Volume control of CoreAudio USB device
Volume control of CoreAudio USB device
- Subject: Volume control of CoreAudio USB device
- From: Alasdair McLeay via Coreaudio-api <email@hidden>
- Date: Tue, 19 May 2020 13:16:54 +0100
I have a CoreAudio compatible device, but drivers are required in order to
control the volume and these have been discontinued so I'd like to create a
basic replacement.
I know what commands I need to send to the device in order to control the
volume, however I get error messages saying that another process has the device
open for exclusive access.
I guess that CoreAudio has exclusive control of the device when it is in use
and I don't see any way to issue USB commands via Core Audio, so I expect the
only way I can control the volume would be via a kernel extension. Does that
sounds right?
Perhaps I can use AppleUSBMergeNub and set some options to let Core Audio know
what USB commands should be used to control the volume? Any pointers greatly
appreciated as this is all fairly new to me.
Linux support for a similar device is here:
https://github.com/torvalds/linux/blob/642b151f45dd54809ea00ecd3976a56c1ec9b53d/sound/usb/mixer_scarlett.c#L47-L65
Thanks,
Ali
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