Why 23.976 and not 24 FPS? (2016) | Hacker News Reader

Why 23.976 and not 24 FPS? (2016)

cinematography.com

262 pointsmfiguiere155 comments

This post was 2016. Six years later, this is no longer true, at least here in my area (Montréal). At my work in a post-production company, we finish around 8-10 long form fiction movies a year and a bigger number of shorts, and I would say around 90% of thoses projects are now shot 24.0 fps.

All high-end cameras like the ones from Arri, RED and Sony can switch easily between 23.976 and 24.0 since many years. The sound recorders can now too, like the Sound Devices, which is the most common brand used (at least here in North America). The choice of shooting in 24.0 was already available in 2016, but not every gig would be used to shoot 24.0 so they chose 23.976 just to be safe, I guess.

Also, in 2016 television was still a major deliverable, but this has changed. Video on demand, which supports any framerates, is now the main distribution channel when a movie has finished playing on the big screen.

Documentaries are more of an exception because they are still aimed at television and also, they often use old footage which was telecine'd at 23.976 so it's easier to edit when everything's 23.976.

>Video on demand, which supports any framerates

I don't think so, majority of displays are still 60Hz without VRR.

But the playback box handles the conversion. With TV there were stricter standards for broadcasts.

A lot of TV displays are now even 120Hz, which is convenient for being able to display 24fps, 30fps, and 60fps content without any conversion

I think they mean the VOD service doesn't restrict the creator on what frame rates they can author their content in, the box just makes it work for whatever the display requires.

Displays will often sync at lower frame rates than their maximum, though I guess I don’t know if they all do non integer factors.

> The sound recorders can now too [record at 24 fps]

What does that mean? I thought 44khz sampling meant 44.000 integers are recorded per second.

I'm guessing, because I'm bored, and hopefully an expert will confirm or correct, but I think it means that they place sync markers every 24th of a second, to make syncing with video efficient.

Frame sync ability?

Production audio and video recorders generate or intake an SMPTE timecode signal, and stamp recordings with this timecode.

This timecode format is a timestamp with seconds resolution plus a frame count within each second. To properly sync, all the timecode generators must use the same framerate. In other words, the audio recorder’s timecode framerate needs to match the camera.

Yes, sound needs to be recorded with proper metadata, otherwise the sync process with the image is going to be pretty tedious. We could just record with a "dumb" audio recorder that doesn't write timecode and fps metadata and it would sync up by hand to any camera FPS (23.976, 24, 25, 29.97, etc). It's not just practical for any professional projects.

The funny thing with timecode, which is hh:mm:ss:ff, is that the frame count is done at 24 frames, even at 23.976. So 1 frame of 23.976 is longer in actual "real time" duration than 1 frame at 24 fps. This can get confusing when going from and to 24/23.976.

There are more sophisticated workflows where the audio is recorded at 48.048 kHz (0.1% faster sample rate) called audio pull-up (or pull-down). The technique is used when shooting, for example, a TV spot, with a film camera at 24 fps. Since the 24 fps picture will be played back at 23.976 at the edit, the audio will follow the same speed down because it will itself play at 48.000 kHz instead of 48.048 kHz. I'm not sure that many productions still shoots TV spots in film, though, contrary to fiction where film is still being used sometimes.

But the timestamp is not recording actual seconds, right? Half the time it's recording intervals of .999 seconds. That is much weirder to handle than merely having the right framerate.

The time code is always incrementing by one frame at the given frame rate. For any of the NTSC-derived framerates, there are then two ways of incrementing. You can increment as if the frame rate is integral--so after 30 frames at 29.97 fps, your timestamp will show that 1 second has passed. The other option is a "drop-frame" timecode, where you skip over certain numbers when incrementing.

In all cases, the time code increments at the frame rate you are using.

It's 44100

> Video on demand, which supports any framerates, is now the main distribution channel

But all the major VOD services, be it Disney+, Netflix, Hulu,... still mainly use 23.976 or 29.97 fps for their video distributions.

I don't know what your production company mainly works on, but these NTSC frame rates ares still the norm across the whole cinematic industry, and it's not going anywhere. It's not limited to documentaries at all.

The YouTubers etc. do use 30/60 fps more often OTOH.

Is that true ? 24fps is even specified in the Netflix requirements for content...

https://partnerhelp.netflixstudios.com/hc/en-us/articles/360...

This is not a guide for framerate. Netflix accepts multiple frame rates.

This is a guide about data bitrate, what it says is that for 24fps, you need at least 240Mbps (means it needs more if it has higher frame rate).

If anything, all the other language versions actually use "23.98" as example instead. E.g. this Deutsch version: https://drive.google.com/file/d/1WLz0O_dwmVWjqHafaHoLav0qvHU...

This guide https://partnerhelp.netflixstudios.com/hc/en-us/articles/441... mentions more about frame rate but it's basically just "don't convert frame rate around, and use constant frame rate for intermediate file".

Good question. Last time I've submitted to Netflix, it was 24, but it goes through a third party "packaging" company before going to Netflix.

So some of them might reconvert to 23.976 even when we submit 24 fps masters as per the contractual agreement. Maybe you are right. I will check.

Low budget web series shot at 23.976 even get delivered and played back at 29.97i on some local platforms here in Canada (Crave, Noovo, tout.tv), so anything's possible nowadays.

On the other end, Blurays can be encoded at both 23 and 24, and Vimeo, Youtube, etc all support 24fps. So 24 fps exists, not just on DCPs.

