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

Deron deron at pagestream.org
Thu Oct 8 19:40:56 CEST 2015

On 10/7/15 1:40 PM, Florian Hesse wrote:
> Are you sure its a problem by the driver? The Blackmagic productpage
> says VANC is supported and as far as i know they developed the drivers?
> There just seems to be a problem with some lines below the SDI switching
> points https://forum.blackmagicdesign.com/viewtopic.php?f=12&t=32029
> Do you know if it works with dectek-cards and drivers?

I'm not sure if you are asking me or someone else, but I'll do my best 
to answer.

VANC is just a means by which Ancillary data can be sent in a SDI 
stream. That data can be all kinds of things, including audio, closed 
captioning, camera control, or private data between devices. The 
Blackmagik Decklink drivers support the capture and play of this data.

The ffmpeg decklink driver sends no VANC data, makes no connections to a 
subtitle stream, and does not support 10bit YUV which using the VANC 
requires. It is not really a "problem", in that support has never been 
added. Not a bug, but a design choice.

The choice of outgoing VANC lines for CC does not mater much. It only 
maters if you are capturing VANC and some other device is putting it on 
one of those lines mentioned in your link in which case it sounds like 
you would need the Decklink Extreme card. Do you know what line your 
device is putting the VANC on?


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