[mythtv-commits] Ticket #12396: Mythvideo subtitle timing problem

MythTV noreply at mythtv.org
Sun Apr 19 10:08:29 UTC 2015


#12396: Mythvideo subtitle timing problem
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 Reporter:  ismota@…                 |          Owner:  jyavenard
     Type:  Bug Report - General     |         Status:  new
 Priority:  minor                    |      Milestone:  0.27.5
Component:  MythTV - Video Playback  |        Version:  0.27.4
 Severity:  medium                   |     Resolution:
 Keywords:  subtitle timing          |  Ticket locked:  0
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Comment (by jyavenard):

 Replying to [comment:2 stichnot]:
 > Lack of complaints likely due to:
 > 1. MythTV doesn't record .avi files (i.e. you have to go to extra work
 to import them), so most people don't play them.
 > 2. Most people don't care about captions/subtitles.
 >

 this has happens to me many times... subtitles are good at first and then
 they start diverging to the point they are unusable. I've never managed to
 reproduce the problem correctly, and often I just blamed the subtitles and
 moved on.

 > IIRC, what's happening is that without a seektable, MythTV must ask the
 decoder (ffmpeg) to seek to the desired frame, but ffmpeg only seeks to
 the nearest keyframe, while MythTV believes it is at the exact frame.  If
 keyframes in the .avi file are far apart, subtitles are likely to be out
 of sync.  But if a seektable is present, MythTV seeks to a keyframe, then
 frame-by-frame advances to the desired frame.

 That seems like a bug to me... Yes ffmpeg will seek to the next keyframe,
 but you still get the right time and adjust the subtitle for that time.
 Also, why not do like with the seek table present a move frame by frame
 then?

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Ticket URL: <https://code.mythtv.org/trac/ticket/12396#comment:4>
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