ALSA audio and YouTube

Question

I want to play youtube videos and programmatically direct firefox's audio out to a particular sound card.

I think I would do something like firefox | aplay -D hw:x,y. Yields:

Playing raw data 'stdin' : Unsigned 8 bit, Rate 8000 Hz, Mono aplay: set_params:1059: Sample format non available Available formats: - S16_LE

Trying firefox | aplay -D hw:1,0 -f S16_LE -c 2

Playing raw data 'stdin' : Signed 16 bit Little Endian, Rate 8000 Hz, Stereo Warning: rate is not accurate (requested = 8000Hz, got = 44100Hz) please, try the plug plugin

Finally, firefox | aplay -D plughw:1,0 -f S16_LE -c 2

Playing raw data 'stdin' : Signed 16 bit Little Endian, Rate 8000 Hz, Stereo

The command-line suggests that it worked, but audio came out of hw:0,0 (the default).

Do I need to make my own plugin? Or do I need to force alsa to take 44100Hz?

Also, I refuse to use pulse since the memory leak bug makes it crash often.

derobert derobert · Accepted Answer · 2012-01-20T18:14:43

I'm pretty sure flash always uses the default sound card, so you need to change pcm.default. You could do so by editing ~/.asoundrc and adding something like:

pcm.!default {
    type hw
    card 0
    device 2
}

Of course, that affects all apps, but I believe can also set ALSA_CONFIG_PATH (in the environment) to specify a different file, so you could do it for just Firefox.

The ALSA FAQ indicates there are ALSA_PCM_CARD and ALSA_CARD environment variables that may work as well.

These variables actually work because they're part of the default also config in /usr/share/alsa/alsa.conf:

    @args.CARD {
            type string
            default {
                    @func getenv
                    vars [
                            ALSA_PCM_CARD
                            ALSA_CARD
                    ]
                    default {
                            @func refer
                            name defaults.pcm.card
                    }
            }
    }

So, you should be able to do this:

ALSA_PCM_CARD=1 ALSA_PCM_DEVICE=3 firefox

using the appropriate card and device numbers from your system. Or of course you could add your own environment variable (or other conditional check) into your ALSA configuration.

ALSA audio and YouTube

2 Answers