How to compare 2 folders in winmerge, but ignore file extension?

I think the right regex, forgive my ignorance on this.

I got some ideas from this useful stack question and the winmerge filter help page

But I can't get it to work. Some help please, much appreciated.

f: *\.insv(.mp4)?$ ## *.insv and *.mp4 files

To exclude both extensions in the same filter you can use:

f: .*(\.insv|\.mp4)$

Or you can use one line to exclude each extension:

f: .*\.insv$
f: .*\.mp4$