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Adapting Video for VI Learners

Design issues and approaches

Summary of Digital Versatile Disc features

Content and features

  • Upwards of 2 hours of high quality digital video (to over 8 on a double-sided, dual-layer disc).
  • Still frames independent of the main Video. Each still frame can be accompanied by audio.
  • DVD can play widescreen movies on standard or widescreen TV sets (4:3 and 16:9 aspect ratios).
  • Audio within any given section is a bit complicated, and differs depending on the local regional standard. There can be up to 8 tracks of digital audio (for multiple languages), each with as many as 8 channels. Each track can be in one of three formats
    • Dolby Digital (formerly AC-3): from 1 to 5.1 channels (note that '5.1' means 5 high quality, + 1 effects channel)
    • MPEG-2 audio: 1 to 5.1 or 7.1 channels
    • PCM: 1 to 8 channels.
  • There can be up to 32 subtitle/karaoke tracks. These are limited in their range of colours, and can be used for simple graphics and animations, as well as scrolling or stationary subtitles.
  • Automatic "seamless" branching of video (for multiple story lines or parental control).
  • Up to 9 camera angles (different viewpoints can be selected during playback).
  • Menus and simple interactive features (for games, quizzes, etc.).
  • Multilingual identifying text for title name, album name, song name, cast, crew, etc.
  • Very fast rewind and fast forward.
  • Search to title, chapter, track, and timecode.

Note that DVD can be used for just audio, and a lot of it: if you stick to just one channel of stereo the lowest capacity disc can hold over 55 hours of high quality sound, which could be indexed and searched at random.


DVD-Videos consist of titles (like movies or albums), and parts of titles (such as chapters or songs). Titles are made up of cells linked together by one or more programme chains (PGC). PGC's can be set up to be sequential play, random play (which may repeat), or shuffle play (with random order but no repeats). Different programme chains can share cells, so allowing (for example) parental control choices to be set up to skip over censored sections.

When designers include extra material for camera angles or branching, this is interleaved together in small chunks. Adding a second camera angle for a programme roughly doubles the amount of space needed, reducing playing time in half.


Interactivity is mainly controlled through menus, searching, and choice of programme chain.

  • Menus each come with a still-frame graphic and up to 36 highlightable, rectangular "buttons". They are selected via the remote controller,using
    • menu key ,
    • up, down, left and right keys,
    • select key and
    • return key.
  • Remote control functions may also include freeze, step, slow, fast, scan, next, previous, audio select, subtitle select, camera angle select, play mode select, search to programme, search to part of title (chapter), search to time, and search to camera angle. Which ones are active depends on the disc content.