Video stream switching
AssigneeBritish Telecommunications public limited company
InventorsRichard J Jacobs, Matthew D Walker, Dimitrios Miras
Life of this patent
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Abstract
A technique is described for providing a client on a packet based network with a stream of encoded video data. The system is able to maximise the bit-rate of the video stream by adapting to fluctuations in network capacity. The technique is characterised in that adaptation of the bit-rate of the transmitted encoded 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 minimised as it is ‘hidden’ in the scene change. The technique is described as applied to hierarchically encoded video data but equally may be applied to other encoding techniques which adapt to network conditions.
Claims14
A method of operating a multimedia server (202), said method comprising;
- providing a stream of video data representing a video sequence to an output of the multimedia server (202), wherein the output of the media server (202) is connected to a packet based network (203),
- measuring a property of the video data in order to determine the occurrence of a scene change in the video sequence,
- detecting the available bandwidth on the network (203),
- varying the bit-rate of the stream of video data,
- wherein the method is characterised in that
- variation in the bit-rate of the video data is controlled to occur in response to variations in the capacity of the network (203) and preferentially with a scene change in the video sequence.
A method of operating a multimedia server 202 in accordance with any of the preceding claims in which the source 201 of video data is stored in encoded form in a database.
A method of operating a multimedia server 202 in accordance with any of the preceding claims wherein, upon detecting a variation in the capacity of the network such as to render it appropriate for a change in bit rate to occur, the server waits for a predetermined time to attempt to detect a change of scene, and if such a change of scene is detected within the predetermined time, the change of bit rate is caused to occur at the time of the change of scene, but if a change of scene is not detected within the predetermined time, then the change of bit rate is caused to occur at the expiry of the predetermined time.
A method of operating a multimedia server 202 in accordance with any of the preceding claims wherein, upon detecting a variation in the capacity of the network such as to render it appropriate for a change in bit rate to occur, the server determines if there is going to be a change of scene within a predetermined time, and if it is determined that there will be such a change of scene within the predetermined time, the change of bit rate is caused to occur at the time of the change of scene, but if it is determined that there is not going to be a change of scene within the predetermined time, then the change of bit rate is caused to occur substantially immediately after having made such a determination.
A multimedia server (202) comprising;
- a reader (302) for reading video data representing a video sequence from a source (301),
- a scene change detector (604) for detecting changes of scene in the video sequence,
- a bit-rate controller (607) for controlling the rate at which the video data is transferred from the reader to an output port, wherein the output port is capable of communicating with a client (204) on a packet network (203);
- the media server further comprising means (608) for detecting available bandwidth between the multimedia server (202) and client (204) on the packet network,
- characterised in that
- the bit-rate controller (607) is arranged to vary the bit-rate of the video data transferred to the output port in dependence on the detected bandwidth preferentially in correlation with a scene change detected by the scene change detector (604).
Dependencies are inferred from the claim text.