Data Organization and Navigation

  • Article

When working with DVD-Video data it is important to distinguish between the way data is organized and how the end user views it. Unlike an audiocassette, for example, data organization and navigation in DVD-Video are decoupled concepts.

Data Organization

DVD-Video data is stored within a hierarchy of organizational groupings. The main organizational division of a DVD-Video disc is a video title set (VTS). A VTS can represent an entire movie or a 30-second video clip. There may be up to 99 VTSs on a disc. Disc authors may divide each title into as many as 999 video object sets (VOBSs). Each video object set can contain 32,767 video objects (VOBs) each of which can be composed of up to 255 cells. Each cell contains final audio or video content. Cells contain clips of multimedia data and they are not constrained in length, thus a single cell has the potential to represent a tremendous amount of data.

The organizational structure of a DVD-Video recording simply provides a framework for storing content data. The organizational structure does not provide any information to the player concerning the order in which the content should be presented to the user. It is possible for DVD-Video content to be authored so that it displays correctly if the player were simply able to enumerate all of the organization constructs and then iterate through them. While this approach is possible, it is certainly not very interesting and misses the point of DVD as an interactive media.

DVD-Video derives its interactive properties from navigational data stored in the recording. The main concepts of navigational data are title (TT), program chain (PGC), program (PG), and cell. At first glance, the navigational concepts appear to be nothing more than surrogates for the organizational concepts, with titles (TT) corresponding to VTSs, PGCs corresponding to VOBSs, and programs corresponding to VOBs.

The key distinction that sets navigational data apart from organizational data is that each piece of navigation data contains a block of information describing how it connects or interacts with other pieces of navigational data. For instance, a program chain can contain information that identifies which program chain to play next after it reaches the end of its play. A program chain can also contain command instructions that control the player's behavior before and after the program chain plays.

 Last updated on Thursday, April 08, 2004

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