A bitstream decoding apparatus for decoding a video signal compressed according to the Moving Picture Experts Group (MPEG) standard within a single clock cycle to convert the compressed video signal into the form of symbols such as video parameters and discrete cosine transform (DCT) coefficients. The bitstream decoding apparatus for performing the decoding operation within a single clock cycle includes a shifter, a variable length decoder, a fixed length decoder, a zero-run & AC decoder, a first multiplexer, a second multiplexer, and a first comparator. In the bitstream decoding apparatus, the compressed video data can be decoded within a single clock cycle to perform transmission of a high-resolution picture signal such as that used in a digital television in an efficient way.

Data compression apparatus in which input data is compressed according to a target output data quantity using a stage of data quantization, the apparatus comprises: one or more trial quantizers for selecting a degree of quantization so that the target output data quantity is not exceeded; a data selector for selecting a subset of the current data to be quantized; a data store for storing the subset of data; a backsearch quantizer and dequantizer for sequentially quantizing and dequantizing the subset of data at a plurality of degrees of quantization including the degree of quantization selected by the trial quantizer(s) and one or more harsher degrees of quantization; a comparator for comparing data quantized and dequantized by the backsearch quantizer with the stored subset of data, to detect errors introduced by the quantization and dequantization by the backsearch quantizer; and a quantization selector for selecting a final degree of quantization for use in compression of the current data, the final degree of quantization being that degree detected by the comparator to introduce the fewest errors during quantization and dequantization of the subset of data by the backsearch quantizer.

When a segment of a compressively coded stream of moving-picture data is rendered unusable by an error, usable decoded data are discarded in a range adjacent to the unusable segment, to avoid picture defects that might result from the use of incorrectly decoded data. The discarding range may extend from one end or from both ends of the unusable segment. When the data are coded in two or more different modes, two or more corresponding ranges of different lengths may be set.

Image data compression apparatus in which data is encoded using a variable degree of quantization selected for areas of an image so that the quantity of encoded data for each area does not exceed a predetermined maximum quantity of data comprises two or more trial encoders operable in parallel to trial encode image data using respective predetermined trial degrees of quantization; a selector for selecting one of the predetermined trial degrees of quantization in response to the quantities of data produced during the trial quantizations; and one or more further trial encoders operable to trial encode image data using degrees of quantization derived from the degree of quantization selected by the selector.

Provided is a method, system, program, and data structure for decompressing a compressed data stream whose decoded output comprises lines of two-dimensional data or other data whose decoding depends upon previously decoded data and where the desired output is only part of sequentially decoded output. Received are a compressed data set, at least one pointer to a location in the compressed data stream whose decoded output comprises a location on a line of data, and decoding information for each received pointer that enables decoding from a point within the compressed data stream addressed by the pointer. For each received pointer, the following steps are performed: (i) accessing the location in the compressed data stream addressed by the pointer in the reentry data set; and (ii) using the decoding information in the reentry data set to decode compressed data from the accessed location.