On disc-based video formats, an audio commentary is an additional audio track consisting of a lecture or comments by one or more speakers, that plays in real time with video. Commentaries can be serious or entertaining in nature, and can add information which otherwise would not be disclosed to audience members. The DVD medium allows multiple audio tracks for each video program. DVD players usually allow these to be selected by the viewer from the main menu of the DVD or using the remote. These tracks will contain dialogue and sound of the movie, often with alternative tracks featuring different language dialogue, or various types of audio encoding (such as Dolby Digital, DTS or PCM). Among them may be at least one commentary track. There are several different types of commentary. The two main types simply define the length of the commentary rather than the type of content. They are: Typically a commentary track will include feature-length commentary from the film's director, cast memb...