Video stream switching

• US 20040172478A1
• Filed: 01/06/2004
• Published: 09/02/2004
• Est. Priority Date: 07/19/2001
• Status: Active Grant

• Current Assignee: British Telecommunications PLC (BT Group PLC)
• Original Assignee: British Telecommunications PLC (BT Group PLC)
• Inventors: Miras, Dimitrios, Walker, Matthew D, Jacobs, Richard J
• Granted Patent: US 8,209,429 B2
• Time in Patent Office: Days
• US Class Current: 709/233
• CPC Class Codes: H04N 19/142 Detection of scene cut or scene change
• CPC Class Codes: H04N 19/179 the unit being a scene or a shot
• CPC Class Codes: H04N 19/87 involving scene cut or scene change detection in combination with video compression
• CPC Class Codes: H04N 21/23418 involving operations for analysing video streams, e.g. detecting features or characteristics television picture signal circuitry for scene change detection H04N5/147; filtering for image enhancement G06T5/00; methods or arrangements for recognising scenes G06V20/00; arrangements characterised by components specially adapted for monitoring, identification or recognition of video in broadcast systems H04H60/59
• CPC Class Codes: H04N 21/234327 by decomposing into layers, e.g. base layer and one or more enhancement layers
• CPC Class Codes: H04N 21/2402 Monitoring of the downstream path of the transmission network, e.g. bandwidth available traffic monitoring in data switching networks H04L43/00; monitoring data switching networks utilization H04L43/0876
• CPC Class Codes: H04N 21/2662 Controlling the complexity of the video stream, e.g. by scaling the resolution or bitrate of the video stream based on the client capabilities
• CPC Class Codes: H04N 21/6437 Real-time Transport Protocol [RTP]

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.

Claims

1. 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.

2. A method of operating a multimedia server (202) in accordance with claim 1 wherein upon detecting a decrease in the available bandwidth the bit-rate of the video data is decreased.

3. A method of operating a multimedia server (202) in accordance with claim 1 wherein the bit-rate of the video data is periodically increased in order to ensure that all of the available bandwidth is being used.

4. A method of operating a multimedia server 202 in accordance with claims 1 to 3 wherein said stream of video data is comprised of a plurality of hierarchically encoded layers.

5. A method of operating a multimedia server (202) in accordance with claim 4 wherein the bit-rate of the video data is varied by adding or dropping layers from the stream of data transferred to the output port.

6. A method of operating a multimedia server (202) in accordance with claims 4 or 5 wherein the objective quality contribution of each layer to the overall quality of the video sequence is measured in order to determine which of the layers is to be added or dropped from the stream of data transferred to the output port.

7. A method of operating a multimedia server 202 in accordance with claims 1 to 3 wherein said stream of video data is comprised of a plurality of independently encoded flows each of which encoded at different bit-rates.

8. A method of operating a multimedia server (202) in accordance with claim 7 wherein the bit-rate of the video data is varied by switching between independently encoded flows.

9. 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.

10. A method of operating a multimedia server 202 in accordance with any of claims 1 to 8 in which the source 201 of video data is encoded in real-time.

11. 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.

12. 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.

13. The method of claim 12 further including the step of, prior to providing a stream of video data to the output of the media server, processing the video data to determine the positions within the video data in which changes of scenes occur and making this information available for permitting whether a scene change will occur within a predetermined period at any point along the stream of video data.

14. 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).