(Source : Philips)

Besides video and audio, a Program Stream may contain other elementary data streams. Because these are not defined in ISO/IEC 13818, the syntax and semantics for these additional data streams are defined specially for the Overlay Graphic data stream.

Overlay Graphics and Text (OGT)

The Overlay Graphics layer is designed for two main applications, namely Movie subtitling and Karaoke lyrics. It is a full screen resolution overlay with 4 colors, and transparency. Multi-color support is provided, to allow for highlighting of song lyrics or other picture highlighting.

The main advantage of OGT is that the graphics and text are not put into the video picture before encoding, but mixed in the decoder, which allows for selectable language and improved picture quality. The encoder model is based on two separate video planes; One for motion video, and one for OGT. The OGT page is displayed on top of the Video picture.

Play Sequence Descriptor ( PSD )

This is a set of control structures that enables the playback of preprogrammed sequences with user selection and interaction. The PSD contains a set of basic control structures i.e. the Play List, Selection List, and the End List. The Play List defines a list of Play Items that are played in sequence. A Play Item may be one of the following items : The whole or part of an MPEG Audio / Video Track. One, or more, MPEG encoded Still Pictures; with or without MPEG Audio.

MPEG Audio with no pictures. Motion Picture; with or without MPEG Audio The Selection List defines the action of the player in response to various user inputs, and may be used to implement menu systems for user selection of sequences. The Selection List may be extended to include hotspot information or commandlists. The player must response to user actions (NEXT, PREVIOUS, DEFAULT SELECTION, NUMERIC, RETURN). The Play List defines a list of Play Items that are to be played sequentially.

The Selection List is used in the PSD.VCD file, and is a List for implementing selection menus and enabling branching under user control. Segment Play Items are encoded as MPEG Sectors and are restricted to the Segment Play Item Area. Segment Play Items allow a Still Picture mode. Play List extensions have been defined for more interactivity by a Command List Interpreter and use of variables for storing scores and other application variables.

USER data

User data is used to encode scan information and closed caption information. The Scan Information Data is mandatory. On a Super Video CD disc it is only allowed to encode user data in the picture layer of the MPEG Video stream.

Scan Information Data

It is mandatory to encode Scan Information in User data groups, and they must be included as user data in the picture layer of all Intra pictures. Scan Information data contains forward and backward pointers to Sectors that contain the start of an Intra picture. Scan Information data is used for both Motion Pictures and Still Pictures.