[mythtv-users] fps drops with DRM sync and bob

[Doug Larrick]

Hamish Moffatt wrote:
> FWIW, switching to audio sync makes things even more entertaining;
> 
> 2007-06-04 00:03:11.062 Using audio as timebase
> 2007-06-04 00:03:11.062 Video timing method: DRM
> 2007-06-04 00:03:11.062 Refresh rate: 19980, frame interval: 40000
> 'video_output' mean = '40064.78', std. dev. = '95.55', fps = '24.96'
> 'video_output' mean = '40070.39', std. dev. = '75.88', fps = '24.96'
> 'video_output' mean = '40070.98', std. dev. = '31.91', fps = '24.96'
> 2007-06-04 00:03:26.951 NVP: 400 interlaced frames seen.
> 'video_output' mean = '39870.29', std. dev. = '2000.35', fps = '25.08'
> 'video_output' mean = '40071.84', std. dev. = '90.21', fps = '24.96'
> 'video_output' mean = '40070.27', std. dev. = '94.98', fps = '24.96'
> 'video_output' mean = '39870.21', std. dev. = '1992.80', fps = '25.08'
> 2007-06-04 00:03:42.960 NVP: 800 interlaced frames seen.
> 'video_output' mean = '40070.83', std. dev. = '38.52', fps = '24.96'
> 'video_output' mean = '40070.87', std. dev. = '47.04', fps = '24.96'
> 'video_output' mean = '39870.67', std. dev. = '1994.86', fps = '25.08'
> 
> Now the fps jitters around 25Hz with huge standard deviation.

Audio as timebase is the normal mode of operation for most folks.  The
standard deviation is in usec, I believe, not fps, so these are not
terribly huge standard deviation values.  On my desktop system (which is
60 Hz refresh, watching video that's 29.97 Hz refresh) I get std. dev.
values in the 4000-ish range, which I attribute to the mismatch.

If you could get your refresh rate to *exactly* 50 Hz I believe these
would go down even further.

How does the picture *look* with audio as timebase?

Also, figuring out how to get realtime priority working would increase
the timing accuracy independent of the timing method used.  The modern
method is using pam_limits (/etc/security/limits.conf, rtprio keyword).

-Doug

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