title: How to Simply Remove Duplicate Frames from a Video using ffmpeg
body: <p>First of all, I'd preface this by saying I'm NO EXPERT with video manipulation,
  although I've been fiddling with ffmpeg for years (in a fairly limited way).  Hence, I'm not too flash with all the <em>language</em> folk often use... and how it affects what I'm trying to do in my manipulations... but I'll have a go with this anyway...</p>
  
  <p>I've checked a few links here, for example:
  <a href="https://stackoverflow.com/questions/37088517/ffmpeg-remove-sequentially-duplicate-frames">ffmpeg - remove sequentially duplicate frames</a></p>
  
  <p>...but the content didn't really help me.</p>
  
  <p>I have some hundreds of video clips that have been created under both Windows and Linux using both ffmpeg and other similar applications.  However, they have some problems with times in the video where the display is 'motionless'.</p>
  
  <p>As an example, let's say we have some web site that streams a live video into, say, a Flash video player/plugin in a web browser.  In this case, we're talking about a traffic camera video stream, for example.</p>
  
  <p>There's an instance of ffmpeg running that is capturing a region of the (Windows) desktop into a video file, viz:-</p>
  
  <pre><code>ffmpeg -hide_banner -y -f dshow ^
        -i video="screen-capture-recorder" ^
        -vf "setpts=1.00*PTS,crop=448:336:620:360" ^
        -an -r 25 -vcodec libx264 -crf 0 -qp 0 ^
        -preset ultrafast SAMPLE.flv
  </code></pre>
  
  <p>Let's say the actual 'display' that is being captured looks like this:-</p>
  
  <pre><code>123456789 XXXXX 1234567 XXXXXXXXXXX 123456789 XXXXXXX
  ^---a---^ ^-P-^ ^--b--^ ^----Q----^ ^---c---^ ^--R--^ 
  </code></pre>
  
  <p>...where each character position represents a (sequence of) frame(s).  Owing to a poor internet connection, a "single frame" can be displayed for an extended period (the 'X' characters being an (almost) exact copy of the immediately previous frame). So this means we have segments of the captured video where the image doesn't change at all (to the naked eye, anyway).</p>
  
  <p>How can we deal with the duplicate frames?... and how does our approach change if the 'duplicates' are NOT the same to ffmpeg but LOOK more-or-less the same to the viewer?</p>
  
  <p>If we simply remove the duplicate frames, the 'pacing' of the video is lost, and what used to take, maybe, 5 seconds to display, now takes a fraction of a second, giving a very jerky, unnatural motion, although there are no duplicate images in the video.  This seems to be achievable using ffmpeg with an 'mp_decimate' option, viz:-</p>
  
  <pre><code>     ffmpeg -i SAMPLE.flv ^                      ... (i)
          -r 25 ^
          -vf mpdecimate,setpts=N/FRAME_RATE/TB DEC_SAMPLE.mp4
  </code></pre>
  
  <p>That reference I quoted uses a command that shows which frames 'mp_decimate' will remove when it considers them to be 'the same', viz:-</p>
  
  <pre><code>     ffmpeg -i SAMPLE.flv ^                      ... (ii)
          -vf mpdecimate ^
          -loglevel debug -f null -
  </code></pre>
  
  <p>...but knowing that (complicated formatted) information, how can we re-organize the video without executing multiple runs of ffmpeg to extract 'slices' of video for re-combining later?</p>
  
  <p>In that case, I'm guessing we'd have to run something like:-</p>
  
  <ul>
  <li>user specifies a 'threshold duration' for the duplicates 
     (maybe run for 1 sec only)</li>
  <li>determine &amp; save main video information (fps, etc - assuming 
     constant frame rate)</li>
  <li>map the (frame/time where duplicates start)->no. of 
     frames/duration of duplicates</li>
  <li>if the duration of duplicates is less than the user threshold, 
     don't consider this period as a 'series of duplicate frames' 
     and move on</li>
  <li>extract the 'non-duplicate' video segments (a, b &amp; c in the 
     diagram above)</li>
  <li>create 'new video' (empty) with original video's specs</li>
  <li>for each video segment
     extract the last frame of the segment
     create a short video clip with repeated frames of the frame 
       just extracted (duration = user spec. = 1 sec)
     append (current video segment+short clip) to 'new video'
   and repeat</li>
  </ul>
  
  <p>...but in my case, a lot of the captured videos might be 30 minutes long and have hundreds of 10 sec long pauses, so the 'rebuilding' of the videos will take a long time using this method.</p>
  
  <p>This is why I'm hoping there's some "reliable" and "more intelligent" way to use
  ffmepg (with/without the 'mp_decimate' filter) to do the 'decimate' function in only a couple of passes or so...  Maybe there's a way that the required segments could even be specified (in a text file, for example) and as ffmpeg runs it will
  stop/restart it's transcoding at specified times/frame numbers?</p>
  
  <p>Short of this, is there another application (for use on Windows or Linux) that could do what I'm looking for, without having to manually set start/stop points,
  extracting/combining video segments manually...?</p>
  
  <p>I've been trying to do all this with ffmpeg N-79824-gcaee88d under Win7-SP1 and (a different version I don't currently remember) under Puppy Linux Slacko 5.6.4.</p>
  
  <p>Thanks a heap for any clues.</p>