As per your error, when you get the 404.3 error, you should know that there is a MIME restriction and the handler needed for it is missing. If the images or videos are not loading, then the required MIME-type is not available. The error can also surface if ASP.NET feature is not enabled.
There are 3 ways to resolve the error -
1. Install ASP.NET feature
2. Adding a Script Handler in your IIS Manager (Internet Information Services)
3. Select MIME type (Multipurpose Internet Mail Extensions)
Fixing the 404.3 HTTP Error: A Complete Guide[
^] hosts the detailed steps on how to achieve the above.