+int ffio_ensure_seekback(AVIOContext *s, int64_t buf_size)
+{
+ uint8_t *buffer;
+ int max_buffer_size = s->max_packet_size ?
+ s->max_packet_size : IO_BUFFER_SIZE;
+ int filled = s->buf_end - s->buffer;
+
+ buf_size += s->buf_ptr - s->buffer + max_buffer_size;
+
+ if (buf_size < filled || s->seekable)
+ return 0;
+ av_assert0(!s->write_flag);
+
+ buffer = av_malloc(buf_size);
+ if (!buffer)
+ return AVERROR(ENOMEM);
+
+ memcpy(buffer, s->buffer, filled);
+ av_free(s->buffer);
+ s->buf_ptr = buffer + (s->buf_ptr - s->buffer);
+ s->buf_end = buffer + (s->buf_end - s->buffer);
+ s->buffer = buffer;
+ s->buffer_size = buf_size;
+ return 0;
+}
+