I am trying to retrieve a CVPixelBufferRef from CMSampleBufferRef in-order to alter the CVPixelBufferRef to overlay a watermark on the fly.

I am using `CMSampleBufferGetImageBuffer(sampleBuffer)` in-order to achieve that. I am printing the result of the returned CVPixelBufferRef, but its always null.

```
- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection {

    CVPixelBufferRef pixelBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);

    NSLog(@"PixelBuffer %@",pixelBuffer);
...

}

```

I there anything I am missing?