Abstract: A global motion vector for a first video frame identifies a shift that, when applied to second video frame, increases the similarity between the two frames. A method comprises: selecting picture elements from the first frame; comparing the selected picture elements with correspondingly positioned picture elements of the second video frame to produce a measure of similarity corresponding to zero shift; comparing, for each of a plurality of trial shifts, the selected picture elements with picture elements of the second video frame that have the same mutual positions but shifted by the respective trial shift, to produce a measure of similarity in respect of that trial shift; identifying the trial or zero shift which gives rise to the highest measure of similarity; and estimating a global motion vector from the identified shift. The selected picture elements are less than 5% of the total number of lines in the frame.

Abstract: Pictures are coded using a coding algorithm with a variable parameter QP so that the quality of the coding varies. First (100), a target value TiMOS is specified for a quality measurement parameter. Then, for each picture (or part of a picture) to be coded, one estimates, independently of the other pictures, a value for the variable parameter QP based on a) the target value for that picture area and b) a masking measure C that depends on the picture content of that picture area. The picture is then coded (112) using the estimated value. The masking measure may be compensated (108, 122) to allow for the effect of the coding quality upon the masking effect.

Abstract: A plurality of video streams is transmitted over a transmission link. At intervals, one determines for each video stream at each of a plurality of encoder settings, having regard to the amount of data buffered at a receiver for that stream, a bit rate sufficient to transmit the remainder of that stream at that encoder setting such as to avoid buffer underflow at the receiver. One determines also a critical point equal to the earliest time at which that bit rate can be reduced while still avoiding buffer underflow at the receiver. An encoder setting is chosen for each video stream such that the sum of said bit rates required for transmission of the streams does not exceed the capacity of the transmission link. Any surplus capacity of the transmission link is allocated to the stream that has the earliest critical point.

Abstract: A video sequence is to be transmitted at a selectable quality from a server over a network. A network control protocol operates in response to a control parameter to allocate to the server a share of available transmission capacity in proportion to the value of the control parameter. First, one determines a plurality of transmission rate values that are needed over successive time periods of the sequence for successful transmission of the sequence at a reference quality; then the control parameter is set, proportional to the transmission rate value and communicated to the control protocol at corresponding time instants. The sequences can then be transmitted, encoded at a quality from time to time selected in dependence upon the actual transmission capacity made available by the network to the server.

Abstract: A sequence to be encoded is divided into a plurality of temporal portions or chunks. The sequence is then analyzed to determine for each chunk, in accordance with a plurality of encoding quality settings, data establishing the relationship between the quality settings and (i) a quality metric for the portion and (ii) the number of bits generated by encoding the portion at that quality setting. Given a target quality, a target bit rate is then set (or vice versa); then one chooses a set of quality settings, one per chunk, that tends to minimize a combined quality cost for the sequence within the constraint that transmission of encoded video at the target bit rate via transmitting and receiving buffers of specified size and initial receiver buffer fullness shall not cause underflow nor overflow.

Abstract: A video signal is coded using predictive coding. The degree of quantization that is applied is varied as a function of measures of predictive power, the idea being that a picture that is useful as a predictor for other pictures is worth coding well. These measures are formed in a pre-analysis of the pictures to obtain, for each macroblock analysed, a measure that depends on its similarity to a region for which it is a potential predictor. Preferably these measures are cumulative.

Abstract: A video encoder using inter-frame differential coding has a store (3) for containing a plurality of reference pictures. For each incoming picture it chooses one (or more) of the stored reference pictures to use. Control means (10) select which locally decoded pictures are to be entered into, and removed from, so that the store always contains at least one relatively older picture that lies within a defined time window and at least one relatively younger picture that is more recent than the time window. When it receives an error message from a receiver, it switches the coder from its normal a state (in which it is allowed to choose any picture as predictor) into a state in which it is permitted to choose only a said relatively older picture for prediction. The beginning of the time window is preferably set according to the estimated (or observed) round trip time between the encoder and decoder such that at least one of the relatively older pictures always predated the error message.

