A method and system of transmitting video data and multimedia data to a plurality of client radio receivers over an air interface, the method comprising transmitting video data to a plurality of client radio receivers simultaneously using an adaptive encoding / transcoding scheme; and updating the adaptive encoding / transcoding scheme in dependence upon received feedback data. A system and method is also described that includes estimating channel states and distortion levels for a plurality of transmission modes, and then selecting that transmission mode for subsequent data transmission that has the lowest distortion level. Control data items can also be extracted from the first data stream to produce a multimedia data stream and a control data stream and the multimedia data stream is transmitted over a first channel; and the control data stream is transmitted over a second channel. The received data stream may be put into a plurality of multimedia slices having a predetermined slice size; and encoded into first data packets of a first predetermined size; which in turn are divided into respective integral second data packets of a second predetermined size and which are aggregated into a stream of third data packets of a third predetermined size.

The invention provides a method of controlling a video transmission system, the method comprising receiving an input indicative of a desired mode of operation, automatically configuring transmission parameters in dependence upon the desired mode of operation indicated by the received input and encoding and transmitting a video datastream over a communications channel using such transmission parameters. Also provided is a video transmission system comprising a video source operable to generate and output a video datastream, a user input device operable to receive a user input indicative of a desired mode of operation, a datastream encoder and transmitter unit operable to receive user input information from the user input device, to configure transmission parameters in dependence upon a desired mode of operation indicated by a received user input, and to encode and transmit a video datastream over a communications channel using transmission parameters.

A method of controlling data transfer in a data transmission system which includes a plurality of video and/or audio data sources, a single transmitter operable to transmit data from the data sources over at least one transmission channel,a plurality of client receivers operable to receive transmitted data, the method comprising estimating available channel capacity for each client receiver, using parameters relating to the at least one transmission channel, and using information from the transmitter and receiver, and using information relating to queuing of data between the data sources and the transmitter; determining a target bit transmit rate for each client receiver in dependence upon the estimated channel capacity, a quality parameter, and an activity parameter for the client receiver concerned; and controlling the data sources and transmitter in dependence upon the determined bit transmit rates.

A gateway apparatus for enabling communication between an object running within a virtual environment hosted by a virtual environment server and a messaging client. A user can send control messages from a messaging client to objects running within the virtual environment on the virtual environment server. A user within the virtual environment can send messages to other users of a messaging client. The gateway apparatus performs message conversion between the various protocols used by the messaging client and the virtual environment.