How do I get the BitRate Mode from an MP3 in C #?

The following class implements a good Helper to retrieve various information from a header of an MP3 file:

class MP3Header
{
    // Public variables for storing the information about the MP3
    public int intBitRate;
    public string strFileName;
    public long lngFileSize;
    public int intFrequency;
    public string strMode;
    public int intLength;
    public string strLengthFormatted;

    // Private variables used in the process of reading in the MP3 files
    private ulong bithdr;
    private bool boolVBitRate;
    private int intVFrames;

    public bool ReadMP3Information(string FileName)
    {
        FileStream fs = new FileStream(FileName, FileMode.Open, FileAccess.Read);
        // Set the filename not including the path information
        strFileName = @fs.Name;
        char[] chrSeparators = new char[] { '\', '/' };
        string[] strSeparator = strFileName.Split(chrSeparators);
        int intUpper = strSeparator.GetUpperBound(0);
        strFileName = strSeparator[intUpper];

        // Replace ' with '' for the SQL INSERT statement
        strFileName = strFileName.Replace("'", "''");

        // Set the file size
        lngFileSize = fs.Length;

        byte[] bytHeader = new byte[4];
        byte[] bytVBitRate = new byte[12];
        int intPos = 0;

        // Keep reading 4 bytes from the header until we know for sure that in
        // fact it's an MP3
        do
        {
            fs.Position = intPos;
            fs.Read(bytHeader, 0, 4);
            intPos++;
            LoadMP3Header(bytHeader);
        }
        while (!IsValidHeader() && (fs.Position != fs.Length));

        // If the current file stream position is equal to the length,
        // that means that we've read the entire file and it's not a valid MP3 file
        if (fs.Position != fs.Length)
        {
            intPos += 3;

            if (getVersionIndex() == 3)    // MPEG Version 1
            {
                if (getModeIndex() == 3)    // Single Channel
                {
                    intPos += 17;
                }
                else
                {
                    intPos += 32;
                }
            }
            else                        // MPEG Version 2.0 or 2.5
            {
                if (getModeIndex() == 3)    // Single Channel
                {
                    intPos += 9;
                }
                else
                {
                    intPos += 17;
                }
            }

            // Check to see if the MP3 has a variable bitrate
            fs.Position = intPos;
            fs.Read(bytVBitRate, 0, 12);
            boolVBitRate = LoadVBRHeader(bytVBitRate);

            // Once the file's read in, then assign the properties of the file to the public variables
            intBitRate = getBitrate();
            intFrequency = getFrequency();
            strMode = getMode();
            intLength = getLengthInSeconds();
            strLengthFormatted = getFormattedLength();
            fs.Close();
            return true;
        }
        return false;
    }

    private void LoadMP3Header(byte[] c)
    {
        // this thing is quite interesting, it works like the following
        // c[0] = 00000011
        // c[1] = 00001100
        // c[2] = 00110000
        // c[3] = 11000000
        // the operator << means that we'll move the bits in that direction
        // 00000011 << 24 = 00000011000000000000000000000000
        // 00001100 << 16 =         000011000000000000000000
        // 00110000 << 24 =                 0011000000000000
        // 11000000       =                         11000000
        //                +_________________________________
        //                  00000011000011000011000011000000
        bithdr = (ulong)(((c[0] & 255) << 24) | ((c[1] & 255) << 16) | ((c[2] & 255) << 8) | ((c[3] & 255)));
    }

    private bool LoadVBRHeader(byte[] inputheader)
    {
        // If it's a variable bitrate MP3, the first 4 bytes will read 'Xing'
        // since they're the ones who added variable bitrate-edness to MP3s
        if (inputheader[0] == 88 && inputheader[1] == 105 &&
            inputheader[2] == 110 && inputheader[3] == 103)
        {
            int flags = (int)(((inputheader[4] & 255) << 24) | ((inputheader[5] & 255) << 16) | ((inputheader[6] & 255) << 8) | ((inputheader[7] & 255)));
            if ((flags & 0x0001) == 1)
            {
                intVFrames = (int)(((inputheader[8] & 255) << 24) | ((inputheader[9] & 255) << 16) | ((inputheader[10] & 255) << 8) | ((inputheader[11] & 255)));
                return true;
            }
            else
            {
                intVFrames = -1;
                return true;
            }
        }
        return false;
    }

    private bool IsValidHeader()
    {
        return (((getFrameSync() & 2047) == 2047) &&
                ((getVersionIndex() & 3) != 1) &&
                ((getLayerIndex() & 3) != 0) &&
                ((getBitrateIndex() & 15) != 0) &&
                ((getBitrateIndex() & 15) != 15) &&
                ((getFrequencyIndex() & 3) != 3) &&
                ((getEmphasisIndex() & 3) != 2));
    }

