Audio Unit RemoteIO Setting interleaved float gives kAudioUnitErr_FormatNotSupported

Question

I am working with Audio Unit RemoteIO's to obtain a low latency audio output. My problem is AFAIK audio unit only accepts several audio formats depending on the hardware. My problem is I have a C++ DSP Sound engine and it works with float interleaved PCM. I do not want to implement a format converter since it can slow things down in the remote IO callback. I tried obtaining a low latency Audio Unit with the following format:

AudioStreamBasicDescription const audioDescription = {
            .mSampleRate        = defaultSampleRate,
            .mFormatID          = kAudioFormatLinearPCM,
            .mFormatFlags       = kAudioFormatFlagIsFloat,
            .mBytesPerPacket    = defaultSampleRate * STEREO_CHANNEL,
            .mFramesPerPacket   = 1,
            .mBytesPerFrame     = STEREO_CHANNEL * sizeof(Float32),
            .mChannelsPerFrame  = STEREO_CHANNEL,
            .mBitsPerChannel    = 8 * sizeof(Float32),
            .mReserved          = 0
        };
        
        status = AudioUnitSetProperty(audioUnit,
                                          kAudioUnitProperty_StreamFormat,
                                          kAudioUnitScope_Input,
                                          kOutputBus,
                                          &audioDescription,
                                          sizeof(audioDescription));

This fails with the error code kAudioUnitErr_FormatNotSupported -10868. If I try to obtain a float PCM NON-interleaved audio stream with the following:

AudioStreamBasicDescription const audioDescription = {
            .mSampleRate        = defaultSampleRate,
            .mFormatID          = kAudioFormatLinearPCM,
            .mFormatFlags       = kAudioFormatFlagIsFloat | kAudioFormatFlagIsPacked | kAudioFormatFlagIsNonInterleaved,
            .mBytesPerPacket    = sizeof(float),
            .mFramesPerPacket   = 1,
            .mBytesPerFrame     = sizeof(float),
            .mChannelsPerFrame  = STEREO_CHANNEL,
            .mBitsPerChannel    = 8 * sizeof(float),
            .mReserved          = 0
        };
        
        status = AudioUnitSetProperty(audioUnit,
                                          kAudioUnitProperty_StreamFormat,
                                          kAudioUnitScope_Input,
                                          kOutputBus,
                                          &audioDescription,
                                          sizeof(audioDescription));

Everything works fine. However I want to obtain an interleaved audio stream for my DSP engine to work without format conversion. Is this possible at all?

PS. waiting for hotpaw2 to guide me :)

score 1 · Accepted Answer · answered Jul 16 '21 at 21:44

1

Your error is probably due to this line:

.mBytesPerPacket    = defaultSampleRate * STEREO_CHANNEL,

answered Jul 16 '21 at 21:44

hotpaw2

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You might be right. How should I replace that line? Also I read from similar questions that remoteio audio units tends to favor noninterleaved float ASBD on IOS So I am afraid to use an interleaved ASBD. – cs guy Jul 16 '21 at 22:39
Where did you hear that? I've been using mostly interleaved stereo float format with RemoteIO for nearly a decade on dozens of different iOS devices and iOS releases. – hotpaw2 Jul 17 '21 at 00:06
I heard it here https://stackoverflow.com/questions/2882015/is-kaudioformatflagisfloat-supported-on-iphoneos , i tried my interleaved setup with `.mBytesPerPacket = sizeof(float),` but it is still not working, any ideas? – cs guy Jul 17 '21 at 07:50
never mind, it needed to be `.mBytesPerPacket = 2 * sizeof(float)` thanks for the help, you are the best! – cs guy Jul 17 '21 at 08:02

Audio Unit RemoteIO Setting interleaved float gives kAudioUnitErr_FormatNotSupported

1 Answers1