Progressive v Interlaced!

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Level 7

22,067 points

Progressive v Interlaced!

My wife wanted a video from 10 years ago so I dug out the SD card and dropped the clips into FCP X letting the project automatically set the specs.

After editing the project was just under 15 minutes long so I set it to export Computer>Faster>H.264 but imagine my horror when it took some 27 minutes to export.

What on earth was going on?

I wracked my brains for several minutes and ended up looking in the inspector which stated the clips were 25i.

So I created a new 1080p project and dropped the clips in. Immediately the top of the timeline revealed a row of dots showing that the footage was unrendered.

My first thought was that things would now be worse as it would take extra time rendering.

To my great relief, the export took less than 4 minutes!

I don't remember interlaced projects being such a pain to export . . . thank the Lord for progressive!

Posted on May 4, 2023 10:40 AM

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Answer 1

Top-ranking reply

Davis_

Level 2

219 points

May 4, 2023 4:52 PM in response to Ian R. Brown

Ian and Luis, I just ran a brief test scenario myself (one time for each export, so times may not be accurate).

Test: 18 minute 1080i29.97 clip in a Project, exported with Computer, H.264, Faster preset. No background rendering and not pre-rendered prior to export. Output file size was 2.7 GB in each case.

Test 1:

Interlaced clip 1080i29.97 in a 1080i29.97 Project. 75% CPU usage, minimal GPU usage.

10m48s

Test 2:

Interlaced clip 1080i29.97 in a 1080p30 Project. 25% CPU usage, minimal GPU usage.

2m52s

Test 3:

Interlaced clip 1080i29.97 with manual deinterlace via checkbox in Settings metadata view in Inspector in 1080p30 Project. 25% CPU usage, minimal GPU usage.

4m42s

I know (according to the FCP user guide) that when you check Deinterlace for a clip, it doubles the frame rate to get a high quality result. I believe that when you just have an interlaced clip in a progressive Project, and don't change any settings, on render/export one field is simply dropped during processing, yielding a lower quality result (especially where there's motion). So, this correlates well with the test times.

Test machine: 2019 Mac Pro, 12 cores, 96 GB RAM, two AMD Radeon Pro W5700X 16 GB GPUs.

My GPUs rarely get any real "exercise" when using FCP, Motion, or Compressor, especially for exporting. The exceptions are when using some 3rd-party plugins. Resolve makes better uses of my computer's available resources. Topaz Video hammers my system, pegging everything at nearly 100%.

Cheers.

P.S. - I do recall working on an hour-long NatGeo project in 2008 (1080i29.97) that took about 4 hours, or so, to export from FCP 6/7 in ProRes 422 (HQ). I remember it well, because the producer kept making last minute changes and was upset about the render/export times (as if I could change the export process)... ;-)

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Answer 2

May 4, 2023 10:45 AM in response to Ian R. Brown

It's a great thing that FCP does such a good job at deinterlacing.

I understand that there is a lot of legacy interlaced content, but why do people still produce interlaced content today (or anytime within the last two decades, for that matter) is beyond my understanding.

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Answer 3

Ian R. Brown Author

Level 7

22,067 points

May 4, 2023 11:19 AM in response to Luis Sequeira1

I can't understand why exporting interlaced took nearly 7 times longer?

Nor do I remember why I shot it as interlaced when my camera was capable of 50p . . . I must have been experimenting with interlaced and forgot to change it back to progressive.

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Answer 4

May 4, 2023 11:25 AM in response to Ian R. Brown

Just an (educated) speculation: probably your mac has hardware suport for encoding of H264, but that support only works for progressive material. If the interlaced has to be encoded entirely in software and not with the benefit of a dedicated hardware encoder, it could easily take a lot more time.

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Answer 5

Davis_

Level 2

219 points

May 4, 2023 12:06 PM in response to Ian R. Brown

Ian, as a test, you might try selecting the interlaced clips in the timeline (of the progressive project) and manually set them to be deinterlaced via the Settings metadata menu in the Inspector. Then, do an export and see if the time changes from your previous test...

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Answer 6

Ian R. Brown Author

Level 7

22,067 points

May 5, 2023 1:17 AM in response to Davis_

Thanks for testing. They more or less reflect my results except with yours, keeping the footage as interlaced takes 4 times as long and with mine it was more like a factor of 7.

I had completely forgotten there was a Deinterlace filter in the Settings so I tried that and the export time was around 11 minutes.

I don't know whether doubling the frame rate is the best way to describe it as 25 fps interlaced is really a sort of 50fps albeit they are "half" frames or fields.

I am guessing that it processes each half frame or field separately as opposed to simply doubling each frame?

Regarding Luis' query as to why so many amateurs shot interlaced, we had no choice with mini-DV and even with the advent of HDV etc. most (if not all) of the shooting modes were interlaced on consumer camcorders.

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Answer 7

Ian R. Brown Author

Level 7

22,067 points

May 5, 2023 1:34 AM in response to Ian R. Brown

I have now had time to examine the 3 different results and can confirm that selecting "Deinterlace" does produce 50 different frames per second and any motion in the image is smoother and flowing.

Simply dropping the footage into a progressive timeline produces 25p where the motion has a slightly staccato effect which is now perfectly watchable as we have got used to seeing it on HD TV.

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