[mythtv] Solving my performance problems...

[Jason Hoos]

> After more investigation, the stuttering is caused by the sound card 
> starving. I salted some snd_pcm_delay calls in AddSamples. As the htdv 
> sample plays, the number of queued sound samples slowly decrease until 
> the underrun occurs. The up-converted sample seems to maintain about 10k 
> or so queued samples and does not underrun. Without the patch, it 
> underruns as well. My 2.8GHz cpu is running about 65% when all this is 
> going on. I have jitter and experimental av sync on and am using xvmc.

This sounds pretty much exactly like the behavior I am seeing on my system,
that I wrote about a few weeks back.  My stutter problems seem to have
decreased lately, after I did a clean rebuild of Myth after one of the CVS
updates.  Not sure if the improvement was due to the rebuild, or (more
likely?) due to some of the new QSocketDevice stuff.  Now the stutters are
reduced to blips rather than half-second drops. 

In any case prior to the rebuild I did the same sort of thing you did with
snd_pcm_delay, and saw the same results.  And I did turn on "extra audio
buffering". :(  I haven't looked at it for a bit since I was out of town, so
I don't remember if I tried that setting after the rebuild or not.  I'll
take another look this weekend.  

Oddly I have noticed that the stutter problem occurs regularly on a 720p
HDTV station, but it doesn't occur on 1080i station.  Those results aren't
conclusive; since I only have two stations I can get right now I can't tell
whether it has more to do with how the streams are encoded than with what
resolution they are.  Especially since the 720p station is the one that has
the GOP issues I've been discussing on another thread.

Jason