[mythtv-commits] Ticket #13176: AVsync is broken at high playback speeds in some streams

MythTV noreply at mythtv.org
Tue Nov 14 02:55:09 UTC 2017


#13176: AVsync is broken at high playback speeds in some streams
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     Reporter:  Brad Martin <mythtv@…>   |      Owner:  jyavenard
         Type:  Patch - Bug Fix          |     Status:  new
     Priority:  minor                    |  Milestone:  needs_triage
    Component:  MythTV - Video Playback  |    Version:  0.28.1
     Severity:  medium                   |   Keywords:
Ticket locked:  0                        |
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 At playback speeds of 1.5x or greater, I have found that the video can
 often surge way ahead of the audio, by tens of seconds or more.  This
 often happens during a commercial break, where I was in sync prior to the
 commercial, but completely lose sync upon the transition.  It may
 eventually sync again when the show comes back on.  FWIW I have a frame-
 doubling interlacer configured, which may be implicated as well.

 I have tracked this down to a couple of causes:
  * The VideoSync class is not being kept up to date with the frame
 interval and frame-doubling state at any given time as the stream and
 playback speed change.
  * The VideoSync is attempting to clamp the maximum sync adjustment to a
 small multiple of the wrong frame interval due to the above.
  * The avsync_predictor is continually dropping frames, because it is
 failing to account for extra time due to the repeat_pict setting on some
 video frames, as well as any dynamically-applied sync delay.

 Attached is a patch against the fixes/0.28 branch that improves these
 issues for me.

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Ticket URL: <https://code.mythtv.org/trac/ticket/13176>
MythTV <http://www.mythtv.org>
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