When blind, or visually impaired people visit the theatre or cinema or watch television, and many of them do, they can frequently make out some shapes and some movements on the stage or screen, and they obviously gain a lot from the sound channel. Their understanding of the action can be helped enormously, however, by a friend whispering in their ear to give them clues as to what is happening and information about the visual elements of scenes. Certain theatres have been providing, via headphones, a commentary of this type, which has become known as audio description. The authors describe the AUDETEL project which provides a packet based system for the provision of a completely separate additional speech channel for this purpose, within the existing bandwidth of the television signal. They also indicate how the use of such a packet system can enable one to maximise the use of a fairly low bit rate shared channel, providing various different users with what they need, without interference from the other users.
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