My way:
http://www.listentoyoutube.com/ or
http://youtubedownload.altervista.org/I usually use Youtube Downloader so i have to download the video which starts out as an FLV or something, so i have to convert it to an MP3 with Youtube Downloader's converter, Listen to Youtube downloads the video's audio in MP3 format, so it's actually easier but load times can be a pain and sometimes it doesn't work
Then i take said MP3 and open it in Audacity, choose an area to have looped, split new, delete the original track, then split stereo track to mono, then merge the two mono tracks together, if they're too loud, i use whatever value amplify gives me and then i use amplify again and put in -3.0 or -5.0 so the song isn't too loud, then i export it as an OGG