    private int getFrameSync()
    {
        return (int)((bithdr >> 21) & 2047);
    }

    private int getVersionIndex()
    {
        return (int)((bithdr >> 19) & 3);
    }

    private int getLayerIndex()
    {
        return (int)((bithdr >> 17) & 3);
    }

    private int getProtectionBit()
    {
        return (int)((bithdr >> 16) & 1);
    }

    private int getBitrateIndex()
    {
        return (int)((bithdr >> 12) & 15);
    }

    private int getFrequencyIndex()
    {
        return (int)((bithdr >> 10) & 3);
    }

    private int getPaddingBit()
    {
        return (int)((bithdr >> 9) & 1);
    }

    private int getPrivateBit()
    {
        return (int)((bithdr >> 8) & 1);
    }

    private int getModeIndex()
    {
        return (int)((bithdr >> 6) & 3);
    }

    private int getModeExtIndex()
    {
        return (int)((bithdr >> 4) & 3);
    }

    private int getCoprightBit()
    {
        return (int)((bithdr >> 3) & 1);
    }

    private int getOrginalBit()
    {
        return (int)((bithdr >> 2) & 1);
    }

    private int getEmphasisIndex()
    {
        return (int)(bithdr & 3);
    }

    private double getVersion()
    {
        double[] table = { 2.5, 0.0, 2.0, 1.0 };
        return table[getVersionIndex()];
    }

    private int getLayer()
    {
        return (int)(4 - getLayerIndex());
    }

    private int getBitrate()
    {
        // If the file has a variable bitrate, then we return an integer average bitrate,
        // otherwise, we use a lookup table to return the bitrate
        if (boolVBitRate)
        {
            double medFrameSize = (double)lngFileSize / (double)getNumberOfFrames();
            return (int)((medFrameSize * (double)getFrequency()) / (1000.0 * ((getLayerIndex() == 3) ? 12.0 : 144.0)));
        }
        else
        {
            int[, ,] table =        {
                            { // 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
                            }
                            };

            return table[getVersionIndex() & 1, getLayerIndex() - 1, getBitrateIndex()];
        }
    }

    private int getFrequency()
    {
        int[,] table =    {   
                        {32000, 16000,  8000}, // MPEG 2.5
                        {    0,     0,     0}, // reserved
                        {22050, 24000, 16000}, // MPEG 2
                        {44100, 48000, 32000}  // MPEG 1
                    };

        return table[getVersionIndex(), getFrequencyIndex()];
    }

    private string getMode()
    {
        switch (getModeIndex())
        {
            default:
                return "Stereo";
            case 1:
                return "Joint Stereo";
            case 2:
                return "Dual Channel";
            case 3:
                return "Single Channel";
        }
    }

    private int getLengthInSeconds()
    {
        // "intKilBitFileSize" made by dividing by 1000 in order to match the "Kilobits/second"
        int intKiloBitFileSize = (int)((8 * lngFileSize) / 1000);
        return (int)(intKiloBitFileSize / getBitrate());
    }

    private string getFormattedLength()
    {
        // Complete number of seconds
        int s = getLengthInSeconds();

        // Seconds to display
        int ss = s % 60;

        // Complete number of minutes
        int m = (s - ss) / 60;

        // Minutes to display
        int mm = m % 60;

        // Complete number of hours
        int h = (m - mm) / 60;

        // Make "hh:mm:ss"
        return h.ToString("D2") + ":" + mm.ToString("D2") + ":" + ss.ToString("D2");
    }

    private int getNumberOfFrames()
    {
        // Again, the number of MPEG frames is dependant on whether it's a variable bitrate MP3 or not
        if (!boolVBitRate)
        {
            double medFrameSize = (double)(((getLayerIndex() == 3) ? 12 : 144) * ((1000.0 * (float)getBitrate()) / (float)getFrequency()));
            return (int)(lngFileSize / medFrameSize);
        }
        else
            return intVFrames;
    }
}

Usage:

var caminhoDoArquivo = "C:\MeuMP3.mp3";
var mp3Reader = new MP3Header();
if (mp3Reader.ReadMP3Information(caminhoDoArquivo)) {
    var bitRate = mp3Reader.intBitRate;
    var isVBR = mp3Reader.boolVBitRate;
}

Source:

link

Along with the ffmpeg installation you will also have the ffprobe command available for reading metadata for video and audio files.

Here is an example of this command with return in JSON

ffprobe -v quiet -print_format json -show_format -show_streams video.mp4