Abstract: Faults resulting in reception of a still, but unknown, frame are recognized by comparing each received frame of the video signal with its predecessor, incrementing a counter in the event that the difference between the frames falls below a threshold; and generating an alarm signal in the event that the count of the counter exceeds a predetermined count. Other types of fault such as loss of signal (i.e. reception of just noise) are recognized by incrementing the counter whenever the difference exceeds a threshold. Similar results may be obtained by instead the monitoring quantization step size and/or number of transmitted bits of a digitally coded signal, and noting that it falls below, or exceeds, a threshold. A preferred option is to compute a complexity measure, being a monotonically increasing function (e.g the product) of the quantization step size and of the number of coded bits and compare this with the threshold value.

Abstract: There is proposed a modification to the ECN protocol to remove the one-to-one relationship between the network signalling congestion and the sender response to that congestion. The result is to allow a receiver terminal to exhibit some control of bandwidth share relative to other receiver terminals. The idea is to calculate the average CE arrival frequency from received data packets and to set ECE flags at a rate determined as a function of the average CE arrival frequency. Preferably, the function is a multiplier applied to the average CE arrival frequency. The effect of averaging the CE arrival frequency as well as application of a multiplier is a decoupling of the ECE marked ACKs sent by a receiver to the sender, and control of the resulting transmission rate at the sender.

Abstract: A data streaming system and method typically use a server arranged to stream one of a plurality of encoded data streams to a client. Each of the plurality of data streams may be an independent representation of a common data source encoded at a different resolution to the other of the plurality of data streams. The server can include a transmitter and a first buffer. The transmitter can be arranged to transmit data packets of the encoded data stream to the client via the first buffer. The transmitter can be arranged to monitor the content of the first buffer and switch to transmit another of the plurality of data streams in the event that predetermined criteria are detected from the first buffer.

Abstract: The present invention concerns the generation of image data, particularly, though not exclusively for motion estimation in the context of video coders employing inter frame differential coding. A method is provided for generating image data using a set of sampled pixels, the sampled pixels being representative of a sampled image, the method including the steps of: (i) at intermediate positions between sampled pixels, interpolating the sampled pixels so as to provide at least one set of interpolated pixels arranged along a plurality of lines, the or each set of interpolated pixels having a respective offset relative to the sampled pixels, and, (ii) storing the or each set of interpolated pixels with a respective address in a memory, the addresses forming an ordered sequence, wherein along a given line, neighbouring interpolated pixels having the same offset are stored with respective addresses that are consecutive to one another in the ordered sequence.

Abstract: There is proposed a modification to the ECN protocol to remove the one-to-one relationship between the network signalling congestion and the sender response to that congestion. The result is to allow a receiver terminal to exhibit some control of bandwidth share relative to other receiver terminals. The idea is to calculate the average CE arrival frequency from received data packets and to set ECE flags at a rate determined as a function of the average CE arrival frequency. Preferably, the function is a multiplier applied to the average CE arrival frequency. The effect of averaging the CE arrival frequency as well as application of a multiplier is a decoupling of the ECE marked ACKs sent by a receiver to the sender, and control of the resulting transmission rate at the sender.

Abstract: A video sequence is to be transmitted at a selectable quality from a server over a network. A network control protocol operates in response to a control parameter to allocate to the server a share of available transmission capacity in proportion to the value of the control parameter. First, one determines a plurality of transmission rate values that are needed over successive time periods of the sequence for successful transmission of the sequence at a reference quality; then the control parameter is set, proportional to the transmission rate value and communicated to the control protocol at corresponding time instants. The sequences can then be transmitted, encoded at a quality from time to time selected in dependence upon the actual transmission capacity made available by the network to the server.

Abstract: A plurality of video streams is transmitted over a transmission link. At intervals, one determines for each video stream at each of a plurality of encoder settings, having regard to the amount of data buffered at a receiver for that stream, a bit rate sufficient to transmit the remainder of that stream at that encoder setting such as to avoid buffer underflow at the receiver. One determines also a critical point equal to the earliest time at which that bit rate can be reduced while still avoiding buffer underflow at the receiver. An encoder setting is chosen for each video stream such that the sum of said bit rates required for transmission of the streams does not exceed the capacity of the transmission link. Any surplus capacity of the transmission link is allocated to the stream that has the earliest critical point.

