[FFmpeg-trac] #1339(avfilter:new): Auto insert fps filter as adapter for overlay filter inputs with different framerates

[FFmpeg]

#1339: Auto insert fps filter as adapter for overlay filter inputs with different
framerates
-------------------------------------+-------------------------------------
             Reporter:  annorax      |                    Owner:
                 Type:  enhancement  |                   Status:  new
             Priority:  wish         |                Component:  avfilter
              Version:  git-master   |               Resolution:
             Keywords:  fps overlay  |               Blocked By:
  filter                             |  Reproduced by developer:  0
             Blocking:               |
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------

Comment (by annorax):

 I'm not sure I know what you mean by "whenever any of its inputs change"
 but I don't think that's the current behavior anyway.

 Here is the behavior I observed:
 * The overlay filter takes every frame of the first (main) input in turn
 and copies it to the output with the same timestamp  while overlaying the
 next frame from the second input (ignoring the timestamps / framerate of
 the second input).
 * If it runs out of frames for the second input before the first one, it
 simply overlays the last frame of the second input on each remaining frame
 of the first input.
 * If it runs out of frames for the first input before the second one, the
 rest of the frames of the second input are ignored.

 This can lead to a situation where the framerate of the overlaid video is
 not the same as the framerate of the output file, so it appears to be
 running in slow/fast motion. Why would it not be a general solution to
 equalize the frame rates? Do you think a user might want one of his
 streams to be slowed down / sped up in the output just because it's been
 overlayed on top of another stream?

 At the very least, I think this would be useful to many users if it were
 included as an optional behavior (i.e. triggered by a config parameter).

-- 
Ticket URL: <https://ffmpeg.org/trac/ffmpeg/ticket/1339#comment:2>
FFmpeg <http://ffmpeg.org>
FFmpeg issue tracker