[mythtv-users] Possible XvMC prebuffering issues solution?

[Tom Lichti]

Steven Adeff wrote:
> On 11/29/06, Michael Tiller <michael.tiller at gmail.com> wrote:
>> On 11/29/06, Alex Halovanic <halovanic at gmail.com> wrote:
>>> Just posting this, hoping it will help someone else :)
>>> I was having lots of problems with XvMC playback of HD streams from my
>>> HDHomerun, with prebuffering pauses causing skips in sound and
>>> messages that the video was 4 or 5 frames ahead of the audio ever few
>>> seconds.  After trying every possible combination of settings possible
>>> (and realizing that the problem also existed in Xine), I think I've
>>> finally found the real solution.  I had been using a modeline with a
>>> vertical refresh of 59.94 hz in an attempt to keep it as close to the
>>> framerate of the videos and official specs.  Increasing this to about
>>> 60.92 hz (That's a dotclock of 74.9 for my 720p modeline) has gotten
>>> rid of nearly all of the pauses.  There's still some prebuffering for
>>> a few seconds after the channel is tuned, and when the program
>>> changes, especially when one commercial changes to another, but then
>>> it will "settle down" for the program, even when skipping about in it.
>>> Sometimes there are a couple of messages that the video is now ahead
>>> of the audio, but these too go away within a few seconds.  Total cpu
>>> usage for my wimpy little machine: 50-60%!
>>> Note: I take no responsibility if you try this and the higher refresh
>>> rate causes your tv to burst into flames
>>>
>>> My set-up:
>>> 1.6 ghz Duron KM400, 512 mb RAM
>>> Geforce 5200 FX, vga thru component converter at 720p to cheap Walmart
>> Sanyo CRT
>>> Nvidia binary driver 1.0-9625
>>> Modeline "720p" 74.9 1144 1320 1376 1650 696 722 728 750 +hsync +vsync
>>> (actually 1144x696, adjusted for overscan)
>>> Myth SVN 11828 compiled for athlon-xp
>>> audio output device-ALSA:default, deinterlace Bob2x, Use Realtime
>>> Priority Threads, Extra Audio Buffering, UseChromaKeyOSD,
>>> UseXvMCForHDOnly
>> Thanks for the info.  I'm outputing to a normal TV-out (composite).  I'm not
>> sure what modeline to specify for that?!? Isn't the refresh rate of the NTSC
>> signal fixed?  What does changing the modeling do in that case?!?
> 
> its fixed, but has some float to it. Plus with tv output chips, they
> don't care about the float, so playing with the modeline frequency
> will help. I think "720x480_30" should work with the nvidia drivers
> for NTSC output without overscan compensation.
> 

I use "1024x768_30" on my system, with good results.

Tom