Karaoke Formats
I barely understand this stuff myself, so if you have questions please let me know and I’ll do my best to answer them.
MP3+G
The MP3+G format is a zip file containing an mp3 for the audio, and a cdg file for the graphics. If you unzip both files to the same directory, you can use various karaoke software packages (including this free one for Windows) to play them on your computer. Fancier software packages let you burn to a CD+G disc, which is one of the standard formats for karaoke machines. And of course if you don’t care about having the lyrics in a video because you only want the audio, buy this format and just throw the cdg file away.
iPod/MP4
The iPod/MP4 format is an MP4 file that will play on an iPod. It also plays fine on a Mac, though we’re not entirely sure about a Windows machine – you need to have the correct codec installed, which you can probably handle by installing Quicktime. Probably.