By the way, the loss of quality from going to/from 23.976 and 24 is not much. I've never heard any artifacts from that kind of conversion. But since cinema theatres are most likely to have a better sound system that a home system, I think it makes more sense to have the unconverted mix playing in the cinema and not vice versa.

But how would you convert from 23.976 to 24? Either you will have a repeated frame once every 1000 frames, or you would need to interpolate every single frame.

Surely the first solution would be preferable. But it would still lead to more than one jitter per minute. I wouldn't call that "no artifacts".

You slow it down to run at 100.1% of its original length. Presto, 23.976FPS converted to 24.

1.7321 cents difference for your audio (100 cents is a half-step)

At the moment, blu-rays are also still predominantly 23.976p.

I do agree we should actively push this relic out, though. Wish Netflix etc. can do more to normalize whole number frame rate to end this. Unfortunately considering TV industry are still using 29.97i for broadcasting, I don't see it's going to happen any time soon. And it's worse in other countries like Japan.

Most other countries apart from Japan use 25i for television broadcasting, with none of the complexities of dropframe. Sadly the general consensus was to go for 1080i25 rather than 720p50 for HD.

Considering that slowing down FPS doesn't alter the images, and audio can be resampled with practically no audible artefacts, I doubt that quality would ever be an issue. As long as it's done with the proper care of course.

I would think the main consideration is workflow these days.

Netflix accepts 24fps

Source: https://partnerhelp.netflixstudios.com/hc/en-us/articles/726...

Is there such a thing as a camera that does simultaneous capture at multiple frame rates that are non-multiples?

Not well versed in video production but really interested layperson.

I understand that the two main reasons for 23.976/24 fps are that it’s:

1) been the standard for a really long time so you know everything will more or less support it (cinemas/vod/broadcast tv).

2) is now in people minds as what film should look like (in that 60 fps somehow looks “off” because we’re trained to expect 24 fps).

Given that analogue broadcast tv is dying off and that digital OTA tv is a similar case to vod in terms of codecs (maybe not receiver support?), wouldn’t a stopgap be some multiple of 24 fps (e.g. 48fps) that would allow better motion handling without the pace seeming off?

At 48fps, a movie already looks way too smooth and uncinematic

I'm quite convincented you already notice it at 30fps (but I'd have to check again)

I think the real reason HFR isn’t used much in cinema is that it ends up exposing a lot of the choreography, set design, special effects, etc. as fake, where before our brains filled in the details due to the low information rate and blurry frames.

Watch either of Ang Lee’s HFR movies (Billy Lynn/Gemini Man) and you’ll understand what I mean. HFR breaks suspension of disbelief. I didn’t want this to be true but I’ve come to accept that it doesn’t really have a place in cinema at least for now.

Wasn’t HFR mostly used in 3D films to get rid of the skipping in high paced scenes? If I remember correctly the first HFR film was The Hobbit?

(I worked in the industry at the time on the technical side, but I’m not a film buff, so the details are forgotten a long time ago. All I remember is that there was a huge amount of work involved to get all the equipment upgraded to support HFR. Cinemas had to upgrade both their playback servers and projectors for thousands of dollars. All for less than a handful of films.)

To be fair, the first line of the response heavily qualifies the answer: "Truth is that most digital projects shot for either broadcast or cinema use 23.976 instead of 24 in the U.S."

Why would anyone in 2022 still record in 24 fps? I assumed most, if not every, recording device is at least 60fps?

Because 60fps and 24fps don't look alike and video shot at a very high frame rate can look off to an audience.

Remember also that typically a 1/2 rule is followed where the exposure of each frame is half the time of its display. So for each of the 1/24s intervals, an exposure is made for 1/48s. A shorter exposure would have less motion blur but look jittery. A longer exposure would look too buttery. People are extremely used to 1/48s exposures displayed for 1/24s (or similar).

48fps video in the Hobbit movies was very negatively perceived. It looked too much like a video game.

24 FPS can look "off" to an audience, too.

As someone who hates 24fps, because it looks way too jerky, and not lifelike, the sooner we lose 24FPS, the better.

You're in the minority, I think. The Hobbit was shot in 60fps and most people found it very uncomfortable to watch. It felt like you were watching a movie set rather than a movie. Suspension of disbelief is pretty important for cinema and 60fps really messes with that.

I also think most jerkiness in 23.976/24 is due to incorrect display settings leading to dropped/skipped/repeated frames. If your display can match 23.976, even panning scenes look pretty smooth. It's the jitter that messes with our brains and looks bad.

I'm also in the 24fps hater camp.

It's not jitter that bothers me, it's the stop motion effect. It's especially bad with action sequences that have a lot of closeup shots.

This is basically every movie with any sort of action in the past decade or so. If you do closeup shots in on some fast action in 24fps you don't have to worry one bit about choreography, since it'll just be a choppy blurry mess and nobody can tell what's going on anyway.

I can agree things like sports are a lot better at high frame rates. You want to see what players are doing precisely in a live setting. But people don't watch sports in movie theaters.

I'd argue stylistically the lower frame rate works a lot better on a big screen. There's also the fact that high frame rates on a big screen seem to cause some people to get motion sick.

I personally have no issue w/ action scenes which are shot at 24fps. Yeah, there is a fair amount of blur but it all seems natural (at least on a cinema projector), and conveys the fast movement, even if it might not be precise.

