AVAudioSession inputNumberOfChannels
@property(readonly) NSInteger inputNumberOfChannels
AVAudioSession inputNumberOfChannels example.
It turns out that when using AVAudioSessionCategoryRecord (or equivalently, kAudioSessionCategory_RecordAudio from the C APIs), you must also disable output on the audio unit:
...
// Disable output
err = AudioUnitSetProperty(unit, kAudioOutputUnitProperty_EnableIO, kAudioUnitScope_Output, kOutputElement, &disableFlag, sizeof(disableFlag));
if (err != noErr) NSLog(@"Error disabling output for audio unit: %ld", err);
...
// Disable output
err = AudioUnitSetProperty(unit, kAudioOutputUnitProperty_EnableIO, kAudioUnitScope_Output, kOutputElement, &disableFlag, sizeof(disableFlag));
if (err != noErr) NSLog(@"Error disabling output for audio unit: %ld", err);
Example of [AVAudioSession inputNumberOfChannels].
- (void)audioAU
{
enum : AudioUnitElement {
kOutputElement = 0,
kInputElement = 1
};
const UInt32 disableFlag = 0;
const UInt32 enableFlag = 1;
OSStatus err = noErr;
NSError *error = nil;
// Configure & activate audio session
AVAudioSession *session = [AVAudioSession sharedInstance];
if (![session setCategory:AVAudioSessionCategoryRecord error:&error]) NSLog(@"Error configuring session category: %@", error);
if (![session setMode:AVAudioSessionModeMeasurement error:&error]) NSLog(@"Error configuring session mode: %@", error);
if (![session setActive:YES error:&error]) NSLog(@"Error activating audio session: %@", error);
NSLog(@"Session activated. sample rate %f", session.sampleRate);
NSLog(@"Number of channels %d", session.inputNumberOfChannels);
// Set up Remote I/O audio unit for audio capture
AudioComponent component = AudioComponentFindNext(NULL, &(const AudioComponentDescription){
.componentType = kAudioUnitType_Output,
.componentSubType = kAudioUnitSubType_RemoteIO,
.componentManufacturer = kAudioUnitManufacturer_Apple,
.componentFlags = 0,
.componentFlagsMask = 0
});
AudioComponentInstance unit;
// Create audio component
err = AudioComponentInstanceNew(component, &unit);
if (err != noErr) NSLog(@"Error instantiating audio unit: %ld", err);
// Enable input
err = AudioUnitSetProperty(unit, kAudioOutputUnitProperty_EnableIO, kAudioUnitScope_Input, kInputElement, &enableFlag, sizeof(enableFlag));
if (err != noErr) NSLog(@"Error enabling input for audio unit: %ld", err);
AudioStreamBasicDescription streamDesc = {
.mSampleRate = session.sampleRate,
.mFormatID = kAudioFormatLinearPCM,
.mFormatFlags = kAudioFormatFlagsAudioUnitCanonical /*matches AudioUnitSampleType*/ | kAudioFormatFlagIsNonInterleaved,
.mBytesPerPacket = sizeof(AudioUnitSampleType),
.mFramesPerPacket = 1,
.mBytesPerFrame = sizeof(AudioUnitSampleType) * session.inputNumberOfChannels,
.mChannelsPerFrame = session.inputNumberOfChannels,
.mBitsPerChannel = 8 * sizeof(AudioUnitSampleType),
.mReserved = 0,
};
err = AudioUnitSetProperty(unit, kAudioUnitProperty_StreamFormat, kAudioUnitScope_Input, kOutputElement, &streamDesc, sizeof(streamDesc));
if (err != noErr) NSLog(@"Error configuring input stream format for audio unit: %ld", err);
AURenderCallbackStruct callbacks = {
.inputProc = renderCallback,
.inputProcRefCon = unit
};
err = AudioUnitSetProperty(unit, kAudioOutputUnitProperty_SetInputCallback, kAudioUnitScope_Input, kOutputElement, &callbacks, sizeof(callbacks));
