Ever since the iPhone first started shooting video, people have decried the use of the vertical orientation. Why would you do that? It looks so horrible! It's unnatural! Hang on a moment while I pass judgement on you.
Let's take a look at the history of film aspect ratios for a moment. Sure, the first film format was 4:3, just like our old TV sets — slightly wider than it is tall. In fact, TV cribbed the 4:3 ratio from film, and it wasn't until TV started sucking away some of the film audience that the movies started to get wider and wider and wider.
The point being, aspect ratio is an artistic choice, and mostly a gimmick to get people back in theaters. None of those aspect ratios are "right" — not even 16:9, which was a compromise between many ratios for an acceptable film "fit" when TV stole widescreen back for itself (and pushed the movies into another 3D frenzy, which is a rant for another day). Even 9:16 (the iPhone's vertical video ratio) is just another choice in a long line of choices.
And why shouldn't you shoot video vertically? Apple's own ads show people chatting on FaceTime with the camera held vertically. Our faces our vertical. There are tall buildings, and kids coming down playground slides. I argue that, sometimes, it's a really good fit.
Most of the arguments against vertical video seem to boil down to one of two things. One is some pseudo-scientific mumbo-jumbo about how our eyes are set horizontally in our heads, so our natural field of vision is wider than it is tall, and we should obey that restraint. (Yes, art is all about obeying natural restraints, and conforming to convention.) The other is an argument that the way that we share video now, via YouTube and AirPlay-ing to our AppleTVs, demands that wide ratio to fit the screen. This latter theory has some merit, but I would argue that the video sharing sites should accommodate multiple aspect ratios in the way they present the videos, instead of letterboxing things inside a widescreen frame. (At least Vimeo and Flickr seem to handle this properly.)
That leads us to Horizon, a new app that uses the accelerometer in the phone to detect the angle of the phone while it's shooting video, and automatically crop the video to a level 16:9 horizontal image.
This is super clever, and certainly fills a need — sometimes you do want perfectly level horizontal video, damn the resolution (the crop in vertical mode has only 32% of the resolution of the full image). Probably most people just want a video that looks nice when they play it on their TV, or share it on YouTube. This will do that, and quite nicely.
The more interesting thing to me, is how it enables a unique interface for the zoom function on the phone. Now you can use the angle of the phone to control the crop, instead of clumsily sliding your finger on the screen while you're trying to hold the phone still.
It's all about using the camera in creative and unique ways — There is no one "right" way to shoot video. Just a plethora of interesting decisions.