How to add watermark image in uploaded videofile

you have to take a frame out of your uploaded video!

Process p;
ProcessStartInfo info = new ProcessStartInfo();
info.FileName = "ffmpeg.exe";
info.WindowStyle = ProcessWindowStyle.Hidden;
info.Arguments = " -i " + your_video_name + " -vframes 1 " + your_extracted_image_name + "%d.jpg";


p = Process.Start(info);


while (!p.HasExited) { Thread.Sleep(10); }

the address of the video should be some thing like this: "c:\inetpub\wwwroot\mysite\videos\video_to_convert.3gp"
"-vframes 1 " take the first frame of your video file!
"%d.jpg": %d is a parameter for ffmpeg.exe that make an auto numbering for new image ,
then it save your image, and then use this article to make a watermark image!
check this out!
Build a Simple Watermarking Utility in C#[^]
I hope this could be helpful!:)