| Hey folks,
Say you have an audio call back:
void compute_audio(const AudioTimeStamp *time, UInt32 numFrames, AudioBufferList *inAudio,AudioBufferList *audio) { //do your DSP … }
If nothing unusual is going on, and you set the preferred IO Buffer duration to 5 msec, then numFrames would be 256.
Also, importantly, lets say you are NOT allowing microphone input.
Now lets say you start playing a track iTunes.
You will see buffer size increases to 1024 - meaning there will be more latency, which is bad for my app as it is used for real-time performance, not merely playback.
Now, let’s say that you DO allow microphone input.
Now repeat the experimentL Start playing a track iTunes. You will see buffer size is 256, which is you wanted in the first place.
The problem is I specifically I do NOT support microphone input in this app, and I don’t want to the user to think there is microphone input.
I did my testing on an iPad2 and iPadPro
Is there any way I can configure core audio so I get the 256 frames I want even if microphone input is not enabled?
This seems like a bug.
You can easily reproduce this with “The Engine Sample”:
Just print out numFrames
Thanks for any insight
- Nick
Here are my mods to The Engine Sample to illustrate the problem (my changes in RED):
// Create an instance of the audio controller, set it up and start it running self.audioController = [[AEAudioController alloc] initWithAudioDescription:AEAudioStreamBasicDescriptionNonInterleavedFloatStereo inputEnabled:NO]; _audioController.preferredBufferDuration = 0.005; _audioController.useMeasurementMode = YES; [_audioController start:NULL];
self.oscillator = [AEBlockChannel channelWithBlock:^(const AudioTimeStamp *time, UInt32 frames, AudioBufferList *audio) { static int passes = 0; if (++passes % 100 == 0) { printf("frame size=%d\n", (int)frames); } for ( int i=0; i<frames; i++ ) { // Quick sin-esque oscillator float x = oscillatorPosition; x *= x; x -= 1.0; x *= x; // x now in the range 0...1 x *= INT16_MAX; x -= INT16_MAX / 2; oscillatorPosition += oscillatorRate; if ( oscillatorPosition > 1.0 ) oscillatorPosition -= 2.0;
((SInt16*)audio->mBuffers[0].mData)[i] = x; ((SInt16*)audio->mBuffers[1].mData)[i] = x; } }];
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