Opened 13 years ago

Closed 13 years ago

Last modified 13 years ago

#1853 closed defect (fixed)

Transcode to mpeg4 doesn't deal with video frame dimension changes.

Reported by: oa@… Owned by: cpinkham
Priority: minor Milestone: unknown
Component: mythtv Version:
Severity: medium Keywords:
Cc: Ticket locked: no

Description

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

Change History (4)

comment:1 Changed 13 years ago by Isaac Richards

Owner: changed from Isaac Richards to cpinkham
Summary: svn-0.19-fixes MPEG2->MPEG4 transcoding corrupts some recordings ("green squiggly mess").Transcode to mpeg4 doesn't deal with video frame dimension changes.

comment:2 Changed 13 years ago by Isaac Richards

Resolution: fixed
Status: newclosed

(In [10548]) Handle size and aspect ratio changes when transcoding to nuv.

Very slight nuv format mod to allow format changes mid-stream. Only handles aspect changing for now - transcoding goes to 1 output res at a time, anyway.

Fixes #1853.

comment:3 Changed 13 years ago by Isaac Richards

(In [10548]) Handle size and aspect ratio changes when transcoding to nuv.

Very slight nuv format mod to allow format changes mid-stream. Only handles aspect changing for now - transcoding goes to 1 output res at a time, anyway.

Fixes #1853.

comment:4 Changed 13 years ago by cpinkham

(In [10559]) Make the comment for the new frame in [10548] match the actual usage. (type 'M' vs 'H'). References #1853.

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