How to combine/merge a video and a gif using FFMPEG?

See more:

video

ffmpeg

GIF

I want to merge a video and Gif.
My video is a picture and a song during 45 seconds and my Gif is a equalizer animation.

I want to combine video and Gif , Gif opacity be 50%.

I can't find any solution but I try do it by C# it doesn't work too.

Thanks a lot.

What I have tried:

private void button2_Click(object sender, EventArgs e)
        {

            string[] files = Directory.GetFiles(@"D:\Temp\tmp");

            //combine them into one image
            System.Drawing.Bitmap stitchedImage = Combine(files);

            //save the new image
            stitchedImage.Save(@"D:\stitchedImage.gif", System.Drawing.Imaging.ImageFormat.Gif);

            
        }


        public static System.Drawing.Bitmap Combine(string[] files)
        {
            //read all images into memory
            List<System.Drawing.Bitmap> images = new List<System.Drawing.Bitmap>();
            System.Drawing.Bitmap finalImage = null;

            try
            {
                int width = 0;
                int height = 0;

                foreach (string image in files)
                {
                    //create a Bitmap from the file and add it to the list
                    System.Drawing.Bitmap bitmap = new System.Drawing.Bitmap(image);

                    //update the size of the final bitmap
                    width += bitmap.Width;
                    height = bitmap.Height > height ? bitmap.Height : height;

                    images.Add(bitmap);
                }

                //create a bitmap to hold the combined image
                finalImage = new System.Drawing.Bitmap(width, height);

                //get a graphics object from the image so we can draw on it
                using (System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(finalImage))
                {
                    //set background color
                    g.Clear(System.Drawing.Color.Black);

                    //go through each image and draw it on the final image
                    int offset = 0;
                    foreach (System.Drawing.Bitmap image in images)
                    {
                        g.DrawImage(image,
                          new System.Drawing.Rectangle(offset, 0, image.Width, image.Height));
                        offset += image.Width;
                    }
                }

                return finalImage;
            }
            catch (Exception ex)
            {
                if (finalImage != null)
                    finalImage.Dispose();

                throw ex;
            }
            finally
            {
                //clean up memory
                foreach (System.Drawing.Bitmap image in images)
                {
                    image.Dispose();
                }
            }
        }