[mythtv-users] 0.19, XvMC, and Prebuffer pause

[Brian Foddy]

On Saturday 04 March 2006 01:24 pm, Joe Silver wrote:
> On 2/25/06, Joe Silver <devils.taco at gmail.com> wrote:
> > So it looks like there has been a trouble ticket opened on this issue:
> > http://svn.mythtv.org/trac/ticket/1361
> > http://www.gossamer-threads.com/lists/mythtv/commits/185733
> >
> > However, it doesn't really look like it's being investigated further.  I
> > could be mistaken, but it sounds like this is being passed off as a
> > performance issue instead of an internal issue.  Hopefully one of the
> > developers has the same issue and can provide the appropriate performance
> > settings to the rest of us to correct this issue.  It sounds like the
> > rest of us are stumped!  Perhaps it's something to do with differences
> > between default settings between 0.18 and 0.19.  Why these defaults would
> > be changed to break something as important as HD playback is a real
> > mystery...
> >
> > -Joe
>
> I'm screwing around some more with this issue... no useable workaround yet,
> but I have discovered that xine will playback the captured livetv streams
> perfectly with xvmc and deinterlacing disabled... the hd captures look
> fabulous.  i'm now ready to claim XVMC playback is broken in mythtv's
> internal player.  probably not a huge surprise, but I am surprised that it
> works in one and not the other.  the only viable workaround i can come up
> with is to buy a faster processor so i don't need XVMC.  I'm a little
> nervous that it wont actually fix the problem (is it really XVMC or the
> internal player???), but to buy one and try it is the only way to test this
> out.  Anyone out there with a fast cpu and nvidia card (FX5200) playing HD
> captures to test this theory out for me?  Does enabling XVMC cause audio
> stuttering (prebuffering pause and buffer underruns)??
>
> Cheers,
> JS

I've been catching up on a month's of messages, and think some of 
my details may be of help here.  I've been using XvMC for quite some
time, my P3-1400 frontend requires it.  Some releases have been very good,
others not so good for XvMC.

When I upgraded to 0.19 I immediately noticed a form of the streams of
NVP prebuffering pauses, sometimes into an infinite loop, until pressing
another FF or RR keystroke.  It also seems worse when the playback hits
a commercial skip so it jumps many minutes.  Again, hitting RR 15 seconds
brings it back out.  And there can be several seconds of horrible A/V sync
after a FF also, when more prebuffer errors occur.  During stable playback
there are generally no problems.

The most interesting thing to me however, is before upgrading to 0.19,
I was using a Jan 21, 2006 SVN snap, and it was the most stable XvMC
playback I've ever seen in Mythtv.  FF/RR would result in near perfect
A/V sync right away, and very few prebuffer pauses, certainly no hangs.
I found 0.18.1 to be ok XvMC.
So something in that 2-3 weeks between Jan 21 and 0.19 seems to be
suspect.  Most all my recordings are either CBS or NBC HD (1080i) played
back at 540p resolutions.  My sound card is configured for passthru
digital sound.  Video card Nvidia 5600, 8178 driver, Linux 2.6.15 kernel.

./configure --enable-proc-opt --arch=pentium3 --disable-joystick-menu 
--disable-firewire --disable-dbox2 --enable-dvb 
--dvb-path=/usr/src/linux/include --enable-xvmc

Hope this can help.
Brian