I've successfully got a playthru working between two AudioQueues, in
PCM.
I've two callbacks. One for an input queue and the other for an
output queue. The input callback receives data and copies it to an
internal array, which the output callback can then use to feed the
output queue.
For VBR - I've got it "kind of working" - I hear a little audio
(perhaps 1-2 seconds), before it stops.
It appears to be because the output callback (to the speakers) is
called more often than the input callback, and sometimes no data is
available because the input callback is called perhaps only twice a
second.
You should have a look through the CAPlayThrough example - it shows
you how to varispeed so you can do playthrough between different
devices (including different sample rates) - using queues the way you
are is not going to work without adjusting for the drift between the
two devices
(But as a matter of form - if you have nothing to play with a queue,
just don't scheduled anything. If the AQ Object gets to a place where
it has not data to play, it just plays silence. So, even with PCM you
don't have to enqueue silent buffers just to play silence).
Bill
In this case (no data to present to the output queue), I attempt to
queue an empty AudioQueueBuffer, but receive
kAudioQueueErr_BufferEmpty as a result.
- (void) handleOutputBuffer:(AudioQueueRef)inAQ bufferRef:
(AudioQueueBufferRef)inBuffer {
// Suck off the next element of our queue
OSStatus err = noErr;
if([packetBuffer count] > 0) {
Intermediate *packet = nil;
@synchronized(packetBuffer) {
packet = [packetBuffer objectAtIndex:0];
[packetBuffer removeObject:packet];
}
@try {
[packet copyBufferTo:inBuffer];
err = AudioQueueEnqueueBuffer(queue, inBuffer, numPackets,
packet.packetDescriptions);
} @finally {
[packet release];
}
} else {
// Give the buffer back - we can't do anything (we have no data)
err = AudioQueueEnqueueBuffer(queue, inBuffer, 0, nil);
}
if(err) {
[self log:@"Error while enqueing, %ld", err];
}
}
What is the recommended (or any way would be nice) way to send
silence and correctly enqueue the buffer if the output format isn't
PCM?
I've tried setting the first byte of the buffer to zero, with a size
of one (this works for the PCM case) - and while this doesn't return
an error, after I do this the output proc for the queue is no longer
called (I presume I've confused it's internal state somehow).
--
Regards,
Neil Clayton
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