Abstract: A video stream is digitally encoded such that the rate at which individual segments of data are encoded varies according to the amount of data required to generate each segment. Frames are selectively omitted from transmission (32) such that the cumulative frame rate does not fall below a predetermined value. This process can be used to ensure that the next frame to be displayed is always available in the buffer store 6 associated with the decoder (2). The decoder (2) is arranged to identify where frames have been omitted from the decoded transmission, and to perform a resynchronisation (7) on the decoded stream by comparison between time stamps in the video stream and a corresponding audio stream. Resynchronisation may be performed by extending the durations of individual frames, or by repeating frames.

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: Recorded material such as video is transmitted in compressed form to a receiver, which has a buffer for smoothing differences between the data rate received and that consumed by a decoder that follows. The whole of the recording is analysed to determine a point at which to commence playing such that no buffer underflow can occur; the decoder commences playing only when this point has been reached.

Abstract: Data for presentation in real time, such as a video or audio sequence, is available on different encoded versions having different degrees Of compression. In order to assess, during transmission of one version, the feasibility of switching to another version, given the data rate known to be available at the time, a server computes, for a candidate version, in respect of at least one portion thereof that has not yet been sent, the maximum value of a timing error that would occur if any number of portions starting with that portion to be sent at the available rate. The selection of the same or a different version for continuing transmission is taken in dependence on a comparison between the computed error and the current state of a receiving buffer. Error values may be computed in advance for a range of transmitting rates, stored and later retrieved for use in estimating an error value corresponding to the actual transmitting rate.

Abstract: Faults resulting in reception of a still, but unknown, frame are recognised 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 recognised by incrementing the counter whenever the difference exceeds a threshold. Similar results may be obtained by instead the monitoring quantisation 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 quantisation step size and of the number of coded bits and compare this with the threshold value.

Abstract: A video sequence (4) is subjected to a signal compression process, in which the video sequence is divided (14) into a plurality of segments such that in each segment the number of bits required to code each frame in uncompressed form falls within a range having a predetermined magnitude, and a quantisation level is selected (17) for the encoding (19) of each segment such that the overall bit rate of the segment corresponds to a predetermined value. This value may be pre-set, or may be set in response to an input from the transmission network (3) or remote decoder (2). The quantisation level Q is determined according to a function of the number of bits per frame R, determined by analysis (10,11,12,13) of the entire sequence prior to transmission.

Abstract: A video stream is digitally encoded such that the rate at which individual segments of data are encoded varies according to the amount of data required to generate each segment. Frames are selectively omitted from transmission (32) such that the cumulative frame rate does not fall below a predetermined value. This process can be used to ensure that the next frame to be displayed is always available in the buffer store 6 associated with the decoder (2). The decoder (2) is arranged to identify where frames have been omitted from the decoded transmission, and to perform a resynchronisation (7) on the decoded stream by comparison between time stamps in the video stream and a corresponding audio stream. Resynchronisation may be performed by extending the durations of individual frames, or by repeating frames.

Abstract: Recorded material such as video is transmitted in compressed form to a receiver, which has a buffer for smoothing differences between the data rate received and that consumed by a decoder that follows. The whole of the recording is analysed to determine a point at which to commence playing such that no buffer underflow can occur; the decoder commences playing only when this point has been reached.

Abstract: Data for presentation in real time, such as a video or audio sequence, is available on different encoded versions having different degrees of compression. In order to assess, during transmission of one version, the feasibility of switching to another version, given the data rate known to be available at the time, a server computes, for a candidate version, in respect of at least one portion thereof that has not yet been sent, the maximum value of a timing error that would occur if any number of portions starting with that portion to be sent at the available rate. The selection of the same or a different version for continuing transmission is taken in dependence on a comparison between the computed error and the current state of a receiving buffer. Error values may be computed in advance for a range of transmitting rates, stored and later retrieved for use in estimating an error value corresponding to the actual transmitting rate.

Abstract: A method of decoding encoded video data, the encoded video data being arranged as a plurality of video picture segments, the data of the video picture segments being arranged so that all header data for the segment are transmitted together and all motion vector data for the segment are transmitted together, the header data and motion vector data being separated by markers, the method comprising: receiving encoded video data; attempting to decode header information of an encoded video segment; when an attempt to decode all of the header information of an encoded video segment is unsuccessful, attempting to decode the motion vectors for the encoded video segment and, when the motion vectors for the encoded video segment have been successfully decoded, using the motion vectors with any successfully decoded header information.

Abstract: A method of video processing comprising: receiving (110) video data; dividing the received video data in segments and encoding the video data of a segment. A field is inserted to indicate the size of the encoded video segment. The video data is decoded by identifying the start of an encoded video segment and decoding the associated data. When an attempt to identify the start of an encoded video segment is unsuccessful, a field indicating the size of the encoded video segment is examined and a search carried out for the start of an encoded video segment in the portion of the bit stream indicated by the examined field. When the start of a video segment is identified, the remaining video data of the encoded video segment is then decoded.