[FFmpeg-user] Export Subtitles live from HD-SDI

[Deron]

On 10/7/15 7:05 AM, florian.hesse at rbb-online.de wrote:
> Hello everyone,
>
> i'm working on a project where we want to livestream one TV-Program with
> MPEG-DASH. There for we need seperate subtitles. The encoder gets the
> signal over HD-SDI wich supports embedded subtitles in Teletext with SMPTE
> 2031.
> Our capturecard will be a Blackmagic Decklink Duo wich supports VANC-Data.
>
>
> I know that ffmpeg can extract closed captions from files. But what about
> Livesignals like from SDI-Signals?
> Thank you,
> Florian
>

I am currently trying to get the decklink card to output CEA-708 closed 
captioning, so I can tell you a little about what I know so far. The 
current driver does not support capture or playback of VANC/closed 
captioning. The capture does support 10bit as I recall, which is the 
first thing you would need just to be able to capture the VANC. I don't 
know anything about SMPTE 2031, but at the very least you would need to 
ask for the correct DID/SDID for SMPTE 2013 and then place that data in 
a Teletext stream. That would require a patch to the current ffmpeg.

When/if I get this output to work, I would certainly be willing to try 
my hand at creating a patch for this. I wish someone out there had a 
decklink card that could capture live tv in North America. Having some 
real world data to look at would make creating the CEA 708 output easier...

Deron