C# .NET - How to prevent video downloading from any software in website

Hello everyone I want to develop a software that can stop downloading from my website. Now requirement is this that the website is in PHP which is developed by any other user and I have to develop a software in .net which can check all the softwares that are using in downloading video from website and stop downloading after detect that softwares. Please Experts tell me how can I do this process. What process I have to use for this

If the video can be viewed in a browser, then it can be downloaded.  Period.  Once someone downloads it, it can be redistributed.  No .NET software is going to stop that.

About the only "reasonably" reliable way is to force streaming of the content and make sure the referrer matches your domain.  This makes it harder but not impossible.