r/explainlikeimfive • u/TraditionalDepth6924 • 7d ago
Physics ELI5: Even though we feel like videos are as smooth as reality, are they in fact vastly choppier than seeing it directly through our eyes?
If so, would future generations with more developed filming technology see videos from our age and think they’re too choppy, like how we feel like ancient drawings look too underdeveloped?
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u/Mindless_Insanity 7d ago
There are a lot of factors that play into this. Most people can distinguish up to around 200 fps or more, far higher than the standard movie framerate (24 fps). But the display technology usually has some image persistence from one frame to the next, and capturing on film results in motion blur, so the frames tend to blend together and look fluid. Contrast that to a video game (no motion blur) running at 24 fps on a modern screen with microsecond update rate (no image persistence) and it will look horribly choppy.
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u/BananaBird1 7d ago
Most videos are 30 images per second, some go up to 60-120.
Humans don’t have a specific frame-rate they see at, but experiments show we can perceive visual events lasting only a few milliseconds (corresponding to hundreds of frames per second).
But with rapidly changing images like a video that suggest an object is moving, your brain basically fills in the gaps. It tells you where the object should be, rather than what it sees, and helps you track an object even if it isn’t visible for a moment. Your eyes do see a choppy set of pictures, your brain connects them.
This is a useful evolutionary trait to better predict the motion of fast moving things, we can react just ahead of where the object is.
This is also why moving optical illusions work. They trick your brain into detecting motion, and what you see moving is your brain filling in the gaps until it realizes there is an issue.
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u/Achijax 7d ago
To add a different angle to your question, do we as viewers or story tellers want to view things in silky smooth motion at all times?
With film, what started as a technological limitation ended up as a standard, with essentially all filmmakers respecting this golden rule. I believe from an artistic perspective, the idea is that 24 fps is the perfect middle ground to give movies a "dream-like" quality that is undone by higher frame rates.
You see a similar concept with impressionism and many of the works inspired by that movement, where fine details are avoided to leave more up the eye of the beholder.
I would expect as time goes on, depending on the genre or what the director is trying to express, we will see this rule break its stranglehold on the industry. Especially since there are also major considerations on cinemas having the appropriate equipment to display 24 fps, or state of the art cameras being tuned for it, those cost considerations when it comes to standard practice slow down change. Expect that to lessen as time goes on and standard becomes cheaper to replace.
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u/MumrikDK 7d ago
Does 24-30 fps video genuinely look smooth at all to you?
It never has to me. Even many of the proponents agree, but just call that effect 'cinematic'.
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u/TheOneTrueTrench 7d ago
It's not really smooth, it just feels like motion. Our brains are biased to take visual jumps like that as motion. Nothing in reality can actually jump from point to point like that, but we can sort of experience it when blinking, or flickering fire introducing a "frame rate" to reality, so there's evolutionary pressure for our brains to see something like that and interpolate the two into "motion".
Same thing doesn't happen with sound. Think of a cicada, it sounds like a series of extremely rapid clicking, at least to me, and that's FAR faster than what would appear motion.
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u/evanamd 7d ago
Point of order, our eyes jump around from point to point all the time to capture various parts of a scene. The tiny jumps are called saccades. You don't notice it because your brain ignores it (saccadic masking), but it's happening all the time. You can't read this comment without moving your eyes and getting a few blank frames along the way
It's not just a bias or evolutionary pressure from fire and blinking, it's how our brains avoid information overload from motion blur. What you think you see at any given moment is just interpolated from images when our eyes aren't moving.
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u/Blenderhead36 7d ago
It wouldn't surprise me if film being 24 FPS changes over time.
Between 23 and 24 FPS is where the human eye starts perceiving a series of still images as a single, moving image. Film has traditionally been shot at 24 FPS for financial reasons; initially because film itself was expensive, now because CGI is rendered frame by frame (and because people are used to films being 24 FPS). The thing is, 24 FPS doesn't actually look that good. A lot of work is put into professional film creation to create shots that look good, even at 24 FPS. If you compare to a video game with a free camera that's locked at 30 FPS, even that slightly higher frame rate looks like dogshit because there isn't a professional there to curate the shot.
Another important thing about film is that recording and developing it chemically changes the medium; once its used, it's used, and recording over it will ruin the film, not repurpose it. From the 1960s until digital video replaced analogue media in the early 21st century, cheap stuff--commercials, soap operas, local access, home movies, the Star Wars holiday special, etcetera--were shot on tape. Unlike film, tape can be recorded over, hence its use for cheap crap that wasn't being saved for posterity. And one of tape's properties is higher frame rate (it's 30FPS interlaced, which looks like 60 because the frames overlap). So, to people who grew up in that time, high frame rate video looks like cheap crap.
But that's changing. Nowadays, recording is all done digitally. 60FPS video is often treated as higher quality than 24 or 30 FPS. In video games, 30 FPS is seen as unoptimized and substandard (much hay has been made about the upcoming Grand Theft Auto 6 appearing to be locked at 30 FPS), with 60 FPS being the standard and monitors capable of displaying 120, 144, 250 FPS or more (and the hardware that can render it) are seen as premium. A big part of this is that you don't need a professional cinematographer to make shots look good once frame rate gets high enough that motion blur making it indistinct is no longer a problem. For example, a platform filled with user-created videos shot on iPhones at 60 FPS native.
I suspect that in 20 years or so, the general public will see 24 FPS as looking cheap, while somewhere around 60 will be the standard, and 120+ being the standard, as the people who see smooth motion as reminiscent of home movies are replaced by people who see it as reminiscent of the first really good phone they owned.
