title: CMTimeMake(duration, fps). What is this mean?
body: <p>I am making video file on my Mac programmatically.
  I want to know that "CMtimeMake" is what's mean.</p>
  
  <p>For example:</p>
  
  <pre><code>AVAssetWriterInputPixelBufferAdaptor * avAdaptor = [AVAssetWriterInputPixelBufferAdaptor assetWriterInputPixelBufferAdaptorWithAssetWriterInput:writerInput sourcePixelBufferAttributes:NULL];
  
  [avAdaptor appendPixelBufferixelBuffer withPresentationTime:CMTimeMake(1, 10)];
  </code></pre>