amixer: Unable to find simple control 'PCM',0

[najihun]

Thank you for contribution!

tried this receiver on my RP3, but got an issue as below.

Checked amixer on my RP3 there is only 'Master' not 'PCM'

Think if I could change the audio source(?), then docker can be run.

Is there any way to custom and fix ?

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amixer: Unable to find simple control 'PCM',0

Traceback (most recent call last):
File "ap2-receiver.py", line 1108, in
setup_global_structs(args)
File "ap2-receiver.py", line 273, in setup_global_structs
volume = get_volume()
File "/airplay2/ap2/utils.py", line 94, in get_volume
line_pct = subprocess.check_output(["amixer", "get", "PCM"]).splitlines()[-1]
File "/usr/lib/python3.7/subprocess.py", line 395, in check_output
**kwargs).stdout
File "/usr/lib/python3.7/subprocess.py", line 487, in run
output=stdout, stderr=stderr)
subprocess.CalledProcessError: Command '['amixer', 'get', 'PCM']' returned non-zero exit status 1.