if (err != noErr) NSLog(@"Error configuring input callbacks for audio unit: %ld", err);
err = AudioUnitInitialize(unit);
if (err != noErr) NSLog(@"Error initializing audio unit: %ld", err);
err = AudioOutputUnitStart(unit);
if (err != noErr) NSLog(@"Error starting audio unit: %ld", err);
// err = AudioComponentInstanceDispose(unit);
// if (err != noErr) NSLog(@"Error disposing audio unit: %ld", err);
}
{
enum : AudioUnitElement {
kOutputElement = 0,
kInputElement = 1
};
const UInt32 disableFlag = 0;
const UInt32 enableFlag = 1;
OSStatus err = noErr;
NSError *error = nil;
// Configure & activate audio session
AVAudioSession *session = [AVAudioSession sharedInstance];
if (![session setCategory:AVAudioSessionCategoryRecord error:&error]) NSLog(@"Error configuring session category: %@", error);
if (![session setMode:AVAudioSessionModeMeasurement error:&error]) NSLog(@"Error configuring session mode: %@", error);
if (![session setActive:YES error:&error]) NSLog(@"Error activating audio session: %@", error);
NSLog(@"Session activated. sample rate %f", session.sampleRate);
NSLog(@"Number of channels %d", session.inputNumberOfChannels);
// Set up Remote I/O audio unit for audio capture
AudioComponent component = AudioComponentFindNext(NULL, &(const AudioComponentDescription){
.componentType = kAudioUnitType_Output,
.componentSubType = kAudioUnitSubType_RemoteIO,
.componentManufacturer = kAudioUnitManufacturer_Apple,
.componentFlags = 0,
.componentFlagsMask = 0
});
AudioComponentInstance unit;
// Create audio component
err = AudioComponentInstanceNew(component, &unit);
if (err != noErr) NSLog(@"Error instantiating audio unit: %ld", err);
// Enable input
err = AudioUnitSetProperty(unit, kAudioOutputUnitProperty_EnableIO, kAudioUnitScope_Input, kInputElement, &enableFlag, sizeof(enableFlag));
if (err != noErr) NSLog(@"Error enabling input for audio unit: %ld", err);
AudioStreamBasicDescription streamDesc = {
.mSampleRate = session.sampleRate,
.mFormatID = kAudioFormatLinearPCM,
.mFormatFlags = kAudioFormatFlagsAudioUnitCanonical /*matches AudioUnitSampleType*/ | kAudioFormatFlagIsNonInterleaved,
.mBytesPerPacket = sizeof(AudioUnitSampleType),
.mFramesPerPacket = 1,
.mBytesPerFrame = sizeof(AudioUnitSampleType) * session.inputNumberOfChannels,
.mChannelsPerFrame = session.inputNumberOfChannels,
.mBitsPerChannel = 8 * sizeof(AudioUnitSampleType),
.mReserved = 0,
};
err = AudioUnitSetProperty(unit, kAudioUnitProperty_StreamFormat, kAudioUnitScope_Input, kOutputElement, &streamDesc, sizeof(streamDesc));
if (err != noErr) NSLog(@"Error configuring input stream format for audio unit: %ld", err);
AURenderCallbackStruct callbacks = {
.inputProc = renderCallback,
.inputProcRefCon = unit
};
err = AudioUnitSetProperty(unit, kAudioOutputUnitProperty_SetInputCallback, kAudioUnitScope_Input, kOutputElement, &callbacks, sizeof(callbacks));
if (err != noErr) NSLog(@"Error configuring input callbacks for audio unit: %ld", err);
err = AudioUnitInitialize(unit);
if (err != noErr) NSLog(@"Error initializing audio unit: %ld", err);
err = AudioOutputUnitStart(unit);
if (err != noErr) NSLog(@"Error starting audio unit: %ld", err);
// err = AudioComponentInstanceDispose(unit);
// if (err != noErr) NSLog(@"Error disposing audio unit: %ld", err);
}