Why isn't my VANC timecode seen by GetTimecode?

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wreuven

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  • Real Name: Reuven Wachtfogel

Why isn't my VANC timecode seen by GetTimecode?

PostMon May 18, 2020 12:45 pm

I think I'm missing some fundamental understanding.

Setup Decklink Monitor connected back to back with Decklink Recorder

Since the SDK doesn't allow the Monitor card to both set TimeCodes and also manipulate VANC for VideoOutput, I figured I could enable VANC without timecodes and use liklvanc to write a VITC timecode to line 9 of the VANC.

I write the Timecode to VANC on the Monitor Card and confirm that the The Recorder card receives the Timecode in the VANC as I wrote it. DID=0x60, SDID=0x60 etc...

What I don't understand is why the BlackMagic SDK doesn't see a timecode on the frame? Shouldn't it be looking into the VANC and see the timecode I wrote? Does it only look in a specific location?

Appreciate any assistance.
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wreuven

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Re: Why isn't my VANC timecode seen by GetTimecode?

PostMon May 18, 2020 6:15 pm

I just tried the same think with PAL instead of 720p and that worked!
I get different results from different resolutions. No idea why.
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Cameron Nichols

Blackmagic Design

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Re: Why isn't my VANC timecode seen by GetTimecode?

PostFri May 22, 2020 3:55 am

Hi Reuven,

Desktop Video products follow the Ancillary Timecode Packet location as defined by SMPTE ST 12-2. You shouldn't need to define your own VANC packets as this will only apply to SD, but instead use IDeckLinkTimecode interface to capture/output timecode in video frame.

Please refer to RP188VitcOutput example for timecode output and CapturePreview sample for timecode capture for examples.

Regards
Cameron
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wreuven

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Re: Why isn't my VANC timecode seen by GetTimecode?

PostMon May 25, 2020 12:37 pm

Hi Cameron,

I am trying to write the timecodes directly to the VANC because:
1) I want to set both RP188 timecodes AND SCTE104.
2) SDK does not allow EnableVideoOutput( ..., bmdVideoOutputRP188 | bmdVideoOutputVANC)

I am using libklvanc to generate the VANC payloads. Are you saying that Decklink Recorder is not seeing it because I need to write the timecode to a particular line or column? If so, could you tell me which line?

You wrote that my solution only applies to PAL. Why? Don't VANC timecodes work in all modes?

Thanks for any and all assistance you can provide,

Reuven
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wreuven

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  • Real Name: Reuven Wachtfogel

Re: Why isn't my VANC timecode seen by GetTimecode?

PostTue May 26, 2020 7:44 am

Hi Cameron,

I am now unable to reproduce the problem (enabling RP188 and VANC together) so consider this closed. Also confirmed the standards recommend for ANC timestamps in HANC so it makes sense that they are ignored in VANC.

Appologies for crying wolf.

What is odd is that I did find a post of someone else describing the same problem.
viewtopic.php?f=12&t=45951&p=266302&hilit=bmdVideoOutputVANC#p266302

all the best,

Reuven

P.S. For anyone who does not wish to pay for SMPTE 12-2, BT.1366 is free https://www.itu.int/dms_pubrec/itu-r/re ... !PDF-E.pdf

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