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Adapting Video for VI Learners

Technical Glossary

A

asset
Any chunk of material which might eventually form part of a video, web site, or multi-media resource. An asset can be a single picture, a clip of video, pages of text, or an animation. Since new versions of multi media will offer better opportunities for alternative presentations of material, it is worth collecting more assets than you currently need and archiving them in uncompressed form for reuse later.
AUDETEL
A European project to investigate and produce tools for audio subtitling for the European broadcasting industry.
audio subtitling
The addition of supplementary commentary for blind and partially sighted viewers. Audio subtitling is often added to existing material, and is constrained by the time available between existing dialogue snippets. It can be open or closed. Audio subtitles are much easier to add to non-linear formats and materials.
AVI
AVI is Microsoft's version of an audio visual lossy compression standard.

B

bandwidth
The amount of the electromagnetic spectrum which has to be given over to a particular transmission. Analogue television channels have a very large bandwidth in comparison to, say, an audio telephone line. Compression techniques are used to reduce the size of the signal, and therefore the bandwidth needed to transmit it. Digital systems lend themselves to compression, so that digital broadcasts are much more bandwidth efficient than analogue ones.

C

CD-ROM
Compact Disc Read Only Memory. A high density storage media based on compact disc technology. The same physical size as a compact disc, a CD-ROM can hold up to 650 megabytes of digital data, including text and any kind of multi-media file which can be held on computer, together with programs and directories.
compression
A collection of techniques used to reduce both the space and the bandwidth needed for digital video, sound and other voluminous multimedia. Text must be stored in "lossless" format: in other words decompression must not have in any way changed the content. Video, graphics, and sound on the other hand can use "lossy" compression where the recovered image is an approximation to the one compressed. Lossy compression works because of the eye's tolerance for small distortions and inaccuracies.

D

databursts
A few rapidly changing frames of text or pictures inserted into a broadcast or a video tape which can be read at leisure using the video recorder's pause control.
Digital VHS (D-VHS)
An upcoming variant on VHS which is capable of recording both analogue signals and the uncompressed MPEG-2 stream which underpins digital television.
dvd
Digital Video Disk. A combination of specifications for a very high density medium (capable of holding complete videos in digital form on discs the size of a compact disc or old style CD-ROM), together with an MPEG-2 based compression standard for storing videos on it. dvd discs come in several densities and can be single or double sided.
dvd-ROM
The underlying storage technology for digital video disc, which in this case can be used as storage medium for other computer files of any format. dvd ROMs can hold between 2 and 8 gigabytes of data depending on whether the disc is single or multi-layer, and single or double sided.

H

HI-8 video
A high quality variant on the 8 mm camcorder standard for domestic video recording.
HTML
Hyper Text Markup Language: the basis for data storage and linkage of files over the world wide web.

I

indexing (on VHS)
A way of marking tape position accurately on a VHS analogue video tape. With appropriate recorders indexing uses a low speed tape head to place a magnetic code mark on the edge of a VHS tape. This mark can be searched for quickly. (The track is similar to that used for low quality audio, but on the other edge of the tape).
Internet
A loose collection of computers and associated networking links which taken together form the basis for services such as world wide web, e-mail, news, and Internet based video phone and telephone.

J

JPEG
An open, nonproprietary compression standard for reducing the size of still images. The term comes from the words Joint Photographic Experts Group who proposed and maintain the standard.

K,L

linear media
A collective term for media such as broadcast radio, broadcast television (digital or analogue), VHS and D-VHS, and digital video tape. In all of these it is difficult or impossible to randomly access the material, and therefore difficult to provide supplementary material other than by using available concurrent information tracks (such as the spare audio tracks in digital TV broadcasts or by borrowing one of the audio tracks on VHS tape).

M

multimedia
A way of bringing together text, video, sound, animation, simulations and interactive control all into one digitised package. Multimedia can be distributed as conventional computer files, or on the Web, or more usually on high density storage media such as CD-ROM or dvd-ROM.
MPEG
A particular form of lossy compression which in its MPEG-2 form is used to compress digital television broadcasts, D-VHS, some multimedia, and dvd. MPEG-2 has the ability to store several concurrent audio tracks, which are useful to designers of video or multi media products wanting to add supplementary information for visually impaired or blind users.

O

non-linear media
A collective term for multi-media and web based information and entertainment resources, which because of the nature of their underlying storage mechanism (CD-ROM or world wide web) can be accessed at random. This makes it straightforward to produce materials in which the user can at any time select alternative chunks of information whilst easily returning to the paused programme.

P

PhotoCD
A proprietary technology which offers an easy way of converting from conventional 35 mm film to CD, with the results stored in JPEG compressed format. The photographer presents the film to a processing house, who returns the film and a CD-ROM with the images on it.
Photo-JPEG (sometimes just JPEG)
An open, nonproprietary compression standard for reducing the size of still images. The term comes from the words Joint Photographic Experts Group who proposed and maintain the standard.

Q

QuickTime
A complex and powerful standard for lossy compression of video and sound which is bordering on a full multi media system in its own right. QuickTime can store multiple video tracks, multiple audio tracks, multiple text, animation, and other media together with internal control and search functions.

S

screen capture (sometimes frame grab)
A way of picking a particular single picture from a video and digitising it ready for manipulation in a computer based graphics editing package.
subtitles (open and closed)
Open subtitles are text messages permanently in view. Closed subtitles are similar text messages which can be hidden for audiences who don't need them. In the UK, closed subtitling is achieved through the teletext system. Other parts of the world use different systems.
Super VHS
A high quality variant on the compact VHS camcorder standard, used for domestic video recording.
S-Video
The best way to connect a camcorder to a digitising card (or any other editing system). S-Video avoids compromising picture quality which would otherwise occur if the video components were combined for transmission through composite video connections.

V

VHS
A storage medium for analogue video and sound. VHS tapes can hold up to four hours of standard speed video recordings, and can have one video track, one low quality and two high quality audio tracks, and an index track. VHS is a linear format.
Video capture
The process of converting video from analogue form (such as that held on a camcorder tape) to digital form. Video capture involves the use of a computer with a specialised interface card, and a large hard disc system able to store the video data before compression.
Video Disc
An early way of distributing video on laser disc. Video Discs are read only, 12 inches across, and analogue.
Video Editing suite
One or several pieces of equipment used to select, modify, and combine clips from several video tapes into one final product. Suites offer ways of adjusting colour balance, contrast, brightness, and other video parameters: they also allow titling, and video effects to be added. Non-linear video editing suites are computer based (usually expensive) variants which first digitise the video clips and then operate in a much more flexible fashion on the digitised assets.

W

World Wide Web (or sometimes Web)
Vastly interlinked collection of files on many different machines all connected to the Internet. Files can be text based, or multimedia. The world wide web is linked using HTML as its formatting language.
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