[FFmpeg-user] Concatenated H.264 or H.265 might not play correctly.drop=#

[Nicolas George]

Le sextidi 6 thermidor, an CCXXII, Luke Davis a écrit :
> Well, it has 15.  At least, that is what it is set to.  It is
> quicktime broadcaster, and I have never read anywhere that its 15
> FPS is actually 14.99, so it should be the 15 that it claims.

You should check for yourself: use ffprobe to dump the timestamps of your
input stream, and then use your favourite data analysis tool (spreasheet,
GNU R, gnuplot...) to see what they look like in detail.

My guess is a small irregularity causes ffmpeg to have a slightly off value;
then it tries to accommodate that value. Converting from 15 FPS to 14.99
will drop a frame about every 100 seconds. Of course, 14.99 may be anything
between 14.985 and 14.995 (not sure about the rounding rules for that
display), that can drop a frame at any interval between 66.66 and 200
seconds. That is consistent with what you reported.

> I'm not at the moment certain how to do that, but I will try to find
> a way.

I suggest you use ffprobe to dump the timestamps both for input and output,
and watch them frame by frame to match them together. Or you can use
drawtext %{pts} to add the timestamps to the frames; do not forget the
-copyts option.

Also, you should try using a format that supports VFR, Matroska or Nut for
example, to see if the problem goes away. That would confirm part of the
theory.

Regards,

-- 
  Nicolas George
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