Originally committed as revision 10175 to svn://svn.ffmpeg.org/ffmpeg/trunk
and then applying it in the horizontal one.
--------------- --------------- --------------- ---------------
|LL0|HL0| | | | | | | | | | | |
-|---+---| HL1 | | L0|H0 | HL1 | | LL0 | HL1 | | | |
+|---+---| HL1 | | L0|H0 | HL1 | | LL1 | HL1 | | | |
|LH0|HH0| | | | | | | | | | | |
|-------+-------|->|-------+-------|->|-------+-------|->| L1 | H1 |->...
| | | | | | | | | | | |