title: Why AVAsset tracks has different timeRange for same video file?
body: <p>Why <code>AVAsset</code> tracks has different timeRanges for same video file? </p>
  
  <p>I have fully loaded media file in <code>AVAsset</code>. I print tracks property of this class and receive this information.</p>
  
  <pre><code>▿ 2 elements
    - 0 : &lt;AVAssetTrack: 0x17000fed0, trackID = 1, mediaType = vide&gt;
    - 1 : &lt;AVAssetTrack: 0x17000fe90, trackID = 2, mediaType = soun&gt;
  </code></pre>
  
  <p>So I have one video and one sound <code>AVAssetTrack</code> of the same media file.</p>
  
  <p>So I print timeRange of each <code>AVAssetTrack</code>.</p>
  
  <p>So for video:</p>
  
  <pre><code>▿ CMTimeRange
    ▿ start : CMTime
      - value : 0
      - timescale : 1000
      ▿ flags : CMTimeFlags
        - rawValue : 1
      - epoch : 0
    ▿ duration : CMTime
      - value : 5000
      - timescale : 1000
      ▿ flags : CMTimeFlags
        - rawValue : 1
      - epoch : 0
  </code></pre>
  
  <p>And for sound.</p>
  
  <pre><code>▿ CMTimeRange
    ▿ start : CMTime
      - value : 0
      - timescale : 1000
      ▿ flags : CMTimeFlags
        - rawValue : 1
      - epoch : 0
    ▿ duration : CMTime
      - value : 5002
      - timescale : 1000
      ▿ flags : CMTimeFlags
        - rawValue : 1
      - epoch : 0
  </code></pre>
  
  <p>So why duration of the sound <code>AVAssetTrack</code> is longer than video one? And that is for same video file.</p>