Letterboxed video is when there is a top and bottom matte on the image in order to fit other aspect ratios into standard definition video. Standard definition is 4:3 (1.33) and HD is 16:9 (1.78). This is most commonly seen when watching DVDs on a standard definition television. We all love letterboxing right? It allows us to see the entire frame, instead of a pan and scan crop to 4:3.
So what am I talking about? I’m talking about the 2 different methods to record 16:9 material onto a standard definition medium. Your options are to put actual black mattes on the top and bottom of your video, or you can squish the video into the 4:3 square and then stretch is back out on playback. We call the black matted video letterbox, and the squished video anamorphic. So who cares right? Well it matters because the letterboxed version is throwing away 1/3 of the available resolution of standard definition video. This doesn’t matter much when played back on a standard definition television, but it becomes a big deal when played back on a widescreen or HD TV or projector.
There are still letterboxed masters being made and used today. I believe it is for supporting legacy non-anamorphic aware equipment, but most playback devices out there can handle anamorphic video. All DVD players are smart enough to letterbox it for SD TVs and send the anamorphic to HD TVs and projectors which are able to stretch it out to its full 16:9 glory. And if you are going to make an encode for web or digital projection video encoding software can easily stretch the video back out to 16:9.
What if you have an aspect ratio wider than 16:9? No problem, all you have to do is place the video in a 16:9 frame with mattes sufficient to retain the correct aspect ratio and then squish that to 4:3. Then when it is stretched back to 16:9 your aspect ratio will be maintained. The same idea works for narrower aspect ratios. For instance if you have some 1.66 material, you just have to put mattes on the left and right of the image in a 16:9 frame.
If you are making a non 4:3 video master do not make a letterboxed master, you will regret it down the road. SD video does not have enough resolution to throw away 1/3 of it needlessly. If for some reason you must have a letterboxed version you can always make it from the anamorphic, but you can’t go the other way without sacrificing quality.