MP3의 총 재생시간을 추출해주는 예제

설명

이 소스의 목적은 MP3파일의 재생시간을 검출하는 것입니다. 간략화 구현한것이라서 조금 검출속도가 느린편입니다.
  1. 파일 열고
  2. 헤더 찾고 (0xffe00000)
  3. 각 정보 추출후 실제 MP3가 사용 가능한 정보인지 구분하고
  4. Frame 수를 누적하여 더한후 적정 Sampling 주파수로 나누어서 초단위 시간을 계산하고
  5. 파일 닫고
  6. 결과 출력하고...

MPEG audio header 를 간략히 정리하면 다음과 같습니다.
/* MPEG audio header 
   Edit by JaeHyuk Cho <mailto@minzkn.com> 
*/ 
    
#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 
/* End of README */


그리고 Bitrate table은 다음을 참조합니다.
/* MPEG audio bitrate table 
   Edit by JaeHyuk Cho <mailto:minzkn@infoeq.com> 
*/ 

#define hint 
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 !) 

#define table 
     [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 

/* End of README */


예제소스




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