MP3 længde

Følgende kode tolker header informationen fra en MP3 fil:

#include <conio.h>
#include <string.h>
#include <stdio.h>

#define  bool int

// MP3 file decoding.
unsigned long bithdr;

int getFrameSync()    { return ((bithdr>>21) & 2047); };
int getVersionIndex()  { return ((bithdr>>19) & 3);  };
int getLayerIndex()    { return ((bithdr>>17) & 3);  };
int getProtectionBit() { return ((bithdr>>16) & 1);  };
int getBitrateIndex()  { return ((bithdr>>12) & 15); };
int getFrequencyIndex(){ return ((bithdr>>10) & 3);  };
int getPaddingBit()    { return ((bithdr>> 9) & 1);  };
int getPrivateBit()    { return ((bithdr>> 8) & 1);  };
int getModeIndex()    { return ((bithdr>> 6) & 3);  };
int getModeExtIndex()  { return ((bithdr>> 4) & 3);  };
int getCoprightBit()  { return ((bithdr>> 3) & 1);  };
int getOrginalBit()    { return ((bithdr>> 2) & 1);  };
int getEmphasisIndex() { return ((bithdr    ) & 3);  };

void loadHeader(char c[4]) {
  // Turn the four bytes into a unsigned long.
  bithdr = (unsigned long)( ( (c[0] & 255) << 24) |
                            ( (c[1] & 255) << 16) |
                            ( (c[2] & 255) <<  8) |
                            ( (c[3] & 255)      )
                          );
} // Load header.

bool isValidHeader(void) {
  // Check that valid MP3 header.
  return ( ((getFrameSync()      & 2047)==2047) &&
          ((getVersionIndex()  &    3)!=  1) &&
          ((getLayerIndex()    &    3)!=  0) &&

          // due to lack of support of the .mp3 format
          // no "public" .mp3's should contain information
          // like this anyway... :)
          ((getBitrateIndex()  &  15)!=  0) &&
          ((getBitrateIndex()  &  15)!=  15) &&
          ((getFrequencyIndex() &    3)!=  3) &&
          ((getEmphasisIndex()  &    3)!=  2)    );
} // isValidHeader

// this returns the MPEG version [1.0-2.5]
float getVersion() {
  float table[4] = {
                    2.5, 0.0, 2.0, 1.0
                  };

  // return modified value
  return table[getVersionIndex()];
} // getVersion

// this returns the Layer [1-3]
int getLayer() {
  return ( 4 - getLayerIndex() );
} // getLayer

int getBitrate() {
  const int table[2][3][16] = {
            {        //MPEG 2 & 2.5
              {0,  8, 16, 24, 32, 40, 48, 56, 64, 80, 96,112,128,144,160,0}, //Layer III
              {0,  8, 16, 24, 32, 40, 48, 56, 64, 80, 96,112,128,144,160,0}, //Layer II
              {0, 32, 48, 56, 64, 80, 96,112,128,144,160,176,192,224,256,0}  //Layer I
            },{      //MPEG 1
              {0, 32, 40, 48, 56, 64, 80, 96,112,128,160,192,224,256,320,0}, //Layer III
              {0, 32, 48, 56, 64, 80, 96,112,128,160,192,224,256,320,384,0}, //Layer II
              {0, 32, 64, 96,128,160,192,224,256,288,320,352,384,416,448,0}  //Layer I
            }
          };

  // the bitrate is not only dependent of the bitrate index,
  // the bitrate also varies with the MPEG version and Layer version
  return table[(getVersionIndex() & 1)][(getLayerIndex() -1)][getBitrateIndex()];
} // getBitrate

unsigned int getFrequency() {
  unsigned int table[4][3] = {
                              {32000, 16000,  8000}, //MPEG 2.5
                              {    0,    0,    0}, //reserved
                              {22050, 24000, 16000}, //MPEG 2
                              {44100, 48000, 32000}  //MPEG 1
                            };
  // the frequency is not only dependent of the bitrate index,
  // the bitrate also varies with the MPEG version
  return table[getVersionIndex()][getFrequencyIndex()];
} // getFrequency

char *getMode(void) {
  switch(getModeIndex()) {
    case 1: return "Joint Stereo";
    case 2: return "Dual Channel";
    case 3: return "Single Channel";
  }
  return "Stereo";
} // getMode

int main(int argc, char *argv[])
{
  FILE *mp3File;
  char  mp3Hdr[4];

  if (argc < 2
  || (mp3File = fopen(argv[1], "rb"))          == NULL
  ||  fread(mp3Hdr, sizeof(mp3Hdr), 1, mp3File) != 1)
  {
    cprintf("Too few arguments (%d), non-existing or invalid file.(%s)\r\n",
            argc, argv[1]);
    return -1;
  };

  // Check if valid MP3 file.
  loadHeader(mp3Hdr);
  if (!isValidHeader())
  {
    cprintf("Header for %s not valid.\r\n", argv[1]);
    return -1;
  }

  // Then display all information about the MP3 file.
  cprintf("MP3 information for \'%s\':\r\n", argv[1]);
  cprintf("=====================%.*s==\r\n", strlen(argv[1]),
          "==============================");

  cprintf("Version    : %1.1f\r\n", getVersion());
  cprintf("Layer      : %d\r\n", getLayer());

  cprintf("Bit-rate  : %u\r\n", getBitrate());
  cprintf("Frequency  : %u\r\n", getFrequency());

  cprintf("Mode      : %s\r\n", getMode());

  return 0;
} // Main

Emnet er behandlet før under http://www.eksperten.dk/spm/18465

Finder programmet også længden (tiden) af MP3 filen?

spiritusanta >> Nej, men den må enten stå i filen, eller kunne beregnes - prøv at søge på google under "MP3 header information" - der er masser af links.

tror bare jeg lukker det her nu og forsøger at få svar,  når jeg får lidt mere tid til at programmere :)

Men ellers tak for hjælpen soepro... du får lidt point her for dit arbejde :)