Mac OS Sound
An Example of Converting a Buffer of Silence to IMA 4:1

The following is an example of how to use the sound conversion architecture to convert a buffer of silence to IMA 4:1, changing the sampling rate in the process.


 
enum {

    kTargetBytes = 20 * 1024

};



void main(void)

{

    SoundConverter sc;

    SoundComponentData inputFormat, outputFormat;

    unsigned long inputFrames, inputBytes;

    unsigned long outputFrames, outputBytes;

    Ptr inputPtr, outputPtr;

    OSErr err;



    inputFormat.flags = 0;

    inputFormat.format = kOffsetBinary;

    inputFormat.numChannels = 1;

    inputFormat.sampleSize = 8;

    inputFormat.sampleRate = rate22050hz;

    inputFormat.sampleCount = 0;

    inputFormat.buffer = nil;

    inputFormat.reserved = 0;



    outputFormat.flags = 0;

    outputFormat.format = kIMA4SubType;

    outputFormat.numChannels = 1;

    outputFormat.sampleSize = 16;

    outputFormat.sampleRate = rate44100hz;

    outputFormat.sampleCount = 0;

    outputFormat.buffer = nil;

    outputFormat.reserved = 0;



    err = SoundConverterOpen(&inputFormat, &outputFormat, &sc);

    if (err != noErr)

        DebugStr("\pOpen failed");



    err = SoundConverterGetBufferSizes(sc, kTargetBytes,

                    &inputFrames, &inputBytes, &outputBytes);

    if (err != noErr)

        DebugStr("\pGetBufferSizes failed");



inputPtr = NewPtrClear(inputBytes);

outputPtr = NewPtrClear(outputBytes);



// fill input buffer with 8-bit silence

{

    int i;

    Ptr dp = inputPtr;



    for (i = 0; i < inputBytes; i++)

        *dp++ = 0x80;

}



    err = SoundConverterBeginConversion(sc);

    if (err != noErr)

        DebugStr("\pBegin Conversion failed");



    err = SoundConverterConvertBuffer(sc, inputPtr, inputFrames,

                    outputPtr, &outputFrames, &outputBytes);

    if (err != noErr)

        DebugStr("\pConversion failed");



    err = SoundConverterEndConversion(sc,

                outputPtr,&outputFrames, &outputBytes);

    if (err != noErr)

        DebugStr("\pEnd Conversion failed");



    err = SoundConverterClose(sc);

    if (err != noErr)

        DebugStr("\pClose failed");

}