This article is from the RCA SelectaVision VideoDisc FAQ, by firstname.lastname@example.org (Tom Howe) with numerous contributions by others.
Several CED titles were issued in letterbox format ("Amarcord," "The
Long Goodbye," "Manhattan," "Monty Python and the Holy Grail," and RCA's
"King of Hearts"). RCA called this their "innovative widescreen
mastering technique," and on the back of the caddy provided an
explanation for the black bands at the top and bottom of the television
screen. CED was the first video format to feature letterboxing, with the
release of "Amarcord" in January 1984. This was eight months prior to
the release of "Manhattan" on LaserDisc, which is often mistakenly
considered the first letterboxed release.