DVD and ASCII Closed Captions

[r0lZ]

I have found this interesting option in mplayer's command line:

-subcc
Display DVD Closed Caption (CC) subtitles. These are not the VOB
subtitles, these are special ASCII subtitles for the hearing
impaired encoded in the VOB userdata stream on most region 1 DVDs.
CC subtitles have not been spotted on DVDs from other regions so far.
Is it really possible to encode ASCII subtitles in the VOBs? This could be interesting to add easily downloaded subpics to a DVD. But I've never seen that (I live in region 2).

How are the players supposed to handle these forced captions? Is it something similar to the way a TV handles the teletext subpics?

[mpucoder]

These are Closed Captions, not subs. They get encoded into line 21 of the video and interpretted and displayed by the television. They are an NTSC thing, so you will not find them on PAL DVDs. McPoodle has a large number of tools at his website for manipulating them.

[r0lZ]

Thanks, mpucoder!

[mrslacker]

They often disappear when processing with DVD-RB. I'm not sure if it is a feature to be or a bug.... never the less, they are (seem to be) exactly what mpucoder described. Too bad I can't remember on which of my discs they are present.

[r0lZ]

Just for my personal erudition: how are these closed captions displayed on screen? Is it the DVD player that must overlay them in the video signal, or the TV?

[eb]

I hope that this drawing can help.

http://img128.echo.cx/img128/4530/napisy12ko.jpg (http://www.imageshack.us)

eb

[r0lZ]

Thanks, it helps.

But it doesn't say if the Line 21 decoding and the overlay has to be done in the DVD player or in the TV. However, I suppose that it's in the DVD player...

[mpucoder]

But I did say :) "They get encoded into line 21 of the video and interpretted and displayed by the television."

They work in the same manner as Teletext.

The reason they disappear is that they are encoded as user data in the video stream (m2v file). If you re-encode, the data is lost.

[r0lZ]

Oh, sorry! Thanks again.

[slk001]

They are marked on the original DVD package as a pair of "C"s in a box that looks like a TV. So look for something like "CC" on the package somewhere.

[slk001]

Here's what the logo looks like:

[IMG]CC.jpg{/IMG]

[r0lZ]

Which logo? ;)

[mpucoder]

These logos:
http://www.mpucoder.com/images/cc_symbols.gif

[r0lZ]

I have only 2 NTSC DVDs in my collection, but unfortunately w/o these logos.
Anyway, it doesn't matter. Thanks again, folks!

[yaz]

Originally posted by mpucoder
...They are an NTSC thing, so you will not find them on PAL DVDs... of course, i believe you, but then ... what's that subst streams on pal dvds marked as 'closed captions'. these are usually for translating text, notes, signs appearing in the film or for sentences in 'foreign' (non-native) language or for signing who's speaking aso aso.
thx
y

[mpucoder]

If I understand you correctly, you are talking about subtitles which are called "captions". These are not the same thing, and they are open, not closed, captions. To captioning people open means you do not need a special decoder to see the captions, closed can be viewed only on televisions equiped with decoders.
Closed captions are transmitted as a series of dots in line 21 of an NTSC video signal. The television detects, decodes, and renders the captions. You choose the language and turn them on and off at the television, not the DVD player (or VCR, they work with them too).

Closed Captions have a PAL counterpart called Teletext, but it is not supported by DVD.

[eb]

The reason they disappear is that they are encoded as user data in the video stream (m2v file). If you re-encode, the data is lost.

I have not such sample with NTSC CC but I think that ProjectX can be used to demux/demultiplex all required streams from VOB's or TS's streams.
After video re-encoding and/or audio and converting CCs to required subtitles type we can mux/multiplex acc. to DVD player.

eb

[mpucoder]

Yes, and that is what one of McPoodle's (http://www.geocities.com/mcpoodle43/SCC_TOOLS/DOCS/SCC_TOOLS.HTML) programs does. There is also a program called CCParser that extracts CC to text.

[str8]

Originally posted by mpucoder
Yes, and that is what one of McPoodle's (http://www.geocities.com/mcpoodle43/SCC_TOOLS/DOCS/SCC_TOOLS.HTML) programs does. There is also a program called CCParser that extracts CC to text.
I was a beta tester of CCParser and it works, but Vobsub (VSRip) has subsequently made the process of ripping CC's to text (*.srt) much simpler. You just have to remember to scroll down to the bottom of the available subtitle languages and manually select "cc -- not detected" because for whatever reason, it often doesn't detect CC's even when they're there.

[zilog jones]

Is it possible to put CC's on PAL DVDs? It appears a lot of PAL VHS tapes have closed captions (especially US films), but I've never seen TV sets over here that could decode them - I think you had to buy a separate decoder box or something.

[mpucoder]

It is possible to put the CC data in, it's just user defined data in the video stream. But I can't say what the DVD player will do with it.

PAL VHS with CC is the result of the way standards conversions are sometimes done, preserving information in the vertical interval. When doing standards conversion for broadcast it is sometimes necessary to preserve VITC, the time code in line 20. CC comes along for the ride.