VANC (Ancillary data, e.g. captions)

[John P Poet]

On Wed, May 18, 2016 at 7:13 AM Sebastian Dröge <sebastian at centricular.com>
wrote:

> On Di, 2016-05-17 at 22:24 +0000, John P Poet wrote:
> >
> > What is the best way to handle VANC?
> >
> > An ex-coworker came up with a patch to add VANC processing to
> > GStreamer version 1.2.3 for Blackmagic cards.   Unfortunately, he
> > never pushed that code upstream before he left.
> >
> > With his patch, the VANC was extracted from the Blackmagic driver and
> > then pushed onto the gstreamer pipeline -- similar to the way video
> > and audio was pushed onto the pipeline in V1.2.3 of Gstreamer.  He
> > then added a VANC sink pad to ffmpegenc to encode the captions.
> >
> > Since version 1.2.3, the GStreamer Blackmagic support has been
> > completely re-written, and it no longer works the same way.  I would
> > like to take the work that my ex-coworker did, and adapt it to the
> > latest version of GStreamer, but I am unclear on what the proper
> > approach would be.  Should I effectively clone gstdecklinkvideosrc
> > into gstdecklinkvancsrc and tweak it as appropriate?
> >
> > I don't see any established support for processing captions.  Has a
> > roadmap been defined?  If I get this working, I am hoping that my
> > work will be accepted upstream, so I would like some guidance on how
> > to do it right.
>
> There's
>   https://bugzilla.gnome.org/show_bug.cgi?id=766419
> for adding specific "processing captions": timecodes :)
>

That is a possibility.  I would have figuring out how to convert VANC
captions into SMPTE time code format.  Or, just add the VANC as more
metadata...


> To me it seems like VANC shouldn't be a separate stream but also
> GstMeta on the audio/video buffers. As it is metadata about those and
> not an independently useful streams.
>

I will look into that.  Either way, the next step is adding sinks for the
appropriate encoders/muxers to deal with that data.


> What do you think? What are your use cases for VANC?
>

I want to have the closed captions available in the resulting mpeg2 and/or
mpeg4 and/or transport stream.  When I play the resulting file in vlc, for
example, I want to be able to select which captions I want to see.

 Thanks for the pointers.

John
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