Re: [Alsa-user] How can you programmatically tell that audio is playing?

[Dominique M. <dom...@vt...>]

Le Fri, 26 Dec 2008 11:53:48 -0500,
Christian Brink <cb...@r-...> a écrit :

> J. Pauli wrote:
> > Christian Brink wrote:
> >   
> >> How can you programmatically tell that audio is playing or at least 
> >> being sent to the soundcard?
> >>
> >> I've got an application that occasionally fails to pick up a remote 
> >> stream, but the process hangs around so I can't tell that it failed just 
> >> by checking the process list. I would like to be able to tell if  the 
> >> application is sending audio or not so I can retry.
> >>
> >> I've checked the archives, googled, and tried cat'ing /dev/audio (which 
> >> seems to return data whether or not audio is playing).
> >>
> >>     
> >
> > Check the files
> > /proc/asound/cardX/pcmYp/subZ/[status|hw_params|sw_params], where X,Y
> > and Z is the soundcard, device and subdevice you want to monitor. If
> > nothing is being sent to the soundcard it should contain "closed".
> > Unfortunately you need to activate "verbose proc something" in your
> > kernel, which most distributions don't have by default.
> >
> > I've also written some small (and really buggy) program to monitor all
> > devices and subdevices of a soundcard but you still need that kernel
> > option or it will crash. You can get it here:
> > http://stinfwww.informatik.uni-leipzig.de/~mai00bgn/aproc/ (source code
> > only). Sorry for the propaganda.
> >
> >   
> Jan -
> 
> Thanks for the info, it's been a great help. I had a couple more 
> questions if you'd being willing to help.
> 
> I've been doing some testing on a couple of different machines (Fedora 
> and Deb). 'closed' only seems to show up when the card is not "open" by 
> an application. So if I have a mp3 player app open (Rhythmbox for 
> example) but not playing or paused, it shows the card not "closed" even 
> though no music is playing.
> Is this normal?

A paused application just pause the playing but doesn't close the thread that
make the playing, so the card will still "see" the app.

If you make a stop instead of pause, a good written app would close the thread
that make the playing and the card would not "see" the app anymore.

> or is this the difference between having the kernel flag on and not?

I don't know.

Ciao,
Dominique