Discover a microphone device, to later discover if it is receiving input

[info]

Can maintainers of this list please give a straight answer: is asking 
questions and leaving comments here a waste of time?

On 2020-10-04 12:22 PM, info wrote:
> Hi all,
>
>
> I am writing a program that aims to auto-discover the microphone 
> device that the user is speaking into. I started off by querying 
> device hints and collected all devices with the IO types of null, 
> since I have not found any devices with the type of Input. I am 
> puzzled how it is possible that there is no Input, where a microphone 
> device should not be able to emit sound. This is the list on my 
> particular machine:
>
> Name of device: sysdefault:CARD=SB
> Description of device: HDA ATI SB, ALC892 Analog
> Default Audio Device
> I/O type of device: (null)
>
> Name of device: front:CARD=SB,DEV=0
> Description of device: HDA ATI SB, ALC892 Analog
> Front speakers
> I/O type of device: (null)
>
> Name of device: surround21:CARD=SB,DEV=0
> Description of device: HDA ATI SB, ALC892 Analog
> 2.1 Surround output to Front and Subwoofer speakers
> I/O type of device: Output
>
> Name of device: surround41:CARD=SB,DEV=0
> Description of device: HDA ATI SB, ALC892 Analog
> 4.1 Surround output to Front, Rear and Subwoofer speakers
> I/O type of device: Output
>
> Name of device: surround50:CARD=SB,DEV=0
> Description of device: HDA ATI SB, ALC892 Analog
> 5.0 Surround output to Front, Center and Rear speakers
> I/O type of device: Output
>
> Name of device: surround71:CARD=SB,DEV=0
> Description of device: HDA ATI SB, ALC892 Analog
> 7.1 Surround output to Front, Center, Side, Rear and Woofer speakers
> I/O type of device: Output
>
> Name of device: sysdefault:CARD=SB
> Description of device: HDA ATI SB, ALC892 Analog
> Default Audio Device
> I/O type of device: (null)
>
> Name of device: front:CARD=SB,DEV=0
> Description of device: HDA ATI SB, ALC892 Analog
> Front speakers
> I/O type of device: (null)
>
> Now, I am more puzzled, because none of them is a microphone device 
> explicitly. How can my program determine which of them is actually a 
> microphone?
>
> Also, why are devices are duplicated in the output from 
> snd_device_name_hint()? The very first device is also repeated as the 
> 2nd last one...
>
>
> Regards,
> Alex
>
>