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Adapting Video for VI Learners
Design issues and approaches
Video clips in multimedia and Web pages
Multimedia = many small files
Multimedia presentations and Web materials are both made up of computer files containing information like text, sound and video clips. Sometimes, these small fragments are all bundled together into one big file containing not only chunks of information but also a program which can present them: a kind of integrated browser. More often, though, the browser or multimedia player is kept separate. For web materials, the resources are very separate, with the information files typically on a computer far away, whilst the browser runs on the machine in front of you. In the case of a multimedia package, you will often be able to see the information files by hunting through the folders on its CD-ROM.
The information files contain both presentation material which you can see, and links to other files. Taken together these links and files form the shape of the overall resource.
Simple video/sound formats
Most folk are pretty used to text files and what is in them. A video file is more novel: what does it contain?
Early video files stored just video and sound (and even now this is mainly the case for Microsoft's AVI format). Sound and video are interleaved, so that they can be played in synchronism without having to move the disk reading hardware too much at any one time: the video component is compressed to an appropriate standard. These kinds of files are therefore easy to understand - a link to the file triggers the right player, which seperates the audio and video, decompresses as needed, and displays and plays.
However, as multimedia, digital TV and the Web evolved, so did video file formats. As we have described elsewhere, MPEG compressed videos carry multiple sound channels, synchronised still picture, graphics and text fields. This means that they can provide much more early formats. For instance, they can be internally searched for content - programs can seek the right start point in long clips. Moreover, text will be produced at just the right time, making closed subtitles easy to create.
Extendible and interactive formats
This process of evolution is at its most well developed in Apple's Quicktime system. Just as with AVI and MPEG, Quicktime provides decompression services for interleaved video and sound. But the decompressors can be of many different types (including AVI and MPEG-1!), so Quicktime is in some ways a universal system. Moreover, whilst other systems carry just one video track, and a predefined number of sound channels, Quicktime can interleave arbitrary numbers of video, sound, text, animation, and other time-related resources in one file. The next step will be to include integral multimedia services, such as transition effects, hotspots controlling the links between files and so on.
The upshot of all this is that although the current generation of multimedia and web systems use video clips as just another data resource to be externally controlled and linked, increasingly the clips themselves will be the structuring elements, and what have been thought of up to now as simple decompressors will evolve into providing the basis for multimedia structuring.
Does this matter to the average producer? It certainly affects those of us who want to add extra supporting materials. Synchronisation of text and animations within the more complex structures will make it much easier to add subtitles and to overlay location cursors, for example. Better internal searching and indexing matter to teachers who want to help students locate particular features. Multiple video tracks makes walk-rounds very easy - loaction changes are automatically synchronised. And hot links right on the film will make it much easier to cue VI users to supplementary support.