[mythtv] Kernel audio buffer overrun

[Ed Wildgoose]

Jim Perry wrote:

> This is a relatively minor issue, but I noticed that I was getting 
> continual audio glitches (very short bursts of white noise) during any 
> kind of high CPU activity, but with no errors mentioned.  Turns out 
> that NuppelVideoRecorder uses SNDCTL_DSP_SETFRAGMENT to create 8 
> kernel buffers of size 1024 bytes, enough for 64ms of sound with the 
> settings I was using.  Keeping the number low is nice and all, but I 
> had to crank up the number of kernel buffers to get MythTV to run on 
> my old, slow computer.
>
> It'd be nice if this was configurable or an error was mentioned in the 
> log (if that's even possible).


It's a good idea.  Have a look at AudioOutputOSS::SetFragSize() and see 
if you can suggest a good patch that is nice and general purpose for our 
uses.  At the moment it tries to make the audio buffer approx 1 frame in 
size which gives good response when you pause the video stream (or fast 
forward).

Your machine really should find it a bit easier to maintain this latency 
though.  Can I suggest trying also the low latency patches.  On a 2.6 
kernel with the low latency stuff and running with realtime priority, I 
can easily maintain a 2 * 512 buffer even in the face of a background 
kernel compile.

Agreed though it would be nice to get the normal settings quite general 
purpose.  Please try to have a little experiment and suggest a suitable 
patch

Thanks

Ed W