title: iOS - trying to understand how movies work
body: <p>I am working on an application that has to be tight control of time flow during a movie recording. </p>
  
  <p>Apple says the iPhone 5 can capture HD video <strong>up to</strong> 30 fps. If shoot a video and play it on quicktime I see a variable FPS, that reaches 30 fps at some moments, but at the same time quicktime reports the video as being 29.75 fps.</p>
  
  <p>As far as I understand, for each second of video, an integer number of frames should be displayed, not a fractional number. I first thought that could be related to drop frames. Then I decided to design an method to measure drop frames and realized that for every second of video, the iPhone drops from 1 to 4 frames. Also discovered that every time a frame is dropped iPhone simply copies the last frame again to fill the gap. So in theory, dropping a frame would make no difference in the total number of frames a move would have. </p>
  
  <p>So, this is my problem. What this 29.75 fps is telling? How this number is obtained? </p>