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For example, I know that HDMI cables explicitly do not send a CC signal to the TV, even if the source and TV both support it.

I assume that coax cable does support it since I can use a digital antenna and receive CC on my TV from digital over the air broadcasts (in the US).

Is there any other cabling that will carry the actual CC signal for the TV to decode?

I am currently sending a DVI signal to projectors in an auditorium and I am sending the same image by VGA over CAT5 to HDTVs in our lobby. We may need to add Closed Captioning to the lobby feed only so I do not want to change the image going to the projectors in the auditorium.

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  • Can HDMI even carry non-decoded video bitstreams? I thought HDMI only carried raw video, like DVI or DisplayPort. So whatever decodes the TV signals into pixel values would have to handle the captions / subtitles. (I know HDMI can carry audio bitstream for AC3, EAC3, DTS, DTS-HD, etc. etc. But I've never read anything about software to bitstream h.264 out of your graphics card over HDMI to a TV, just audio.) Commented Feb 26, 2015 at 21:57
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    Whether captions appear on a TV rarely has anything to do with the cable used, because there generally is no separate 'CC signal'. If you omit the assumption that it's affected by the cable, maybe you could reframe the question to focus on a specific concern. Commented Feb 26, 2015 at 21:57
  • @JimMack Under analog broadcast TV, my understanding is that CC signal is sent under Line 21. This only exists because of a timing gap where no image is sent to allow for the CRT to move back to the top of the frame to begin the next pass. I also understand that this method does not apply to modern TVs and their respective signals. Commented Feb 27, 2015 at 22:01
  • @MilesCarmany That's true (EIA-608), but I don't see what that has to do with cables. In digital systems caption data is interleaved as packets in the stream (EIA-708), not sent as a separate signal or on a separate cable. Commented Feb 27, 2015 at 23:00

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Your question was initially confusing because you had focused on "cables" which is not the correct way of looking at this.

Once you've decoded a video signal to components, the closed captions are no longer available. If they were not inserted as open captions (aka subtitles) then they're simply not there.

So any transport that removes the Line 21 caption data or the digital caption packets eliminates your ability to defer captioning at the distant end -- you must insert the captions / subtitles before transport. That's the case with DVI / VGA / HDMI.

If you must allow the ability to choose a captioned or non-captioned display at the distant end, you would have to send two component feeds (e.g. two CAT5s), one captioned and one plain, and A/B switch them at that end.

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The closed caption information in the HDMI component is lost when you convert that digital format into a VGA signal, which is analog: The closed caption information is not injected into line 21 of such standard therefore the closed caption information is not there. Closed caption information is handled very different in a digital signal than in the NTSC standard. You need a microprocessor to extract the signal from the digital HDMI cable and re-build and inject it into line 21 of your analog VGA signal. In other words: VGA and NTSC both use the same Closed Caption analog format. HDMI and VGA & NTSC are two different worlds and the digital information will never be available to your monitor the way it needs it. By design the information is simply not there. To handle this need you have three solutions assuming you want to use the CC decoding capabilities and features of your VGA/NTSC monitors: a) One is the offered before: It requires a separate processor to decode from HDMI and encode to VGA/NTSC standard. This is easily accomplished using Linux-based software gear. b) The other solution is to keep your transmission DIGITAL through your UTP cabling all the way. This means not to convert to Analog and inject the signal directly to your HDMI input in your remote monitors (assuming you have HDMI input capabilities in such monitors). For this purpose you need to get HDMI UTP extensors (not VGA) like these: http://www.ebay.com/bhp/hdmi-over-cat5 . c) A very elegant alternative would be to use HD modulators and send the signal in a unused HDTV channel (for instance 39.1) and feed the signal through a coax cable to the tuner connector of each TV monitor (assuming they have an HDTV tuner circuitry). Something like these can do the job: http://www.pviusa.com/MICROMOD-Compact-HD-RF-Modulator_p_72.html?gclid=CjwKEAjwz9HHBRDbopLGh-afzB4SJABY52oFUGrfVR-DYY4ljXhNVtX5lBiCUwFMPvYUBERhZUVGpRoCH8Hw_wcB . If recabling is not an option and your monitors are, indeed, HDTV and you have to stick to UTP cabling then your best option is (b): HDMI extensors through UTP. It is a mistake changing from HD Digital format to VGA Analog and then to HD digital again in the other end!. I guess you may want to grab some of these gadgets from EBAY.

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I don't mind the question. I think of it in those terms too. So HDMI, DVI, VGA no. Composite, SDI, and RF yes. Composite is typically a Yellow RCA or can be BNC coax. SDI (HD, SD, 3G) is also BNC Coax. When you say Coax above you are referring to RF, which comes in both analog NTSC and digital ATSC versions, both of which support CC, and typical cable ends are F connectors. Composite and NTSC are SD resolution, so if you want to go HD your choices are SDI or ATSC RF. For the latter, a simple monitor will not do, it has to include an ATSC tuner. But if HDMI is anywhere in the chain, CC is lost. SDI connectors on monitors are rare/expensive, so probably not an option. Only other option is to decode the image twice in your studio, one with opened captions and one without, and send one to the lobby and the other to your projectors.

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This HDMI closed captions information is wrong -- there is explicitly no Closed Captions information in the HDMI signal. Standard document CEA-861-E, published May 2008, which defines the HDMI data signal, explicitly states:

The physical/link standards in Annex B, Annex C and Annex D do not support transport of closed captioning (CEA-608-C [44] and CEA-708-C [45]); therefore, the source processes these elements.

Specifically, if closed captioning is to be displayed, it is decoded by the source, inserted into the video, and displayed as open captions. Similarly, if system Information, program information, events, service descriptors, etc. are displayed, related graphical information is inserted into the video by the source.

Control of closed captioning settings, programs, events, etc. is a feature of the source, not supported by this interface and beyond the scope of CEA-861-E.

“source device” = cable set top box.

Currently, the only source of Closed Captions is the Composite Video signal (yellow cable/connector), but that is an outdated 720×480 resolution video signal. To force the HDMI source and sink device manufacturers to include and display Closed Captions requires federal legislation in Washington, DC. Call your US Congressman/Senators.

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  • In the US, closed captioning is not limited to composite / NTSC video (EIA-608) but has been available for digital transmission for many years (EIA-708). I don't see what you think legislation would accomplish? Commented Jan 8, 2020 at 17:57
  • There are numerous questionable features (e.g. Ethernet) which are expensive to implement which Are being added to this HDMI spec. For some reason, they explicitly state in this specification that they will Not implement Closed Captions, which is relatively easy to implement. Thus the CEA-861 members' refusal to carry Closed Captions in their digital form, translated into a designated Infoframe, indicates the presence of some members on the 861 committee who are resisting Closed Captions transport between the Cable Set Top Box and the TV -- most likely, Hollywood. Commented Jan 21, 2020 at 4:39
  • For clarification purposes, the purpose of Closed Captions is to deliver captions or subtitles to the TV or TV support equipment as Data. This allows the TV and other TV support equipment to manipulate the text Data and deliver new features and products which could have assisted the Deaf/Hard-Of-Hearing community over the past decade. While the Set Top Box remains the terminus for this data, it cripples the ability to provide TV visual and audio enhancement features to this community. Commented Jan 29, 2020 at 8:42

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