When 16:9 video is displayed on an SD 4:3 monitor, you’ll see bars at the top and bottom
of the picture because a 16:9 image cannot entirely fill a 4:3 screen. This presentation
mode is called letterboxing and is often used synonymously with the term widescreen.
Widescreen video requires letterboxing only when displayed on a 4:3 display.
Letterboxing should be used only for displaying images—not recording them. For
example, you could easily mask the top and bottom of a 4:3 camera during recording
to create letterboxed 16:9 footage, but many video lines would be wasted this way,
reducing video resolution. Similarly, after you capture 16:9 anamorphic video, you
should keep it in anamorphic mode as long as possible and avoid letterboxing the
footage unless you have to. Even during export and output, there are many devices
that can properly display 16:9 anamorphic footage. For example, most DVD players
can stretch your footage when connected to a 16:9 display or letterbox footage when
connected to a 4:3 display.
16:9 video letterboxed
in a 4:3 display.