There is no such thing as a full-screen video. This is a misnomer that has been applied to home video. 35MM film stocks have an aspect ratio of 1.37:1, and since the 1880's or so up until the late 1940's this was the standard projection ratio. Then with the advent of television in people's home, theater attendance went way down. So many new innovative film processes were developed to bring people back, such as Cinerama, with it's deep curved screen, and the more well-known Cinemascope, with it's "widescreen" 2.35:1 aspect ration. The reality is, Cinemascope uses special lenses to squeeze more picture into that same 1.37:1 film stock. And then there are films that are filmed flat, or "spherical". The normal 1.37:1 film stock is used, then when the film is projected theatrically, special plates in the projector mask off a portion of the image, to give a "widescreen" aspect ratio, of 1.66:1, or most commonly 1.85:1. Some films are filmed in the Super 35 process, which uses the 1.37:1 film stock, but then the theatrical aspect ratio of 2.35:1 is cut from the 1.37:1 negative, then optically cropped and printed with anamorphic lenses to get a "widescreen" image. John Cameron is fond of this process, films like The Abyss and Titanic were done this way, for the most part. It's a cheaper way to film as it uses the standard sperical lenses, as anamorphic lenses are expensive to rent. But the real bugger is when a theatrical film is prepared for home video. So the aspect ratio of a standard TV is 1.33:1, so the film has to be adapted for this screen. If a film has been filmed spherically, it has a negative ratio of 1.37:1, so no editing has to be done, just zoomed in slightly to adapt to the 1.33:1 ratio, in what is called an "open matte" presentation (this method has is flaws, as very often the open matte will reveal things that would be hidden by the masking, such as boom mics moving back and forth over actor's heads, and other practical effects. A perfect example is the film Pee Wee's Big Adventure. In one scene, Pee Wee pulls a seemingly endless chain from the sidebag on his bike. In the theatrical projection, the illusion of the endless chain is preserved, but in the open matte home video version, you can clearly see the chain coming through a hole in the bottom of the sidebag, ruining the joke). However, if a film was done in a truly anamorphic process, as much as half of the original image can be lost in the adaptation from 2.35:1 down to the 1.33:1. This is called the "pan and scan" process, and is disliked by most true film buffs, as it destroys the original image, and alters the director's and cinematographer's original vision of the film. As an example of what I mean, here is an image from the film Poltergeist, that shows the original anamorphic image, and the white area which shows the area from the "pan and scan" version:
So you can see how much of the original image is lost in the adaptation to home video, at least for the 1.33:1 TV. The original shot composition is completely destroyed. This is most noticeable when the subjects in the frame are at the extreme ends of the 2.35:1 frame, this is when you get the infamous "talking noses" in some films. However, with the advent of DVD, the proper aspect ratio of the film is preserved, though some films have not received this treatment, and are just available in the "pan and scan" ratio. In the days of laserdisc, and early DVD, the aspect ratio was preserved with so-called "letterboxing', where the image is shrunk down to fit the 2.35:1 image into the 1.33:1 frame, with the so-called 'black bars' on the top and bottom of the screen. Another interesting development is films that are recorded digitally, onto a computer or digital video tape, and not the traditional film stock. These films can be produced in any aspect ratio desired, and most often presented on DVD in that original ratio. But another thorn in the side of videophiles is when a film is suposedly "upgraded" to HD. It isn't a problem when a film's intended ratio is 1.85:1, as HD is 1.78:1, so the cropping off the top and bottom is minor and not really noticeable. But when a film that is 2.35:1 is cropped down to the 1.78:1 for HD, the original vision is destroyed. It's almost worse than the old "pan and scan" process for 1.33:1. So when it comes to a true videophile, the "black bars" that preserve aspect ratio really don't matter in the end, just as long as it shows what the director and cinematographer intended.
I could go even deeper than this, but it's enough for now. Geek rant over.
Well I thought I kind of understood Bicker, but Sosai just went right over my head. 
Ditto. The thought that Sosai could go further made me break out in hives but I don't like pan and scan either so I THINK we're in agreement. 
