[Alsa-user] How to capture not muted sound only?

[Alexander K. <ako...@gm...>]

Hi all,

could somebody advise on how to omit capturing of a muted sound in the
following situation?

There's an application that check presence of auto-initiated audio on some
web pages.
The application prepares environment (creates appropriate ~/.asoundrc file),
launches a browser,
opens a web page in the browser, waits some time, closes the browser, and
checks presence
of file with captured audio stream.

Here's content of ~/.asoundrc file:

pcm.app_writer {
     type file
     slave {
         pcm null
     }
     file { @func getenv
         vars [ APP_AUDIO_FILE ]
         default "/dev/null"
     }
     format "wav"
}

pcm_slave.app_converter {
     pcm app_writer
     format u8
     channels 1
     rate 100
}

pcm.app_transmitter {
     type plug
     slave app_converter
}

pcm.!default {
     @func refer
     name { @func concat
             strings [ "pcm."
             { @func getenv
                 vars [ ALSA_DEFAULT_PCM ]
                 default null
             }
         ]
     }
}

Here're CLI commands used to launch the browser:

export APP_AUDIO_FILE=/tmp/sound
export ALSA_DEFAULT_PCM=app_transmitter
firefox <http://...> &

And everything works properly... except one thing: in case a muted flash
movie is played on
web page then the corresponding audio stream is redirected into /tmp/sound
as well.
(But I'd like to capture not muted sound only).

So, is there a way to capture not muted sound only? E.g. (random ideas):
a) Modify ~/.asoundrc file so that it doesn't redirect audio stream into
APP_AUDIO_FILE
in case sound is muted.
b) Ask ALSA about current audio settings of flash player before closing the
browser.

-- 
Alexander O. Kobernik