British Telecommunications Public Limited Company

Patrick J Mulroy

Michael Erling Nilsson

Stephen Clifford Appleby

Ian Barry Crabtree

Rory Stewart Turnbull

A plurality of video streams is transmitted over a transmission link. At intervals, one determines for each video stream at each of a plurality of encoder settings, having regard to the amount of data buffered at a receiver for that stream, a bit rate sufficient to transmit the remainder of that stream at that encoder setting such as to avoid buffer underflow at the receiver. One determines also a critical point equal to the earliest time at which that bit rate can be reduced while still avoiding buffer underflow at the receiver. An encoder setting is chosen for each video stream such that the sum of said bit rates required for transmission of the streams does not exceed the capacity of the transmission link. Any surplus capacity of the transmission link is allocated to the stream that has the earliest critical point.

Multiplexed video streaming

A video sequence is to be transmitted at a selectable quality from a server over a network. A network control protocol operates in response to a control parameter to allocate to the server a share of available transmission capacity in proportion to the value of the control parameter. First, one determines a plurality of transmission rate values that are needed over successive time periods of the sequence for successful transmission of the sequence at a reference quality; then the control parameter is set, proportional to the transmission rate value and communicated to the control protocol at corresponding time instants. The sequences can then be transmitted, encoded at a quality from time to time selected in dependence upon the actual transmission capacity made available by the network to the server.

Video streaming

A video encoder using inter-frame differential coding has a store () for containing a plurality of reference pictures. For each incoming picture it chooses one (or more) of the stored reference pictures to use. Control means () select which locally decoded pictures are to be entered into, and removed from, so that the store always contains at least one relatively older picture that lies within a defined time window and at least one relatively younger picture that is more recent than the time window. When it receives an error message from a receiver, it switches the coder from its normal a state (in which it is allowed to choose any picture as predictor) into a state in which it is permitted to choose only a said relatively older picture for prediction. The beginning of the time window is preferably set according to the estimated (or observed) round trip time between the encoder and decoder such that at least one of the relatively older pictures always predated the error message.

Reference pictures for inter-frame differential video coding

The bitrate for any practical video streaming system will vary considerably as a function of the difficulty of encoding the sequence in question. This variation is even more apparent when comparing different video clips of different genres for example where sports clips might require a higher average bitrate and fluctuate more due to the high activity of typical scenes, whereas a news report clip might require a much lower bitrate and be relatively static. As such, to deliver video streams at a constant quality to users sharing a contended network, a constant bandwidth method is not efficient to use across all the streams. The bandwidth allocated to each stream must be allowed to dynamically vary in time in accordance with the precise demands of the video being streamed at that time and also be within any network bandwidth constraints. The present invention defines such a method.

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Vizcaya, Spain

Patrick J Mulroy