[SOLVED]XBMC Alsa Nvidia HDMI cant get dmix working with plughw:1,

Question

With 2.6.34 i'm able to get audio through my Asus (Nvidia chipset) GF210. 
The issue is that in order to get audio in XBMC, i have to specify a custom audio device as plughw:1,7 and that seems to disable dmix -- ergo, no more two sounds at once (so no crossfade during music playback).
this is the only card description that works; it basically tells XBMC to output to the raw hardware directly on card 1 device 7 skipping all layers of abstraction (including dmix). 
this method is only recommended for applications that will do all their own mixing (think jackd).  so the behavior is to be expected.
some online docs say dmix will only work with the "default" device, others say it might work if i don't use the hw descriptor, but omitting the "hw" --> no sound at all.
the only other way i can get sound at all is to redefine pcm.!default as the plughw:1,7 device in /etc/asound.conf and then specify "default" in XBMC (this makes sense) but this still seems to mean no dmix.
obviously, resetting everything and using the normal VGA + Headphone-out mixes and crossfades just fine.
So, does anyone know:
  * a way to get dmix going with a custom plughw card/device
  * a way to tell XBMC to do the mixing on its own before sending the sound to plughw -- is this possible?
any help appreciated, it's more of a want than a need right now.
up to date 64bit, stock 2.6.34.1-1 kernel, and xbmc 9.11-17 if that matters.
Last edited by brisbin33 (2010-07-10 01:16:54)

Answer 1

Getting dmix to run through a custom device is easy:
pcm.dmixer {
type dmix
ipc_key 2048
slave {
pcm "hw:1,7" # Always use pure hw. dmix will reformat/resample audio.
period_size 512 # If you get stuttering/or non-working audio, fiddle around with these
buffer_size 4096
rate 48000 # HDMI, I'll assume 48kHz
format S16_LE # Should be default for pretty much any soundcard.
bindings {
0 0
1 1
pcm.!default {
type plug
slave.pcm dmixer
Using this approach, everything will pass through dmix, which passes to hw:1,7.
Last edited by Themaister (2010-07-09 21:58:01)