[mythtvnz] 0.25 video frame jitter.

[Brett]

> 
> 64kB is only good enough for stereo output (that includes AC3 and DTS
> which fundamentally are 44.1-48kHz stereo PCM streams)
> 
> More than that, in particular LPCM multichannels stream and you will
> get buffer underruns.
> 
> Ubuntu sets the default alsa buffer to 4MB.
> When using TrueHD or DTS-HD MA, which are 16 bits, 8 channels, 192kHz
> PCM. You'll need close to 4MB.
> So setting 4MB alsa buffer is actually a value that makes sense and
> that will work across the spectrum of content you could play
> 
My lucid/alsa 1.0.24.2 (user libs) defaults to 64.
Mythtv complains it requires 128..
But I only use 48KHz AC3 & PCM with Mythtv.

I (like many) ignored the alsa buffer errors reported because they
seemed to have no consequence with 0.24.

The real point was that 0.25 is badly affected by alsa buffer problem.
This issue was good motivation to fix (hack) the alsa /proc/asound
permissions/ownership. 

What is the proper fix/soln to alsa /proc/asound ?:
- alsa code mods
- udev rule
- module options (possible in the past)
My solution was none of these, just chown/chmod in /etc/rc.local.

The frame jitter standard deviation with 0.24 is in the range 17-40.
The best jitter stddev with 0.25 is in range 80 - 400, these values do
not cause any visible impact (PQ).
These measurements are on the same machine & recordings & 0.24+fixes
backend.

Thanks,
Brett