MPEG Audio Frame Header 간략정리

시작하기전에

우리가 쉽게 접할수 있는 MP3파일에 대한 Frame Header구조를 간단명료하게 정리하였습니다.

MPEG Audio Frame Header 구조

#define Frame header preview  
  32bit big endian - AAAAAAAA AAABBCCD EEEEFFGH IIJJKLMM 

#define Frame header bit index
  A[31..21] : Frame sync
  B[20..19] : MPEG audio version indentification
  C[18..17] : Layer description
  D[16]     : Protection bit
  E[15..12] : Bitrate index
  F[11..10] : Sampling rate frequency index
  G[9]      : Padding bit
  H[8]      : Private bit
  I[7..6]   : Channel mode
  J[5..4]   : Mode extension
  K[3]      : Copyright 
  L[2]      : Original
  M[1..0]   : Emphasis

#define Frame header description
    A: 11bit - Frame sync (All bit '1')
               '11111111 111'
    B:  2bit - MPEG audio version identification
               '00': MPEG version 2.5
	       '01': Reserved
	       '10': MPEG version 2.0 (ISO/IEC 13818-3)
	       '11': MPEG version 1.0 (ISO/IEC 11172-3)
    C:  2bit - Layer description
               '00': Reserved
	       '01': Layer III
	       '10': Layer II
	       '11': Layer I
    D:  1bit - Protection bit
               '0': Protected by CRC (16bit crc follow header)
	       '1': Not protected
    E:  4bit - Bitrate index
               See also mpeg_audio_bitrate.txt
    F:  2bit - Sampling rate frequency index
               MPEG version 1.0
                 '00': 44100
		 '01': 48000
		 '10': 32000
		 '11': Reserved
               MPEG version 2.0
                 '00': 22050
		 '01': 24000
		 '10': 16000
		 '11': Reserved
               MPEG version 2.5
                 '00': 11025
		 '01': 12000
		 '10': 8000
		 '11': Reserved
    G:  1bit - Padding bit
               '0': Frame is not padded
	       '1': Frame is padded with one extra slot 
	       Layer I frame size
	         ((12000 * Bitrate / Samplerate) + Padding) * 4
	       Layer II/III frame size
	         (144000 * Bitrate / Samplerate) + Padding
    H:  1bit - Private bit
    I:  2bit - Channel mode
               '00': Stereo
	       '01': Joint stereo (Stereo)
	       '10': Dual channel (Stereo)
	       '11': Single channel (Mono)
    J:  2bit - Mode extension (Only if joint stereo)
               Layer I/II
                 '00': Bands 4 to 31
		 '01': Bands 8 to 31
		 '10': Bands 12 to 31
		 '11': Bands 16 to 31
               Layer III
	         '00': Intensity stereo off, MS stereo off
	         '01': Intensity stereo on , MS stereo off
	         '10': Intensity stereo off, MS stereo on
	         '11': Intensity stereo on , MS stereo on
    K:  1bit - Copyright
               '0': Audio is not copyrighted
	       '1': Audio is copyrighted
    L:  1bit - Original
               '0': Copy of original media
	       '1': Original media
    M:  2bit - Emphasis
               '00': None
	       '01': 50/15ms
	       '10': Reserved
	       '11': CCIT J.17




각 MPEG version 및 Layer에 따른 Bitrate 참조 table

A: MPEG version 1.0, Layer I 
B: V1,Layer II 
C: V1,Layer III 
D: V2,Layer I 
E: V2, L2 & L3 
-: Free format
x: Not use (Invalid bitrate !)

     [A] [B] [C] [D] [E]
0000   -   -   -   -   - 
0001  32  32  32  32   8 
0010  64  48  40  48  16 
0011  96  56  48  56  24 
0100 128  64  56  64  32 
0101 160  80  64  80  40 
0110 192  96  80  96  48 
0111 224 112  96 112  56 
1000 256 128 112 128  64 
1001 288 160 128 144  80 
1010 320 192 160 160  96 
1011 352 224 192 176 112 
1100 384 256 224 192 128 
1101 416 320 256 224 144 
1110 448 384 320 256 160 
1111   x   x   x   x   x



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