title: What does forcing key frames mean?
body: <p>What does forcing key frames mean?</p>
  
  <p>As per the <a href="https://ffmpeg.org/ffmpeg.html" rel="nofollow noreferrer">doc</a> </p>
  
  <blockquote>
    <p>-force_key_frames[:stream_specifier] expr:expr (output,per-stream) Force key frames at the specified timestamps, more precisely at the
    first frames after each specified time.  If the argument is prefixed
    with expr:, the string expr is interpreted like an expression and is
    evaluated for each frame. A key frame is forced in case the evaluation
    is non-zero.</p>
  </blockquote>
  
  <p>Still I am not able to understand what does forcing key frames at specified timestamp means and what is its use?I can see this command is used while segmenting video.What is its purpose there?</p>