[mythtv] [mythtv-commits] mythtv commit: r26286 by jyavenard

Colin Guthrie mythtv at colin.guthr.ie
Tue Sep 14 18:17:17 UTC 2010

'Twas brillig, and mythtv at cvs.mythtv.org at 13/09/10 06:56 did gyre and
>       Author: jyavenard
>         Date: 2010-09-13 05:56:54 +0000 (Mon, 13 Sep 2010)
> New Revision: 26286
>    Changeset: http://svn.mythtv.org/trac/changeset/26286
> Log:
> mythfrontend need root privileges to be able to change the ALSA audio buffer size which by default is 64kB. This may not be sufficient for playing high-quality audio (like 24bits, 192kHz). We display the command line to run as root on how to increase the alsa buffer:
> echo 512 > /proc/asound/card1/pcm7p/sub0/prealloc
> Modified:
>    trunk/mythtv/libs/libmyth/audiooutputalsa.cpp

Just for reference, I know that on Mandriva, Fedora and IIRC Ubuntu too,
the default value for this is 4megs on HDA cards.

$ cat /proc/asound/card0/pcm0p/sub0/prealloc

This was done some time ago to enable larger buffers (e.g. 2s+) which
can give power savings when used with PulseAudio's timer based
scheduling and a well-behaved client that requests large buffers.

I didn't look at the code surrounding it, but I presume this is only
tried when it's not big enough, e.g. if it's already set to 4096, then
it wont be decreased down to 512?



Colin Guthrie

Day Job:
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Open Source:
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  PulseAudio Hacker [http://www.pulseaudio.org/]
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