[mythtv] [PATCH] Missing keyframes on mpeg4 transcode

[Cory Papenfuss]

On Sun, 27 Feb 2005, Jay Merrifield wrote:

> Ever since upgrading to .17, I've been having problems transcoding
> RTJpeg files into mpeg4. The video is transcoded just fine, but the
> seek table always seems to be screwed up to some degree or another. So
> I finally got the time to tear through the code and what follows is a
> summary of what I found, and how I fixed it (more like how I found the
> change in CVS that broke my setup and backed it out). Hopefully this
> will be useful for others. Investigation into broken files found that
> all files had a perfectly normal/uncorrupt header/seek table but no
> keyframes were being stored. Upon checking the transcoding process,
> NuppelVideoRecorder was never executive the code to write keyframes.
> Further investigation found that inside nuppeldecoder.cpp, keyframes
> were being decoded correctly, but the isLastFrameKey() function was
> always returning false. Appears lastKey and framesPlayed were always
> off by 1 frame, so the keyframes were never being sent to the
> NuppelVideoRecorder. Subsequent patch to correct this problem lead me
> to the CVS change log and where the original change that broke my
> system was made. Revision 1.54 commented out some frame adjustment
> code in favor of alternate frame tracking code. This change broke
> transcoding on my system. Here's the diff -u with the latest CVS and
> the changes I made: The second change in the diff -u was done in the
> hopes of not breaking the original patch.
>
 	Interesting... I wonder if this is the cause of my mplayer nuv2avi 
copying attempt problems.  I patched mplayer with a moldy-old patch (that 
still applies cleanly) to play transcoded (MPEG4) .nuv files.  Trying to 
extract a useful .avi out of it with:

mencoder infile.nuv -oac copy -ovc copy -o outfile.avi -force-avi-aspect 1.33

results in these errors while copying:
1 duplicate frame(s)!
Pos: 100.0s   2973f (18%) 2003fps Trem:   0min 141mb  A-V:-0.067 
[2066:128]
1 duplicate frame(s)!
Pos: 100.4s   2983f (18%) 1999fps Trem:   0min 140mb  A-V:-0.067 
[2063:128]
1 duplicate frame(s)!
Pos: 100.8s   2994f (18%) 2004fps Trem:   0min 140mb  A-V:-0.069 
[2059:128]
1 duplicate frame(s)!
Pos: 110.8s   3295f (20%) 2088fps Trem:   0min 140mb  A-V:-0.067 
[2034:128]

 	The result plays, but has no keyframes (so seeking is broken).  I 
don't remember if I was using 0.17 or 0.16 when I transcoded this show, 
however.  Sound likely?

-Cory

*************************************************************************
* Cory Papenfuss                                                        *
* Electrical Engineering candidate Ph.D. graduate student               *
* Virginia Polytechnic Institute and State University                   *
*************************************************************************