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Doing playthru, using AudioQueue

Subject: Doing playthru, using AudioQueue
From: Neil Clayton <email@hidden>
Date: Tue, 22 Jan 2008 22:21:17 +1300
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Hi,

I'm attempting to construct a playthru using AudioQueue as opposed to CoreAudio, simply because ... it's simpler. I've got recording to a file going (compressed, CAF format) - which plays back in QT just fine. Qt then shows me it's AAC, or whatever format I've chosen.

I *believe* I've setup the AudioQueue to play back OK, but I am getting a -50 back from my handler:

- (void) handleInputBuffer:(AudioQueueRef)inAQ
				 bufferRef:(AudioQueueBufferRef)inBuffer
				 timeStamp:(const AudioTimeStamp*)timeStamp
				numPackets:(UInt32)numPackets
				packetDesc:(const AudioStreamPacketDescription*)packetDesc {

	OSStatus err = noErr;
	if(numPackets > 0) {
		if(fileID) {
			err = AudioFileWritePackets(fileID,
										false,
										inBuffer->mAudioDataByteSize,
										packetDesc,
										recordBuffer.currentPacket,
										&numPackets,
										inBuffer->mAudioData);
		}
		if(err == noErr) {
			recordBuffer.currentPacket += numPackets;

// If we have playthru - shove it there as well if(playbackBuffer) { err = AudioQueueEnqueueBuffer(playbackBuffer.queue, inBuffer, numPackets, packetDesc); if(err != noErr) { [self log:@"Couldn't playthru, %ld", err]; } } } } if(playthru) { [recordBuffer enqueue:inBuffer]; } }

In this case what I'm attempting to do is receive the audio packets / data from one AudioQueue and record them. I'd like to then pass the same packets to my Playback Buffer, which is setup to output to some other device. The playback buffer appears to be setup correctly to receive AAC (or whatever format I choose) data. This is using code similar to that in aqplay.cpp.

Thus, my logging shows: 2008-01-22 22:12:15.113 CoreAudioRecorder[15791:813] [Main] [AQBuffer] - Using device Built-in Line Output, with format: AAC, 44100 Khz, 2 channels 2008-01-22 22:12:15.117 CoreAudioRecorder[15791:813] [Main] [AQBuffer] - New stream description after making queue: AAC, 44100 Khz, 2 channels 2008-01-22 22:12:15.120 CoreAudioRecorder[15791:813] [Main] [AQBuffer] - Setup cookie on PlaybackBuff:Built-in Line Output (AAC, 44100 Khz, 2 channels) OK 2008-01-22 22:12:15.121 CoreAudioRecorder[15791:813] [Main] [AQBuffer] - PlaybackBuff:Built-in Line Output (AAC, 44100 Khz, 2 channels) ready to rock 2008-01-22 22:12:15.134 CoreAudioRecorder[15791:813] [Main] [Controller] - Playthru setup for Soundflower (16ch) -> Built-in Line Output

It seems like it's quite probably invalid for me to pass one buffer from an input queue to an output queue (I'm guessing here). If this is indeed the case, what's the recommended way to copy the contents from one of these buffers to the playback buffers (given that the formats are the same)? Just memcpy or would that be a "bad idea" (tm)?

--
Regards,
Neil Clayton,  http://shinywhitebox.com

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