Abstract: Video data compression apparatus in which successive groups of two or more images are encoded subject to a predetermined limit on the quantity of output encoded data to be generated for each group of images, comprises a trial encoder for encoding at least a subset of images of a current group of images to generate trial-encoded data for each trial-encoded image; a data quantity allocator, responsive to the quantities of trial-encoded data generated by the trial encoder, for allocating respective quantities of output encoded data for each image in the group of images; and a final encoder for encoding each image of the group of images in accordance with the quantities of output encoded data allocated to that image by the data quantity allocator.

Abstract: Video data compression apparatus in which successive groups of two or more images are encoded subject to a predetermined limit on the quantity of output encoded data to be generated for each group of images, comprises a trial encoder for encoding at least a subset of images of a current group of images to generate trial-encoded data for each trial-encoded image; a data quantity allocator, responsive to the quantities of trial-encoded data generated by the trial encoder, for allocating respective quantities of output encoded data for each image in the group of images; and a final encoder for encoding each image of the group of images in accordance with the quantities of output encoded data allocated to that image by the data quantity allocator.

Abstract: A video signal processor interpolating lines in a vertical filter (24) in dependence on whether the lines are of a 625 line frame or a 525 line frame. The interpolated lines are filtered in a horizontal filter (26). The resultant lines are vertically and horizontally decimated by controlling the writing of the lines into a FIFO (28). A reduced size image is produced which has the same number of lines and pixels per line for both 525 and 625 line frames. The reduced size image is data compressed in a JPEG codec (50). The compression factor for a 525/60 signal is 6/5 of that for a 625/50 signal so the data rate per unit time is the same for both signals.

Abstract: NTSC signals have a frame rate of 29.97 frames per second. In SDI, audio data is sampled at a rate 30n where n is an integer, e.g. 48K samples per second. Thus there are 1601.6 samples per frame. Although there are an integer number 8008 samples per five frame sequence, two frames have 1601 samples and 3 frames have 1602 samples. This creates a variable storage requirements from frame to frame and causes problems in editing. The SDI audio data is separated from associated video and decimated by a factor h, where h=4 for example in a signal processor 2, 3, 4, 5 and 6. The decimated data is written into a FIFO circuit at the rate 30n/h synchronously with frame timing under the control of a frame reference generator 10, 9. A fixed integer number n/h of samples is written into the FIFO 7 in each frame under the control of a write control circuit 8. n/h=400 for example, where n=1600 and h=4. Any additional sample in each frame is dropped. The 400 sample frames are stored on a disc 14.

Abstract: Data buffering apparatus comprises a data memory in which input data are written to the memory in contiguous groups at memory addresses defined by a write pointer and data are read from the memory at a memory address defined by a read pointer; and means for writing a dummy group of data at the end of at least some of the input data groups, the dummy groups of data being read from the memory and discarded before a subsequently written input data group is read.

Abstract: Video data compression apparatus in which successive groups of two or more images are encoded subject to a predetermined limit on the quantity of output encoded data to be generated for each group of images, comprises a trial encoder for encoding at least a subset of images of a current group of images to generate trial-encoded data for each trial-encoded image; a data quantity allocator, responsive to the quantities of trial-encoded data generated by the trial encoder, for allocating respective quantities of output encoded data for each image in the group of images; and a final encoder for encoding each image of the group of images in accordance with the quantities of output encoded data allocated to that image by the data quantity allocator.

Abstract: An apparatus for recording video data with a multi-level arrangement of error correction coding. Input video data is demultiplexed so as to form a plurality of data streams each having a plurality of data blocks. A stream error correcting code is generated for each of the plurality of data streams, which is adaptable to allow correction of a data block. The respective data blocks and stream error correcting code of each data stream is distributed or arranged in a predetermined manner. The distributed data blocks and stream error correcting code of each data stream are recorded on recording tracks of a recording medium by n recording heads such that only either a data block or a stream error correcting code of a respective data stream is recorded at corresponding positions along n adjacent recording tracks of the recording medium.

Abstract: Video data compression apparatus in which successive images are encoded, comprises a data quantity allocator for allocating respective quantities of output encoded data for two or more complementary areas of each image; and an encoder for encoding each area of each image of the group of images in accordance with the quantity of output encoded data allocated to that area.

Abstract: Digital audio data occurs in groups of data samples spaced apart in time. The data rate in the groups is much greater than the audio data sampling rate. The audio data may be embedded in the horizontal blanking interval of a video signal as in SDI. The audio data is extracted (2) from the video signal and the samples stored in a FIFO (3). The FIFO (3) removes the spacing between the groups of samples. Sets of the samples are weighted and summed in a multiplier (4) and accumulator (5). Each set to be weighted and summed is displaced by a preset number of samples relative to the previous set to decimate the audio data.

Abstract: A data compression system decorrelates input data into sets of frequency component data. Different sets of frequency component data are entropy encoded using different coding tables matched to the data values characteristic of the sets of frequency component data they are used to compress. Matching the coding tables to the sets of frequency component data improves compression. The order in which the data values from within each set of frequency component data is fed to the entropy encoder is varied to exploit any intra-set correlation.

Abstract: A data compression apparatus is described which applies a dynamically variable degree of quantisation Q.sub.s to input data so as to control blocks of output data to have a predetermined maximum size. The dynamic control can be carried out on an inter-block basis or an intra-block basis. An overflow detector is provided for inserting an overflow indicator within blocks of compressed data to indicate when overflow has occurred.