[Ffmpeg-devel] [PATCH] fix frame duration computation in find_stream_infos
Fred Rothganger
fred
Sat Mar 31 15:44:36 CEST 2007
Michael Niedermayer wrote:
> NO r_frame_rate is not the average framerate
>
We need something like "useful_frame_rate" that matches our intuitive
notions of the true speed of the file. :)
In particular, I need a value that allows me to calculate a timestamp
based on a frame number in a fixed rate video. Unfortunately, it seems
that the fixed rate videos in my possesion, and apparently in the
possession of others as well, don't have clean enough timestamps to
produce a usable r_frame_rate.
You've explained in a previous thread that the job of r_frame_rate is to
give the (inverse of the) smallest time quantum that all the timestamps
in the file fall on. In a mixed frame rate file this will be something
like the LCM of the framerates. In that thread you agreed to the idea
of adding an "avg_frame_rate", but I still haven't gotten around to it. :)
A coworker of mine described a variable rate video he generated in which
some frames last over a minute and others less than a second. This is
probably an extreme case, but it is an existence proof that average
frame rate can be made useless. However, it should be possible to
determine the true frame rate of an essentially fixed-rate video using
the average.
-- Fred
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