[alsa-devel] 5.1 to stereo using libasound

[Eric Desjardins]

Thanks, my file didn't use the default channel map.
Where are the defaults are defined?

Many thanks!
Eric

Le dim. 8 sept. 2019 à 03:48, Tanu Kaskinen <tanuk at iki.fi> a écrit :

> On Sat, 2019-09-07 at 10:07 -0400, Eric Desjardins wrote:
> > Hi,
> >
> > I am playing a mkv with 5.1 channels from a mkv. I configure libasound
> for
> > 6 channels and I feed them interleave audio using snd_pcm_writei. I use
> the
> > default pulse audio device.
> >
> > So far, nothing is wrong. However, I do not ear things correctly. I
> listen
> > this on my stereo speaker. There is no mixdown to stereo and I was
> > wondering how to do that. I tried to use chmap api but anything I try on
> > the default device returns an error.
> >
> > I was wondering what was the correct way to do that?
> > Using the mixing api?
> > How do we detect that my device output stereo if chmap doesn't work?
> >
> > I am on a ubuntu 18.04 linux box.
>
> The pulse plugin takes your audio and sends it to PulseAudio without
> any modification. The ALSA API doesn't allow the application to tell
> the channel map of the stream, so if you send 6 channels, the pulse
> plugin assumes that you are using the default 5.1 channel map (front-
> left,front-right,rear-left,rear-right,front-center,lfe).
>
> The PulseAudio daemon then downmixes the audio to stereo in some way
> (the details depend on PulseAudio configuration). You can't detect from
> your ALSA application whether the device that PulseAudio is using is a
> stereo device or something else.
>
> Since it's apparently not working as you expect, does your application
> use the default 5.1 channel map that I mentioned above? Is PulseAudio
> configured to do remixing ("pulseaudio --dump-conf" should show
> "enable-remixing = yes")?
>
> --
> Tanu
>
> https://www.patreon.com/tanuk
> https://liberapay.com/tanuk
>
>