filter_name} is the name of a supported MPlayer filter,
@var{filter_params} is a string containing the parameters accepted by
the named filter.

The list of the currently supported filters follows:
@table @var
@item dint
@item eq2
@item eq
@item fil
@item fspp
@item ilpack
@item mcdeint
@item perspective
@item phase
@item pp7
@item pullup
@item qp
@item sab
@item softpulldown
@item spp
@item uspp
@end table

The parameter syntax and behavior for the listed filters are the same
of the corresponding MPlayer filters. For detailed instructions check
the "VIDEO FILTERS" section in the MPlayer manual.

@subsection Examples

@itemize
@item
Adjust gamma, brightness, contrast:
@example
mp=eq2=1.0:2:0.5
@end example
@end itemize

See also mplayer(1), @url{http://www.mplayerhq.hu/}.

@section mpdecimate

Drop frames that do not differ greatly from the previous frame in
order to reduce frame rate.

The main use of this filter is for very-low-bitrate encoding
(e.g. streaming over dialup modem), but it could in theory be used for
fixing movies that were inverse-telecined incorrectly.

A description of the accepted options follows.

@table @option
@item max
Set the maximum number of consecutive frames which can be dropped (if
positive), or the minimum interval between dropped frames (if
negative). If the value is 0, the frame is dropped unregarding the
number of previous sequentially dropped frames.

Default value is 0.

@item hi
@item lo
@item frac
Set the dropping threshold values.

Values for @option{hi} and @option{lo} are for 8x8 pixel blocks and
represent actual pixel value differences, so a threshold of 64
corresponds to 1 unit of difference for each pixel, or the same spread
out differently over the block.

A frame is a candidate for dropping if no 8x8 blocks differ by more
than a threshold of @option{hi}, and if no more than @option{frac} blocks (1
meaning the whole image) differ by more than a threshold of @option{lo}.

Default value for @option{hi} is 64*12, default value for @option{lo} is
64*5, and default value for @option{frac} is 0.33.
@end table


@section negate

Negate input video.

This filter accepts an integer in input, if non-zero it negates the
alpha component (if available). The default value in input is 0.

@section noformat

Force libavfilter not to use any of the specified pixel formats for the
input to the next filter.

This filter accepts the following parameters:
@table @option

@item pix_fmts
A '|'-separated list of pixel format names, for example
"pix_fmts=yuv420p|monow|rgb24".

@end table

@subsection Examples

@itemize
@item
Force libavfilter to use a format different from @var{yuv420p} for the
input to the vflip filter:
@example
noformat=pix_fmts=yuv420p,vflip
@end example

@item
Convert the input video to any of the formats not contained in the list:
@example
noformat=yuv420p|yuv444p|yuv410p
@end example
@end itemize

@section noise

Add noise on video input frame.

The filter accepts the following options:

@table @option
@item all_seed
@item c0_seed
@item c1_seed
@item c2_seed
@item c3_seed
Set noise seed for specific pixel component or all pixel components in case
of @var{all_seed}. Default value is @code{123457}.

@item all_strength, alls
@item c0_strength, c0s
@item c1_strength, c1s
@item c2_strength, c2s
@item c3_strength, c3s
Set noise strength for specific pixel component or all pixel components in case
@var{all_strength}. Default value is @code{0}. Allowed range is [0, 100].

@item all_flags, allf
@item c0_flags, c0f
@item c1_flags, c1f
@item c2_flags, c2f
@item c3_flags, c3f
Set pixel component flags or set flags for all components if @var{all_flags}.
Available values for component flags are:
@table @samp
@item a
averaged temporal noise (smoother)
@item p
mix random noise with a (semi)regular pattern
@item t
temporal noise (noise pattern changes between frames)
@item u
uniform noise (gaussian otherwise)
@end table
@end table

@subsection Examples

Add temporal and uniform noise to input video:
@example
noise=alls=20:allf=t+u
@end example

@section null

Pass the video source unchanged to the output.

@section ocv

Apply video transform using libopencv.

To enable this filter install libopencv library and headers and
configure FFmpeg with @code{--enable-libopencv}.

This filter accepts the following parameters:

@table @option

@item filter_name
The name of the libopencv filter to apply.

@item filter_params
The parameters to pass to the libopencv filter. If not specified the default
values are assumed.

@end table

Refer to the official libopencv documentation for more precise
information:
@url{http://opencv.willowgarage.com/documentation/c/image_filtering.html}

Follows the list of supported libopencv filters.

@anchor{dilate}
@subsection dilate

Dilate an image by using a specific structuring element.
This filter corresponds to the libopencv function @code{cvDilate}.

