Smoother sailing: Studying audio imperfections in Steamboat Willie
windytan.com
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In more practical terms, people who actually listen to vinyls get to appreciate the "cracks", and they wouldn't really see the point in such a product. Major studios have surely developed similar tools internally. The method is probably a scientific curiosity, mostly of educative interest, like observing the helium in the sun atmosphere with a hand-made spectometer built with an old CD and a cereal box.
That bothered me like crazy - how did they scan the audio whilst the frame was physically stopped? Then I realized how it was done: the soundtrack of frame A is stored in frame B, where frame B is far enough away that it has constant velocity.
Oh, I love ingenious solutions like that!
There is a buffer!
Long:
So the frame being projected has to stop. Otherwise you'll get blurring unless your shutter is very fast, but then you'd burn out the film from the intensity of the light.
The film is stopped.
But, of course, you cant start-stop a 15 lb spinning reel 24 times a second millions -> itll all fall apart.
So the feed is a simple rotation at constant velocity (linear? Angular?). Then a piece of film ten to twenty (?) frames long gets put into a buffer (an empty box) and a mechanism akin to a sowing machine single steps through each individual frame.
Now the stepping mechanism only has to start-stop ten frames worth of film, a negligible amount of mass compared to the mechanism itself and the projector can last a long time of heavy use with simple maintenance.
Aint it neat?
The sync though is actually pretty easy, at least compared to computers and electronics - shafts and gears ensure synchronization with little effort (or you'd brake a shaft!)
It would be interesting to see if anyone has made remarks on the sound quality and whether the flutter has been noticeable over the past 50+ years.
not a hand-cranked/fps mismatch
I kind of wonder if the cameramen cranked slower sometimes to save film
(By that I meant in "professional" settings, like a commercial release. You see people stretching 4:3 videos to 16:9 all the time on YouTube, Tiktok etc. but at least Warner Bros. isn't going to do that. However the FPS incorrectness used to be prevalent even in the industry.)
Today, we do key-framing and other tricks to make transfers from different FPSes easy and imperceptible (plus with digital stuff we can playback at any FPS), but back in the 80's and 90's the tech was a lot less advanced to turn a film image into an analog or digital format, and in previous decades you didn't even have analog or digital, you just had to use 1:1 frame transfers to get onto a larger or smaller film format.
3:2 pulldown, which has been done for decades.
You can also just duplicate frames (un-evenly). It will introduce jitter but most of people aren't very sensitive to that, and it's better than playing at wrong speed.
In PAL countries, 24fps movies are often played a bit fast at 25fps on TV so that each frame fits nicely in the 50hz signal. It's not a "Squeeze more adverts in" thing, it's the best way to show the film, otherwise you'd have to introduce an extra frame every second, which would look jarring.
Of course, it's worse with online tv with ad breaks. The online ads cut in 2-5 seconds before or after the program break, so it interrupts the content, and if you skip back to try it again, they play another ad, also inserted incorrectly. To make it even worse, the ads are usually at a different framerate and resolution from the content, so you get a new resync and a new hdcp handshake, so there goes another few seconds of content; unless you set your player to fixed resolution and framerate which isn't ideal.
I'm in prime circumstances to be a couch potato in front of the tv, but it's so damn frustrating, it's not worth it. You can't even channel surf, because tuning a new channel takes too long, so you've got to plan your changes.
Old-time footage isn't always at 24 fps, but once the film industry standardized hard on 24 fps, not standard film becomes very hard to use correctly, even in a projection environment --- projectors were engineered around 24 fps all the time, and likely can't be adjusted.
Tv of course was fixed at 60 fields per second (or close enough) or 50 in Europe. Even today, a US market tv is going to do terrible things with a 50 fps signal (although I gather EU market tvs work at 50 and 60 and probably 24). If your old-time film was shot at 22.3 fps, you don't have good options to show it, except on a computer with a VRR display, and even then, I don't know if the whole chain will actually be fine with it. Options are: pretend it is 24 fps and it plays a bit fast and you can use your 24fps pipeline; show some frames twice and have nasty judder; interpolate 24 fps from the data you have which is kind of terrible and only recently a real option.
I've tried to google it multiple times, but every time, I can only find various forum posts which are all over the place (if not straight up contradict to each other).
In the context of video, I think the most common use of "judder" is about the deterministic and periodic variation in timing that occurs when content of one frame rate is shown on a different-rate display. The most common situation is a "3:2 pulldown," where 24 frame-per-second film content is adapted to a 60 field-per-second or frame-per-second video signal. This is done by repeating one film frame for 3 video fields/frames (so 3/60 seconds), and then the next film frame for 2 video fields/frames, then the next one for 3, then 2, then 3, then 2, etc. (2/5 = 24/60 so it works out on average.) That repeating variation in frame duration or number of repetitions is seen as "judder." With a cinema projector or recent TV, you don't have this; the frames are shown 1/24 s apart and with an equal number of flashes each. But on an older 60 Hz TV, you'll have judder.
(I've also seen "judder" occasionally used to refer to the stuttery motion that comes from showing 24 fps content on a sample-and-hold display, like an OLED [without black-frame insertion] or a "good" LCD that just shows each frame with constant brightness for the entire 1/24 s and then almost-instantly switches to the next frame. But I don't think this is the correct usage.)
On the other hand, judder is often due to a limitation of the system. Fixed frequency displays can't display off frequency content without compromises. And TV broadcasting was tied to fixed frequency displays. NTSC had no hope of 24fps support, sending two fields per frame at 48Hz or three fields per frame at 72Hz would both be way too far from the spec frequency of 60 Hz. I wonder if PAL@48Hz could have worked though --- 4% off spec is a lot, but also not that much.
And bringing it back to old time film that's not at 24 fps, that's definitely more hopeless.
ATSC and I presume DVB can broadcast content as 24fps, and the decoder will do the 3:2 pulldown as needed, but variable rate displays can show 24 fps (it's also usually not too hard to detect and invert 3:2 pulldown, at the cost of adding a few frames of delay). I don't think modern broadcasting does better for a 22fps old-timey film than analog broadcasting did though; it's still not something the system was built for, and you're still going to have off speed playback or a pattern of some frames shown more times than others (which is my essential definition of judder)
Low tech, simple, and effective.
Some of my old family movies were converted to VHS that way.
https://en.wikipedia.org/wiki/Telecine
And going the other way, before the introduction of videotape, the only way to store TV programs was to use a kinescope to produce a film recording of the broadcast:
It could invert negative film to positive, and it could color correct scene by scene by looking at correction codes or counting frame numbers, then applying the correct color correction.
Later, broadcast TV started using flying spot scanners instead of just a video camera in front of a film projector. ²
The vast majority of midrange and better TVs can also spot 24 fps content being sent in a 60 hz signal and render it properly.
Most TVs however will not look good with 50 fps content in a 60 hz signal and you will want to set your output device to adjust its refresh rate based on the frame rate of the content being played. Set top streaming boxes actually worth using have this option, but it is usually disabled by default.
A little flutter was an unavoidable part of our audio for a very long time.
I think producers sometimes add a little flutter even to modern music productions to make them sound less digital. At least that is my assumption from the number plugins that are available for that purpose and from the obsession producers and mixing engineers have with vintage tape machines.
More speculatively it seems to me like AI is approaching the level of image understanding where it could draw new in between frames in a much, much smarter way than typical terrible frame interpolation. That would be a great project and potentially commercially valuable. Steamboat Willie is animated at 24 FPS but it's common for animated TV shows to be done at 8 FPS and they could really benefit.