How to grab YUV formatted video from the camera, display it and process it

Question

I am writing an iphone (IOS 4) program that capture live video from the camera and process it in real time.

I prefer to capture in kCVPixelFormatType_420YpCbCr8BiPlanarF

Answer 1

Answering my own question. this solved the problem I had (which was to grab yuv output, display it and process it), although its not exactly the answer to the question:

To grab YUV output from the camera:

AVCaptureVideoDataOutput *videoOut = [[AVCaptureVideoDataOutput alloc] init];
[videoOut setAlwaysDiscardsLateVideoFrames:YES];
[videoOut setVideoSettings:[NSDictionary dictionaryWithObject:[NSNumber numberWithInt:kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange] forKey:(id)kCVPixelBufferPixelFormatTypeKey]];

To display it as is, use AVCaptureVideoPreviewLayer, it does not require any much code. (You can see the FindMyiCon sample in the WWDC samples pack for example).

To process the YUV y channel (bi-planer in this case so it's all in a single chunk, you can also use memcpy instead of looping) :

- (void)processPixelBuffer: (CVImageBufferRef)pixelBuffer {

    CVPixelBufferLockBaseAddress( pixelBuffer, 0 );

    int bufferHeight = CVPixelBufferGetHeight(pixelBuffer);
    int bufferWidth = CVPixelBufferGetWidth(pixelBuffer);

    // allocate space for ychannel, reallocating as needed.
    if (bufferWidth != y_channel.width || bufferHeight != y_channel.height)
    {
        if (y_channel.data) free(y_channel.data);
        y_channel.width = bufferWidth;
        y_channel.height = bufferHeight;
        y_channel.data = malloc(y_channel.width * y_channel.height);        
    }

    uint8_t *yc = CVPixelBufferGetBaseAddressOfPlane(pixelBuffer, 0);
    int total = bufferWidth * bufferHeight;
    for(int k=0;k<total;k++)
    {
        y_channel.data[k] = yc[k++]; // copy y channel
    }

    CVPixelBufferUnlockBaseAddress( pixelBuffer, 0 );
}