[mythtv] Ticket #5749: Internal player stutters on 720p content

Daniel Kristjansson danielk at cuymedia.net
Sat Oct 4 23:49:31 UTC 2008

On Sat, 2008-10-04 at 14:12 -0500, David Engel wrote:
> On Sat, Oct 04, 2008 at 12:20:17PM -0400, Michael T. Dean wrote:
> > On 10/03/2008 11:54 AM, zgeggy2k wrote:
> > >  One thing I haven't tried is running it as root _with_real_time_priority_
> > >  settings (which hopefully even CFS would honor). I'll give it a try.
> > 
> > Do they enable GROUP_SCHED?  If so, are they using USER_SCHED as the 
> > "Basis for grouping tasks?"  If so, that's almost definitely the issue 
> > and your system configuration should be fixed.
> I have GROUP_SCHED and USER_SCHED enable in my self-compiled kernel
> but haven't done anything to explicitly enable it at run-time on
> Debian Sid.  For grins, I rebuilt and tested a kernel with GROUP_SCHED
> and USER_SCHED disabled.  It made no difference -- the stuttering is
> still there.
> David

The problem Michael identified is very interesting and it explains why
I was having performance problems with recent kernels, but I think
Janne just found the root of your problem, the audio in your files is
500 ms behind the video, but in AVFormatDecoder we only read audio 
packets as far ahead as we read video packets. Fixing that problem
is not a trivial undertaking, but on the positive side with a just
a little extra work it will probably also speed up channel flipping
and may make XvMC decoding work much more effectively.

Note: To work well, XvMC currently requires a faster CPU than software
decoding, which makes it pretty darn useless. This is probably in large
part because it requires the audio to be decoded in much less time since
we only have 5 usable XvMC frames instead of the 31 we currently have
for software decoding. We may also be able to greatly reduce that 31
frame number with the AVFD refactor in place.

-- Daniel

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