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Old 07-11-2013, 07:49 AM   #1
Registered: Jul 2007
Distribution: Slackware
Posts: 220

Rep: Reputation: 26
Alsa Channel Mapping and VLC : no stereo with 5.1 source audio

I have a strange issue with ALSA since 1.0.27 and VLC : VLC does not downmix 5.1 audio to stereo anymore with recent git pulls.
I have a self compiled VLC git package made in april that works well. Slackware upgraded to 1.0.27 in may and then to in june. Any newer VLC package I create do not apply downmix.
I asked for help on the VLC forums and the VLC developpers told me channel mapping was an addition to alsa-lib 1.0.27 whose support was added to VLC in december 2012.
Basically, my audio (HDA ATI SB) is now claiming that it is a 6 channels chip and so VLC applies a 6-channels setting, even though I only have two speakers. Which means I basically have only two channels being played and thus weird results (disappearing voices, missing sounds, etc.)
I tried to force alsa to downmix by adding the following lines to /etc/asound.conf :

pcm.!surround51 {
    type vdownmix
    slave.pcm "default"
pcm.!surround40 {
    type vdownmix
    slave.pcm "default"
but it didn't solve my problem.
If anybody has a clue, I'm interested.

Last edited by rvdboom; 07-11-2013 at 07:50 AM.


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