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briankendall / proxy-audio-device

A virtual audio driver for macOS to sends all audio to another output
The Unlicense
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Channel Mapping #50

Open Torinth opened 1 month ago

Torinth commented 1 month ago

Hi there, wondering if its possible to change which channels are mapped to the proxied device. For example i have a 16 channel audio interface and channel 16 is my generic audio output. when i use apps like spotify i cant choose which channels it uses so it would be great to say map virtual channel 1 to proxied device 16 (i would just mute channel 2 or leave it unmapped and configure spotify to output mono) so that i can choose the virtual output device and it get routed to channel 16 on my audio interface

Torinth commented 1 month ago

If i were to build this myself is it this line i would change to 16 and the next to 15 (then i would mute channel 2 of the virtual device or could i change it somehow to not route channel 2 to anything)?

https://github.com/briankendall/proxy-audio-device/blob/13cbdb8055232c68ffd28900c4d28182b5ecafe2/proxyAudioDevice/ProxyAudioDevice.cpp#L3056

briankendall commented 1 month ago

That line wouldn't do it, and you'd want to keep that as is. What you do want to do is change the contents of this loop starting here: https://github.com/briankendall/proxy-audio-device/blob/13cbdb8055232c68ffd28900c4d28182b5ecafe2/proxyAudioDevice/ProxyAudioDevice.cpp#L5420

You can see it's copying audio data from the proxy device to the proxied device, and it's only doing it for at most the first two channels.

I think if you change these lines:

5421:         UInt32 numChannelsToProcess = std::min(outputChannelCount, currentInputDeviceChannelCount);

5426:            Float32 *out = (Float32 *)outOutputData->mBuffers[bufferIndex].mData + channelIndex;

To this:

5421:         UInt32 numChannelsToProcess = 1;

5426:            Float32 *out = (Float32 *)outOutputData->mBuffers[bufferIndex].mData + 15;

that would map proxy device channel 1 to your audio interface's channel 16. But of course I haven't tested this, and given we're dealing with pointer arithmetic getting this wrong could easily cause the audio server to crash. But I think this or something like it should get what you want without too much trouble.

Torinth commented 1 month ago

ok awesome i will give it a try! thank you