[FFmpeg-devel] [PATCH] avdevice/decklink_dec: Extract 1080i and NTSC VANC

Ray Tiley raytiley at gmail.com
Tue Jan 23 06:20:10 EET 2018

On Mon, Jan 22, 2018 at 11:12 PM Devin Heitmueller <
dheitmueller at ltnglobal.com> wrote:

> Hi Ray,
> > On Jan 22, 2018, at 10:47 PM, Ray Tiley <raytiley at gmail.com> wrote:
> >> Could you confirm whether you are capturing via SDI or analog (i.e.
> >> composite/component)?  Also what is the capturing device and SDK version
> >> you are using?  I’ve found various bugs in the numbering of VANC lines
> in
> >> some cards, particularly with interlaced formats, and it would be good
> to
> >> understand if perhaps this is a card-specific issue.
> >>
> >> I'm capturing SDI, the only decklink card I have access to is the
> Decklink
> > mini recorder, and I was using the latest sdk ( I can check exact version
> > tomorrow during work.) It's definitely possible I expanded the search
> lines
> > a bit too far, I was just hacking until I found the data.
> Ok, so it’s possible that in the three cases you’ve changed, the start
> line was actually fine to begin with and the problem was just the end line
> was wrong.  I could totally believe that.
> I can say that all three start lines are correct according to RP 168, but
> I would have to do the math to check the end lines (there was a time I
> could tell you from memory where the active video starts/ends for each
> video standard, but those days are long gone).
> >
> > The source equipment was again a Matrox LE4. The source file was 1080i
> > while I was testing the NTSC output, so it was perhaps a scaling issue.
> > However the spec says that VANC data will be on the luma channel for high
> > definition sources, so that is why I tried extracting it from the
> > interleaved and was able to successfully parse the VANC packets.
> Right.  At least in libklvanc I don’t even bother looking at the chroma
> channel, since I’ve never seen a piece of equipment that puts any VANC
> there.  For CEA-608 payloads and CEA-708 CDP packets, SMPTE ST 334-1:2015
> Sec 4 clearly states that it must be in the luma channel for HD sources.

I'm reading 334-1:2017 Sec 4
"When the ANC packets defined in this standard are carried in a high
definition signal, they shall be carried in the Y stream."

I couldn't find anywhere in the document where it calls out standard

Conversation is here:
https://video-dev.slack.com/archives/C0XKDDH5Y/p1516141555000074 with
kierank at obe.tv who I believe is in the ffmpeg-devel IRC.

> >
> > I chatted with someone in the video developers slack community and they
> > suggested that for NTSC the data is indeed interleaved.
> Hmmm, this is a pretty ambiguous explanation.  Got a link to the
> conversation?
> I also wouldn’t rule out a decklink bug, but it’s too early to make such
> an assertion.
> If you can get a dump of the raw VANC line data that I can review, that
> would be helpful.
> >
> > I have access to some SD captioned files that I can play out my test
> > hardware to eliminate scaling.
> Great.  I think you’ve definitely found some issues - it’s just a question
> of whether we really have to deviate from the spec in order to work
> properly for your use case.
> Devin
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