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Motion Cadence / Stutter / Strobing


Matthew Capowski

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Greetings,

One of the hardest concepts I've grappled with in understanding digital cinematography is motion cadence.  As best I've understood, some cameras render motion in a superior and/or more cinematic manner than others.  Is there any objective way to discern this?  This may in part (or whole?) be due to the codec (e.g., All-I versus Long-GOP) and may be in part due to other reasons (processing of the image off of the sensor?) or other factors that I'm not considering.

Then there is perhaps a separate issue (or is related to the motion cadence?) where some panning looks horrible due to stutter or jutter or some other term? And then there's flickering and strobing related to artificial lights and frame rates?  Watching stutter hurts my eyes to watch.  It's like there is some kind digital artifact leaving a resonance or afterimage in the image and looks unnatural and unpleasant.  These are some examples of this:

 

Maybe I'm not understanding the above video on how to avoid stutter as all the pans look like they stutter to me.

I understand how shutter speed/angle can become a relevant variable in the equation, but if one is shooting at a 180 degree shutter angle shouldn't that solve the issue?

And then to add more complexity, there is the question of the screen that you're playing back on, and its refresh rate.  And many of the videos I'm watching are on YouTube -- so is you YouTube doing something to make the equation worse? But I've seen this on my own files from my own cameras. And I've tried watching videos on TVs or monitors or phones and I can still see that ugly stutter from some (too fast?) pans from digital video cameras.  

The practical reason I ask this question in part is due to pans I'm taking with various mirrorless cameras looking bad like the above videos.  When I watch professionally produced video (I mean mostly Hollywood stuff here) I don't ever recall seeing this judder or stutter.  Is their movement simply slow and stabilized enough to avoid this all together?  Or does their cinema cameras mitigate this significantly? Or something else?

And how much is it worth to chase good motion cadence and ALL-I codecs?

Thanks for any guidance or information on this subject.

-MC

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There are a lot of reasons for what I think you're seeing, and the reason I put it like that is that it isn't necessarily clear that what I'm seeing may not entirely match what you're seeing.

Mostly I don't think you're seeing any artefact of the camera or the codec. Most cameras in 2022 use a rolling shutter which can cause some motion artefacting, but I don't think that's what you're seeing here; it causes a distortion of the image as opposed to the stutter you're describing. Likewise, codecs don't really affect motion rendering unless you have the bitrate cranked down to such a disgustingly low level that the whole thing starts to fall apart into a cloud of rippling blocks. Very few modern cameras, even quite budget ones, will have any setting that goes so low. That's the sort of problem you'll get on streaming internet video under particularly trying conditions, not from a reasonably expensive video-capable stills camera.

What I think you may be seeing is simply frame rate mismatch. Your device, whether that's a laptop, desktop workstation or phone, runs its display at a fixed rate. For a lot of devices, that rate is 60 frames per second, although you may anything from 50 to 120 is possible. You may have shot material at 24. That mismatch has to be made up somehow and effectively all devices will (through various mechanisms) do that by simply doubling and tripling frames. In the case of a 60 frame display with 24 frame material, you'll see, mainly, three frames duplicated, followed by two frames duplicated, in an approximately repeating pattern. That's visible and it isn't very nice.

In situations where 24-frame material has been dropped onto a 60-frame timeline in edit software you may see the same thing baked into the material, and it may then be messed with further on playback on any given device, so this can get complicated. There isn't really a solution to it.

P

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What Phil said about difference of capture rate of camera and playback rate of viewing device.

That's one thing.

Another is the speed of panning and/or the motion of subject/object in the frame.
For the panning there was a chart in the ASC Manual - what panning speed for chosen frame rate & focal length.

I had an image from those pages but could not find it.
Found this online. I'm not sure, but i think it is the same:

3D3aulH.jpg



A good article with video examples on that topic is from RED:

RED.COM/RED-101 - Panning Speed Best Practices

and an online panning speed tool calculator for their cameras:

RED.Com - Panning Tool

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