Delay when using AudioQueueStart()

Question

I am using the Audio Queue services to record audio on the iPhone. I am having a latency issue though when starting recording. Here is the code (approx):

OSStatus status = AudioQueueNewInput(
     &recordState.dataFormat, // 1
     AudioInputCallback, // 2
     &recordState,  // 3
     CFRunLoopGetCurrent(),  // 4
     kCFRunLoopCommonModes, // 5
     0,  // 6
     &recordState.queue);  // 7

// create buffers
for(int i = 0; i < NUM_BUFFERS; i++)
{
    if (status == 0)
        status = AudioQueueAllocateBuffer(recordState.queue, BUFFER_SIZE, &recordState.buffers[i]);
}

DebugLog(@"Starting recording\n");
OSStatus status = 0;
for(int i = 0; i < NUM_BUFFERS; i++)
{
    if (status == 0)
        status = AudioQueueEnqueueBuffer(recordState.queue, recordState.buffers[i], 0, NULL);
}
DebugLog(@"Queued buffers\n");
if (status == 0)
{
    // start audio queue
    status = AudioQueueStart(recordState.queue, NULL);
}
DebugLog(@"Started recording, status = %d\n", status);

The log output looks like this:

2009-06-30 19:18:59.631 app[24887:20b] Starting recording
2009-06-30 19:18:59.828 app[24887:20b] Queued buffers
2009-06-30 19:19:00.849 app[24887:20b] Started recording, status = 0

Note the 1-second delay between the "Queued Buffers" message and 2nd "Starting recording" message. Any ideas how I can get rid of it, apart from starting recording as soon as I start my app?

BTW, the 1-second is pretty consistent in the Simulator and Device, and doesn't seem to be affected by number or size of buffers. Using good old mono 16-bit PCM.

Answer 1

Mike Tyson covers this in his blog.

However, if you're looking to quickly start recording you would do better to use a remote audio unit, or AVAudioEngine.