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Old February 26th, 2009, 02:06 AM   #1
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Jittery motion on 720p 50

After reading a few threads here about how good action scenes were when shot in 720p 50 I decided to give it a go using the pp as recommended by the BBC for film type look.

I had to get some shots of a guy running and the results are somewhat odd in that I can only describe them as jittery, when viewed in Final Cut. It is particularly noticeable when moving vehicles come into shot, anything but smooth. Does anyone have any suggestions?

The footage is sitting on a raid which is easily capable of delivering the required data rate.

As I did some overcranking I shot to Sony SxS cards.

The settings in FC all look good so I am a bit at a loss. Does anyone have any suggestions?
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Old February 26th, 2009, 03:19 PM   #2
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What shutter speed did you use?
Have you tried to make a self contained Quicktime movie to look at it elsewhere?

Sounds strange as I have been shooting extreme sports for a week, paragliding, speed flying, base jumping, skiing etc and the results have been super smooth, in slo-mo as well.
We chose 720 50P to be on the safe side due to all the fast action.
We never had faster shutter speed than 1/120 (in 60fps) and mostly shot with shutter off.

Check it out here.
YouTube - TEAM INSOMNIA - NIssan Outdoor Games

Specially from 4.40 you have really fast action.
Itīs compressed for Youtube so it looks better in real life
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Old February 26th, 2009, 03:34 PM   #3
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Still Jitttttery

Hi

Yes this is a strange one. I used a shutter speed of 100 for the 50fps as I though that would give smooth movement, was this a mistake? What is odd is I have this guy running down some steps, and I am panning with him, he then sets off running away from my position, and at the same time a car and van drive by, and while the motion of other passers by look fine the motion of the van is best described as jittery and hesitant. It is almost as though the vehicles and people are existing in a different time frame!
I have other shots of just the runner and he appears to be going along smoothly then, it is almost as though he hesitates. Again the funny thing is, it was a windy day, and the long grass blowing beside which he was running appears to be moving normally!
I concluded that it must be something to do with the speed of the van/runner, frame rate and shutter speed? or does anyone have a better answer.

Yes I have tried all sorts of re-rendering in Compressor, nothing appears to work
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Old February 26th, 2009, 05:14 PM   #4
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Have you tried rendering out a movie from the FCP timeline at, say, SD resolution and playing it back to see if it shows the same jittering?

Could you post up an example for us to see because the term 'jittery' can mean different things to different people.
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Old February 26th, 2009, 05:23 PM   #5
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<I had to get some shots of a guy running and the results are somewhat odd in that I can only describe them as jittery, when viewed in Final Cut. >

Final Cut viewing does not show final quality.
One must output it to see the final.
You may only be seeing a 15fps video.
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Old February 27th, 2009, 04:15 AM   #6
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Hi,

please assure if the video looks that way too if played directly from the cam (via HD SDI out or Component etc.)?

Thats just to clarify if its the recording or the editing causing your experiences.

Regards

ULI
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Old March 2nd, 2009, 11:38 AM   #7
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Quote:
Originally Posted by Eric A Robinson View Post
Does anyone have any suggestions?
Don't forget 720p50 is double the trouble of 720p25 - even if the disk array is up to the job, something's got to give, including the processing power required to 'rehydrate' the compressed movie onto the screen. This may sound strange but have you tried using less compression? A frame based codec?

I did some tests on 720p50 and downconverting to PAL, if that's your methodology. There's some preliminary notes AND a downloadable DVD image which goes through various permutations here:

EX1: Downconverting

OTOH, it can be a reinterlace issue. This very afternoon, was laying off some 720p25 projects to DVCAM and saw the jitters on my CRT monitor - silly me, forgot to tell FCP that we're working in progressive and that the footage is progressive. With everything set, it's perfect.

Final thought: I edit on a MacBook Pro 17", and sometimes - with everything else that's going on in such a limited machine - I get 'gritty' playback. Jittery? Not quite. But once a movie's exported and playing in its intended environment, the grittiness has gone.

Oh - and one more thing: haven't actually done any definitive test on this yet, but over-cooked detail or sharpness settings can reportedly exacerbate stutter. Most of the Picture Profiles here have detail and sharpness wound down or off, but I know of many EX1 shooters who are still using default settings.
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Old March 2nd, 2009, 02:14 PM   #8
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Good read Matt,
I was thinking that I shoot @ 720/50p and go to SD DVD. If compressor is throwing away everyother field to acheive 25p why do I shoot in this format.

The only reason that I shoot in720/50p is I get better looking SD DVD's, smooth motion and smooth speed change in FCP.

Have you done tests using 720/25p and if so what conclusions did you come to.
I know shooting 25p you have to be carefull panning and 50p , well it reacts a bit like 50i.

Regards
Simon
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Old March 2nd, 2009, 02:30 PM   #9
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Originally Posted by Simon Ash View Post
If compressor is throwing away everyother field to acheive 25p why do I shoot in this format.
Ack! It may need another re-write - I've obviously not quite got the info clear in the document.

So, in the Inspector Window, with your compression settings already dragged into the batch window - where you put a compression setting onto a source movie)... and yes, I can see why this isn't quite as clear as I'd like...

Enable frame controls (third tab) by clicking the gear icon, then choose 'On' from the pop-up. Set Output fields to Upper (DVD presets) or Lower (DV presets).

And then you're pretty much done.

I'm going to make this into a screencast - it will be short. So much simpler to see it being done rather than writing it out long-hand.

But honestly, once these little wrinkles are smoothed out, this whole 25p & 50p thing - your choice - is not really a problem. I'm pretty sure (speaking for FCP only, here) that the problem is that stutter comes from helpful software trying to reinterlace where it shouldn't be OR not re-interlacing when it should be.
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Old March 2nd, 2009, 02:56 PM   #10
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Cool Matt,
I've gotta say that once I made the change from 1080p to 720/50p my DVD's are looking better and also having sharpness down to 25 on the EX1 also helped in this change.

Simon
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