Change iPhone 6S video aspect ratio to 4:3

Just bought one of those clip on fisheye lenses to film some skate videos while on vacation, and while the photo setting on the 6S camer shows the fisheye just fine, switching to video barely shows anything. The field of view is too zoomed in to even see a noticeable lens curve, let alone the fisheye boarder.

I understand there's little I can do in the settings to "zoom out" in video mode, so I'm primarily looking for an app that'll record a video in the Photo aspect ratio (4:3 I believe) so I can get a proper fisheye view. The cheaper the app, the better. Not looking for fancy features since everything will be adjusted in final cut anyway.