AudioOutputUnitStart very slow... any ideas?
AudioOutputUnitStart very slow... any ideas?
- Subject: AudioOutputUnitStart very slow... any ideas?
- From: Jean-Yves Avenard <email@hidden>
- Date: Fri, 13 Apr 2012 23:33:56 +1000
Hi there
I have a code that plays mono audio event (short beeps at various
frequencies). I create an AudioOutputUnit, stop it, and whenever I
need to play the audio. I start it. When I've played it for the
required time, I stop it.
Sounds simple enough.
However, AudioOutputUnitStart will take usually 180ms to return on my
iPhone 4S (with iOS 5.1), this is way too much.
Here is the creation/initialisation of the AudioOutputUnit
void createAOU()
{
m_init = false;
// find the default playback output unit
AudioComponentDescription defaultOutputDescription;
defaultOutputDescription.componentType = kAudioUnitType_Output;
defaultOutputDescription.componentSubType = kAudioUnitSubType_RemoteIO;
defaultOutputDescription.componentManufacturer =
kAudioUnitManufacturer_Apple;
defaultOutputDescription.componentFlags = 0;
defaultOutputDescription.componentFlagsMask = 0;
// Get the default playback output unit
AudioComponent defaultOutput = AudioComponentFindNext(NULL,
&defaultOutputDescription);
if (defaultOutput == NULL)
return;
OSErr err = AudioComponentInstanceNew(defaultOutput, &m_toneUnit);
if (err != noErr)
return;
// single channel, floating point, linear PCM
AudioStreamBasicDescription streamFormat;
streamFormat.mSampleRate = m_framerate;
streamFormat.mFormatID = kAudioFormatLinearPCM;
streamFormat.mFormatFlags =
kLinearPCMFormatFlagIsFloat |
kAudioFormatFlagsNativeEndian | kLinearPCMFormatFlagIsPacked;
streamFormat.mBytesPerPacket = sizeof(float);
streamFormat.mFramesPerPacket = 1;
streamFormat.mBytesPerFrame = sizeof(float);
streamFormat.mChannelsPerFrame = 1;
streamFormat.mBitsPerChannel = sizeof(float) * 8;
err = AudioUnitSetProperty (m_toneUnit,
kAudioUnitProperty_StreamFormat,
kAudioUnitScope_Input,
0,
&streamFormat,
sizeof(AudioStreamBasicDescription));
if (err != noErr)
return;
// Attach callback to default output
AURenderCallbackStruct input;
input.inputProc = RenderTone;
input.inputProcRefCon = this;
err = AudioUnitSetProperty(m_toneUnit,
kAudioUnitProperty_SetRenderCallback,
kAudioUnitScope_Input,
0,
&input,
sizeof(input));
if (err != noErr)
return;
float aBufferLength = 0.001; // In seconds
AudioSessionSetProperty(kAudioSessionProperty_PreferredHardwareIOBufferDuration,
sizeof(aBufferLength), &aBufferLength);
err = AudioUnitInitialize(m_toneUnit);
if (err != noErr)
return;
reset();
m_init = true;
}
To start it, I would simply call:
OSErr err = AudioOutputUnitStart(m_toneUnit);
When done:
OSErr err = AudioOutputUnitStop(m_toneUnit);
I've tried various things: making the
kAudioSessionProperty_PreferredHardwareIOBufferDuration property to a
very small value (like 5ms) Reduce the framerate (tried 48kHz,
44.1kHz, 8kHz)
No matter what I do... First time the audiounit is started,
AudioOutputUnitStart only returns after 160-180ms. If I stop and start
it right away, then it only takes about 5m which is much more
acceptable.
Latency in my application is rather important, and 180ms is definitely
not acceptable.
Any suggestions? I've seen a few people asking similar questions, but
they usually never got an answer.
I'm hoping this time things will be different :)
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