I have an onboard sound card, and also a connected bluetooth headset. I have configured the bluetooth device in /etc/asound.conf:

# cat /etc/asound.conf

pcm.bluetooth 
 type bluetooth
 device 12:34:56:78:9a:bc
 profile "auto"


ctl.bluetooth 
 type bluetooth

By default, the onboard card is used for all sound (apparently, the default onboard card does not even need to be listed in asound.conf)

When I want an application to use my bluetooth alsa device, I have to specify it, such as:

mplayer -ao alsa:device=bluetooth file.mp3

That's fine for me. But I need a way to tell my browsers to use bluetooth alsa device as well.

I have found a way how to start chromium using the --alsa-output-device commandline option:

chromium --alsa-output-device=bluetooth

I need a similar way to start firefox, but I could not find any.

How can I tell firefox to use my bluetooth alsa device, without having to modify /etc/asound.conf or ~/.asoundrc every time ?

UPDATE:

I have followed @lgeorget's advice and my /etc/asound.conf now looks like this:

pcm.!default 
type plug
slave.pcm 
 @func getenv
 vars [ ALSAPCM ]
 default "hw:0,0"
 


pcm.bluetooth 
 type bluetooth
 device 12:34:56:78:9a:bc
 profile "auto"


ctl.bluetooth 
 type bluetooth

When I start firefox using ALSAPCM=bluetooth firefox, I do get sound in my bluetooth headset, but firefox runs at 100% CPU (on my 4 cores) and the youtube video plays at 10x speed (and the sound is correspondingly (garbled). I don't understand what's happening. When I start firefox without ALSAPCM=bluetooth, everything is OK, and sound plays on default alsa device.

Apparently there is no option for firefox, but you can manipulate the ALSA output through environment variables.

Try for example:

ALSA_PCM_CARD=bluetooth firefox

Alternatively, if this does not work, try scripting a little your .asoundrc

pcm.!default 
type plug
slave.pcm 
 @func getenv
 vars [ ALSAPCM ]
 default "hw:hdmi"
 

(replace "hw:hdmi" with your normal pcm). Then if you want a program to use a specific PCM, use:

ALSAPCM=bluetooth firefox

Sources:

• Archlinux-wiki


• Stackoverflow.com

It looks like an incarnation of this bug. There are some solutions suggested, but they seem to be Intel specific.

Try using pulseaudio. If it works, you can redirect your ALSA programs to pulseaudio with the following asound.conf:

pcm.pulse 
 type pulse

ctl.pulse 
 type pulse

pcm.!default 
 type pulse

ctl.!default 
 type pulse

If that doesn't help, try adding rate 44100 or rate 48000 to the pcm.bluetooth section of your asound.conf. Maybe ALSA will come to its senses then.

You might also try Html5 Youtube Video Speed Controller, though I doubt it will help.

_{Remark: Current Firefox versions seem to ignore ~/.asound.conf on unknown reasons.}

If you don't use pulseaudio (it is mainly an unneeded layer over alsa, despite that most distros install it), then in most cases, you only need to select the default audio output to a different one.

This can be done with the following .asound.conf in your home:

pcm.!default 
 type hw
 card N


ctl.!default 
 type hw 
 card N

Substitute N with a small integer, 0 for your first sound card (which is the default), 1 for your second, and so on.

The ! in !default isn't negation here! It is an overriding of the previously (system-wide defined) global alsa.conf .

More tricky configurations can be read here.