AudioQueue Output fails playing audio almost immediately?

Question

Created Sep ’25

Replies 2

Boosts 0

Participants 2

On macOS Sequoia, I'm having the hardest time getting this basic audio output to work correctly. I'm compiling in XCode using C99, and when I run this, I get audio for a split second, and then nothing, indefinitely.

Any ideas what could be going wrong?

Here's a minimum code example to demonstrate:

#include <AudioToolbox/AudioToolbox.h>
#include <stdint.h>

#define RENDER_BUFFER_COUNT 2
#define RENDER_FRAMES_PER_BUFFER 128
// mono linear PCM audio data at 48kHz
#define RENDER_SAMPLE_RATE 48000
#define RENDER_CHANNEL_COUNT 1
#define RENDER_BUFFER_BYTE_COUNT (RENDER_FRAMES_PER_BUFFER * RENDER_CHANNEL_COUNT * sizeof(f32))

void RenderAudioSaw(float* outBuffer, uint32_t frameCount, uint32_t channelCount)
{
    static bool isInverted = false;
    float scalar = isInverted ? -1.f : 1.f;
    for (uint32_t frame = 0; frame < frameCount; ++frame)
    {
        for (uint32_t channel = 0; channel < channelCount; ++channel)
        {
            // series of ramps, alternating up and down.
            outBuffer[frame * channelCount + channel] = 0.1f * scalar * ((float)frame / frameCount);
        }
    }
    
    isInverted = !isInverted;
}

AudioStreamBasicDescription coreAudioDesc = { 0 };
AudioQueueRef coreAudioQueue = NULL;
AudioQueueBufferRef coreAudioBuffers[RENDER_BUFFER_COUNT] = { NULL };

void coreAudioCallback(void* unused, AudioQueueRef queue, AudioQueueBufferRef buffer)
{
    // 0's here indicate no fancy packet magic
    AudioQueueEnqueueBuffer(queue, buffer, 0, 0);
}

int main(void)
{
    const UInt32 BytesPerSample = sizeof(float);
    
    coreAudioDesc.mSampleRate = RENDER_SAMPLE_RATE;
    coreAudioDesc.mFormatID = kAudioFormatLinearPCM;
    coreAudioDesc.mFormatFlags = kLinearPCMFormatFlagIsFloat | kLinearPCMFormatFlagIsPacked;
    coreAudioDesc.mBytesPerPacket = RENDER_CHANNEL_COUNT * BytesPerSample;
    coreAudioDesc.mFramesPerPacket = 1;
    coreAudioDesc.mBytesPerFrame = RENDER_CHANNEL_COUNT * BytesPerSample;
    coreAudioDesc.mChannelsPerFrame = RENDER_CHANNEL_COUNT;
    coreAudioDesc.mBitsPerChannel = BytesPerSample * 8;
    
    coreAudioQueue = NULL;
    
    OSStatus result;

    // most of the 0 and NULL params here are for compressed sound formats etc.
    result = AudioQueueNewOutput(&coreAudioDesc, &coreAudioCallback, NULL, 0, 0, 0, &coreAudioQueue);
    
    if (result != noErr)
    {
        assert(false == "AudioQueueNewOutput failed!");
        abort();
    }
    
    for (int i = 0; i < RENDER_BUFFER_COUNT; ++i)
    {
        uint32_t bufferSize = coreAudioDesc.mBytesPerFrame * RENDER_FRAMES_PER_BUFFER;
        result = AudioQueueAllocateBuffer(coreAudioQueue, bufferSize, &(coreAudioBuffers[i]));
        if (result != noErr)
        {
            assert(false == "AudioQueueAllocateBuffer failed!");
            abort();
        }
    }
    
    for (int i = 0; i < RENDER_BUFFER_COUNT; ++i)
    {
        RenderAudioSaw(coreAudioBuffers[i]->mAudioData, RENDER_FRAMES_PER_BUFFER, RENDER_CHANNEL_COUNT);
        coreAudioBuffers[i]->mAudioDataByteSize = coreAudioBuffers[i]->mAudioDataBytesCapacity;
        
        AudioQueueEnqueueBuffer(coreAudioQueue, coreAudioBuffers[i], 0, 0);
    }

    AudioQueueStart(coreAudioQueue, NULL);

    sleep(10); // some time to hear the audio
    
    AudioQueueStop(coreAudioQueue, true);
    AudioQueueDispose(coreAudioQueue, true);
    
    return 0;
}

Boost

Answer 1

ssmith_c OP

Sep ’25

instead of sleeping for 10 (what? seconds?) try running a runloop for a while:

CFRunLoopRunInMode(kCFRunLoopDefaultMode, 10, false);

It gets a bit tedious during development if you always have to wait until your program is done (even if it isn't working), so you can set up a runloop dispatch source before hand. Hitting any key then return should exit your program. This example is Objective-C++, I'm sure you can adapt it to C, or just make your main file a .mm file.

dispatch_source_t source = dispatch_source_create(
            DISPATCH_SOURCE_TYPE_READ, // dispatch_source_type_t  _Nonnull type,
            STDIN_FILENO,              // uintptr_t handle,
            0,                         // uintptr_t mask, (unused)
            DISPATCH_TARGET_QUEUE_DEFAULT);
    dispatch_source_set_event_handler(source, ^{
        std::cout << "exiting\n";
        exit(0);
    });
    
    dispatch_activate(source);
    do {
        CFRunLoopRunInMode(kCFRunLoopDefaultMode, 10, false);
    } while (true);

0

Answer 2

KableChannel OP

Sep ’25

Thanks for the suggestion.

I should have clarified that the standard sleep() function takes seconds, it's just to minimize code amount.

Sadly, this does not resolve the issue.

0