Abstract: Delivery of recorded audio or video material over a telecommunications link from a server is accomplished by dividing the material into a sequence of sub-files each of which is independently requested by the terminal, which thereby has control of the rate of delivery. Provision may be made for switching between alternative sub-file sets representing alternative delivery modes or data rates.

Abstract: A system for transmitting audio signals over a telecommunications link generates the signals as two or more alternative feeds, for example at different data rates. The two feeds are encoded using coding methods having a frame structure with different frame lengths. To facilitate switching between the two, the input signal is notionally divided into temporal portions and each is coded by taking it, plus enough of the next (or preceding) portion to make up a whole number of frames, and encoding it, whereby the encoded portions overlap—at least for one of the feeds. The overlap is lost upon decoding by discarding duplicate material.

Abstract: Delivery of recorded audio or video material over a telecommunications link 2 from a server 1 to a terminal 3 is accomplished by dividing the material into a sequence of sub-files each of which is independently requested by the terminal, which thereby has control of the rate of delivery. Provision may be made for switching between alternative sub-file sets representing alternative delivery modes or data rates.

Abstract: A system for transmitting audio signals over a telecommunications link generates the signals as two or more alternative feeds, for example at different data rates. The two feeds are encoded using coding methods having a frame structure with different frame lengths. To facilitate switching between the two, the input signal is notionally divided into temporal portions and each is coded by taking it, plus enough of the next (or preceding) portion to make up a whole number of frames, and encoding it, whereby the encoded portions overlap—at least for one of the feeds. The overlap is lost upon decoding by discarding duplicate material.

Abstract: The current frame of the picture is compared block-by-block with the previous frame to identify changed picture elements (pixels). The resulting matrix is matched ("vector quantized") to one of a set of standard matrices ("VQ shapes"). Only those pixels flagged by the selected VQ shape are transmitted plus a "VQ shape code". This technique is modified in that the current frame is also compared with a "background" frame stored at the transmitter and at the receiver. Where, for any block, all the pixels flagged by the VQ shape are indicated by the second comparison as being the same as the background, the pixels are not sent--instead a shape code plus a "copy background" instruction is transmitted.

Abstract: The present invention relates to signal coding, and particularly, though not exclusively, to coding of video signals, especially using conditional replenishment coding, where information is transmitted only in respect of elements of a frame of the picture which have changed relative to the previous frame; the transmitted data being used at a receiver to update a stored version of the picture. According to one aspect of the present invention there is provided a method of coding a set of values comprising selecting that one of a plurality of possible sequences of the values which has the highest correlation between successive values in the sequence, and supplying representations of those values to an output; wherein some of the representations are the differences between the relevant value and a prediction based on at least the immediately preceding value in the selected sequence. Although the method is applicable to other forms of signal, it finds particular application in video coding.

Abstract: A two dimensional pattern such as a movement matrix generated in an inter-frame video coder is classified by forming a weighted sum modulo x of a set of values representing the pattern. The values may be pattern element values, or quantised representations of groups of elements. The weighted sum is used to access a look-up table containing class identification words. Optionally, motion vectors may be generated by comparing class identification words derived from successive frames of a picture.