50p - Recorded Frames backwards I think? Any Fix?

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skatajkid

Active member
So I shot some 50p on the F35 to an O7Q this weekend and I was working fast and when I plugged in both SDI cables for 50p I'm 99% I had it backwards - it looked fine on the odyssey from what I remember, but the DPX sequence that was recorded definitely has some funky issues. I think the interlacing is backwards or something? Or maybe the frames were recorded backwards (i.e. - 1 should be 2, and 2 should be 1, and so on)

Is there any easy fix? In after effects when I tried to deinterlace using upper or lower fields first I get CRAZY jitters.... should I try renaming the files? Any easy way to do this with like automator or something?

figured maybe someone ran into this before - and if anything else - ALWAYS MAKE SURE YOUR SDI CABLES ARE GOING TO THE RIGHT PLACE!
 
Just thinking about this now - not sure why it would be interlaced as it's 50p, but it is for whatever reason the O7Q recorded it that way.... this is super annoying. I think I may just have to make them 25p and delete every other frame or something....
 
skatajkid said:
Just thinking about this now - not sure why it would be interlaced as it's 50p, but it is for whatever reason the O7Q recorded it that way.... this is super annoying. I think I may just have to make them 25p and delete every other frame or something....
Click to expand...

So, it's 50p over dual link. Isn't each cable carrying a 25p stream? You would only have interlace issues if each cable is carrying 50i and it's being merged. But...

If each is a 25p stream, that means each frame is a real, full, progressive frame. But if you cabled them wrong, then you might have them out of order for playback.

ABCDEF becomes BADCFE which means you step back one frame, then jump forward three frames, then back one again. So you would have a freak stuttering effect.

But if that's what it is, in theory there's no reason either an NLE filter or a stand-alone executable couldn't be used to reorder the frames. It's fairly simple and predictable math.
 
Btw, thinking about this - despite what I said, your 50p file shouldn't have interlace issues, but depending on your playback method, the playback might. The reason being, if your 50p files are playing out over 50i interlace hardware, those out of order progressive frames are being interlaced for playback. But the fix is with the progressive files I think, not with interlace filters.
 
Yeah - I'm not really sure what was happening in the camera or the O7Q... I would have assumed it was a 25p signal from each, but I think you're right in assuming it's a 50i getting mixed. Therefore my fields are all off cause it was mixing one frame forward and one frame backwards instead of both being in step with each other.... I had done it before and didn't even consider this as I did it right that time and had no issues haha. The reduce interlace flicker in AE solved the issue, but made everything awfully soft which is depressing. I might try an NLE next as none of the re-ordering modes in AE are doing it right as far as I can tell....
 
skatajkid said:
Yeah - I'm not really sure what was happening in the camera or the O7Q... I would have assumed it was a 25p signal from each, but I think you're right in assuming it's a 50i getting mixed. Therefore my fields are all off cause it was mixing one frame forward and one frame backwards instead of both being in step with each other.... I had done it before and didn't even consider this as I did it right that time and had no issues haha. The reduce interlace flicker in AE solved the issue, but made everything awfully soft which is depressing. I might try an NLE next as none of the re-ordering modes in AE are doing it right as far as I can tell....
Click to expand...

Can't you parse through the frames on an NLE one by one using the progressive computer monitor for single frame viewing? Take any external hardware out of the picture for the troubleshooting. See if you can pick individual frames as edits, and move them around each other. make sure the timeline is 50p as well.

If it was recorded as 50p from two 25p streams, it should be a reordering issue.

Any chance you can upload or drop box a short 5 second clip?
 
Conformed to 23.98 in the O7Q - you can set the timebase when you record DPX. The original DPX sequence is the exact same way. Comes into AE and Resolve as 23.98 already conformed from the 50p signal. You can re-conform it to 50p and thats what I got from the Odyssey.
 
Gotcha.

K. Just read a document on 50p and it looks like it does send 50i over each link. So by mixing the order you get the interlace error you have.

Any chance you have two dual link recorders than can handle 50p, and can reconform the footage to 50p?

Because, I wonder if you could fix this by feeding the video from one recorder to another, and just reversing the cable wiring a second time. That might just do the same interlace error in reverse, fixing the problem.
 
Haha it's worth a shot! I was thinking about maybe trying that somehow, but I have to see what I have. Or maybe it just even plays back ok from the O7Q... I'm going to toy with hardware tonight with it as no software is really getting me there.

Good to know on the 50i - and good for EVERYONE ELSE TO KNOW TO NOT SWAP YOUR CABLES haha.
 
So, here's a theory. I was looking carefully at the arm in your video file. It shows the interlacing the most clearly. I think it every pair of lines is out of order vertically.

So get this. It's sending two 50i streams over dual link. But as far as I can tell, it's sending them in simultaneous lockstep, which suggests that each link is sending one field of the full image (as opposed to each link sending full frames one link at a time). That means that one link is always sending the upper fields, and one link is always sending the lower fields. By flipping them, your vertical lines read 214365 instead of 123456. That is, each pair is out of order.

A custom NLE or photoshop filter could be written to fix this, I think. But it might be most practical to simply cross the wires and re-record in realtime over 50p.
 
Yeah - I think that's correct, which is frustrating as it seems like the most difficult fix. I tried making a pixel mask in AE to move the fields into sync, and MAYBE that could work, but I didn't really get good results the first time I tried. It didn't line up as expected, but I just shifted one field back a frame which I don't think is the solution, I think it's as you're saying they need to be reversed... I think I can do it though...

I'm gonna try re-recording it to a pix at 23.98 but I don't think that will work. I wish I had another O7Q to try this crossing wire thing on... I could output it from an NLE maybe but I have to figure out how to get the signal to output in the right way so that crossing the wires will fix it.

I have the footage in a useable state, but its like probably about half rez maybe? Which sucks, as it should be so much more resolute.
 
So, I have a solution for you. I used it on your test clip and it worked.

1. Take your 23.98p clip and conform it to 29.97p
2. Drop it in a 60i timeline on Premiere
3. Under "Field Options" put a checkmark on "reverse field order"
4. At this point you should see the problem visually correct itself when you confirm the change. But now we need to get your footage back to progressive 23.98.
5. Export your timeline, saving it to a 29.97p file. The saved file should preserve the now flopped (and corrected) field order.
6. Now re-conform your 29.97p file back to 23.98p.

I expect DaVinci could do the conform, but I used Cinema Tools. My testing was done in an OSX environment.
 
Hmmmm - i just tried this and I still got the weird interlace jitter... maybe I didn't do it right, but I'm messing with it....
 
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