Cannot find a container format for the ".mp4" file extension.

[xinchencai]

I got a System.NotSupportedException thrown when trying to run the following function:

    using FFMediaToolkit;
    using FFMediaToolkit.Encoding;
    using System.Drawing.Imaging;
    using FFMediaToolkit.Graphics;

    private static void image2video(string[] files, int width, int height, string output)
    {
        FFmpegLoader.FFmpegPath = path;

        var settings = new VideoEncoderSettings(width: width, height: height, framerate: 25, codec: VideoCodec.H264);
        settings.EncoderPreset = EncoderPreset.Fast;
        settings.CRF = 17;
        using (var file = MediaBuilder.CreateContainer(output + "video.mp4").WithVideo(settings).Create())
        {
            foreach (var inputFile in files)
            {
                var binInputFile = File.ReadAllBytes(inputFile);
                var memInput = new MemoryStream(binInputFile);
                var bitmap = Bitmap.FromStream(memInput) as Bitmap;
                var rect = new System.Drawing.Rectangle(System.Drawing.Point.Empty, bitmap.Size);
                var bitLock = bitmap.LockBits(rect, ImageLockMode.ReadOnly, PixelFormat.Format24bppRgb);
                ImageData bitmapData = ImageData.FromPointer(bitLock.Scan0, ImagePixelFormat.Bgr24, bitmap.Size);
                file.Video.AddFrame(bitmapData); // Encode the frame
                bitmap.UnlockBits(bitLock);
            }
            file.Dispose();
        }
    }

Here's the error that I got

    Exception thrown: 'System.NotSupportedException' in FFMediaToolkit.dll
    Exception thrown: 'System.NotSupportedException' in mscorlib.dll
    An unhandled exception of type 'System.NotSupportedException' occurred in mscorlib.dll
    Cannot find a container format for the ".mp4" file extension.

Can anybody tell where this error is coming from?