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I had a video that someone made where they thought they were being artistic and reversed it so it was playing backwards. I had this itching to see it forward, and set out on a quest to figure out how to play video backwards under Linux with mplayer. Here's what I did:

1. Create an empty directory, and change to it
2. Use the following command to convert all the frames in the movie to individual JPEG files:
   

   $ mplayer -vo jpeg:quality=100 \
         /path/to/video/backwards.avi

   
   You will end up with a directory full of files like 00000001.jpg. Each one of these files is a single frame of the video you are attempting to reverse.
   
3. Now create a subdirectory called TARG - this will contain the same JPEG files linked in reverse order. Do not change into it just yet...
   
4. Create the following silly perl script (substitute the $a=2800 for the number of the last file in your directory):
   

   #!/usr/bin/perl
   
   $a = 2800;
   $b = 1;
   
   while ($a > 0) {
         $sa = sprintf "%08d.jpg", $a;
         $sb = sprintf "%08d.jpg", $b;
   
         link("$sa", "TARG/$sb");
         $a = $a - 1;
         $b = $b + 1;
   }
   
   exit 0;

5. Now change into the TARG directory. There will be a list of files like before, but they will be named in reverse order. Use the following command to reassemble them:
   

   $ mencoder "mf://*.jpg" -mf fps=12 \
         -o /path/to/new/movie/rev_movie.avi \
         -ovc lavc -lavcopts vcodec=mpeg4

   
   You will likely need to adjust the fps (frames per second) - this may take some trial-and-error if you don't know anything about the original movie. You can try this out (without doing the encoding) by using:
   

   $ mplayer "mf://*.jpg" -mf fps=12

6. Enjoy. You can wipe out all those frames now...