Abstract: Variable-length codes are widely adopted for losslessdata compaction in many digital video applications,e.g., videophone and high definition television (HDTV).However, error propagation is still a major concern forpractical applications. In general, since there are noexplicit word-boundaries in the variable- length codeddata stream, a transmission error will cause thesucceeding codewords to be decoded erroneously. One wayto confine the error propagation is through theperiodic use of synchronizing words that have a specialbit pattern which can be recognized in the coded bitstream as long as there are no errors in the wordsitself. We call such codewords 'clear' codewords. Abasic property of the clear codewords is that theycannot be formed by any concatenation of othercodewords. These clear codewords are useful not onlyfor the detection and confinement of errors but alsofor the multiplexing and demultiplexing of multiplevariable-length coded bit streams. The construction ofefficient variable-length codes with clear codewords isan interesting and important issue for many practicalapplications. In this paper, a systematic method isprovided for the construction of such codes.!13
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