UCB Source Coding Jean Walrand EECS Outline UCB Compression Losless Audio Huffman Lempel Ziv Examples Differential ADPCM SUBBAND CELP Video Discrete Cosine Transform Motion Compensation UCB Goal Compression Reduce the number of bits to encode source Approaches Lossless For data Lossy For voice video UCB Huffman Encoding Lossless Key Idea Use shorter code words for more frequent symbols EX1 UCB Huffman Encoding EX2 continued UCB Huffman Encoding continued If the symbols are independent and identically distributed the Huffman encoding is the prefix free code with the minimum average number of bits Note The Shannon encoding requires fewer bits but requires encoding large blocks of symbols Both codes assume that the distribution is known UCB Lempel Ziv Lossless Symbols are not independent Distribution is not known Want to minimize the average number of bits Typical application any file Approach Build dictionary and replace string with location of prefix in the dictionary UCB Lempel Ziv Example continued UCB Audio Examples Speech PCM ADPCM SBC VSELP CELP 64kbps 32 64kbps 16 32kbps 2 4 8kbps Audio PCM MPEG 1400kbps 48 384kbps UCB Audio c d Differential Encoding also used for Video Key Idea is that differences between successive samples may be small Difficulty Error Propagation UCB Audio c d Differential Encoding c d UCB Audio c d ADPCM Adaptive Differential PCM Predict next value encode error UCB Audio c d Sub Band Coding Improves performance UCB Audio c d CELP Code Excited Linear Predictor Video UCB Discrete Cosine Transform Objective Extract Visible Information f x y m n F m n cos mx cos ny Video UCB cd Motion Compensation Idea Track motion of picture Encode motion vector modification
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