SplitFileMethod

namespace SplitFile
{
    class SplitInFiles
    {
        static void Slice(string sourceFile, string destinationDir, int parts)
        {
            int bufferSize = 4096 * 4;
            byte[] buffer = new byte[bufferSize];
            FileStream inputStream = new FileStream(sourceFile, FileMode.Open);
            using (inputStream)
            {
                int index = 1;
                int partSize = (int)Math.Ceiling( (double)inputStream.Length / parts);
                while (inputStream.Position < inputStream.Length)
                {
                    using (var outputStream = new FileStream(string.Format("{0}part{1}.mp4", destinationDir, index), FileMode.Create))
                    {
                        int bytesRead = 0;

                        while (bytesRead < partSize)
                        {

                            int bytes = inputStream.Read(buffer, 0, (int)Math.Min(partSize - bytesRead, buffer.Length));
                            if (bytes == 0)
                            {
                                break;
                            }
                            outputStream.Write(buffer, 0, bytes);
                            bytesRead += bytes;
                        }
                    }
                    index++;
                }
            }

        }

        static void Main()
        {
            string sourceFile = @"../../Video.mp4";
            string resultDirectory = @"../../Result/";
            Slice(sourceFile, resultDirectory, 4);
        }
    }
}