Half-life: Opposing Force uses the same soundtrack as the other Half-Life expansion developed by Gearbox, Half-life: Blue Shift. There was no extracting or decoding necessary for this one because the music files are readily available for anyone in the media folder of the gearbox game files. One thing I found odd is the numbering of the tracks. The first track you hear in-game during the opening cinematic inside of the military helicopter is "Scientific Proof" which is numbered as Audio Track 02.. I did some searching on various forums and found bits and pieces of information—although not very clear. The original soundtrack by Chris Jensen was dropped when the game was uploaded on Steam. So, I found my old physical Opposing Force disc, ripped the music off it and found the numbering is the same as the Steam game files. "Scientific Proof" is still track 02 and there are no missing tracks on there. I saw that there were a couple of tracks written by Jensen that were used for Half-life 2 Trailers but I'm not interested in them for the sake of this soundtrack. I just re-named Scientific Proof as Track 01 and progressed from there.
We included two short additional tracks as well, the Civilian and Marine Victory Themes for capture the flag multiplayer(which were in mono, so I converted them to stereo). I labeled the tracks according to the titles that were applied when ripping the audio from the CD to my computer. It's mostly the same as the titles you see uploaded on other sites but combines both the titles for Opposing Force and Blue Shift(example: 04 - Spooky Oozings AKA Listen).