AudioConverter bug?

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    // .....

    AudioStreamBasicDescription inputASBD = [AppDelegate interleaved16BitStereoAudioDescription];
    AudioStreamBasicDescription outputASBD = [AppDelegate interleaved16BitStereoAudioDescription];

    // Or, to see this work properly:
    //    AudioStreamBasicDescription inputASBD = [AppDelegate nonInterleaved16BitStereoAudioDescription];
    //    AudioStreamBasicDescription outputASBD = [AppDelegate nonInterleaved16BitStereoAudioDescription];

    AudioConverterRef converter = NULL;
    checkResult(AudioConverterNew(&inputASBD, &outputASBD, &converter), "AudioConverterNew");

    UInt32 channelMap[2] = {0, 0};
    checkResult(AudioConverterSetProperty(converter, kAudioConverterChannelMap, sizeof(channelMap), channelMap), "AudioConverterSetProperty(kAudioConverterChannelMap");

    UInt32 frameCount = 64;

    AudioBufferList *inputBufferList  = allocateAndInitAudioBufferList(inputASBD, frameCount);
    AudioBufferList *outputBufferList = allocateAndInitAudioBufferList(outputASBD, frameCount);

    for ( int i=0; i<frameCount; i++ ) {
        if ( inputASBD.mFormatFlags & kAudioFormatFlagIsNonInterleaved ) {
            ((SInt16*)inputBufferList->mBuffers[0].mData)[i] = 2*i;
            ((SInt16*)inputBufferList->mBuffers[1].mData)[i] = 2*i + 1;
        } else {
            ((SInt16*)inputBufferList->mBuffers[0].mData)[2*i] = 2*i;
            ((SInt16*)inputBufferList->mBuffers[0].mData)[2*i + 1] = 2*i + 1;
        }
    }

    OSStatus result = AudioConverterFillComplexBuffer(converter,
                                                      fillComplexBufferInputProc,
                                                      &(struct fillComplexBufferInputProc_t) { .bufferList = inputBufferList, .frames = frameCount },
                                                      &frameCount,
                                                      outputBufferList,
                                                      NULL);
    checkResult(result, "AudioConverterFillComplexBuffer");

    printf("Expected\t\tActual\n");
    for ( int i=0; i<frameCount; i++ ) {
        printf("%3d\t%3d\t\t%3d\t%3d\n",
               2*i + (int)channelMap[0],
               2*i + (int)channelMap[1],
               outputASBD.mFormatFlags & kAudioFormatFlagIsNonInterleaved ? ((SInt16*)outputBufferList->mBuffers[0].mData)[i] : ((SInt16*)outputBufferList->mBuffers[0].mData)[2*i],
               outputASBD.mFormatFlags & kAudioFormatFlagIsNonInterleaved ? ((SInt16*)outputBufferList->mBuffers[1].mData)[i] : ((SInt16*)outputBufferList->mBuffers[0].mData)[2*i+1]);
    }

    return YES;
}

#pragma mark - Helpers

+ (AudioStreamBasicDescription)interleaved16BitStereoAudioDescription {
    AudioStreamBasicDescription audioDescription;
    memset(&audioDescription, 0, sizeof(audioDescription));
    audioDescription.mFormatID          = kAudioFormatLinearPCM;
    audioDescription.mFormatFlags       = kAudioFormatFlagIsSignedInteger | kAudioFormatFlagIsPacked | kAudioFormatFlagsNativeEndian;
    audioDescription.mChannelsPerFrame  = 2;
    audioDescription.mBytesPerPacket    = sizeof(SInt16)*audioDescription.mChannelsPerFrame;
    audioDescription.mFramesPerPacket   = 1;
    audioDescription.mBytesPerFrame     = sizeof(SInt16)*audioDescription.mChannelsPerFrame;
    audioDescription.mBitsPerChannel    = 8 * sizeof(SInt16);
    audioDescription.mSampleRate        = 44100.0;
    return audioDescription;
}

+ (AudioStreamBasicDescription)nonInterleaved16BitStereoAudioDescription {
    AudioStreamBasicDescription audioDescription;
    memset(&audioDescription, 0, sizeof(audioDescription));
    audioDescription.mFormatID          = kAudioFormatLinearPCM;
    audioDescription.mFormatFlags       = kAudioFormatFlagIsSignedInteger | kAudioFormatFlagIsPacked | kAudioFormatFlagsNativeEndian | kAudioFormatFlagIsNonInterleaved;
    audioDescription.mChannelsPerFrame  = 2;
    audioDescription.mBytesPerPacket    = sizeof(SInt16);
    audioDescription.mFramesPerPacket   = 1;
    audioDescription.mBytesPerFrame     = sizeof(SInt16);
    audioDescription.mBitsPerChannel    = 8 * sizeof(SInt16);
    audioDescription.mSampleRate        = 44100.0;
    return audioDescription;
}

struct fillComplexBufferInputProc_t { AudioBufferList *bufferList; UInt32 frames;  };
static OSStatus fillComplexBufferInputProc(AudioConverterRef             inAudioConverter,
                                           UInt32                        *ioNumberDataPackets,
                                           AudioBufferList               *ioData,
                                           AudioStreamPacketDescription  **outDataPacketDescription,
                                           void                          *inUserData) {
    struct fillComplexBufferInputProc_t *arg = inUserData;
    for ( int i=0; i<ioData->mNumberBuffers; i++ ) {
        ioData->mBuffers[i].mData = arg->bufferList->mBuffers[i].mData;
        ioData->mBuffers[i].mDataByteSize = arg->bufferList->mBuffers[i].mDataByteSize;
    }
    *ioNumberDataPackets = arg->frames;
    return noErr;
}

AudioBufferList *allocateAndInitAudioBufferList(AudioStreamBasicDescription audioFormat, int frameCount) {
    int numberOfBuffers = audioFormat.mFormatFlags & kAudioFormatFlagIsNonInterleaved ? audioFormat.mChannelsPerFrame : 1;
    int channelsPerBuffer = audioFormat.mFormatFlags & kAudioFormatFlagIsNonInterleaved ? 1 : audioFormat.mChannelsPerFrame;
    int bytesPerBuffer = audioFormat.mBytesPerFrame * frameCount;

    AudioBufferList *audio = malloc(sizeof(AudioBufferList) + (numberOfBuffers-1)*sizeof(AudioBuffer));
    if ( !audio ) {
        return NULL;
    }
    audio->mNumberBuffers = numberOfBuffers;
    for ( int i=0; i<numberOfBuffers; i++ ) {
        if ( bytesPerBuffer > 0 ) {
            audio->mBuffers[i].mData = malloc(bytesPerBuffer);
            if ( !audio->mBuffers[i].mData ) {
                for ( int j=0; j<i; j++ ) free(audio->mBuffers[j].mData);
                free(audio);
                return NULL;
            }
        } else {
            audio->mBuffers[i].mData = NULL;
        }
        audio->mBuffers[i].mDataByteSize = bytesPerBuffer;
        audio->mBuffers[i].mNumberChannels = channelsPerBuffer;
    }
    return audio;
}