Saw the C4D post about fitting a plane to a camera and realised that that's something I do fairly often myself, so I finally put together an HDA, which is Houdini's version of a Capsule to do this for me.
While this can technically work with any geometry, including 3D geo, I really only tested it with flat geometry.
The asset isn't blackboxed, so edit it as you wish.
houdini_Hedg0xR1EY.mp4
avi.fit_to_camera.hdalc