Changing the Quality of a Stream Video C #

I need to change the quality of a video that is being scanned by my Api, I'm already sending the file, now I need to change the quality of it at the time of transmission, follow my code below:

               var buffer = new byte[65536];

                using (var video = File.Open(_filename, FileMode.Open, FileAccess.Read))
                {
                    var length = (int)video.Length;
                    var bytesRead = 1;

                    while (length > 0 && bytesRead > 0)
                    {
                        bytesRead = video.Read(buffer, 0, Math.Min(length, buffer.Length));
                        await outputStream.WriteAsync(buffer, 0, bytesRead);
                        length -= bytesRead;
                    }
                }

Is there any way to change at the time of streaming or do I need to physically have it in other qualities?