[mythtv-users] ALSA/surround and mythtv

[osma ahvenlampi]

On 11/17/06, Rodney Fluharty <rfluharty at 321online.net> wrote:
> "ALSA:surround51" gives me nothing.  "ALSA:surround51:0" and
> "ALSA:plug:surround51:0" all fail.  "ALSA:default" is the only thing
> that works, but then just for 2 channels.

If what you wanted was analog 5.1 output, that's not a standard
option. However, there is a patch for it, that applies relatively
cleanly to 0.20-fixes (one reject, but it's for something already
changed so it doesn't matter).

http://cvs.mythtv.org/trac/ticket/1104

This introduces a new option for 2 or 6 channel audio output, and
works with AC3 sources using software decoding. One note: using
ALSA:surround51 I had channels output in mixed order, but I played
with this a few evenings back, and found that just plain ALSA:nforce
with the 6 channel option on was what I really needed.

Another trick that I've found nice is "fake 5-channel stereo" with an
upmix .asoundrc:

pcm.upmix {
  type plug
  slave {
    pcm "nforce"
    channels 6
  }
  ttable.0.0 1
  ttable.1.1 1
  ttable.2.2 1
  ttable.2.0 0.2
  ttable.2.1 0.2
  ttable.0.2 0.4
  ttable.1.2 0.4
  ttable.3.3 1
  ttable.3.0 0.2
  ttable.0.3 0.4
  ttable.4.4 1
  ttable.4.1 0.2
  ttable.1.4 0.4
  ttable.5.5 1
  ttable.5.0 0.2
  ttable.5.1 0.2
  ttable.0.5 0.4
  ttable.1.5 0.4
}

Not as good as mplayer's "surround,sub" audio filter naturally since
it doesn't do Dolby Pro Logic matrix decode, but at least it puts the
whole audio system into use.

-- 
Osma Ahvenlampi   <oa at iki.fi>       http://www.fishpool.org