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Desktop Video AGOCG Report

CODECs for Desktop Videoconferencing

It is this lack of standardisation in desktop video protocols and equipment that has led to a relatively slow rate of uptake in the technology and many of the negative comments raised in the survey reported in Section 5 below.

Most of today's compression algorithms are not capable of sending a TV quality signal through a 64 Kbps ISDN channel. In order to do this, the algorithm would have to discard more than 99 percent of the data without seriously degrading the image.

As a result most desktop videoconferencing systems compromise by offering smaller windows, grainier colour and lower frame rates. Many CODECs achieve these levels of compression, but require more time to compress than to decompress. As mentioned above, MPEG and Cinepak are two such asymmetric CODECs which are therefore better suited for store-and-forward applications than for real time videoconferencing.

Even when the CODEC works in real time there may be a network lag, depending on the size and volume of the traffic on the network. A delay of more than 250 milliseconds is considered to interfere with a natural dialogue.

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