It accepts the parameters: @var{struct_el}|@var{nb_iterations}.

@var{struct_el} represents a structuring element, and has the syntax:
@var{cols}x@var{rows}+@var{anchor_x}x@var{anchor_y}/@var{shape}

@var{cols} and @var{rows} represent the number of columns and rows of
the structuring element, @var{anchor_x} and @var{anchor_y} the anchor
point, and @var{shape} the shape for the structuring element, and
can be one of the values "rect", "cross", "ellipse", "custom".

If the value for @var{shape} is "custom", it must be followed by a
string of the form "=@var{filename}". The file with name
@var{filename} is assumed to represent a binary image, with each
printable character corresponding to a bright pixel. When a custom
@var{shape} is used, @var{cols} and @var{rows} are ignored, the number
or columns and rows of the read file are assumed instead.

The default value for @var{struct_el} is "3x3+0x0/rect".

@var{nb_iterations} specifies the number of times the transform is
applied to the image, and defaults to 1.

Follow some example:
@example
# use the default values
ocv=dilate

# dilate using a structuring element with a 5x5 cross, iterate two times
ocv=filter_name=dilate:filter_params=5x5+2x2/cross|2

# read the shape from the file diamond.shape, iterate two times
# the file diamond.shape may contain a pattern of characters like this:
#   *
#  ***
# *****
#  ***
#   *
# the specified cols and rows are ignored (but not the anchor point coordinates)
ocv=dilate:0x0+2x2/custom=diamond.shape|2
@end example

@subsection erode

Erode an image by using a specific structuring element.
This filter corresponds to the libopencv function @code{cvErode}.

The filter accepts the parameters: @var{struct_el}:@var{nb_iterations},
with the same syntax and semantics as the @ref{dilate} filter.

@subsection smooth

Smooth the input video.

The filter takes the following parameters:
@var{type}|@var{param1}|@var{param2}|@var{param3}|@var{param4}.

@var{type} is the type of smooth filter to apply, and can be one of
the following values: "blur", "blur_no_scale", "median", "gaussian",
"bilateral". The default value is "gaussian".

@var{param1}, @var{param2}, @var{param3}, and @var{param4} are
parameters whose meanings depend on smooth type. @var{param1} and
@var{param2} accept integer positive values or 0, @var{param3} and
@var{param4} accept float values.

The default value for @var{param1} is 3, the default value for the
other parameters is 0.

These parameters correspond to the parameters assigned to the
libopencv function @code{cvSmooth}.

@anchor{overlay}
@section overlay

Overlay one video on top of another.

It takes two inputs and one output, the first input is the "main"
video on which the second input is overlayed.

This filter accepts the following parameters:

A description of the accepted options follows.

@table @option
@item x
@item y
Set the expression for the x and y coordinates of the overlayed video
on the main video. Default value is "0" for both expressions. In case
the expression is invalid, it is set to a huge value (meaning that the
overlay will not be displayed within the output visible area).

@item eval
Set when the expressions for @option{x}, and @option{y} are evaluated.

It accepts the following values:
@table @samp
@item init
only evaluate expressions once during the filter initialization or
when a command is processed

@item frame
evaluate expressions for each incoming frame
@end table

Default value is @samp{frame}.

@item shortest
If set to 1, force the output to terminate when the shortest input
terminates. Default value is 0.

@item format
Set the format for the output video.

It accepts the following values:
@table @samp
@item yuv420
force YUV420 output

@item yuv444
force YUV444 output

@item rgb
force RGB output
@end table

Default value is @samp{yuv420}.

@item rgb @emph{(deprecated)}
If set to 1, force the filter to accept inputs in the RGB
color space. Default value is 0. This option is deprecated, use
@option{format} instead.

@item repeatlast
If set to 1, force the filter to draw the last overlay frame over the
main input until the end of the stream. A value of 0 disables this
behavior, which is enabled by default.
@end table

The @option{x}, and @option{y} expressions can contain the following
parameters.

@table @option
@item main_w, W
@item main_h, H
main input width and height

@item overlay_w, w
@item overlay_h, h
overlay input width and height

@item x
@item y
the computed values for @var{x} and @var{y}. They are evaluated for
each new frame.

@item hsub
@item vsub
horizontal and vertical chroma subsample values of the output
format. For example for the pixel format "yuv422p" @var{hsub} is 2 and
@var{vsub} is 1.

@item n
the number of input frame, starting from 0

@item pos
the position in the file of the input frame, NAN if unknown

@item t