Abstract: Real-time data (e.g. video) is streamed over packet networks (e.g. the Internet). Streamed video is provided without the start-up delay by transmitting data from a video streamer to the video viewer more rapidly than the video viewer consumes the data and using the excess data to build a buffer at the video viewer. When a suitable sized buffer is built the transmission rate of data to the buffer may be reduced. In order to deliver the best quality material for the available bandwidth, the supply of video data may be switched to a higher bit-rate source when the reservoir is filled. Fluctuations in network throughput may be accommodated during the transmission of data on a fine scale by adjusting the transmission rate of the data and on a coarse scale by switching between data streams encoded at different bit-rates.

Abstract: Pictures are coded using a coding algorithm with a variable parameter QP so that the quality of the coding varies. First (100), a target value TiMOS is specified for a quality measurement parameter. Then, for each picture (or part of a picture) to be coded, one estimates, independently of the other pictures, a value for the variable parameter QP based on a) the target value for that picture area and b) a masking measure C that depends on the picture content of that picture area. The picture is then coded (112) using the estimated value. The masking measure may be compensated (108, 122) to allow for the effect of the coding quality upon the masking effect.

Abstract: A data streaming system and method typically use a server arranged to stream one of a plurality of encoded data streams to a client. Each of the plurality of data streams may be an independent representation of a common data source encoded at a different resolution to the other of the plurality of data streams. The server can include a transmitter and a first buffer. The transmitter can be arranged to transmit data packets of the encoded data stream to the client via the first buffer. The transmitter can be arranged to monitor the content of the first buffer and switch to transmit another of the plurality of data streams in the event that predetermined criteria are detected from the first buffer.

Abstract: A video encoder using inter-frame differential coding has a store (3) for containing a plurality of reference pictures. For each incoming picture it chooses one (or more) of the stored reference pictures to use. Control means (10) select which locally decoded pictures are to be entered into, and removed from, as that the store always contains at least one relatively older picture that lies within a defined time window and it least one relatively younger picture that is more recent than the time window. When it receives an error message from a receiver, it switches the coder from its normal a state (in which it is allowed to choose any picture as predictor) into a state in which it is permitted to choose only a said relatively older picture for prediction. The beginning of the time window is preferably set according to the estimated (or observed) round trip time between the encoder and decoder such that at least tine of the relatively older pictures always predated the error message.

Abstract: In order to measure the rate at which a terminal 2 can receive data from a source 5, 6, 7 the source temporarily increases it transmitting rate. The time taken to receive these higher-rate transmissions is measured at the terminal (or acknowledged by the terminal and measured at the transmitter) and the rate calculated. Inter alia, these measurements can be used for control of layered coding where apparatus for transmitting signals to video or other terminals 2 has coding means 5 for receiving the signals to generate a base signal stream B which is a coarse representation of the signal to be transmitted and at least one higher order stream E1, E2 containing finer detail of the signal not present in any lower order stream. These streams are sent by transmitting means 6 to the terminals, but at least some of the terminals do not receive all of the higher order streams.

Abstract: The present invention concerns the generation of image data, particularly, though not exclusively for motion estimation in the context of video coders employing inter frame differential coding. A method is provided for generating image data using a set of sampled pixels, the sampled pixels being representative of a sampled image, the method including the steps of: (i) at intermediate positions between sampled pixels, interpolating the sampled pixels so as to provide at least one set of interpolated pixels arranged along a plurality of lines, the or each set of interpolated pixels having a respective offset relative to the sampled pixels, and, (ii) storing the or each set of interpolated pixels with a respective address in a memory, the addresses forming an ordered sequence, wherein along a given line, neighbouring interpolated pixels having the same offset are stored with respective addresses that are consecutive to one another in the ordered sequence.