4:3 vs. Letterbox
Conventional television uses a 4:3 width to height ratio, while HDTV uses a 16:9 "wide screen" width to height ratio. Over time movies have used a variety of formats but these are almost all variants of a "wide screen" format. When wide screen content is converted for use on a conventional 4:3 screen a section of the screen has to be selected for use or what is more commonly done is the content is converted to a letterbox format with a black area at the top and bottom of the screen to compensate for the different ratio. Both YouTube and Revver use the conventional 4:3 ratio.
Letterbox in LG15
In the LG15 series, it seems that the letterbox format is used when the characters are filming outside their standard location. For instance, when the camera is taken away from its normal position on Bree's desk where she makes her normal videoblogs, the editors tend to use the letterbox format.
There are 3 variations of letterbox format used: