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Old June 22nd, 2004, 01:49 PM   #1
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FCP slow motion/strobe issue

Every time I slow my clip down below 70% I get this strange strobe effect. If I bump it up to 80% it goes away. Any advice on keeping it slow but strobe free?

Thanks in advance.

Michael
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Old June 22nd, 2004, 02:49 PM   #2
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The clip in question was shot at _____ fps on a ________ camera.

The footage (is)(is not) deinterlaced?

You are observing this "strobing" while viewing the footage on ____________?
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Old June 22nd, 2004, 02:55 PM   #3
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Sorry for the lack of those details. It's shot at 30i. And I observe the strobing while viewing playback on FCP and on a monitor as well.

How do I deinterlace my footage?

Thanks Ken for the attention.
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Old June 22nd, 2004, 04:54 PM   #4
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I don't mean to be pedantic, Michael, but there is really no such thing as "30i". (If you've discovered it, that would explain your stobing!). I think you mean "60i"; two interlaced fields captured 30 times per second...standard NTSC, eh.

FCP's intrinsic ability to create slow footage is somewhat limited. Most good footage with limited motion can be slowed to 50%. But beyond that, you'll probably have to spend money. The issue is that the program must create synthetic intermediate frames to fill-in between the real frames. The greater the speed reduction, the more frames must be synthesized.

Beyond this basic explanation I doubt that anyone will be able to tell you exactly why you're encountering this at this specific point. Perhaps the footage was shot under standard fluorescent light and you've reached a timing boundary that's now replicating, and thus magnifying, darker frames?

There are 3rd party products, such as Twixtor, that are dedicated to this job and can produce a better effect.
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Old June 22nd, 2004, 05:05 PM   #5
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I think you probably mean 60i at 1/30 sec shutter speed? For starters you might try shooting at the standard 1/60 sec shutter speed. That will give FCP twice the data to use in creating slow motion and give you better results. When you shoot at 1/30 second your camera essentially loses 50% of its vertical resolution since the same data is being written to each of the interlaced fields.

But I'm a little surprised that you see a stobe effect at 70%. I found that shooting at 1/60 sec I could get acceptable slow-mo at 25% speed (for my application, which was sort of "artsy"). The strobe effect usually is the result of shooting at too high a shutter speed, like 1/100 or faster. Are you sure the camera was in manual mode and not automatically increasing shutter speed?

De-interlacing can be done with an FCP plug-in like Joe's Filters or a standalone program like DVFilm Maker (or some other options as well). However if you do want to deinterlace (which isn't at all necessary but can help a bit with a "film look") then it should be done as a final step AFTER you have slowed down your footage. Otherwise you will limit the amount of temporal data FCP has to work with during the speed change.
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Old June 22nd, 2004, 07:05 PM   #6
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Sorry guys...it was a typo...I meant I shot in 30fps interlaced.

The shot is naturally lit outdoors. It's disappointing that FCP can't handle this because the result is definitely disturbing.

Thanks for the words of wisdom.
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Old June 22nd, 2004, 07:59 PM   #7
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Michael, did you look at my earlier suggestions? Sorry to nitpick, but you still have not told us what your shutter speed was. FPS=Frames Per Second. This is completely independent of how long the shutter was open while capturing each frame. If you're shooting at 1/30 sec shutter speed I wouldn't expect slow motion to look very good. If you're unsure what the settings were on the camera, play the tape back and turn on the "data code" which will display what your shutter speed was.

And as I said, I 've been quite happy with FCP's ability to do slow motion. We slowed down quite a lot of long sequences which we showed with a 10,000 lumen DLP projector on a 44' wide screen in one of our operas. The video got a rave revue and nobody noticed any "strobing". Perhaps you need to define that term, to me it means that the video is flashing on and off. Do you just mean that the motion is jerky? Or perhaps you just have an unrealistic expectation of what's capable with 60i video?
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Old June 23rd, 2004, 11:27 AM   #8
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Boyd, sorry for the lack of specificity. The footage is shot with a TRV that does not have manual control, therefore I assume it's shooting 1/60th of a second. When I shoot, I never shoot 1/30th or less unless I'm looking for a specific effect.
The effect is a strong flashing on and off in the image, and would be very conspicuous to anyone from the layman to the pro. This effect as is makes the footage unusable but I have to use it for this project because it is an event that only happened once. I've edited a lot of footage before, and like you I've never seen this effect before. Also, I've never seen it with any footage that I've personally shot. No, this is not a limitation of 60i, but the only thing I can think of is possibly a condition in the camera or a substandard tape. What do you think?

and it's all right to nitpick, any idea may conjure up an idea.

Thanks,

Michael
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Old June 23rd, 2004, 11:42 AM   #9
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I would not assume the shutter speed is locked at 1/60 on a cheap camera without manual controls. I think it's pretty common for the camera to increase the shutter speed to compensate for bright outdoor conditions, especially if it doesn't have builtin ND filters. Maybe you can play your tape in another camera that offers the "data code" function so you can see what the shutter speed was.

If the video was shot with a high shutter speed, like 1/500 for example, you might get the effect you describe. This is because each frame captured is a sharp image without any motion blur and only represents a 1/500 second slice of a 1/30 sec window. When FCP tries to synthesize a new frame from two very different adjacent frames it will give poor results. You might try turnng off frame blending (if it's enabled in the speed dialog box) and see if that helps. This would still give jerky motion, but might help since it will just duplicate existing frames instead of trying to make new ones.

Sorry, other than that I don't know what the problem might be. A tape problem seems unlikely and I really doubt that FCP is causing a strobe effect. That would narrow things down to something in the camera....
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