If you are trying to download just a regular YouTube video (non-copy protected) you would use the YouTube Downloader. If you are trying to download a video that is (DRM) copy protected on a non-VIP provider's website, you would use either DRM MPD or DRM M3U8, depending on the method used by the provider, either DASH or M3U8. StreamFab will decide that for you, you don't have to. And finally, as @october262 stated, if you are trying to get a YouTube movie, you would use the YouTube Movie Downloader.