[Ffmpeg-devel] Re: MPEG and ClosedCaption

Gamester17 gamester17
Sun Jul 31 14:06:50 CEST 2005

Foushee, Carey-P55376 wrote:
> Is it possible to pull out the closed caption text using FFMpeg?

No (but it would be nice if we could), if you want to code a patch see: 

CC (Closed Captions) software decoding for hearing impaired:

CC (Closed Captions) pass-through for hearing impaired:

More info on Closed Captions (CC, line 21 data):

FYI; A couple of Closed Caption FAQ's: 

Q: Are there captions on all DVDs?
A: Standards were created very late for DVDs, so there are
several different ways to put captions on them. The
most common approaches are to either embed Line-21-
style captions in what are called the "user bits" or to
use "subpictures" to display captions that look like
subtitles. Your DVD player must support the same
method that was used to encode the DVD, although
many DVDs use both of these methods. When using
subtitles, DVDs support captioning in multiple languages. 

Q: What's the difference between subtitles and captions?
A: Generally speaking, subtitles are intended for hearing
audiences and captions for deaf audiences. Subtitles
may translate the dialog into a different language, but
rarely show all of the audio. For example, captions show
sound effects (e.g., "phone ringing" and "footsteps"),
while subtitles don't. 

Q: Why does my DVD show subtitles and captions simultaneously?
A: In an effort to work with as much equipment as possible,
some DVDs are encoded with both
subtitles and closed captions. If your TV is set to show
captions, and you turn on the DVD
subtitles, you'll see the captions over top of the
subtitles. If you're getting both, you'll have to
either turn off subtitling on the DVD player, or turn off
captions on the television set. 

Q: Can you use captions for anything else?
A: Closed Captions pass-through signals are also used by
third-party external CC readers such as TV
Guardian and Cursefree TV to censor/filter audio/speach
DVD's in TV (can auto mute the audio on
programed CC signals), this does not work on normal

PS! I believe Closed Captions (CC, or line 21 data) is only broadly used in 
the U.S.A., is a simple feature that is included in most US (NTSC) DVD-Video 
movies (VOB files), and some DVD player pass-through that signal to a TV 
that supports CC the TV will decode and display them on demand. For the 
hearing impaired CC are a must to fully enjoy DVD movies as they display 
text of audio that going on that only the hearing can hear and the normal 
subtitles do not show. When using subtitles, DVDs support captioning in 
multiple languages. 

Regards / Gamester17

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