I've been working on a more advanced confiuration for my linux box, in
particular playing multi channel audio through two soundcards for
surround. As a starting point I've decided to try playing 5.1 audio with
back channels mixed with the front. Long time ago I've created two route
devices:
pcm.51to31 {
type route
slave {
pcm "onboard"
channels 6
}
ttable.5.3 1 # LFE
ttable.4.2 1 # center
ttable.0.0 0.8 # front left
ttable.1.1 0.8 # front right
ttable.2.0 0.4 # rear left
ttable.3.1 0.4 # rear right
hint {
show on
description "5.1 to 3.1 downmix"
}
}
pcm.odd51to31 {
type route
slave {
pcm "onboard"
channels 6
}
ttable.3.3 1
ttable.2.2 1
ttable.0.0 0.8
ttable.1.1 0.8
ttable.4.0 0.4
ttable.5.1 0.4
hint {
show on
description "5.1 to 3.1 downmix intended for mplayer"
}
}
This way it worked with mplayer, but as you can see I've became aware
that sometimes order of channels differs.
Today I want to use mpv, which supports alsa channel maps (a great idea,
given the problem above). Unfortunately, the above gives me mpv output
(for one of the devices):
channel map reported by ALSA: FL FR FC LFE FL FR
I've written to the mpv author and he kindly added an option to
disregard the alsa map.
Yet, the simplest option would rather be to craft a channel map for this
device. Is it possible to force alsa to present a channel map of my
choosing for a device. Documentation seems not to permit this for route
devices.
Michał Goliński
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