just to add another possible solution, that may be much simpler if you want to add different videos.
There are a lot of VJ software or Multitrack Audio/Video software, which accept MIDI signals as triggers. (for ex, on a C 4th octave play the video n°2, on E play n°4 ect..)
sending MIDI notes out of Arduino is really simple. Hardware part is very simple too.
This way (maybe for future installations) you can have different sensors, each one triggering different Videos, just adding another Note generated by another sensor (maybe 6 lines of code more.)