Video: only single sub to add Jurassic Park Dinosaur Stomp.
Video and Music: two subs, hopefully located adjacent to the fl and fr.
Low Bass may start out room filling mono, no direction home, however the many overtones definitely have directional info, thus a Stereo pair of subs is desirable.
I'm no fan of ports, and of course self-powered sub(s) helps your main receiver/amp.