Streaming multimedia data over a network having a variable bandwith

1. A method of streaming multimedia data over a network having a variable bandwidth, the method comprising:

encoding data coming from a multimedia source,

supplying a set of encoded streams formed with stream elements containing encoded multimedia data, each encoded stream being encoded at a different predetermined bit rate,

determining common values for at least a part of the decoding parameters suitable for at least a group of streams of various predetermined bit rates within the set of encoded streams so that a decoder can use the common decoding parameter values for decoding all stream elements from all streams within the group of streams, and

building the group of streams to which common decoding parameter values are assigned.

2. A method as claimed in claim 1 , wherein

the decoder is configured according to an MPEG-4 (Moving Picture Expert Group 4) recommendation, and

the decoding parameters, to which common values are assigned, include a “low_delay” parameter and a “time_increment_resolution” parameters.

3. A method as claimed in claim 2 , wherein

a value corresponding to a highest probability of using B-VOP (Bidirectional Video Object Planes) within the group of encoded streams is assigned to the “low_delay” parameter.

4. A method as claimed in claim 2 , wherein

a value corresponding to a smallest time increment resolution needed within the group of encoded streams is assigned to the “time_increment_resolution” parameter.

5. A method as claimed in claim 2 , wherein:

the client application decoder is configured according to recommendation ISO 14496-2 MPEG-4 visual,

each encoded stream includes a video encoded stream and an audio encoded stream for separately encoding audio and video data, and

wherein

the video stream is formed with consecutive stream elements called Access Units according to said recommendation, including:

a first Access Unit for transmitting the common decoding parameter values,

a second Access Unit for transmitting a predetermined fixed image of the Intra type according to said recommendation and

a third and subsequent Access Units comprising Random Access Point information for transmitting an absolute time reference and a piece of information of the type: “VOP_not_coded” according to said recommendation, which indicates to the client application decoder to copy the previous Access Unit.

6. A computer program product for an encoder computing a set of instructions which when loaded into the encoder, causes the encoder to carry out the method as claimed in claim 1 .

7. A signal for carrying a computer program, the computer program being arranged to carry out the method as claimed in claim 1 .

8. An encoding system comprising:

an encoder that is configured to:

encode data coming from a multimedia source, and

provide a set of encoded streams formed with stream elements containing the encoded multimedia data, each encoded stream being encoded at a different predetermined bit rate, and

a switch that is configured to:

determine common values for at least a part of the decoding parameters suitable for at least a group of streams of various predetermined bit rates within the set of encoded streams so that a decoder can use the common decoding parameter values for decoding all stream elements from all streams within the group of streams, and

build the group of streams to which common decoding parameter values are assigned.

9. A server for serving a client application with an encoded stream selected within a set of encoded streams built by a media encoder with stream elements containing encoded data coming from a multimedia source, each encoded stream being encoded at a different predetermined bit rate, wherein the server is configured to:

determine common values for at least a part of the decoding parameters suitable for at least a group of streams of various predetermined bit rates within the set of encoded streams so that a decoder of the client application can use the common decoding parameter values for decoding all stream elements from all streams within the group of streams, and

supply the group of streams to which common decoding parameter values are assigned to the client application.

10. A transmitter for streaming multimedia data over a network having a variable bandwidth, the transmitter comprising:

a media encoder that is configured to:

encode data coming from a multimedia source, and

provide a set of encoded streams formed with stream elements containing encoded multimedia data, each encoded stream being encoded at a different predetermined bit rate,

a switching system that is configured to:

determine common values for at least a part of the decoding parameters suitable for at least a group of streams of various predetermined bit rates within the set of encoded streams so that a decoder can use the common decoding parameter values for decoding all stream elements from all streams within the group of streams, and

build the group of streams, to which common decoding parameter values are assigned, and

a media server that is configured to provide the common values and the group of streams to a client application.