In "virtual dub" (version 1.10.4) we find filters e.g. "blend layers" or "merge layers" which need an input of two or more video files to work correctly.

I could not find out how to manage an input of these files and I did not find any help concerning these filters.

What I get is: "an instance of filter 'blend layers' has too few inputs (expected 2, got 1)" or "an instance of filter 'merge layers' has too few inputs (expected 3, got 1)

Can anybody help? Thank you so much!