On a DVD, information related to what will be played and when is stored in a special bitstream is called the Presentation Stream. The presentation stream doesn't contain any information that's visible or audible during playback. Instead, it takes input from and gives instructions to the Firmware or software of the DVD player
Internally, DVD players have two basic components, the navigation engine and the presentation engine. All direct user interaction is with the Navigation engine. It interprets user input through the remote, such as selecting buttons, and executes commands related to that input to give instructions to the presentation engine. The presentation engine determines what output (video, audio, subtitles, etc,...) should be played based on a combination of that input and the contents of the presentation stream.
The presentation stream can also interact with your DVD player. Restrictions such as region coding, parental controls, and prohibited user operations are programmed into the presentation stream for interpretation by the presentation engine.
