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

Deron deron at pagestream.org
Wed Oct 7 17:31:32 CEST 2015

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...


More information about the ffmpeg-user mailing list