Take Jackie Chan's Drunken Master epic final fight scene for example - yes it's a bit blurry but I can make sense of everything going on. If anything it enhances the feeling of action - if this was shot at 60fps, it would look much more "real" and be a lot less enjoyable.

1: https://www.youtube.com/watch?v=lwDU3IOBEIk

It’s worst on panning shots where everything is noticeably jittery.

I am curious if the video game effect is a function of the fps or exposure time. Would a video of 48 fps with 1/48s exposure look off?

Not sure how a camera would be built that could do this...

The overlong exposure would make the video twice as bright, and if lighting is adjusted, twice as noisy instead.

Technically one can shoot at whatever fast enough, then apply the right pulldown, exposure and blur to compensate.

Hobbit's 48 fps version was not as badly received as you make it, though the unreal slow 24 fps shoot does give it more of a fairytale character.

I wonder what the viewing experience would be like if it were shot in 48fps, but then most alternating frames were dropped so it still felt like 24fps, except for certain key visual sequences - action, big effects shots, etc. You could even transition between the two frame rates over a few seconds.

There are always a lot of unsatisfying hand-wavy answers to this question just saying that high framerate video looks "off" or "like a soap opera". I'd like to point out that the biggest factor here is probably the lighting.

Cinematographers have to pick particular aperture and ISO to get the depth of field and film grain they want, so they can only really adjust exposure though shutter speed. If you double the framerate, the minimum possible shutter speed halves. Therefore (unless you are shooting outside on a sunny day) it is very likely that your shot is underexposed, and the only thing you can do about it is add more lighting. This can be both logistically complicated and technically very hard to pull off without looking unnatural, especially in scenes that are supposed to be dark and moody.

Actors in heavy costume will get hot under that much lighting, even with LEDs. Makeup melts. Higher frame rate increases editing costs.

I've completed a video shot at 24fps, some footage was recorded at higher frame rate for slow motion, but you can tell the diference. The 24 fps is the best, as it looks and feels better in the eyes for most people and also my audience :)

As others have said, 60fps can actually look "off" to some audiences. It definitely looks "off" to me, and I can't quite put my finger on it/why. It could just be my age (late 30s) and my brain grew up on 24-30fps.

Many new TVs interpolate 24/30 fps to be 60fps. This is knows as "The Soap Opera Effect", and has been written about here before. [0].

To me, 24/30fps feels "smooth", almost "buttery". 60fps feels crisp. 60fps feels almost too real. It makes it more difficult for me to suspend disbelief, whereas 30 makes it easier to suspend disbelief and get lost in the imaginary world that's being presented to me as if it were real. It's really difficult for me to explain....

[0] https://news.ycombinator.com/item?id=10613575

The horrible "motion smoothing" interpolation is the first thing anybody should turn off on a new TV. I absolutely hate it, just ruins the look of movies!

MELS?

I prefer to write them as 24000/1001, 30000/1001, 60000/1001 fields-per-second to avoid the ugly decimals and because I think it makes it a little more intuitively clear what’s going on to achieve those numbers.

But don’t you then have to then explain this every time you try to communicate with these numbers to someone else. Are you just writing this down for yourself?

> Are you just writing this down for yourself?

“Teachable moment” I guess? I usually use that notation in my nfo blurb when encoding DVDs for a modern flatscreen target. Anecdotally, nobody has ever asked me to clarify. Small sample size though due to niche nature.

Unfortunately most digital video formats don’t actually store them this way, either because the editing software rounds it off incorrectly or because the format itself stores timestamps in decimals for some reason (Matroska).

<rant>Ah...Matroska was nearly perfect, and then they chose nanosecond-precision timestamps. Countless attempts at frame-perfect seeking thwarted and videos imbued with jitter over the years, subordinate to the tyranny of 33 34 33 33 34 33...

Even worse, not only is the recommended precision only 1 ms, but almost all muxers support nothing else, ffmpeg included*. A shame that despite such versatility, mkv is scuffed as an intermediate/archival format by lossy muxing, yet almost no one is aware.

* https://lists.ffmpeg.org/pipermail/ffmpeg-devel/2021-May/280... matroska precision parameter coming soon? It's been over a year, though - looks like the patch is dead. Meanwhile, the bikeshedding of rational timestamps in the matroska lists can now be expressed with a timebase of decades....

Not that I know much more than how to merge multiple audio tracks into a single file and do the Faststart stuff so the video starts faster, isn't the issue then really only that everyone only does milliseconds with mkv, and theoretical otherwise? Surely, when using nanoseconds and just moving the error to the next frame, jitter should be unperceivable, not even measurable on even high refresh rate displays?

There most likely aren't playback issues; it's just silly that a concept that is never anything but a rational number is being stored in a way that can't store rational numbers.

Exact timestamps are aesthetically nice but frame-perfect seek should not have any problems with sub-millisecond jitter.

When you seek to a timestamp from the source, or write a temporary matroska file and go over it in parallel in a second pass, timestamps being rounded variously up or down will cause off-by-ones and dropped frames and desyncs.

1 ms is pretty imprecise for audio seeks, however - mkvtoolnix actually increases precision to sample rate when there's audio. But why do all tracks have the same timescale? Oh right, TrackTimeStampScale was in the spec all along and could be used to solve all of this...apart from being floating-point.

> When you seek to a timestamp from the source, or write a temporary matroska file and go over it in parallel in a second pass, timestamps being rounded variously up or down will cause off-by-ones and dropped frames and desyncs.

