Abstract: A signal processing method and apparatus are described for demultiplexing selected components (especially audio signals) from a multiplexed data stream. Each of the desired channel components has a unique identification code detected by a processor parsing the contents of a received data buffer between the disc reader and the demultiplexer. The demultiplexer is set up to output received data channel streams having a specific identification code different from any of those assigned to the channel streams originally. Prior to demultiplexing, the identification code for a desired one of the channel streams is altered by the processor to the specific identification code as it passes through the buffer in order to avoid re-setting the demultiplexer.

Abstract: A method and apparatus are provided for encoding of digital video signals in the form of video clips (A,B) to enable them to be seamlessly joined without requiring reset of a decoder to a starting state. The system uses an encoder having a coding stage and an encoder buffer, and comprises successively encoding the pictures of a clip according to a predetermined coding scheme (suitably according to MPEG standards), reading the encoded pictures into the buffer, and subsequently reading the encoded clip out of the buffer at a substantially constant bit rate. To enable simple joining of the clips, a predetermined encoder buffer occupancy (B.sub.ic) is specified with a controllably varied target number of bits being used to encode a picture. The targeting produces an encoder buffer occupancy substantially equal to the predetermined buffer occupancy (B.sub.ic) at the moment the last picture of the segment has been read into the buffer.

Abstract: A system is provided for encoding clips of video data for multiplexing into a system level stream with associated audio and control data. By deriving a relationship between encoder and decoder buffer occupancy levels, and taking into account buffer fill rate, the multiplexer targets a starting occupancy for the video system layer buffer (the MPEG STD) at that for the decoders video buffer (the MPEG VBV). With knowledge of fill rate, the decoder buffer need only be filled to a predetermined level prior to reading out clips for decoding, rather than filling the buffer completely, and seamless joining of video clips can then be simply achieved. The technique has particular application to interactive multimedia systems where continuous display is required.

Abstract: A method is provided for encoding of digital video signal segments which are interleaved to form a single system stream (video STD plus audio STD). In order to enable seamless joining of the segments, control of the video system layer buffer loading is related to the loading of the video layer buffer (VBV occupancy). Starting from an idealised match at the point the first picture is to be read out of the decoder buffer, the point at which the first picture is to be read out of the system layer buffer is adjusted by an amount determined by the predicted duration of the segment and the point at which the last frame of the segment is due to be read out. The adjustment prevents possible overlap of segment timing values derived initially from the idealised match case. The technique has particular application to interactive multimedia applications where real time splicing of video clips is required with minimal visual discontinuity.

Abstract: An audio signal editing method and apparatus for use with original sound data which is already compressed and encoded in predictive form, for example ADPCM. To edit a desired portion from the original audio data, the method and apparatus reconstruct (encoded PCM) audio data from the original (ADPCM) audio data and encode a non-predictive unit to replace a first original audio data unit of the desired portion. Thus, the desired portion is rendered independent of preceding sample values, without having to be recoded entirely. An enhanced method and apparatus encode further replacement units to eliminate noise introduced by the basic method.