MP3 header reader

• Download demo project - 8.72 Kb
• Download source - 13.9 Kb

Introduction

This program reads the first frame of an MP3 file and displays all the header information like, version, layer, bit rate, sampling frequency, etc.

Using the code

This happens to be the simplest thing on this planet! Check out the source code... you need to know about the MPEG header.

    // finding first frame for MPEG 1 LAYER III
    do
    {
        curch=fgetc(fp);
        if(curch==255)
        {
            curch=fgetc(fp);
            if(tolower(curch/16)==15) flag1=1;
        }
    }while(flag1==0);

    // position of first frame header......
    fpos_t filepos;
    char firstframeposition[10];

    fgetpos(fp,&filepos);
    filepos-=2;

    int firstheaderpos=filepos;
    _ltoa(firstheaderpos,firstframeposition,10);
    m_strinfo="First frame found at byte :"; 
    m_strinfo+=firstframeposition;
    m_ctlinfo.AddString(m_strinfo);


    // version check MPEG 1/2...
    int impegversion=tolower(((curch%16)/4)/2);
    if(impegversion==1) m_strinfo="MPEG 1 ";
    if(impegversion==0) m_strinfo="MPEG 2 ";


    // layer check....
    int layer=tolower((((curch%16)/4)%2)*2+(((curch%16)%4)/2));
    CString mpeglayer[4]={"Reserved","Layer III","Layer II","Layer I"};
    m_strinfo+=mpeglayer[layer];
    m_ctlinfo.AddString(m_strinfo);

    if(layer!=1) return 1;

    // CRC check.......
    int protectbit=tolower(((curch%16)%4)%2);
    if(protectbit==1) m_strinfo="CRCs : No";
    else m_strinfo="CRCs : Yes";
    m_ctlinfo.AddString(m_strinfo);


    //get next byte to read 3rd byte of header. 
    curch=fgetc(fp);


    // bitrate info
    int bitratetable[2][16]={0,8,16,24,32,64,80,56,64,128,160,
      112,128,256,320,0,0,32,40,48,56,64,80,96,
      112,128,160,192,224,256,320,0};
    int mp3bitrate=bitratetable[impegversion][tolower(curch/16)];  
    char mp3bps[2];
    _itoa(mp3bitrate,mp3bps,10);
    m_strinfo="Bitrate (kbps) : ";
    m_strinfo+=mp3bps;
    m_ctlinfo.AddString(m_strinfo);


    // frequency info
    long int frequencytable[2][4]={22050,24000,16000,0,44100,48000,32000,0};
    int mp3frequency=frequencytable[impegversion][tolower((curch%16)/4)];
    char mp3fs[10];
    _itoa(mp3frequency,mp3fs,10);
    m_strinfo="Frequency (Hz) : ";
    m_strinfo+=mp3fs;
    m_ctlinfo.AddString(m_strinfo);


    // padding bit
    int paddingbit=tolower(((curch%16)%4)/2);
    if(paddingbit==0) m_strinfo="Padding : No";
    else m_strinfo="Padding : Yes";
    m_ctlinfo.AddString(m_strinfo);


    // private bit
    int privatebit=tolower(((curch%16)%4)%2);
    if(privatebit==0) m_strinfo="Private : No";
    else m_strinfo="Private : Yes";
    m_ctlinfo.AddString(m_strinfo);


    // get next char to read 4th byte of header.
    curch=fgetc(fp);

    //channel mode
    CString channelmode[4]={"Stereo","Joint Stereo",
                             "Dual Channel","Single Channel"};
    int ichannelmode=tolower((curch/16)/4);
    m_ctlinfo.AddString(channelmode[ichannelmode]);


    // mode extension ignored.

    // copyright bit
    int copyrightbit=tolower(((curch%16)/4)/2);
    if(copyrightbit==1) m_strinfo="Copyrighted : Yes";
    else m_strinfo="Copyrighted : No";
    m_ctlinfo.AddString(m_strinfo);


    //original bit
    int originalbit=tolower(((curch%16)/4)%2);
    if(originalbit==1) m_strinfo="Original : Yes";
    else m_strinfo="Original : No";
    m_ctlinfo.AddString(m_strinfo);


    //emphasis
    int emphasis=tolower((curch%16)%4);
    if(emphasis==0) m_strinfo="Emphasis : None";
    if(emphasis==1) m_strinfo="Emphasis : 50/15 ms";
    if(emphasis==3) m_strinfo="Emphasis : CCITT J.17";
    m_ctlinfo.AddString(m_strinfo);



    // all header info over..... calculating frame size.
    int iframesize=(144000*mp3bitrate/mp3frequency)+paddingbit;
    char framesize[5];
    _itoa(iframesize,framesize,10);
    m_strinfo="Framesize : ";
    m_strinfo+=framesize;
    m_ctlinfo.AddString(m_strinfo);


    //no. of frames...
    int iframes=(filesize-firstheaderpos)/iframesize;
    char frames[10];
    _itoa(iframes,frames,10);
    m_strinfo="Frames : ";
    m_strinfo+=frames;
    m_ctlinfo.AddString(m_strinfo);


    //song length...
    int iplaytime=toupper(iframes*26/1000);
    char playtime[5];
    _itoa(iplaytime,playtime,10);
    m_strinfo="Length (in sec) : ";
    m_strinfo+=playtime;
    m_ctlinfo.AddString(m_strinfo);

Points of Interest

I learned about the MP3 file format... And this is my first project that I am uploading to the net.