[alsa-devel] Detect when sound card is in use

Hi everyone,

I have a problem and I dont't know where to ask my questions anymore, so I hope this mailing list can help me make progress with my problem....

I have a speaker set connected to an USB-Power-Plug (by which I can turn the speakers on and off )

Now I want to detect, when the soundcard is in use and when not. (to turn the speakers on when needed...) (I am a C++ programmer so I can mess some things up)

So my question is: Which way is best to detect wheather my sound card is in use or not ? Is there a general overview/documentation of the sound kernel modules which describes the general relationship between them ? What would you do ?

PLEASE help !

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Mit freundlichen Grüßen / Best regards Claus Ilginnis