Page "Multitrack recording" Paragraph 12

When recording is completed, the many tracks are " mixed down " through a mixing console to a two-track stereo recorder in a format which can then be duplicated and distributed.

( Movie and DVD soundtracks can be mixed down to four or more tracks, as needed, the most common being five tracks, with an additional Low Frequency Effects track, hence the " 5. 1 " surround sound most commonly available on DVDs.