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Interlaced / progressive conversion / export

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Adrienne Liron
Interlaced / progressive conversion / export
on Feb 8, 2018 at 8:17:07 am

Hi, I hope someone can help with a tricky question!

We have a programme shot in 1080 50i. We chose interlaced because that's how we have to deliver the programme to the broadcasters.

However the programme includes an intro from another source which is p.

When we added the progressive material to beginning of the programme, the entire project changed to p. (I assume the project was set to base itself on the first clip on the timeline.) The multicam clips that make up 99% of the project also changed to p. We didn't realise this had happened and we made an export, thinking we were making an interlaced export.

When we took the file to do some compositing on it, the compositor remarked that the video info described itself as i, but the exported material was actually p.

When we look at this accidental progressive conversion on a computer monitor, it looks good.
However we got the post-production facility to test it properly, and on a professional monitor, 'it looks like it was shot at 50 and then exported at 25'. The tester's theory is that the FCPX 'conversion' from i to p 'threw away' half the frames.

We showed a clip of the progressive export to one of the broadcasters awaiting the programme, and they said it looked good, and they would be happy to receive the project in progressive. However based on the test we did, I feel very unconfident doing this! I would really appreciate the advice of the experts on this forum!

I am assuming that since we shot in i, the best course of action is to modify the project settings and the multicam clips, switch them back to interlaced, and re-export.

Will this also make the progressive footage in the intro interlaced?

Is this our best bet in terms of quality?

Any advice much appreciated...

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Sam Lee
Re: Interlaced / progressive conversion / export
on Feb 8, 2018 at 1:39:26 pm
Last Edited By Sam Lee on Feb 8, 2018 at 1:40:09 pm

I worked on this conversion regularly on many 1080-25i originate materials. What irritates me the most is broadcaster adding interlaced ending credits to a progressive content (opposite of what you have) instead of spending a bit more time getting a true progressive scan master. A good way to test the resolution is to have a camera source shoot a resolution chart in 1080-25i and 25p. Perform various field interpretation and export it out to check for sharpness. I found out FCP X does a OK job of fully taking two fields from a 1080-25i and merge them into a full resolution 1080-25p if the clip is properly interpreted it prior to adding it into the project. Prior to this, I relied on Compressor and it was a mistake. Compressor will not merge the 2 fields of a PsF interlaced content properly. I have to manually specify the scan type in FCP X instead of doing an easy global export out setting in Compressor.

PsF can be either interlaced or progressive. This has downsides. It's adding unnecessary extra work to properly categorize the scan type to prevent artifacts or softness if the 2 fields are not properly treated when using it as progressive scan. Many times I was fooled by the setting until I noticed the footage is just a bit soft due to improper field interpretation setting. Arghh. There's no other way except to eyeball and set it correctly.

Be very careful about combing artifacts if the interlaced footage is not properly de-interlaced into a progressive scan project. This is not needed if it's originally shot in progressive scan but exported out as interlaced. Mostly applies to live broadcast cam 50i or 60i materials. Also look for signs of aliasing and jaggies or any other abnormalities during the de-interlacing process.

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Jeff Kirkland
Re: Interlaced / progressive conversion / export
on Feb 9, 2018 at 8:44:29 pm

I’ve alawys been wary of FCPX’s ability to deinterlace properly. I’ve definitely had material rejected by broadcasters here in Australia when I’ve let FCPX handle it - but it’s going to vary from one QA department to another.

Setting the project to interlaced and re-exporting is definitely the best way forward.

Jeff Kirkland | Video Producer & Cinematographer
Hobart, Tasmania | Twitter: @jeffkirkland

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