pixelBuffer2RGB

-(void)pixelBuffer2RGB:(CVPixelBufferRef)pixelBuffer destWidth:(int)wanted_input_width destHeight:(int)wanted_input_height destChannel:(int)wanted_input_channels
{
    assert(pixelBuffer != NULL);
    
    OSType sourcePixelFormat = CVPixelBufferGetPixelFormatType(pixelBuffer);
    assert(sourcePixelFormat == kCVPixelFormatType_32ARGB ||
           sourcePixelFormat == kCVPixelFormatType_32BGRA);
    
    uint8_t *rgbBuffer = (uint8_t *)malloc(wanted_input_width*wanted_input_height*wanted_input_channels);
    
    const int sourceRowBytes = (int)CVPixelBufferGetBytesPerRow(pixelBuffer);
    const int image_width = (int)CVPixelBufferGetWidth(pixelBuffer);
    const int fullHeight = (int)CVPixelBufferGetHeight(pixelBuffer);
    
    CVPixelBufferLockFlags unlockFlags = kNilOptions;
    CVPixelBufferLockBaseAddress(pixelBuffer, unlockFlags);
    
    unsigned char* sourceBaseAddr = (unsigned char*)(CVPixelBufferGetBaseAddress(pixelBuffer));
    
    int image_height;
    unsigned char* sourceStartAddr;
    if (fullHeight <= image_width) {
        image_height = fullHeight;
        sourceStartAddr = sourceBaseAddr;
    } else {
        image_height = image_width;
        const int marginY = ((fullHeight - image_width) / 2);
        sourceStartAddr = (sourceBaseAddr + (marginY * sourceRowBytes));
    }
    const int image_channels = 4;
    assert(image_channels >= wanted_input_channels);
    uint8_t* in = sourceStartAddr;

    uint8_t *out = rgbBuffer;
    for (int y = 0; y < wanted_input_height; ++y) {
        uint8_t* out_row = out + (y * wanted_input_width * wanted_input_channels);
        for (int x = 0; x < wanted_input_width; ++x) {
            const int in_x = (y * image_width) / wanted_input_width;
            const int in_y = (x * image_height) / wanted_input_height;
            uint8_t* in_pixel = in + (in_y * image_width * image_channels) + (in_x * image_channels);
            uint8_t* out_pixel = out_row + (x * wanted_input_channels);
            for (int c = 0; c < wanted_input_channels; ++c) {
                out_pixel[c] = in_pixel[c];
            }
        }
    }
}