[mythtv-commits] Ticket #1853: svn-0.19-fixes MPEG2->MPEG4 transcoding corrupts some recordings ("green squiggly mess").

MythTV mythtv at cvs.mythtv.org
Wed May 24 09:46:52 EDT 2006


#1853: svn-0.19-fixes MPEG2->MPEG4 transcoding corrupts some recordings ("green
squiggly mess").
-----------------------+----------------------------------------------------
 Reporter:  oa at iki.fi  |       Owner:  ijr
     Type:  defect     |      Status:  new
 Priority:  minor      |   Milestone:     
Component:  mythtv     |     Version:     
 Severity:  medium     |  
-----------------------+----------------------------------------------------
 DVB-T recordings get frequently corrupted if transcoded to MPEG4,
 apparently without regard to exact transcoding profile settings. This
 seems to be caused by the MPEG2 decoder rather than the MPEG4 encoder, and
 may to be related to aspect ratio changes or other stream disruptions as
 it usually is triggered by a change into/out of/between commercials.

 A 40MB example of a beginning of a recording which demonstrates this is at
 http://www.fishpool.org/misc/mythtv-dvb-capture-fails-libmpeg2.mpg.
 Additionally, I have found that this file plays correctly (prior to
 transcoding) in MythTV when using the "Standard" (ffmpeg) decoder, fails
 with the same symptoms with the "Libmpeg2" decoder, and exhibits spurious,
 minor blocking with the "Standard XvMC" decoder. The same behavior can
 also be demonstrated with "mplayer -vfm ffmpeg" vs "mplayer -vfm
 libmpeg2".

 As further evidence that the error probably is in the decoder, I've seen
 the problem with various transcoder bitrates, HQ, 4MV and deinterlacing
 options on and off, and with or without rescaling of the frame size. What
 I can't understand, however, is that to the best of my understanding,
 mythtranscode should be using ffmpeg's decoder, and I've NEVER encountered
 the problem with untranscoded recordings when using the Standard playback
 decoder.

 As far as the test material, you won't see the error at the immediate
 beginning of the recording (though on some recordings it _does_ happen
 immediately), but watch through the first minutes, and it should happen
 reliably. The problem has been in 0.19-fixes for a long time, and is
 demonstrable with at least up to 9850.

 Discussion on the -users list: http://mythtv.org/pipermail/mythtv-users
 /2006-May/136019.html

-- 
Ticket URL: <http://cvs.mythtv.org/trac/ticket/1853>
MythTV <http://www.mythtv.org/>
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