[alsa-devel] How to inform application about sample rate changed from device.

[Takashi Iwai]

On Mon, 03 Dec 2018 17:45:24 +0100,
Clemens Ladisch wrote:
> 
> Chakravarthi Pradeep wrote:
> > When device is generating audio sample rate of 44.1KHz then how to
> > inform VLC that use 44.1KHz sample rate(same is for 96KHz)
> 
> ALSA PCM devices have constraints that restrict what parameters
> applications can configure.
> 
> Usually, the constraints are installed when the PCM device is opened.
> Change runtime->hw.rate_min/_max to the same value.

Right.  So this can be interpreted: it's currently an unsupported
scenario, hence we have no standard way to achieve that.

I guess the best would be to make the further operation returning an
error after such hardware change, so that user-space can re-open and
re-setup the things.

In theory, you can make the hw_constraints dynamic and let user-space
setting up things again via hw_free / hw_params sequence without
re-opening the device, too.  But I'm not sure whether it's easier for
applications.


thanks,

Takashi