[mythtv-commits] Ticket #5628: Correct jitter on skip (normally only noticable on HD)

MythTV mythtv at cvs.mythtv.org
Sat Aug 16 12:31:42 UTC 2008

#5628: Correct jitter on skip (normally only noticable on HD)
 Reporter:  mythtv at modified.cc  |       Owner:  ijr    
     Type:  defect              |      Status:  new    
 Priority:  minor               |   Milestone:  unknown
Component:  mythtv              |     Version:  head   
 Severity:  medium              |     Mlocked:  0      
 When skipping on HD content mythtv has nasty jitters.  This shows itself
 as lots of A/V divergence corrections and audio buffer underruns.

 The AV divergence problem is caused by the audio timecode being reset to 0
 during a skip, causing massive A/V divergence.  On some HD content this
 can continue for several seconds, occasionally tens of seconds.

 The audio buffer underrun seems to be caused by a secondary set of diverge
 code that looks left over, and appears to duplicate an existing function,
 but in a different way.  Removing this code removes the problem and does
 not affect A/V sync.

 These problems are corrected with the attached patch.  After the patch is
 applied the following issues remain.

 1. After the audio timecode is restored to a valid value there is a slight
 video jitter as the actual correction is made.  This is sub-second.

 2. Under high system load (compiling with make -j3) whilst watching mythtv
 the audio buffer underrun can still occur.

 The patch also introduces a high and low water mark for A/V divergence
 correction.  A/V divergence will correct down to 0.05 frames error and
 then allow itself to drift up to 0.5 frames error before correcting again.
 If there is a slow drift in A/V divergence this results in less correction
 (and thus less jitter) then the current method of correcting down to a
 value and then correcting immediately that value is reached again.

 Since I use PAL some default values have been changed from 30 to 25.

Ticket URL: <http://svn.mythtv.org/trac/ticket/5628>
MythTV <http://www.mythtv.org/>

More information about the mythtv-commits mailing list