Question Recorder not working in Build, what are my options?

I want to capture video clips from my unity app, have built a UI that lets me configure a ScriptedMovieRecorder but now i discovered, that the ScriptedMovieRecorder also only works when the app is started from the editor (I can't create a successful build with it)

The only thing I can think of right now is doint it manually: putting every frame in a renderTexture and saving the clip as a .png sequence and converting that into a video afterwards (maybe just run ffmpeg after the capture is done?)
Also need to think about update timing then - unity recorder provides convenience in delivering Time.deltaTime to fixed frame intervals, even if the actual frames take longer to render - is that easy to accomplish manually?

Any easier solutions I'm missing here? In the asset store i so far only found other editor extensions...

Cross Platform would be nice, but primarily looking for Windows...

 

thanks, great pointers!