title: Get a frame count of a MP4 file
body: <p>I made my own MP4 parser (it recursively parses an atom tree and the content of some atoms).</p>
  <p>I already see the duration of a video (in seconds) and I know how to find a start of a frame at a specific time (in seconds). However, I don't know how to find a number of frames (and compute the FPS) without decoding actual frames.</p>
  <p>I was using the <code>moov - trak - 0 - mdia - minf - stbl - stsz</code> array, which usually has one value per frame. But now, I found a MP4 video, which has 370 values in &quot;stsz&quot; (370 video samples), but only 184 frames.</p>