Why? It shouldn't. A millisecond-resolution timestamp unambiguously identifies a specific frame, at least until you start going over 400fps. You just need to go to the closest frame rather than rounding up/down. And rounding up/down can break very easily even if you're using ultra precise numbers, especially if you don't have a fixed framerate for the entire file.

Many multimedia formats, frameworks and libraries actually store them that way.

In Mpeg 4, each track header has a “time scale” integer field. For a video track of 23.976 FPS the value can be 23976, or half of that, 11988. Audio tracks typically have different time scale field, often 48000 for 48kHz audio.

In Media Foundation, MF_MT_FRAME_RATE media type attribute is a rational number with uint32_t numerator and denominator. In DXGI, the RefreshRate field of DXGI_MODE_DESC structure which contains a refresh rate of a monitor is a rational number, for instance my display actually uses 59997/1000 Hz frame rate, not exactly 60 Hz.

I think part of the parent’s complaint is that, although 23976/1000 fps is much more accurate than 24 fps, it’s still very slightly slower than the correct value 24000/1001 fps, by about 2.1 frames per day.

Mpeg-4 can do that just fine.

Here’s what MediaInfo tool shows about the video stream of some *.mp4 file on my computer. The content was first released in 1997, before modern digital stuff.

  Frame rate mode: Constant
  Frame rate: 23.976 (24000/1001) FPS

Specifically, the timescale value in "mdhd" box (overall information about the media, defined in section 8.4.2 of the ISO/IEC 14496-12 spec) is 24000, and "stts" box (time-to-sample, defined in section 8.6.1.2 of that spec) says all video frames have the same sampleDelta = 1001.

Reminds me of Facebook's Flicks, which are a super short tiny common denominator time unit:

> A flick (frame-tick) is a very small unit of time. It is 1/705600000 of a second, exactly.

> 1 flick = 1/705600000 second This unit of time is the smallest time unit which is LARGER than a nanosecond, and can in integer quantities exactly represent a single frame duration for 24 Hz, 25 Hz, 30 Hz, 48 Hz, 50 Hz, 60 Hz, 90 Hz, 100 Hz, 120 Hz, and also 1/1000 divisions of each, as well as a single sample duration for 8 kHz, 16 kHz, 22.05 kHz, 24 kHz, 32 kHz, 44.1 kHz, 48 kHz, 88.2 kHz, 96 kHz, and 192kHz, as well as the NTSC frame durations for 24 * (1000/1001) Hz, 30 * (1000/1001) Hz, 60 * (1000/1001) Hz, and 120 * (1000/1001) Hz.

Guess the project got archived. Seemed like a semi sensible high res time format that was very media friendly.

https://github.com/facebookarchive/Flicks

Similar idea to the EMU (English-Metric Unit) used in OOXML: https://en.wikipedia.org/wiki/Office_Open_XML_file_formats#D...

Why bother with the EMU when we have nanometers (or some small multiple thereof)? Even 1/64 inch, 1 PostScript point, or 1 traditional point are an integral number of nanometers.

There are 7200 / 254 = 3600 / 127 PostScript or CSS points and 7227 / 254 TeX points in a centimetre. Neither of those is a finite decimal fraction.

And that's what I get for not checking that my calculator was rounding on me. Apologies. (And I even used the good calculator, too, so I wouldn't screw up the units....)

The code amounts to a definition of the unit in a way that’s usable with the C++ standard library, there are no exchange formats or anything. That the repo got archived might mean that they are not planning to promote it, but neither the code nor the unit itself really need any further development—if you have a place where you want to use them, you can just do that.

The amount of hidden engineering in Analog systems is mind blowing. Imagine how many hours were spent in a lab figuring out the exact right timings, chemical mixtures, and circuit design needed to make modern Cinema exist as we know it.

Sometimes it makes me sad how "boring" digital transmission is. Just pack up your data and send it over IP. Life is too easy.

There are plenty of difficulties hiding in the OSI stack. MTU is a fun one.

OSI stack is dead, TCP/IP won.

Tcp/ip is only 1 layer (transport) of the osi stack..

You made me stop and question myself for a second, but this definitely isn't right. Usually when people talk about "TCP/IP" it's shorthand for the whole "Internet Protocol Suite", but even naively TCP and IP are two different layers.

Yep, the slash is meaningful. I think of writing "TCP/IP" that way as in a fraction -- "TCP over IP" or "TCP on IP". At least, that was how my brain learned it.

TCP and IP exist as part of the Internet stack. The OSI stack consisted of an alternate set of standards (like LAPB and X.400) which were not widely adopted.

Even if you map Internet protocols to the OSI model -- which is imprecise at best -- TCP represents the transport layer, and IP the network layer. They're not a single component.

Usually the protocol stack is PHY/MAC/IP/TCP/TLS/application which is 6 layers. It's the same as the OSI stack except for the lack of a session layer, which is somewhat split between TCP 3-way handshake and TLS authentication/authorization.

There are still a ton of complications for digital video. Compression, color spaces, transfer functions, etc.

The digital data in many cases is still transformed into sine waves before being transmitted and received. There is a bunch of rf involved.

Except now we have to deal with codecs, DRM, color space, and not knowing if your cable meets the spec. Definitely not easy.

Only because you are sitting on top of a million prebuilt tools and products. Essentially the same as someone who just purchased the hardware and plugged a video feed in from the camera.

