[alsa-devel] What are subdevices?

[dE]

On 10/26/14 14:41, Clemens Ladisch wrote:
> dE wrote:
>> A device seems like the output streams the sound card supports. Like HDMI, DP, analog etc...
>>
>> So what's a subdevice?
> A subdevice is an output streams the sound card supports.
>
> Typically, a device has multiple subdevices if the card supports hardware mixing; all
> the subdevices end up at the same physical output.
>
>
> Regards,
> Clemens

Ok, so a device list is a list of different streams the card can 
supports simultaneously and they'll be output via different channels 
without mixing.

Thanks for clarifying this.

But, typically cards have a single analog device but support 
multichannel output. So how does this work at the software level? If 
ALSA can't send multiple streams of audio to one device, then how does 
ALSA send  separate output to different channels of the device?

Is the PCM sent to the sound card codified? Is this the same way how 
stereo work?