How to enable/disable input or output channels from an aggregate CoreAudio device? - macos

Question

I have thoroughly read the question and answer in this thread:
How to exclude input or output channels from an aggregate CoreAudio device?
And it appears to be missing information on the solution:
I have created an aggregated device containing multiple audio devices. When calling core audio to receive the number of streams (using kAudioDevicePropertyStreams) the return value is always 1. I have also tried the implementation in CoreAudio Utility classes: CAHALAudioDevice::GetIOProcStreamUsage. Still I could not see how to access sub-streams and disable/enable them as mentioned here.
What needs to be done to accomplish disable/enable of sub-streams?
EDIT
Here is CAHALAudioDevice::GetIOProcStreamUsage for reference:
void CAHALAudioDevice::GetIOProcStreamUsage(AudioDeviceIOProcID
inIOProcID, bool inIsInput, bool* outStreamUsage) const
{
// make an AudioHardwareIOProcStreamUsage the right size
UInt32 theNumberStreams = GetNumberStreams(inIsInput);
UInt32 theSize = SizeOf32(void*) + SizeOf32(UInt32) + (theNumberStreams * SizeOf32(UInt32));
CAAutoFree<AudioHardwareIOProcStreamUsage> theStreamUsage(theSize);
// set it up
theStreamUsage->mIOProc = reinterpret_cast<void*>(inIOProcID);
theStreamUsage->mNumberStreams = theNumberStreams;
// get the property
CAPropertyAddress theAddress(kAudioDevicePropertyIOProcStreamUsage, inIsInput ? kAudioDevicePropertyScopeInput : kAudioDevicePropertyScopeOutput);
GetPropertyData(theAddress, 0, NULL, theSize, theStreamUsage);
// fill out the return value
for(UInt32 theIndex = 0; theIndex < theNumberStreams; ++theIndex)
{
outStreamUsage[theIndex] = (theStreamUsage->mStreamIsOn[theIndex] != 0);
}
}

Answer 1

For reference, here is the function my program uses the accomplish the results described in the linked question:
// Tell CoreAudio which input (or output) streams we actually want to use in our device
// #param devID the CoreAudio audio device ID of the aggregate device to modify
// #param ioProc the rendering callback-function (as was passed to AudioDeviceCreateIOProcID()'s second argument)
// #param scope either kAudioObjectPropertyScopeInput or kAudioObjectPropertyScopeOutput depending on which type of channels we want to modify
// #param numValidChannels how many audio channels in the aggregate device we want to actually use
// #param rightJustify if true, we want to use the last (numValidChannels) in the device; if false we want to use the first (numValidChannels) in the device
// #returns 0 on success or -1 on error
// #note this function doesn't change the layout of the audio-sample data in the audio-render callback; rather it causes some channels of audio in the callback to become zero'd out/unused.
int SetProcStreamUsage(AudioDeviceID devID, void * ioProc, AudioObjectPropertyScope scope, int numValidChannels, bool rightJustify)
{
const AudioObjectPropertyAddress sizesAddress =
{
kAudioDevicePropertyStreamConfiguration,
scope,
kAudioObjectPropertyElementMaster
};
Uint32 streamSizesDataSize = 0;
OSStatus err = AudioObjectGetPropertyDataSize(devID, &sizesAddress, 0, NULL, &streamSizesDataSize);
if (err != noErr)
{
printf("SetProcStreamUsage(%u,%i,%i): AudioObjectGetPropertyDataSize(kAudioDevicePropertyStreamConfiguration) failed!\n", (unsigned int) devID, scope, rightJustify);
return -1; // ("AudioObjectGetPropertyDataSize(kAudioDevicePropertyStreamConfiguration) failed");
}
const AudioObjectPropertyAddress usageAddress =
{
kAudioDevicePropertyIOProcStreamUsage,
scope,
kAudioObjectPropertyElementMaster
};
Uint32 streamUsageDataSize = 0;
err = AudioObjectGetPropertyDataSize(devID, &usageAddress, 0, NULL, &streamUsageDataSize);
if (err != noErr)
{
printf("SetProcStreamUsage(%u,%i,%i): AudioObjectGetPropertyDataSize(kAudioDevicePropertyIOProcStreamUsage) failed!\n", (unsigned int) devID, scope, rightJustify);
return -1; // ("AudioObjectGetPropertyDataSize(kAudioDevicePropertyIOProcStreamUsage) failed");
}
AudioBufferList * bufList = (AudioBufferList*) malloc(streamSizesDataSize); // using malloc() because the object-size is variable
if (bufList)
{
int ret;
err = AudioObjectGetPropertyData(devID, &sizesAddress, 0, NULL, &streamSizesDataSize, bufList);
if (err == noErr)
{
AudioHardwareIOProcStreamUsage * streamUsage = (AudioHardwareIOProcStreamUsage *) malloc(streamUsageDataSize); // using malloc() because the object-size is variable
if (streamUsage)
{
streamUsage->mIOProc = ioProc;
err = AudioObjectGetPropertyData(devID, &usageAddress, 0, NULL, &streamUsageDataSize, streamUsage);
if (err == noErr)
{
if (bufList->mNumberBuffers == streamUsage->mNumberStreams)
{
Int32 numChannelsLeft = numValidChannels;
if (rightJustify)
{
// We only want streams corresponding to the last (N) channels to be enabled
for (Int32 i=streamUsage->mNumberStreams-1; i>=0; i--)
{
streamUsage->mStreamIsOn[i] = (numChannelsLeft > 0);
numChannelsLeft -= bufList->mBuffers[i].mNumberChannels;
}
}
else
{
// We only want streams corresponding to the first (N) channels to be enabled
for (Uint32 i=0; i<streamUsage->mNumberStreams; i++)
{
streamUsage->mStreamIsOn[i] = (numChannelsLeft > 0);
numChannelsLeft -= bufList->mBuffers[i].mNumberChannels;
}
}
// Now set the stream-usage per our update, above
err = AudioObjectSetPropertyData(devID, &usageAddress, 0, NULL, streamUsageDataSize, streamUsage);
if (err != noErr)
{
printf("SetProcStreamUsage(%u,%i,%i): AudioObjectSetPropertyData(kAudioDevicePropertyIOProcStreamUsage) failed!\n", (unsigned int) devID, scope, rightJustify);
ret = -1; // ("AudioObjectSetPropertyData(kAudioDevicePropertyIOProcStreamUsage) failed");
}
}
else
{
printf("SetProcStreamUsage(%u,%i,%i): #Buffers (%u) doesn't match #Streams (%u)!\n", (unsigned int) devID, scope, rightJustify, bufList->mNumberBuffers, streamUsage->mNumberStreams);
ret = -1;
}
}
else
{
printf("SetProcStreamUsage(%u,%i,%i): AudioObjectSetPropertyData(kAudioDevicePropertyIOProcStreamUsage) failed!\n", (unsigned int) devID, scope, rightJustify);
ret = -1; // ("AudioObjectGetPropertyData(kAudioDevicePropertyIOProcStreamUsage) failed");
}
free(streamUsage);
}
else ret = -1; // out of memory?
}
else
{
printf("SetProcStreamUsage(%u,%i,%i): AudioObjectGetPropertyData(kAudioDevicePropertyStreamConfiguration) failed!\n", (unsigned int) devID, scope, rightJustify);
ret = -1; // ("AudioObjectGetPropertyData(kAudioDevicePropertyStreamConfiguration) failed");
}
free(bufList);
return ret;
}
else return -1; // out of memory?
}