typedef struct AudioChannelLayout {
    AudioChannelLayoutTag mChannelLayoutTag;
    UInt32 mChannelBitmap;
    UInt32 mNumberChannelDescriptions;
    AudioChannelDescription mChannelDescriptions[1];
} AudioChannelLayout;

typedef struct AudioChannelDescription {     AudioChannelLabel mChannelLabel;     UInt32 mChannelFlags;     Float32 mCoordinates[3]; } AudioChannelDescription;

#define fieldOffset(type, field) ((size_t) &((type *) 0)->field)

const int kNumChannelDescriptions = 2;

#include <Carbon/Carbon.h>
#include <QuickTime/QuickTime.h>
#include <AudioToolbox/AudioToolbox.h>
#include <assert>

// Set the channel layout of the movie audio for playback to the device. 
// We assume a movie with a single stereo stream (two channels) of audio. 
// The first channel of audio is set to play to LeftSurround, and the 
// second channel of audio is set to play to RightSurround.

void setAudioTrackChannelLayout(Track inTrack)
{
    UInt32 trackChannelLayoutSize;
    AudioChannelLayout* trackChannelLayout = NULL;

    // Allocate a layout of the required size.
    trackChannelLayoutSize = fieldOffset(AudioChannelLayout, 
        mChannelDescriptions[kNumChannelDescriptions]);
    // Allocate buffer to hold the layout, initialize all bits to 0.
    trackChannelLayout = (AudioChannelLayout*)calloc(1, trackChannelLayoutSize);
    assert(trackChannelLayout != nil);

    // A tag that indicates the type of layout used.
    // Our channel layout is described using audio channel descriptions -- see 
    // AudioChannelLayout.mChannelDescriptions below.
    trackChannelLayout->mChannelLayoutTag = kAudioChannelLayoutTag_UseChannelDescriptions ;

    // A bitmap that describes which channels are present.
    // We are not using channel bitmaps to describe our layout, we are using
    // the array of AudioChannelDescriptions to define the mapping.
    trackChannelLayout->mChannelBitmap = 0;

    // The number of channel descriptions in the mChannelDescriptionsarray. 
    // We are using 2 channel descriptions -- one description for Left Surround, 
    // the other for Right Surround.
    trackChannelLayout->mNumberChannelDescriptions = kNumChannelDescriptions ;

    // A label that describes the role of the channel. In common cases, such as 
    // “Left” or “Right,” role implies location. In such cases, mChannelFlags 
    // and mCoordinates can be set to 0.
    // In this example, we set the first channel to play to Left Surround, and
    // the second channel to play to Right Surround.
    trackChannelLayout->mChannelDescriptions[0].mChannelLabel = 
        kAudioChannelLabel_LeftSurround ;
    trackChannelLayout->mChannelDescriptions[1].mChannelLabel = 
        kAudioChannelLabel_RightSurround ;

    // Flags that indicate how to interpret the data in the mCoordinates field. 
    // If the audio channel does not require this information, set this field to 0.
    trackChannelLayout->mChannelDescriptions[0].mChannelFlags = kAudioChannelFlags_AllOff ; 
    trackChannelLayout->mChannelDescriptions[1].mChannelFlags = kAudioChannelFlags_AllOff ;

    // A set of three coordinates that specify the placement of the sound source for the 
    // channel in three dimensions, according to the mChannelFlags information. 
    // If the audio channel does not require this information, set this field to 0.
    trackChannelLayout->mChannelDescriptions[0].mCoordinates[0] = 0;
    trackChannelLayout->mChannelDescriptions[0].mCoordinates[1] = 0;
    trackChannelLayout->mChannelDescriptions[0].mCoordinates[2] = 0;

    trackChannelLayout->mChannelDescriptions[1].mCoordinates[0] = 0;
    trackChannelLayout->mChannelDescriptions[1].mCoordinates[1] = 0;
    trackChannelLayout->mChannelDescriptions[1].mCoordinates[2] = 0;

    // Set the channel layout properties on the audio track
    OSErr err = QTSetTrackProperty(inTrack, 
                                   kQTPropertyClass_Audio,
                                   kQTAudioPropertyID_ChannelLayout, 
                                   trackChannelLayoutSize, 
                                   trackChannelLayout );
    assert(err == noErr);

    free((void *)trackChannelLayout);
}