10G-BaseT is pretty complicated though, getting 10Gbps over copper takes some pretty involved signal processing.

We’ve just moved it.

Don't worry, various encoding format, containers and other crap got you covered on complexity.

Hell, just look at ffmpeg commandline if you miss some complexity in your life

Yeah, I read stuff like this and think the engineers back in the 50's were some of the smartest. I certainly would not have been able to cut the muster back then.

Certainly I think we should ignore the trope that we've left that analog crap behind up and realise that those are just some of the giants whose shoulders we stand upon.

Every generation has its challenges, but we can be greatful that the generation before us gave us new ones. It has not always been the case.

It's possible for analogue engineering to be incredibly challenging impressive and, to put it crassly, a bit crap.

I certainly don't miss the days of adjusting tint settings, headroom, over-scan and interlacing. Digital isn't without its issues of course, but even a lot of those trace their history back to analogue hacks - article case in point.

There is this side effect of digital lowering the bar though. Back in the analogue days, you needed to be a wizard to get anything done, which meant a lot of the people then seemed to care about the details more than they do now. Digital makes everything so easy that anyone can do it, which can go both ways.

The difference is that analog is EVERYWHERE.

Spinning rust drives store analog magnetics that get error corrected to digital. Same with electron potentials in ram. Same with SSDs. Signals over HDMI are converted to analog to display.

Sure, it's nice to deal with crisp neat digital signals... But to get there, you always need to deal with analog.

It's often in retrospect as well. It can take time for the impact of certain innovations to unfold, and it often begins with a small group of people. The breadth of human innovation is now so wide that a scientist/engineer from the 1950s simply doesn't have the same scope of problems and areas of study to work on.

That's why people like Leonardo da Vinci could exist, the scope of human understanding was much smaller and so their work was much more wide-reaching and foundational. Today, you can dedicate your life's work to some hyper-specific problem in a very specific field. Tomorrow, this work might seem fundamentally primitive or foundational in the way that previous generations are perceived.

Phrase tidbit: it’s “pass muster” or “cut the mustard” that you could or couldn’t do.

Hey, don't spoil it. I was enjoying the image of him standing alone, pulling out a sword and charging at a battalion of soldiers arrayed on a parade ground.

Pass the mustard?

Numerous examples in early digital era as well, see e.g. fast inverse square root, cga color hacks (also entire demoscene) and endless tricks in software that has been outrunning hardware for a while.

Later these were declared wrong, considered harmful, having bad smell, not passing code review and it all became a boring task of combining lego blocks. Sure these analog guys had insane tricks in their sleeves, but our “collective industry” would probably stigmatize them immediately if met today.

Different circumstances call for different trade-offs.

Exactly. Their era called for getting things done no matter how. Our era calls for iterability.

Great answer for where 29.97 came from, but I seem to be missing the explanation of 23.976 fps which is suddenly introduced as just an effect of audio post, but not how or why exactly...

Edit: more specifically, if audio was being converted to NTSC for dailies, why would it be 23.976 and not 29.97?

The traditional frame rate for film is 24fps, which is converted using 3:2 pulldown to 30 fps. 23.976 fps converts using 3:2 pulldown to 29.97 fps (23.976*30/24=29.97).

While reading about 3:2 pulldown, I saw that for PAL (25 fps) there is 2:2:3:2:3 pulldown to 30 fps.

but rarely does anyone actually do this. normally, a 4% speed change is done to get the frame rate to match. as for the audio, it totally depends on how much effort someone put into it to correct the pitch so that the frequencies are the same in both frame rates. typically, nope. things sound higher pitched in 25fps than they do at the original 24 or 24000/1001 frame rates

I remember living in the UK 20 years ago when my friend had got into Buffy the Vampire Slayer. He insisted I watch some episodes. But because the target demographic was 'nerdy night owls' on a non-prestige TV channel, they cheaped out on the conversion and by the end of each 45 minute episode the dialog had gone badly out of sync.

My friend insisted I was just imagining it, but only one of us went on to have a career doing post-production in the US market. To be completely frank I've looked down on UK/EU broadcast techs a little ever since because being able to set everything to 25fps and forget about it is easy street.

I've made a career of taking pull down sequences out of videos to prep for DVD->Blu-ray->streaming. Where others have failed, I have properly restored. "Others" for example are FAANG's streaming services. Everyone wants it to be a single button IVTC, "set it and forget it" like you said. Shot on 24fps film, edited at 29.97 with pull down where every edit is a break in cadence, 30i graphics/bumpers, and some shows (I'm looking at you The Shield) where they shot 30fps film for a special look/feel during certain scenes, and a set-it-forget IVTC will not do well at all.

> To be completely frank I've looked down on UK/EU broadcast techs a little ever since because being able to set everything to 25fps and forget about it is easy street.

My experience has been the reverse. Because they can, people in UK/EU have historically cared much more about frame accuracy. It’s only in the last 10 years or so that people in North America have started caring about frame accuracy. In the past it’s been quite hard to do because of the non integer frame rate.

Parent was obvious talking about converting 25fps PAL video to 30fs NTSC frame rate, which happens ALL THE TIME...

NOT about converting from film to PAL. You are arguing with no-one.

