Decklink 4K cards and 480i/576i

I reported this 9 months ago but I don't recall getting much of a response on this...

The Decklink 4K cards in our test bench seem to have a problem with 480i and 576i where the second field is shifted down about 8 lines than normal, which makes for some very jittery output. Some of our clients want to do 480i output with the cards. When will this be addressed?

The same cards provide a 480i downsampled composite signal just fine if programmed to do 720p HD-SDI output.

Here's another interesting bit about the problem: It only happens on our systems if the code writes to the vertical ancillary area. Turning off VANC support eliminates the issue, turning it back on brings the shifted field problem back.

It has something to do with whether or not our code creates AncillaryData buffers and attaches them to frames, apparently.

One more thing.

It looks like it's tied to whether or not our code is requesting the ancillary scanlines from the vertical ancillary buffer. What scanlines we request and what field it comes from seems to factor into how many scanlines the image is shifted down on the second field.

If we only request scanlines from the object for the first field, then the second field is shifted down 1 (based on visual inspection) scanline. The 4 scanline shift is if ancillary scanlines from both field are requested.

I know that 480i frames actually arrive to the SDK as 720x486 and usually the bottom 6 rows are black for me, so I just ignore them, and they usually can't be compressed easily either since 486 is not a multiple of 4 (a requirement for some encoders), but I suppose you may be actually using those lines for data. I have not used the VANC support so not sure if this helps but just thought I would chime in.

Good luck!