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Old 03-10-2016, 08:07 PM   #1
trs79
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VBI closed caption information on composite video missing for HD broadcasts

I noticed that when I use an AV cable and connect the composite video from a Tivo to my tv, line 21 VBI closed caption data is only transmitted if the OTA broadcast is 480i. For any higher resolutions, the caption information is not transmitted. (I don't mean the captions you can display using the Tivo menu, but rather the hidden VBI caption information that is transmitted over composite video). Does anyone know if there is a way to enable the captions for all OTA resolutions?

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Old 03-10-2016, 08:46 PM   #2
cosmicvoid
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I believe VBI data is only for analog video. Any resolution higher than 480i will be digital and has no VBI and is down-converted to 480i on the AV output. The caption data in the converted digital stream is not put into the VBI.

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Old 03-10-2016, 09:17 PM   #3
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I was afraid of that, my Dish receiver would output VBI data (through composite video) for pretty much any HD show. I was hoping the Tivo would do the same.

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Old 03-10-2016, 09:35 PM   #4
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Originally Posted by trs79 View Post
I was afraid of that, my Dish receiver would output VBI data (through composite video) for pretty much any HD show. I was hoping the Tivo would do the same.
I don't know that Tivo doesn't do this as a hard fact, but I haven't seen any evidence that it does.

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Old 04-03-2016, 08:06 PM   #5
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Update: I just discovered that the Tivo is outputting VBI caption data for some 720p channels too. Unfortunately the captions are scrambled, I can make out a few words here and there but it doesn't match the on-screen captions the Tivo is displaying. Some channels don't have any VBI data at all.

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Old 04-04-2016, 05:13 PM   #6
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So you're watching HD recordings on an SDTV via composite? Do you have the same TiVo connected to an HDTV via HDMI?

If you're only using it for the SDTV then have you tried setting the TV mode to 4:3 and making sure that 480i is the only resolution checked in the resolution list?

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Old 04-04-2016, 10:17 PM   #7
trs79
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Quote:
If you're only using it for the SDTV then have you tried setting the TV mode to 4:3 and making sure that 480i is the only resolution checked in the resolution list?
I tried making sure 480i was the only resolution checked and set the aspect ratio to 4:3, but the captions were still garbled.

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Old 04-05-2016, 06:03 AM   #8
JoeKustra
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Quote:
Originally Posted by trs79 View Post
Does anyone know if there is a way to enable the captions for all OTA resolutions?
Yes. Buy a digital TV and use HDMI and any content with CC will show on the display. It works for cable.

For some really boring information: https://en.wikipedia.org/wiki/Closed_captioning


Last edited by JoeKustra; 04-05-2016 at 06:58 AM.
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Old 04-05-2016, 08:54 AM   #9
trs79
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Quote:
So you're watching HD recordings on an SDTV via composite? Do you have the same TiVo connected to an HDTV via HDMI?
I actually have the HDMI cable going to a digital TV, and the composite video cable going into a TV Guardian device (it monitors the captions and mutes if it detects certain words). I have the device set to always display captions, which is how I'm seeing the garbled words.

Quote:
For some really boring information: https://en.wikipedia.org/wiki/Closed_captioning
Thanks, yeah there is a lot of information there

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Old 04-05-2016, 04:52 PM   #10
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For TiVo to do this they basically have to generate the line 21 data themselves from the HD caption stream. Apparently they're not doing that correctly. Captions for 720p are different then captions for interlaced sources. We have a feature in VideoReDo that generates line 21 data from digital captions and we too had an issue with 720p sources that we had to use special code to fix.

Since TiVo has their own internal caption parser I'm not sure they have a lot of incentive to fix this issue. Your setup is quite unique.

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