how can i register the vidieo clip on xscreensaver

i can understant what this mean

To play MP4, MPEG, QuickTime, FLV and AVI videos:

    Install MPlayer 1.0 or newer, and add something like the following to the `programs' preference in your .xscreensaver file:

         "My Movie" mplayer -really-quiet -nosound -nolirc \
                       -nostop-xscreensaver \
                       -wid $XSCREENSAVER_WINDOW \
                       -fs -loop 0 \
                       $HOME/movies/my_movie.mp4 \n\

    Duplicate those lines for each other movie you would like to play.

    It's also possible to encapsulate the above into a single shell script which would pick a movie file at random from a directory and play that. Several people have written such things; Google it.

i can find 'programs' preference .xscreensaver file