[mythtv] Mythtv mpeg frame counting - patch?

Ian Caulfield ian.caulfield at gmail.com
Fri Jun 15 13:03:33 UTC 2007

On 15/06/07, Bill <level42 at sympatico.ca> wrote:
> Ok now I'm confused. I decided to look at the frame counting on the
> playback
> side first, since the decode is already been done, its a little easier to
> get started and familar with the code.  But it looks it me like the frame
> counting is ok on playback; its incremented only after a successful decode
> and anyway, av_read_frame performs some partial parsing and is suppose to
> return only complete video frames.
> So I ran a test based on a tutorial using ffmeg at
> http://dranger.com/ffmpeg/tutorial01.html to count the frames of a file I
> have problems with.  Since the tutorial should be doing frame accurate
> counting, I thought it would give different numbers than mythtv, but it
> didn't.  So what am I missing?????
> Here's the facts, the last value in the filemarkup position map for the
> mpeg
> is 148891.  Due to the way mythtv generates the position map this is not
> quite the end of the file, but close, close enough.  As the position map
> is
> generated using calls to av_read_frame in mythtv, the frame counting for
> the
> position map is correct.
> My tutorial based test file gives 148903 total frames, similar to mythtv,
> so
> mythtv is counting frames ok on playback.  The mpeg header reported by
> dump_format is 1:42:23 for length and 29.97 for frame rate. The length
> calculated by Mythtv is 148891 / 29.97 = 1:22:48 which is too short.  The
> actual play time by Mythtv is 1:42, but the OSD will show the 1:22 time.
> What am I missing for this problem?  I checked the repeat_pic field in
> AVFrame (I think it is); this is not the problem.  It is almost as if the
> actual frame rate is 24, or the frame rate is not constant or for DVB
> broadcast they are playing some other tricks to save bandwidth.

Is the mpeg telecined (ie the stream frame rate is marked as 29.97 fields
per second, but only 23.97 are actually transmitted)? - check if the
repeat_first_field flag is set on every other frame.

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