[mythtv-users] HD performance problems

[Tom Lichti]

Allan Wilson wrote:
> On 11/20/06, *Tom Lichti* <tom at redpepperracing.com 
> 
>     Along with all that, I would check that your modeline is setup with the
>     correct frequency for your area. NTSC requires a multiple of 30, when my
>     system was using an unknown frequency (close to PAL I think) I got tons
>     of prebuffer pauses, hiccups, etc, playing HD on a dual core P4 2.8GHz,
>     which should have been more than capable of playing HD. When using XvMC,
>     the mythfrontend log will show the average FPS of the display. If it's
>     not running near your TV standard, you WILL get prebuffer pauses and
>     audio/video sync problems. Mine was running at around 24 FPS average,
>     and the playback was terrible. Once I got my modeline correct and it
>     was
>     running at 30 FPS (or very close to it, either 29.9 or 30.1) playback is
>     perfect, even without XvMC. I actually have less CPU usage without XvMC
>     than with it, and that is with BOB de-interlace on.
> 
>     For reference, my nVidia mode is the built-in '1024x768_60' with NO
>     defined modelines in XF86Config-4 (or xorg.conf). PAL would probably
>     want '1024x76_50'.
> 
>     HTH
> 
>     Tom
> 
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> 
> 
> This is a very interesting point and describes why my PIV 3.0 GHz system 
> is having such a hard time displaying HD. What do you mean by TV 
> standard and how do you tell the fps? I would love to check this out on 
> my system and see if it is the same thing.
> 
> Allan

If you are in North America, the standard is NTSC at 60Hz refresh, and 
Europe is PAL at 50Hz refresh. I may get the terms wrong, but the 
numbers are correct. The only way I've been able to see the FPS is by 
turning on XvMC and then running:

mythfrontend -v playback

and either run that in a terminal window, or redirect to a file like I do:

mythfrontend -v playback > /var/log/mythfrontend.log

and you will periodically see lines like this:

'video_output' mean = '34865.50', std. dev. = '7006.43', fps = '28.68'

As long as the fps is a multiple of the base rate, I do not experience 
any issues. For me with NTSC, as long as the fps is near 30, I get near 
perfect playback. When I was having massive stuttering and pauses, the 
fps was at about 24, when I got it up at or near 30, it was perfect. It 
didn't matter what I did with de-interlace, vsync, nvidia-settings, 
audio buffers, etc, I ALWAYS got stutter until I got the fps correct. 
For PAL, your target would be 25fps, I would assume. Other areas, I have 
no idea.

HTH

Tom