Detecting if a pcm device is a digital or analog one

Detecting if a pcm device is a digital or analog one

[Jean-Yves Avenard]

Hi there...

I was wondering if there was any way to accurately distinguish between
audio device, if it has an analog or a digital output.

I would prefer not parsing the name (like analog71 is obviously an
analog device, while "hdmi" is digital)

I see that on some devices the IEC958 bit is set, but this doesn't
seem reliable (on another PC, the IEC958 bit isn't set).

Any suggestions would be greatly appreciated...

Thank you
Jean-Yves

Re: Detecting if a pcm device is a digital or analog one

[Clemens Ladisch]

Jean-Yves Avenard wrote:
> I was wondering if there was any way to accurately distinguish between
> audio device, if it has an analog or a digital output.

Not really.  There are devices where the same stream is routed to both
analog and digital outputs, and sometimes the driver cannot know if
there is a DAC further down the line.  In any case, this would be very
hardware specific.

What do you need this for?


Regards,
Clemens

Re: Detecting if a pcm device is a digital or analog one

[James Courtier-Dutton]

On 25 June 2010 09:21, Clemens Ladisch <clemens@ladisch.de> wrote:
> Jean-Yves Avenard wrote:
>> I was wondering if there was any way to accurately distinguish between
>> audio device, if it has an analog or a digital output.
>
> Not really.  There are devices where the same stream is routed to both
> analog and digital outputs, and sometimes the driver cannot know if
> there is a DAC further down the line.  In any case, this would be very
> hardware specific.
>
> What do you need this for?
>
My guess is that if one knew, one could decide if it was sensible to
send AC3 encoded data to the PCM or not.
Without knowing which PCM is sending data to which outputs, it would
be very difficult to accurately distinguish them.
Alsa does have a device name "iec958" that one can use instead of
"front" or "default" that will ensure the output goes to a digital
output if one exists.

James
_______________________________________________
Alsa-devel mailing list
Alsa-devel@alsa-project.org
http://mailman.alsa-project.org/mailman/listinfo/alsa-devel