Yup, switching the platform toolset from "Visual Studio 2015 (v140)" to "Visual Studio 2019 (v142)" breaks it.
Choosing "Visual Studio 2017 (v141)", then it works. so the breakage is between 141 and 142
Edit2: compiling dshowhelper shows 104 warnings (with v140, v141 as well as v142 so no extra ones to check). And none of them stand out to point to the issue at hand...
Really strange, I should expect only a change in the toolset wouldn't have that much influence... I mean, it compiles and no extra warnings.
That could possibly happen to anyone, so any c++ project upgrading it's toolset could potentially break in non-expecting places...
So either we do some really nasty things in dshowhelper, or microsoft messed up... (Don't know for which one I'm rooting )