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,
- 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
- 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.