As an overview, there are 2 separate methods to deliver caption information to the DVD users; NTSC closed captions and subtitles. It is important to note that when you get your results from CaptionSync, the information contained within both these is the same (i.e. both contain speaker IDs, parenthetical comments like
[ Applause ] ) and both are generally considered meet Section 508/504 requirements. When you are authoring your DVD in DVD Studio Pro, Encore, DVDit Pro, DVD Lab Pro or the like you can choose either or both.
NTSC closed captions are extracted from the MPEG and converted to line-21 VBI information by the DVD Player. The display of these closed captions is controlled by the television set. While all television sets greater then 13 inches are mandated by the FCC to have closed caption decoding capabilities, LCD displays used in the lecture halls are not televisions sets per se and hence often don't have a closed caption decoder built-in. Furthermore, if the DVD player is an “up-converting” variety that delivers video via HDMI cable, it will not display captions because HDMI does not carry caption data.
Subtitles are on the other hand are controlled by the DVD player and do not have the aforementioned issues that closed captions do – i.e. they will work with LCD displays, plasma displays, up-converting DVD players, etc. Furthermore, they are more flexible in terms of line-length, font, and character sets. The only thing subtitles do not have that closed captions do, is the music symbol.