Interlaced from Progressive

[Shane Ross]

First off, are you sure it’s REQUIRED to have interlaced? If so…shoot interlaced and deinterlace the progressive master.

Second…1080/59.94 in progressive and interlaced is actually different frame rates. 1080i59.94 (interlaced) runs at 30fps (29.97). 1080p59.94 (progressive) runs at 60fps (59.94). What the number after the “i” and “p” stands for is “images per second.” Interlaced footage is even and odd fields, and two fields per frame…so 60 images, 2 images per frame…30fps. Progressive footage is one image per frame…so 59.94 is 60 frames per second.

Best to shoot interlaced…then deinterlace the footage when delivering the progressive master. I don’t know of an encoding software that will turn full frames into even and odd fields. If there is, someone PLEASE correct me. But DVD encoding is so old, does it even know how to deal with 60fps?

[Dennis Couzin]

So you need a 30p and a 60i, because those are allowed DVD formats.

With any monitor other than a CRT, the 60i DVD gets deinterlaced. Often this is “double deinterlacing” so one sees pseudo 60p video, which looks damned good. With luck, the 30p DVD looks like 30p.

If you shoot 60i and then deinterlace it to make pseudo 30p there will invariably be some deinterlacing artefacts in that. So you would ideally shoot 60p and make both the 30p and the 60i from it. Making the 30p is trivial but making the 60i is some work.

The brutish DIY method requires a mask with clear and black lines that alternates top line black, top line clear from frame to frame. In FCP7, you lay it on the 60p — Modify > Composite Mode > Multiply — and export the thing. Then you add — Modify > Composite Mode > Add — the thing to itself shifted by 1 frame. Then you discard every other frame by doubling the speed. You attended to the field dominance, so finally you dub it the 60i (30 fps) interlaced product using QT Edit or another metadata editor.

I was delighted to discover that Compressor v.3.5.3 can be tricked into doing the interlacing work for you. I fed a 60p clip into Compressor. In Standard Video Compression Settings, Frame Rate was 60 and Interlaced was selected with Bottom field first. In Frame Controls, Output Fields were selected Bottom first and Duration was set to 200%. Compressor worked hard on this and produced a strange 60p giant in which every other frame was interlaced! Since the first frame wasn’t interlaced, I chopped it off in FCP7, and then sped the thing to 400% speed. The result is the desired 60i, and it only needs to be dubbed as such using QT Edit or equivalent.