1:  /// <summary>

   2:  /// C# algorithm which computes hash of video file. Computed hash is then used to find matching subtitles.

   3:  /// </summary>

   4:  /// <param name="filePath">Absolute path to video file.</param>

   5:  /// <returns>Computed hash value formated as hexadecimal string (52 characters). Returns null on failure.</returns>

   6:  public static string Compute(string filePath)

   7:  {

   8:      try

   9:      {

  10:          if (!System.IO.File.Exists(filePath))

  11:          {

  12:              return null;

  13:          }

  14:   

  15:          List<byte> hash = new List<byte>(26);

  16:   

  17:          //0: reserved

  18:          hash.Insert(0, 0x0);

  19:   

  20:          //1-2: video length in seconds

  21:          short runTime = new VideoInfo(filePath).RunTime;

  22:          if (BitConverter.IsLittleEndian)

  23:          {

  24:              hash.InsertRange(1, Invert(BitConverter.GetBytes(runTime)));

  25:          }

  26:          else

  27:          {

  28:              hash.InsertRange(1, BitConverter.GetBytes(runTime));

  29:          }

  30:   

  31:          //3-8: file length in bytes

  32:          long fileLength = new FileInfo(filePath).Length;

  33:          if (BitConverter.IsLittleEndian)

  34:          {

  35:              hash.InsertRange(3, GetLastBytes(Invert(BitConverter.GetBytes(fileLength)), 6));

  36:          }

  37:          else

  38:          {

  39:              hash.InsertRange(3, GetLastBytes(BitConverter.GetBytes(fileLength), 6));

  40:          }

  41:   

  42:          //9-24: MD5 hash for first 5 MB of file

  43:          hash.InsertRange(9, ComputeMD5FromFile(filePath, 5 * 1024 * 1024));

  44:   

  45:          //25: control byte

  46:          int sum = 0;

  47:          for (int i = 0; i < 25; i++)

  48:          {

  49:              sum += hash[i];

  50:          }

  51:          hash.Insert(25, Convert.ToByte(sum % 256));

  52:   

  53:          //convert to hex string

  54:          StringBuilder sbResult = new StringBuilder();

  55:          for (int i = 0; i < hash.Count; i++)

  56:          {

  57:              sbResult.AppendFormat("{0:x2}", hash[i]);

  58:          }

  59:          return sbResult.ToString();

  60:   

  61:      }

  62:      catch

  63:      {

  64:          return null;

  65:      }

  66:  }