[mythtv-users] Stuttering and loss of sync after transcoding some recordings

Per Öberg oberg at isy.liu.se
Tue May 19 07:17:14 UTC 2009


In Sept 29 Peter Scahchte reported problems with mythtranscode for some 
recordings.

http://www.gossamer-threads.com/lists/mythtv/users/351511?do=post_view_threaded

I have the exact same problem but I didn't manage to find any solution. 
The problem is that occasionally transcoded recordings
(MPEG2 from DVB-T transcoded to MPEG 4) become damaged so that at some 
point in the recording the sound starts to stutter and mythtranscode 
never recovers. The playback is out of sync 1-2s and mythfrontend spits 
out loads of "WriteAudio: buffer underrun" messages.

In my opinion it seems like the video is slowed down while the audio 
keeps the same rate so that the audio buffer is emptied before the video 
buffer and for this reason there is not enough data to play sound for 
the whole interval, hence the stutter.

xine, mplayer and vlc all give different errors at the same stream 
position so there is definitely something wrong with the file. Sometimes 
the errors occur right after a commercial break but sometimes it's in 
the middle of the program. Some channels seem to be more error prone and 
some channels seems to be immune. I have two cards but I haven't managed 
to find any correlation with card number.

As with Peter I did not experience this in 0.20. My system is Gentoo on 
an AMD64 with mythtv-0.21_p18116.


Best regards, and thanks for any help
Per Öberg



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