title: Having issue with AVAssetWriterInput parameter sourceFormatHint
body: <p>I am working with <code>AVAssetWriterInput</code> but <code>sourceFormatHint</code> parameter is giving this warning:</p>
  
  <blockquote>
    <p>Incompatible integer to pointer conversion sending 'int' to parameter
    of type 'CMFormatDescriptionRef' (aka 'const struct
    opaqueCMFormatDescription *')</p>
  </blockquote>
  
  <p>here is code:</p>
  
  <pre><code>AVAssetWriterInput* videoWriterInput = [AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeVideo outputSettings:settings sourceFormatHint:kCMMediaType_Video];
  videoWriterInput.expectsMediaDataInRealTime = YES;
  videoWriterInput.transform = videoTrack.preferredTransform;
  AVAssetWriter *videoWriter = [[AVAssetWriter alloc] initWithURL:outputURL fileType:@"public.mpeg-4" error:nil];
  [videoWriter addInput:videoWriterInput];
  </code></pre>
  
  <p>What parameter should I pass in <code>sourceFormatHint</code>?</p>