Change 2:2 Telecine field cadence?

Question

Hi!I stumbled across a weird problem while working on a problem with a lot of SD footage from DVD. A quick primer to set the stage:The material in question was originally shot on film and comes from PAL DVDs. Europe deals with film on TV in a straight forward way. It is played back at 25fps and every frame is shown as two frames of video - so there is no real difference between progressive and interlaced DVDs like in the US. All DVDs are 25fps and you either treat it as progressive or 50Hz interlaced. My problem:Most of the material is fine. Every frame of film was scanned as two frames of video (top field- bottom field) when it was telecined back in the 80s and when it was digitzed those two fields became one frame again.But for a little over 30% the cadence is wrong. and it was telecined as bottom field - top field. Back in the days of CRTs this was no issue but now every digital frame consists of to fields that don't belong together. On a base level I would need to split a frame (F1) into to fields (F1a and F1b) and then match F1b with F2a, F2b with F3a and so on. I could treat the footage as interlaced but that leads to a loss in resolution. Is there a way to correct what someone messed up in 1983? &#128516;Thank you

Björn25807059coj1 · Accepted Answer

"Baked in" is a relavtive term. There is no interlacing in digital video. It's just progressive frames with the information to display all odd lines at a different point in time than the even lines.

Nevertheless... I did it. I'm not proud of HOW I did it, but I did it anyway. So, if nobody knows a better method, here's what I did:

1. I created a PNG file (720*576) with alternating lines of garish green and transparency. Feel free to download mine if you need one.

2. Next I created a new sequence (Sequence 1) with the messy source and added my grill pattern on top. The video and sequence are set to progressive and all is set be be interpreted as the same PAR.

3. Then I used Ultra-Key to key out the garish green. This leads to a picture with half of the lines missing.

4. After that I created a second sequence (Sequence 2) with the original file at the bottom and sequence 1 above it and shifted this sequence one frame to the right. This leads to the top field being one frame ahead of the bottom field and the picture is as good as it can be.

5. Of course I had to mute one of the two audio tracks.

So... that's a solution but there has to be a better way. Today I received two older movies on DVD with exactly the same problem...

Ann Bens · Answer

If it's baked in (as in a progressive file), you are stuck with the interlaced artifacts.

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