Due to the rush to production, many cutscenes - including this one - were cut from Star Wars Knights of the Republic II (KOTOR2). This one features a showdown of sorts between Darth Sion and Darth Nihilus.
The mod was originally made by Darkwarrior (a member of the TSLRP forums). Link to the module so you can play it yourself (in your PC game):
You might want to let the whole video load before playing. The video doesn't lag at all.
One note: I will not respond to questions that are answered in this "About This Video" section