Firefox, WebRTC, and ALSA playback and capture devices

NathanZachary · Moderator Joined: 30 Jan 2007 Posts: 2608

Hello,

For quite some time, I've had to keep Chromium for the single purpose of video calls. I don't use PulseAudio or PipeWire, but instead just ALSA directly. For video calls, I need my output (ALSA playback device) to be one card and my input (ALSA capture device) to be a particular device on my C920 webcam. I thought that I would be able to just create an ~/.asoundrc file for this purpose, but I can't get it to work:

Dominique_71 · Posted: Tue Apr 09, 2024 8:48 am Post subject:

With multiple sound cards, in order to be sure to get the same card between reboot, the best practice is to define the card order in /etc/modprobe.d/alsa.conf, as example:

NathanZachary · Moderator Joined: 30 Jan 2007 Posts: 2608

Thank you for your response. I'm starting to think that Firefox is just stubborn about ALSA.

I have changed my .asoundrc and now I get audio playback in Firefox (and other applications), but Firefox still uses 'default' for my microphone instead of the one that is in the C920 webcam:

NathanZachary · Moderator Joined: 30 Jan 2007 Posts: 2608

Sadly, I'm starting to think that it may not be possible to get direct ALSA to work for my needs. I have tried various .asoundrc configurations but to no avail; I have audio playback but no input via my webcam microphone. I may have to admit defeat and go the route of:

1. Install media-sound/apulse with the 'sdk' USE flag
2. Rebuild Firefox with the 'pulseaudio' USE flag enabled

It looks like doing so in that order will allow Firefox to build against apulse instead of actually pulling in a full PulseAudio installation:
https://gitweb.gentoo.org/repo/gentoo.git/tree/www-client/firefox/firefox-124.0.2.ebuild#n1392

Dominique_71 · Posted: Wed Apr 10, 2024 10:42 am Post subject:

I am using firefox with JACK here. It is very easy to make the ALSA applications to work with JACK, what is needed is a configured loopback (kernel module snd_aloop) default ALSA card, and the jack ALSA plugin (media-plugins/alsa-plugins[jack]) with an .asound file configured to archieve that : (ALSA application -> snd_aloop -> jack plugin -> JACK -> ALSA device (sound card)).

Everything just work fine here with that config. My desktop launch cadence at start-up and cadence start JACK, so I have JACK running all the time. In practice that setup archive the same things than pulseaudio, but with the advantages of jack: a professional sound server with constant latency (don't set it too low when running firefox with audio), and a simpler solution than pulseaudio (all that was needed to do that, in addition to what was already in existence, is the ALSA jack plugin).

If You want to try that way, I can share my config.
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Dominique_71 · Posted: Wed Apr 10, 2024 1:27 pm Post subject:

pa4wdh · l33t Joined: 16 Dec 2005 Posts: 881

In my experience firefox/webrtc simply doesn't work with alsa. Regular playback like sound samples from wikipedia work fine, but webrtc doesn't.
So, besides you specific setup, maybe it's good to see if it can work without tinkering with the alsa config, just to see if it actually works. If it does you can tune it to your setup so you just have to troubleshoot your alsa config, knowing it can work.
I haven't found a solution (alsa-only system here), but if you found one i'll be happy to give it a try

.
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Dominique_71 · Posted: Wed Apr 10, 2024 2:20 pm Post subject:

NathanZachary · Moderator Joined: 30 Jan 2007 Posts: 2608

@Dominique_71, thank you for the details regarding JACK and for putting that information on the Wiki. I may give it a try as well in order to see a comparison between JACK and apulse.

@pa4wdh, that has been my experience as well. Without having an .asoundrc, I don't even get the ability to change sound output (let alone the microphone inputs). WebRTC just doesn't work with direct ALSA, and I think it is because Firefox looks ONLY for the device named 'default' for the microphone. So, if one's microphone is on another device, there's not really any way to make it work.

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NathanZachary · Moderator Joined: 30 Jan 2007 Posts: 2608

Wow, so even using apulse, I still can't select my webcam microphone when in a video chat in Firefox. Though I really don't like using Chromium, my audio and video "just work" in it.
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pa4wdh · l33t Joined: 16 Dec 2005 Posts: 881

IIRC Firefox has dropped alsa support. I can't find the relevant link to an authoritative source anymore, but the message was "We won't remove the support that's there, but if it breaks we won't fix it".

Does apulse work (except for the device selection)? Maybe you could configure a new device in asoudrc consisting of the correct input and output and use that with apulse?
_________________
The gentoo way of bringing peace to the world:
USE="-war" emerge --newuse @world

My shared code repository: https://code.pa4wdh.nl.eu.org
Music, Free as in Freedom: https://www.jamendo.com

NathanZachary · Moderator Joined: 30 Jan 2007 Posts: 2608

That's true that Firefox did drop "support" for ALSA quite some time ago. However, it's still available using the '--enable-audio-backends' option at compile-time. The Gentoo ebuild automatically enables ALSA if the 'pulseaudio' USE flag is not set and apulse is not installed:
https://gitweb.gentoo.org/repo/gentoo.git/tree/www-client/firefox/firefox-124.0.1.ebuild#n927

So, I decided to run some tests:

1. Emerge apulse WITH the 'sdk' USE flag and then re-emerge Firefox:
* In about:support under the 'Media' section, the 'Audio Backend' shows 'pulse-rust' --> indicating that the apulse headers and libraries are in place
* In about:support under the 'Media' section, the 'Input Devices' still only shows 'default_source_name' though, which isn't my USB webcam microphone

2. Emerge apulse WITHOUT the 'sdk' USE flag and then re-emerge Firefox:
* In about:support under the 'Media' section, the 'Audio Backend' shows 'alsa' (even when running `apulse firefox`)

These tests show me that apulse may not actually function as intended any longer, but that's not surprising since development hasn't been active for years and it has deviated from the full PulseAudio implementation a lot.

I found a thread on the PuppyLinux forum that might explain the problem:
https://forum.puppylinux.com/viewtopic.php?t=9169

It seems like Firefox only looks for the "default" input device and lazily passes the responsibility of determining that device to pavucontrol (part of PulseAudio). As such, I think that's why I can't select my microphone properly.

I'm not sure where this leaves me on options for getting rid of Chromium because I don't see great choices for getting my microphone to work in Firefox for WebRTC-based video chats (like Jitsi, Google Meet, or Zoom).

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“Truth, like infinity, is to be forever approached but never reached.” --Jean Ayres (1972)
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NathanZachary · Moderator Joined: 30 Jan 2007 Posts: 2608

I also found that there is an open issue for cubeb (the cross-platform audio library in Firefox) to support switching input and output devices in WebRTC:
https://github.com/mozilla/cubeb/issues/694

In particular, this comment:
https://github.com/mozilla/cubeb/issues/694#issuecomment-1076671185

shows that the WebRTC spec allows for switching, and that feature is implemented in Chromium but not in Firefox.
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Dominique_71 · Posted: Fri Apr 12, 2024 7:15 pm Post subject:

With the jack USE flag, I get
* In about:support under the 'Media' section, the 'Audio Backend' shows 'jack'.
* Output device: JACK playback
* Input device: JACK capture

Between jack and pulseaudio, I will always choose jack, that because with the setup I put into the wiki, You get all the advantages of pulseaudio - the ALSA applications are even auto-connecting into the JACK graph, a professional sound server (which pulseaudio will never be because it doesn't implement a constant latency, and when its latency increase, the only way to return to a lower value is to restart it), and a setup that doesn't change with time and is portable between different machines with very few minors changes into /etc/modules.conf/alsa.conf.
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