I don’t know what you are doing, or what you are trying to do. I use unrtreot, I have the codec pack CCCP Combined Convergence Codec Pack, it was available with a torrent, it prolly still is. It plays Xvid, Divxx, DVDrip and numerous others. It won’t play Flac or RAR files. Most people urge K-lite codec pack, it may be better, I’ve never tried it.
I use MacX YouTube Downloader. I usually download videos from YouTube, Dailymotion, Facebook, Vimeo, Vevo, and it is said that 300+ online video sites are supported by this downloader.
Or you can use web add-on, such as videodownloader helper.