Closed Captioning – VANC data - Blackmagic Design

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Closed Captioning – VANC data

Posted by Andy Forest on September 22, 2005 at 2:53 pm

I am really happy with the flexibility of the Blackmagic products. I can use them to output closed captioning data to the proper portion of the video signal, outside of the visible area.

However, to get this to work properly, I had to use a strange work-around, so I thought other people might be able to benefit from this information.

I have a Decklink HD card, and a Multibridge. I am using this combination to output SD video to a Sony UVW-1800 Betacam SP deck. I have generated line 21 closed captioning data from Unisay’s Subtitler program, and overlaid the CC data on line 3 of the video file.

The Decklink control panel lets you output specific lines of the video file onto specific lines of the VANC data. I tried outputting line 3 to line 21 of the VANC data, which is where the CC information is supposed to go, but this did not work. Through trial and error, I came up with these settings in the control panel for CC data to be output properly to tape:

Video line 1 – VANC line 18
Video line 2 – VANC line 19
Video line 3 – VANC line 20

This makes no sense to me, as according to these settings, it is not even outputting anything to line 21! I did some more tests, and captured some video with closed captioning from a Betacam tape that had been prepared with a completely different system. Here are the settings that I used for capturing the video:

Video line 1 – VANC line 19
Video line 2 – VANC line 20
Video line 3 – VANC line 21

Somehow, using these settings, the VANC line 21 CC data ends up on line 2 of the video. If I output this video back to tape using these exact same control panel settings, the CC data is not output properly. I have to change the settings back to this on output:

Video line 1 – VANC line 18
Video line 2 – VANC line 19
Video line 3 – VANC line 20

So for CC data on line 2 or line 3, these settings work for output.

Thanks,
Andy Forest

http://www.dimentians.com

Luke Maslen replied 20 years, 10 months ago 2 Members · 1 Reply
1 Reply

Luke Maslen
September 26, 2005 at 6:13 am

Hi Andy,

Thank you for your clear and detailed report. We’ll check it out on our test suite and see if we can work out what is going on.

Regards,

Luke Maslen
Blackmagic Design

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Closed Captioning – VANC data