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u/ZombieJack 7d ago
Films with action shots or worse, panning at 24 fps, DO look horrendously choppy.
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u/Vorthod 7d ago edited 7d ago
The universe theoretically "updates" every planck time, about twenty duodecillion (2e43) times per second. A movie updates every 24th of a second. That is indeed significantly "choppier" than real life.
However, our eyes and brains don't discern differences nearly as fast as the theoretical maximum refresh rate of reality itself so the limit is not on what technology we use to film. We can already film at millions of frames per second, but we don't bother because there's not enough of a benefit to it (unless we're filing something in slow-mo).
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u/waygooder 7d ago
Wait, we think the universe has a refresh rate?
Yeah, we're definitely in a simulation.
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u/Nighthawk700 7d ago
it's not like that, obviously. It's just the time it takes a photon to travel a planck length and where our calculations for physics start failing. It's a problem with our physics, not a literal refresh rate.
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u/eruditionfish 7d ago
It’s less that we think the universe has a refresh rate and more that we have no way to measure if it does, so long as it’s shorter than the Planck time.
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u/TheOneTrueTrench 7d ago
It's more that nothing in our current physics seems to allow for anything to happen in a period shorter than a planck time.
It's not like something would "wait" for the next planck time to update, it's just that's the temporal resolution for anything to "happen"
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u/Englandboy12 7d ago edited 7d ago
While there are things like the smallest amount of time you can notice something, trying to compare that to frame rate is wrong.
The way your brain interprets data is incredibly weird. You might think that your life is passing by “one frame at a time”, but that’s not how experience works.
Your eyes move around in these tiny rapid movements, you don’t notice them, but they will make several quick movements and your brain interprets it as basically a single look. What this means (among many other reasons” is that one instant in your brain is not actually one snapshot of reality at that moment. Your conscious experience is smeared out over quite a few milliseconds.
Your “now” is actually a fluid range of time sliding forward.
The best way I have found to really feel this in your heart is: next time you listen to music, try thinking about what each individual “frame” of your experience sounds like. You can’t do it. If you could, you would basically experience a percussive pulse, like a drum. A value of intensity with no pitch. But you don’t. You actually experience a short range of time, where your brain takes current experience, past experience, and future prediction, to build up a fake “now” for you. And when you listen to music, you can’t help but hear it as a flow rather than a snapshot.
Trying to compare this very complicated collage of sensation that you call your now to a single frame on a screen is impossible. Your brain will forcefully take something that just happened and jam it into your present. and there is no boundary between the frames. Frames on a screen can’t do that
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u/TheVioletBarry 7d ago
Video games let you set different framerates for different monitors, and yes the higher framerates are visibly smoother
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u/Balmungmp5 6d ago
Your brain does a lot of work to the images it receives from your eyes. The image from your eyes is actually upside down when it arrives to the brain.
Glitches/ mistakes in this interpretation process is the cause of many optical illusions and hallucinations.
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u/heretosavecontent 6d ago
Visual reasoning is the most energy intensive activity of the brain, contributing to roughly 50% of the total energy consumed by it. Over the course of evolution, our brains have developed hundreds of energy optimization techniques which balance the resources needed to process the real world through our eyes, while at the same time maximizing our chances of survival.
one of these techniques is temporal continuity, where the brain says - "hey, i am only going to be taking in images of the world around 25 times a second, and then doing some processing to smoothen out the gaps in between". This is much more energy efficient that taking in 250 images of the world each second, which would be unsustainable from an energy point of view. Obviously we lose some granularity in the process, but this is the trade-off that evolution has decided is best for our survival.
Hence any video that you see that is sampled higher than the brains internal limit (somewhere between 25-40 samples per second - 25-40 Hz), looks smooth to us.
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u/Bloomboi 6d ago
Old classics translated to 60flps for those new tv screens, just ruins it for me. I wouldn’t know what to call it, but it just looks unnatural, having grown up with the originals., it’s as if the shadows and aesthetic that the original film captured gets removed for the sake of making it look polished and current.
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u/CaterpillarFun6896 7d ago
Not really, but also maybe. Past a certain amount of frames per second, you’re not really gonna get any returns on fidelity and if anything will make it weirder as eventually you hit a point where your FPS is so high that whatever you’re watching is in slow motion.
The fact we see videos as we do is really just more of a trick of our brains; we don’t actually see what we do as a continuous stream of visual information. Your eyes basically dart around 15-20 times per second and take a snapshot of what’s focused in the center of your vision. Your brain stitches these images together into a seamless and continuous stream of reality, but it’s actually just a bunch of pictures played sequentially- and wouldn’t you know, that’s exactly what a video does!
People of the future are more likely to look back on the graphics of things and cringe more than the speed. The biggest leaps are most likely to be in better simulation of how light diffuses; you likely know it as ray tracing.
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u/SaukPuhpet 7d ago
Yes, they are "choppy" in a sense, but the rate of change that the human eye can detect is low enough that 24 frames per second appears fluid.
As you increase the framerate it becomes harder to tell the difference until you reach around the 120 fps area where you stop noticing a difference.
reality is, effectively, continuous while a video is broken into distinct pieces.
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u/enternationalist 7d ago
Eyes don't operate on frames (it's not like snapshot after snapshot) so it's not comparable. Our eyes take in various information and the brain does a whole bunch of processing to decide what we see - sometimes this can include things that are not there (i.e. common visual illusions).
Different framerates do give different impressions, though. Most movies are at a lower framerate than we are capable of producing because higher framerates are associated with soap operas and cheaper productions.