[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)
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Reporter: mythtv at modified.cc | Owner: ijr
Type: defect | Status: new
Priority: minor | Milestone: unknown
Component: mythtv | Version: head
Severity: medium | Mlocked: 0
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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.
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Ticket URL: <http://svn.mythtv.org/trac/ticket/5628>
MythTV <http://www.mythtv.org/>
MythTV
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