Learn FFmpeg the hard way
&gt;In summary this is the very basic idea behind a video: a series of pictures &#x2F; frames running at a given rate.<p>&gt;Therefore we need to introduce some logic to play each frame smoothly. For that matter, each frame has a presentation timestamp (PTS) which is an increasing number factored in a timebase that is a rational number (where the denominator is know as timescale) divisible by the frame rate (fps).<p>Constant framerate is a very dangerous assumption to make. It&#x27;s true for video recorded by professional cameras, but if you check video recorded by most mobile phones you notice that it&#x27;s wrong.