[mythtv-users] Video is X frames ahead of audio, doubling video frame interval to slow down

Mark Kendall mark.kendall at gmail.com
Fri Nov 11 11:29:57 UTC 2011

On 11 November 2011 09:20, Dom H <speedsix.lists at googlemail.com> wrote:
> I've installed the linux-firmware-nonfree package instead of using
> firmware extracted manually from the Windows binary and I've watched
> the BBC HD preview now for about an hour and the problem seems to have
> gone away. Will see how it goes.
> Can someone explain what the 'mean' and 'std dev' values are on the
> output. Obviously averages but of what exactly?

The mean is the average period between displaying each frame, measured
in microseconds. So for BBC HD this should be around 40,000 (i.e.
1,000,000 / 25).

The standard deviation gives an indication of the variability of the
samples relative to that mean - the lower the better.

Generally speaking, for smooth playback you want the mean to remain
close to the target frame rate and low standard deviations. A high
standard deviation might be indicative of playback jitter - though
this is not always the case as some video display methods (e.g. VDPAU)
use a different thread to drive the actual frame presentation, so the
standard deviation may be misleading.



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