Yes, I have no idea what I'm talking about. I forget that sometimes. However, maybe you've forgotten that a lot of 25fps was shot progressive so 25psf more than 50i so that the video conversion was 25->24->29.97 which happens all the time as well. Glad to know there's an expert on the boards I can have second guess me though. I'll hit you up next time I might think I know something from 30 years of experience

> Glad to know there's an expert on the boards I can have second guess me though. I'll hit you up next time I might think I know something from 30 years of experience

I suggest you get over yourself. I am indeed a video expert with decades of IVTC experience.

The first line of your reply was:

"but rarely does anyone actually do this"

That is factually incorrect, no matter how many years of experience you may have.

Because audio for 23.976fps film is playing at the same speed as 29.97fps video. Which is really interlaced video at 59.94 fields per second. 3:2 pulldown is used to synthesize extra video frames to transfer to NTSC video so for a given instance of time, for every 4 frames of film you get 5 frames of video. (23.976/29.97 = 4/5) The instance of time remains unchanged so the audio is playing back at the same speed. This is all inherited from the CRT days before progressive video playback on flatscreens, and the video fps was tied to the local electrical frequency (50 Hz in Europe vs 60 Hz in USA / Japan) which is how the CRT timings were derived.

Coincidentally PAL video plays back at 25fps, to convert film to PAL they just speed it up from 24 to 25fps, audio and all, which is why if you watch a Euro DVD release of the same film all the actors sound like they just ingested helium before the scene because the audio is playing back ~4% faster. This was largely fixed with Blu-Ray as films play back at their native rate[1] on progressive displays but our European friends who have only seen films on VHS/DVD or TV and not in the theatre or Blu-Ray have been done a disservice, because the video and audio is sped up on playback and not as the director intended it to be shown.

[1] A notable exception is some unscrupulous distributors abroad release shitty PAL 25fps Blu-Rays of films which are simply upscaled PAL DVD versions that they then market as Blu-Ray but are worse than DVD quality but at marked up prices. This is more common than you think. Official releases from the studios are encoded at 23.976fps on the disc. TV shows shot on PAL video (native 25fps) will always play back at 25fps.

Pitch correction exists.

It's not straightforward and might introduce artifacts.

There are algorithms that are better than others.

For example, ffmpeg's pitch correction using "atempo" filter (WSOLA) is average and might present artifacts depending on source audio.

ZTX (was Dirac) is another algorithm that's commercial and pretty much artifact free.

Btw, sound studios responsible for the 24-25 pitch shift often have the possibility to process the pitch shift on separate dialogue, music and effects tracks, limiting even more the artifacts in the converted output.

Frame rate screw-up story time:

Around 2009, my street flooded and I decided to record it and sell it to a local news station. I had one bite and I took my camera over to the TV station (CTV).

When I got there, I was beyond disappointed that (1) they didn’t have an HDV player and that (2) I forgot my FireWire cable. I rushed home, imported/exported it in FCP, burnt it to a DVD and rushed back.

In the rush, I forgot to ensure the right frame rate was set. When I got there, the techs were able to ingest it no problem, but my heart dropped when I noticed the import rate on a little VFD was 1080/50i. Fortunately, it worked out and when my video aired, it looked like it was from an international source because of the pulldown.

I ended up getting a cheque for $135 for 8 broadcasted seconds of video and a day’s work of rushing back and forth. I’ve extrapolated it to be my most valuable piece of work at about $60,000 per hour.

That PAL speedup drives me nuts. I thought I was losing my mind the first time I noticed it. Nobody else did. Eventually I reasoned out why and found the appropriate name for the phenomenon.

You can get pitch-shifters, but on DVD players, the only ones with this feature I can find happen to function as karaoke machines.

On the topic of playback rate/pitch fuckery, Janet Jackson's "Rhythm Nation" was sped up ever so slightly after recording (as was sometimes done at the time to make the music sound more "exciting" or "intense"), and that's one of the hypotheses for why playing it interferes with laptop hard drives: the dominant E frequency/pitch got shifted up to somewhere slightly sharp of E (but not quite E#), which just so happens to be closer to some drives' resonant frequency.

> This is all inherited from the CRT days before progressive video playback on flatscreens, and the video fps was tied to the local electrical frequency (50 Hz in Europe vs 60 Hz in USA / Japan) which is how the CRT timings were derived.

I'll have you know, there were CRTs that did progressive scan too. Early HDTVs were CRTs, before flat screen TVs got big.

Plenty of PAL CRTs can accept NTSC at 60Hz on a 50Hz supply too, of course. It's nice to tie the supply and video rates together to reduce interactions between the two rates.

>Because audio for 23.976fps film is playing at the same speed as 29.97fps video. Which is really interlaced video at 59.94 fields per second. 3:2 pulldown is used to synthesize extra video frames to transfer to NTSC video so for a given instance of time, for every 4 frames of film you get 5 frames of video.

would you explain this to me like I'm 5?

NTSC television video is interlaced. First you draw the even lines of the image, then you draw the odd lines. Each set of lines is called a field.

Originally NTSC was 60 fields per second, based on the 60hz frequency of the North American power grid. 60 interlaced fields per second is pretty similar to 30 frames per second, but is not the same thing. The interlaced signal refreshes twice as quickly, but with half the vertical resolution per refresh.

When colour was added to NTSC, the frequency was shifted to 59.94 fields per second.

