British Telecommunications Public Limited Company

Richard J Jacobs

Matthew D Walker

Michael Erling Nilsson

Dimitrios Miras

A client on a packet based network is provided with a stream of encoded video data. The system is maximizes the bit-rate of the video stream by adapting to fluctuations in network capacity. Adaptation of the bit-rate of the transmitted enclosed video data is timed to occur upon a scene change in the video sequence. In this way the interruption to the viewer when the perceived quality of the video sequence increases or decreases is minimized as it is 'hidden' in the scene change. The technique may be applied to hierarchically encoded video data and to other encoding technique which adapt to network conditions.

Video stream switching

Real-time data (e.g. video) is streamed over packet networks (e.g. the Internet). Streamed video is provided without the start-up delay by transmitting data from a video streamer to the video viewer more rapidly than the video viewer consumes the data and using the excess data to build a buffer at the video viewer. When a suitable sized buffer is built the transmission rate of data to the buffer may be reduced. In order to deliver the best quality material for the available bandwidth, the supply of video data may be switched to a higher bit-rate source when the reservoir is filled. Fluctuations in network throughput may be accommodated during the transmission of data on a fine scale by adjusting the transmission rate of the data and on a coarse scale by switching between data streams encoded at different bit-rates. Fluctuations in network throughput are determined by counting the number of missing packets at the video viewer which information may then be fed back to the video streamer to adjust the flow of data accordingly.

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Woodbridge, United Kingdom

Richard J Jacobs