Apple

Hi, I was wondering if someone could help. I am trying to decipher a buffer so I can verify that I understand how it works. It is a render callback that takes samples from an audio file that is referenced by the object musicPlayerState. The original code walks through the samples one at a time and copies them over to the buffer using memcpy in a for loop.

musicPlaybackState->samplePtr stores the position of the audio file.

currentframe is declared globally and initialised to zero.

What I am trying to do is remove the for loop so the callback simply dumps the entire 512 frames into the ioData buffer and then exits and thus avoiding the need to use the for loop. The code is a little convoluted. I have posted the original unmolested code underneath for clarity. It is taken from Chris Adamson's DalekSingalong code.

I've been at it for days and I just can't seem to figure out whats going wrong or if it is even possible.

OSStatus MusicPlayerCallback (

void * inRefCon,

AudioUnitRenderActionFlags * ioActionFlags,

const AudioTimeStamp * inTimeStamp,

UInt32 inBusNumber,

UInt32 inNumberFrames,

AudioBufferList * ioData) {

MusicPlaybackState *musicPlaybackState = (MusicPlaybackState*) inRefCon;

AudioSampleType *sample = musicPlaybackState->samplePtr;

size_t count= 1024;

AudioBuffer buf = ioData->mBuffers[0];

memcpy(buf.mData + ((currentframe)*(2)),

sample,

count);

currentframe+=512;

sample +=512;

musicPlaybackState->samplePtr = sample;

return noErr;

}

////////////Original code that works fine/////////////