WMA(WindowsMediaAudio)解码器详解_wma解码

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WMA Version 7.0

An Overview of Windows Media Audio

Decoding

MICROSOFT CONFIDENTIAL

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WMA VERSION 7.0
Table of Contents
  WMA VERSION 7.0..............................................................................................................................................I
 AN OVERVIEW OF WINDOWS MEDIA AUDIO DECODING.......................................................................I
 TABLE OF TABLES...........................................................................................................................................IV
 TABLE OF FIGURES..........................................................................................................................................V
 AUDIENCE AND DISCLAIMER......................................................................................................................VI
 SUMMARY..........................................................................................................................................................VI
INTRODUCTION...............................................................................................................................................1
1  NOTATION.......................................................................................................................................................3
1.1  Arithmetic Operators................................................................................................................................3
1.2  Logical operators.....................................................................................................................................4
1.3  Relational operators.................................................................................................................................4
1.4  Bitwise operators.....................................................................................................................................4
1.5  Assignment...............................................................................................................................................4
1.6  Mnemonics...............................................................................................................................................4
1.7  Constants.................................................................................................................................................5
1.8  How to Read the Bitstream Syntax?..........................................................................................................5
BITSTREAM SYNTAX/DECODE PROCESS..................................................................................................7
1  OVERALL DECODE PROCESS............................................................................................................................7
2  PACKET LAYER DECODER...............................................................................................................................8
3  FRAME LAYER DECODER.................................................................................................................................9
3.1  Subframe Header.....................................................................................................................................9
3.2  Subframe Coefficient (Run-Level) Decoding............................................................................................13
4  PARAMETER DEFINITIONS..............................................................................................................................13
DECODER INITIALIZATION........................................................................................................................15
1  SAMPLES PER FRAME....................................................................................................................................15
2  CUTOFF FREQUENCIES...................................................................................................................................16
3  WEIGHTING MODE........................................................................................................................................16
4  ALLOW SUPER AND/OR SUB FRAMES.............................................................................................................16
5  MAXIMUM NUMBER OF SUBFRAMES IN A FRAME...........................................................................................16
6  BITS PER SAMPLE..........................................................................................................................................17
7  BITS TO INDICATE FRAME SIZE.......................................................................................................................17
8  DITHERING LEVEL.........................................................................................................................................17
9  PARAMETERS FOR NOISE SUBSTITUTION........................................................................................................17
PACKET LAYER DECODING.......................................................................................................................20
FRAME LAYER DECODING.........................................................................................................................21
1  SUBFRAME HEADER DECODING.....................................................................................................................21
1.1  Bark Band Computation.........................................................................................................................21
1.2  Noise Substitution Header......................................................................................................................23
1.3  Decoding LPC Header...........................................................................................................................24
1.4  Maximum Level Size, if Escape Code is Used..........................................................................................25
MICROSOFT CONFIDENTIAL – INTERNAL USE ONLY
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WMA VERSION 7.0
2  RUN-LEVEL (ENTROPY) DECODER.................................................................................................................25
3  INVERSE QUANTIZER & NOISE SUBSTITUTION................................................................................................27
3.1  An Implementation of qrand().................................................................................................................28
4  QUANTIZATION NOISE SHAPING (WEIGHTING FACTORS)................................................................................29
4.1  Computing Un-normalized Weights from Mask Information....................................................................29
4.2  Computing Un-normalized Weights from LPC Parameters......................................................................30
4.3  Normalizing Weights..............................................................................................................................30
4.4  Applying Weight Factors........................................................................................................................31
4.5  Reducing the Overhead of Weighting Factors..........................................................................................31
5  MULTI-CHANNEL TRANSFORMATION.............................................................................................................32
6  INVERSE MODULATED LAPPED TRANSFORM..................................................................................................33
6.1  DCT-IV..................................................................................................................................................33
6.2  Window Function Generation.................................................................................................................34
6.3  Obtaining Reconstruction Values............................................................................................................36
7  AFTER DECODING A SUBFRAME....................................................................................................................37
INTERFACING WITH APPLICATIONS (INFORMATIVE).......................................................................38
1  SOFTWARE API FOR MICROSOFT’S WMA DECODER......................................................................................40
TABLES.............................................................................................................................................................54
1  CONSTANTS...................................................................................................................................................54
2  BARK FREQUENCIES......................................................................................................................................54
3  LSF RECONSTRUCTION VALUES....................................................................................................................55
4  RUN-LEVEL VARIABLE LENGTH CODING (HUFFMAN)TABLES........................................................................56
4.1  Group Huffman-RLC-44Q......................................................................................................................56
4.2  Group Huffman-RLC-44O......................................................................................................................69
4.3  Group Huffman-RLC-16.........................................................................................................................93
5  MASK VARIABLE LENGTH CODING (HUFFMAN) TABLE................................................................................103
6  NOISE POWER VARIABLE LENGTH CODING (HUFFMAN) TABLE....................................................................105
PARAMETER RESTRICTIONS ON LEGAL WMA BITSTREAMS & COMPLIANT WMA DECODERS
..............................................................................................................................................................................106
1  LEGAL WMA VERSION 7 BITSTREAMS........................................................................................................106
2  MAXIMUM BUFFER SIZE REQUIREMENTS......................................................................................................106
2.1  max_push_buffer_size...........................................................................................................................106
2.2  max_pull_buffer size.............................................................................................................................107
3  COMPLIANT WMA VERSION 7 DECODERS...................................................................................................107
3.1  Measuring Compliance of Decoders.....................................................................................................107
GLOSSARY.........................................................................................................................................................1
MICROSOFT CONFIDENTIAL
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WMA VERSION 7.0
TABLE OF TABLES
Table 1 Conditionals & loops in the syntax description.........................................................................5
Table 2 Array notation........................................................................................................................... 6
Table 3 Syntax of decode_packet_layer().............................................................................................8
Table 4 Syntax of decode_packet()....................................................................................................... 8
Table 5 Syntax of decode_packet_header().......................................................................................... 8
Table 6 Syntax of decode_subframe_layer().........................................................................................9
Table 7 Syntax of decode_subframe ()..................................................................................................9
Table 8 Syntax of decode_subframe_header().....................................................................................9
Table 9 Syntax for decode_frame_header_bark()...............................................................................10
Table 10 Syntax for decode_frame_header_lpc()...............................................................................11
Table 11 Syntax for decode_frame_header_noisesub()......................................................................12
Table 12 Syntax of decode_runlevel().................................................................................................13
Table 13 Windows Media Audio Decoder API.....................................................................................40
Table 14 Constants used by the decoder............................................................................................54
Table 15 Bark Frequencies.................................................................................................................54
Table 16 LSF Reconstruciton Values.................................................................................................. 55
Table 17 Huffman-RLC-44Q-Mono.....................................................................................................56
Table 18 Huffman-RLC-44Q-Diff.........................................................................................................63
Table 19 Huffman-RLC-44O-Mono.....................................................................................................69
Table 20 Huffman-RLC-44O-Diff.........................................................................................................81
Table 21 Huffman-RLC-16-Mono........................................................................................................ 93
Table 22 Huffman-RLC-16-Diff............................................................................................................ 98
Table 23 Huffman Table for Mask Information..................................................................................103
Table 24 Huffman Table for Noise Power Information.......................................................................105
Table 25 Parameter limitations of WMA 7.0 legal bit streams...........................................................106
Table 26 Modes of Microsoft's WMA Version 7 Encoder.......................................................................1
MICROSOFT CONFIDENTIAL
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