Movies shot on film are filmed at 24 frames per second. To convert a 24fps film to 60 field per second video, something called a 2:3 pulldown is used. The wiki explanation for how this works is pretty good: https://en.wikipedia.org/wiki/Telecine#2:3_pulldown

A 2:3 pulldown on 24fps film matches the 60 fields per second of the original black and white NTSC signal, but is slightly off for colour NTSC. The original article talks about how this can lead to problems like audio desync in production workflows.

Digital cameras offer the option to capture at 23.976fps. When you apply a 3:2 pulldown to 23.976fps video, you get an interlaced 59.94 fields per second video.

Fantastic. Thank you

It’s the same ratio. 30/29.97 = 24/23.976

The answer is a bit more complex when it comes to the transition to modern high definition television. It's a bit of a long story with very interesting twists and turns that involve politics, national security, the Pentagon, US Congress and none other than Donald Rumsfeld (CIA and Defense Secretary).

The story is well chronicled in a book I read about twenty years ago:

https://www.amazon.com/Defining-Vision-Broadcasters-Governme...

The title is intriguing enough:

"Defining Vision: How Broadcasters Lured the Government into Inciting a Revolution in Television"

I can't possibly do it justice here. I'll just mention that one would not be wrong to call Donald Rumsfeld the father of high definition television. His approach to wrangling the ATSC and FCC into adopting a cornucopia of standards was, from a business perspective, nothing less than genius while, from a technical perspective, a complete mess. The fractional frame rates would have evaporated from this planet had it not been for this part of the story.

Well worth reading for anyone interested in the technology or working in associated industries. Your jaw will most definitely drop as you get deeper into the story.

One bewildering thing that I think isn't covered there is that old Quicktime video was specified as 23.98 simply because they were using fixed precision. An apparently harmless issue until you tried reading metadata and converting frame rates assuming that just doing the maths would work.

Technology Connections on YouTube goes into this quite in-depth: https://www.youtube.com/watch?v=dX649lnKAU0

Stand-up Maths has a great explanation: https://www.youtube.com/watch?v=3GJUM6pCpew "Why is TV 29.97 frames per second?"

“… by introducing a color subcarrier of precisely 3.579545 MHz (nominally 3.58 MHz). The precise frequency …”

Does anyone have a circuit diagram for any of this? What were they using as a timing reference in the 50s that allowed a frequency lock accurate to 7 significant figures? There must be a fairly large error allowed.

It's 315/88. Chosen to be a half-integer multiple of the line rate. The line rate was also adjusted so that the audio subcarrier is a multiple of the line rate. The audio subcarrier is 4.5 MHz.

So it's really 4.5 MHz, multiplied by 35/44.

In practice, you might buy a 3.579545 MHz crystal oscillator and then use dividers and PLLs to make all the other frequencies you need. The actual error is going to be based on the oscillators you use, but for the past few decades, we've just been using ordinary crystal oscillators and that means something like 50ppm, maybe (for cheap ones).

Crystal oscillators were available prior to the invention of NTSC. Quartz oscillators achieved 0.1ppm accuracy at some point in the 1920s.

This morning I was trying to get a monitor working a noticed the 60 and 59.94 options in Windows, and wondered what the 59.94 was all about. Now I know!

This doesn't answer the question considering NTSC isn't used anymore. Why not 60 fps considering it's the standard refresh rate of practically all displays that are in use?

If you're asking why movies aren't shot at 60 fps instead of 24/23.976 fps, there are "HFR" movies shot at higher frame rates: https://en.wikipedia.org/wiki/List_of_films_with_high_frame_...

From what I can find as I write this, the only movies distributed at high-framerates on Blu-ray are Gemini Man and Billy Lynn’s Long Halftime Walk.

Although HFR is technically an improvement, not everyone's a fan of the "feel". Relevant HN thread: https://news.ycombinator.com/item?id=14616930

24fps has an aesthetic that "looks cinematic" because we have all watched decades of cinematic films at 24fps. From jump cuts, montage and flashbacks to the color saturation and frames per second of film, you've learned an entire visual language over all of these years of watching moving pictures!

In the 1970s it seemed common for tv shows to be shot on video in the studio but on film outside, perhaps because video cameras were too large or sensitive for outdoor use. The audience simply became accustomed to the large difference in appearance between indoors and outdoors in tv shows. IIRC, Doctor Who and Benny Hill went through this change during episodes frequently. It also reminds me of the first time I went over to a friend's house who had a large tube standard def tv after I had switched to HD. The scanlines that had always been invisible to my brain were suddenly very obvious. Funny how we adjust.

Apparently, many people are so used to 24 fps that films shot at higher framerates are slightly unsettling (even if they don't realize why), and have even been, ironically, described as unnatural. I've noticed it myself; I watched a YouTube video recently that was at 60 fps and my attention kept going to the hands of the person talking as he waved them around. The motion was too fluid. Slightly distracting. I guess my brain is used to interpolating what it would have looked like from a blur at 24 fps, rather than actually seeing the fine details. Though I'm sure we'll get used to it soon enough.

It's also kind of happened for audio quality where when someone is being interviewed, its natural for the host to be in crisp quality while the guest has crappy airpods mic quality. And how games show black bars on the top and bottom for cut scenes. It's beyond just limitations and now part of your expectation.

I will say that seeing 60fps video on youtube is very very noticeable, much more than the resolution. I personally much prefer it but I can see how others don't since it is such a difference to the normal.

I have the opposite. Panning shots at low frame rate look odd and make my head hurt, especially with 3:2 pull-down.

The first time I saw a film at 48 fps it finally felt so natural and immersive.

