RemoteIO callback buffer length wonky on iphone
RemoteIO callback buffer length wonky on iphone
- Subject: RemoteIO callback buffer length wonky on iphone
- From: Doug McCoy <email@hidden>
- Date: Mon, 12 Apr 2010 17:28:47 -0700
I am using the RemoteIO AudioUnit on iphone for live IO.
I have been setting this up with various sample rates and buffer sizes to tune my algorithm. For 44.1K and 22K, I get expected results for the number of frames in the callback IO buffer.
For 16K, I get strangeness.
My setup goes like this:
set kAudioSessionProperty_PreferredHardwareSampleRate = 16K
set kAudioSessionProperty_PreferredHardwareIOBufferDuration = 0.032 seconds (512 frames)
AudioSessionSetActive(true)
get kAudioSessionProperty_CurrentHardwareSampleRate = 16K
get kAudioSessionProperty_CurrentHardwareIOBufferDuration = 0.02322
seconds (371.52 frames, i round up to 372)
I then setup the remoteIO with:
AudioStreamBasicDescription audioFormat;
memset(&audioFormat, 0, sizeof(audioFormat)); audioFormat.mSampleRate = 16000; // FS
audioFormat.mFormatID = kAudioFormatLinearPCM; audioFormat.mFormatFlags = kLinearPCMFormatFlagIsSignedInteger | kLinearPCMFormatFlagIsPacked;
audioFormat.mChannelsPerFrame = 1; audioFormat.mFramesPerPacket = 1;
audioFormat.mBitsPerChannel = sizeof(short) * 8; // 16-bit audioFormat.mBytesPerFrame = audioFormat.mBitsPerChannel / 8 * audioFormat.mChannelsPerFrame;
audioFormat.mBytesPerPacket = audioFormat.mBytesPerFrame * audioFormat.mFramesPerPacket;
I enable input and the input output formats are identical.
My callback is declared as such:
static OSStatus PerformThru(
void *inRefCon, AudioUnitRenderActionFlags *ioActionFlags,
const AudioTimeStamp *inTimeStamp, UInt32 inBusNumber,
UInt32 inNumberFrames, AudioBufferList *ioData)
For the first callback,
inNumberFrames == 372
and
ioData->mBuffers[0].mDataByteSize == 372 * 2 (16bit samples, mono)
This is to be expected.
But subsequent callbacks have
inNumberFrames == 1 or 2
and
ioData->mBuffers[0].mDataByteSize == 2 or 4 respectively
This discrepancy is causing havoc in my processing.
I notice the first case above will occur if the audio session changes and the remoteIO AU is re-created and started anew, but it quickly reverts to the latter bad case.
For 44.1k and 22K the callback buffers are all at the expected size. For 16K the buffer length is not consistent.
Is there a know issue with this?
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