[mythtv-commits] Ticket #11213: cutting and lossless mpeg2 transcoding generate strange files

MythTV noreply at mythtv.org
Mon Oct 14 01:22:21 UTC 2013


#11213: cutting and lossless mpeg2 transcoding generate strange files
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 Reporter:  mythtv@…                |          Owner:
     Type:  Bug Report - General    |         Status:  new
 Priority:  minor                   |      Milestone:  unknown
Component:  MythTV - Mythtranscode  |        Version:  0.26-fixes
 Severity:  medium                  |     Resolution:
 Keywords:                          |  Ticket locked:  0
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Comment (by finlay@…):

 While manually running some lossless transcodes on US OTA video files
 (480i in mpegts) I noticed that even though I was setting the cut points
 on keyframes, mythtranscode was reporting that it was converting some B
 and P frames to I frames at the cut points. In addition it would report
 the need to insert a large number of frames (e.g.1000000+). By varying the
 cut frame specification I found that generally by specifying a frame one
 greater than the keyframe (as found by myth editing) I could get
 mythtranscode runs that would not convert frames. The resulting files
 could be analyzed by avconv and report the correct duration and could also
 be post-processed by mythffmpeg without a problem. Note this does not
 occur for all files that I have tried but does occur for the majority.

 My speculation is that:
     the myth editing process produces keyframe numbers that are different
 than the keyframe numbers that mythtranscode encounters; and,
     the mythtranscode conversion of B frames (and possible P frames) to I
 frames introduces some error that causes mythffmpeg, vlc and avconv to
 fail to correctly analyze the video.

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Ticket URL: <http://code.mythtv.org/trac/ticket/11213#comment:7>
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