I know what you mean about the panning. If you've never looked into it, film shutter angles are an interesting topic. Conventionally, the shutter is open for 50% of the frame. At 24fps, that does create a noticeable judder, but also makes movement less blurry. You can reduce or increase the angle, but it's a trade-off either way at 24fps.

48+fps makes motion both a lot smoother and less blurry, however for me, it makes their costumes look a lot more like... costumes. For example when I watched The Hobbit in 48fps, it felt more like a LOTR themed fancy dress party than a film.

I suspect, in time, most people will get used to high frame rates as it becomes more common and learn to suspend disbelief the same way they do at low frame rates. Objectively, it looks fantastic.

> felt more like a LOTR themed fancy dress party than a film

Ooh, I experience this too. Great way to put it.

Would be nice to have variable frame rate, so both panning and action could look good. Shoot everything in 120fps (divisible by 24, 30, 60) and simply skip frames when appropriate.

This is the correct answer.

I realise I'm in the minority, but I had the opposite reaction watching The Hobbit in 48fps. It looked no more like a set with costumes than other films do, but I was no longer unpleasantly distracted by any fast movement or panning.

As far as I'm concerned, everything should be shot and delivered at 120.

Hopefully higher frame rates become common with IMAX movies. The content matter is usually stunning but panning shots can be very jerky on such large screens, especially at the edges.

The opening of Apocalypse Now would look like dog shit at > 24fps.

For a good comparison, watch the few Twilight Zone episodes (the original from the 60s) from season 2 that were shot on videotape, as opposed to film for the rest of the series. They look downright weird.

I think we are awaiting the first blockbuster artist who understands how to use HFR to create an even more cinematically immersive film, paired with the producer willing to take a risk on them. This film will change tastes permanently. One side effect of it is that it should ruin moviegoers’ taste for the smeary CG aesthetic of Marvel movies, so don’t expect this film to come from Disney. :)

Except disney does a bunch of CGI animated films, which have NO EXCUSE to be low framerate.

Well, right, we are talking about live action. There is expectation of 24fps-style motion blur in animation but that can be emulated.

Because the cinematic feel of 24 fps is extremely different from the video feel of 30fps, which in turn is completely different from the reality TV show feel of 60 fps.

Thats old people talk. Young dont even know what reality tv is, they hardly know what TV is in the first place. Tiktok is 30 (well, 29.97), most of YT and twitch already 60, games >60.

"Billy Lynn's Long Halftime Walk" was shot at 120fps and displayed in cinema and at home on 120fps or 60fps.

This is a drama film. Both critics and viewers hated the look of it.

Marvel comic book films should def be shot at 60/120 though. Why haven't anyone tried this with audiences?

Even if YT lets you play back at 1080p60 (or higher), any channel with videos that have cinematic looking segments (even something as simple as product review channel) have that look because those segments weren't actually shot at 60fps. The temporal smoothing of 24fps is critically important to get that look. And people still notice them and comment on how insanely good those segments are =)

NTSC may be gone now, but to avoid the need for frame rate conversion during simultaneous analog and digital broadcasts, and for compatibility with older equipment and recordings, the U.S. broadcasters all adopted (and continue to use) SD and HD digital formats with 30/1.001 or 60/1.001 frame rates.

(See also: drop frame time code.)

> Why not 60 fps considering it's the standard refresh rate of practically all displays that are in use?

Actually, I'd say 50fields/sec is the most popular frame-rate in-use around the world. Theatres still use 24fps or perhaps 48fps.

Shooting at 1200fps would make everybody happy. But 24fps works pretty well.

Because ATSC inherited the NTSC frame rate.

NTSC at this point is just a blanket term for any standard/tech stemmed from NTSC.

NTSC's components, including framerates, are still widely used in various (previously NTSC) countries.

Now image having these same discussions circa 2000 ish on IRC channels devoted to re encoding pirated VCD/SVCD to Microsoft’s accidentally released DiVX 3.11 alpha codec on multi pass encodings to hit 700mb exact

The strangeness of PAL vs. NTSC lives on

The difference between 23.976 and 24fps is 1.7321cents, for the musically minded.

I fear that I will always be A lonely number like root three A three is all that's good and right, Why must my three keep out of sight Beneath a vicious square root sign, I wish instead I were a nine For nine could thwart this evil trick, With just some quick arithmetic I know I'll never see the sun, as 1.7321 Such is my reality, a sad irrationality When hark! What is this I see, Another square root of a three Has quietly come waltzing by, Together now we multiply To form a number we prefer, Rejoicing as an integer We break free from our mortal bonds And with a wave of magic wands Our square root signs become unglued And love for me has been renewed.

It's not actually 23.976fps. That's just the friendly, rounded notation we all use in discussion.

It's actually 24000/1001, or in integers: 23.976023976023976... fps.

1.730369 cents then!

So this probably explains why my 60 fps screen slightly jitters about once every 2-3 minutes... Looks like a dropped frame, and is really frustrating when you've spent lots of money on AV gear...

59.94 fps vs 60 fps...

I still don't understand why can this be needed when everything is digital signal received over IP and presented over HDMI nowadays. Or do many Americans still watch RF TV?

But is therea benefit to 24? I know its a nice round number, but aren't they all arbitrary numbers anyways

Less human error is a meaningful benefit, even if it has nothing to do with the tech itself.

A new generation is always behind us, and explaining a nice, even 24.0 to them will just be a better situation.

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