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

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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




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