Question

every time callback function of the audio unit is being called, i get another number of samples which is strange because NSLog(@"%ld",inNumberFrames); gives me always 512.

when i do this :

NSLog(@"%li",strlen((const char *)(&bufferList)->mBuffers[0].mData));

i get numbers such as: 50 20 19 160 200 1 …

which is strange.
each call back, i have to get the full buffer 512 samples no ?

i know i dont get all needed samples because if i input a sin 2khz , i get zero crossing of about 600, and if i put nothing, i g et the same.

to retrieve data i do :

static OSStatus recordingCallback(void *inRefCon, 
                                  AudioUnitRenderActionFlags *ioActionFlags, 
                                  const AudioTimeStamp *inTimeStamp, 
                                  UInt32 inBusNumber, 
                                  UInt32 inNumberFrames, 
                                  AudioBufferList *ioData)
{


    AudioBuffer buffer;

    buffer.mNumberChannels = 1;
    buffer.mDataByteSize = inNumberFrames * 2;
    //NSLog(@"%ld",inNumberFrames);
    buffer.mData = malloc( inNumberFrames * 2 );

    // Put buffer in a AudioBufferList
    AudioBufferList bufferList;
    bufferList.mNumberBuffers = 1;
    bufferList.mBuffers[0] = buffer;



    OSStatus status;
    status = AudioUnitRender(audioUnit, 
                             ioActionFlags, 
                             inTimeStamp, 
                             inBusNumber, 
                             inNumberFrames, 
                             &bufferList);  
    //checkStatus(status);
    NSLog(@"%li",strlen((const char *)(&bufferList)->mBuffers[0].mData));
    int16_t *q = (int16_t *)(&bufferList)->mBuffers[0].mData;
    for(int i=0; i < strlen((const char *)(&bufferList)->mBuffers[0].mData); i++)
    {
         ....

any help with this will save me days !
thanks .

Answer 1

A strlen() of the audio sample buffer is not related to the number of samples. Instead, look at the number of frames given as the callback function’s parameter.