VARIABLE LENGTH DECODER FOR DECODING DIGITALLY ENCODED VIDEO SIGNALS

摘要

A variable length decoder (VLD) (104) for decoding MPEG-1 and -2 syntax compliant video bit streams. The VLD (104) includes a micro-sequencer (134) and VLD command decode/execution unit (136) for controlling the MPEG decoding process using a novel instruction set (214a, 214g). The instruction set (214a-214g) includes a set of commands for decoding the video data and a set of flow control instructions. A rotator/barrel shifter (158) is provided for making a predetermined number of encoded bits from the video bit stream available to the VLD (104) and a variable length table decoder (186) for variable length decoding using the MPEG standard variable length code (VLC) tables. The variable length table decoder (186) shares a prefix pattern matching scheme across all of the VLC tables and organizes the variable length codes into a series of subtables. Each subtable corresponds to one of the unique prefix patterns. Variable length codes are decoded by identifying a leading pattern in the video data bit stream and, in parallel, accessing the subtable corresponding to that leading pattern. Run-length and amplitude level DCT coefficient symbols are stored in compressed form, and decoded as needed by an inverse transform unit (208). Motion vectors are also stored until needed by a motion compensation unit (212).