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The second Avatar movie is the latest in a (very) short list of major films to use HFR or High Frame Rate footage. This hyper-smooth frame rate is divisive, but some filmmakers are gaga for it, yet it's quite unlikely to become mainstream.
What Is an HFR Movie?
HFR stands for "high frame rate," and it describes movies shot and displayed at a higher frame rate than the traditional 24 frames per second (fps). HFR movies are typically shot at a frame rate of 48fps or higher, with some experiments even reaching up to 120fps.
The goal of HFR movies is to provide a more immersive and realistic viewing experience by reducing motion blur and increasing the perceived smoothness of the image. Some people have reported that HFR movies have a more "video-like" quality, as the higher frame rate can make the footage appear more lifelike and less "cinematic."
HFR movies work particularly well for 3D films, since it removes most of the motion blur and stutter than can make fast-paced 3D footage difficult to watch. In James Cameron's Avatar: The Way of Water, the director actually switches between 24fps and 48fps on the fly, depending on where the strengths of HFR are most needed in the film.
The 48fps Hate Is Irrelevant
It's easy to think that the widespread distaste for the look of HFR is the reason we're unlikely to see HFR become the mainstream format. In truth, frame rates are somewhat arbitrary, and the "cinematic" perception we have of 24fps is as much a function of expectation and experience as it is of photons hitting retinas.
Given time, current and future viewers would simply get used to the higher frame rate, making this a non-issue. The question is whether HFR will ever become mainstream enough to get this chance, but there are a few problems standing in the way.
HFR Will Blow Up Movie CG Budgets
While capturing movies at 48fps isn't a huge deal in terms of camera equipment, or even raw footage storage, as soon as you start rendering CG (computer-generated) effects or entire CG scenes, a huge problem rears its head.
Movie CG is rendered "offline," which means that each frame is rendered over long periods using massive computer farms. Filming at 48fps merely means taking twice as many photos in a second compared to 24fps film, but doubling the frame rate means doubling the rendering workload for CG. If you needed three months of render time to complete the CG in your movie, you now need six months, resulting in twice the cost.
Avatar: The Way of Water proved such a heavy film to render that it exceeded what the effects wizards at WETA could do with their in-house data center. So the film was rendered in the cloud using Amazon Web Services.
This was necessary even though the entire film isn't rendered at 48fps! Given how future films are likely to become more and more CG-heavy, HFR would need a strong case, and we suspect a commensurate increase in ticket sales would not cover the extra cost. A film like the Avatar sequel is very much the exception here.
HFR Creates Problems for Streaming
The internet already strains under the weight of 24fps and 30fps 4K video streams. If future content were to be 48fps or greater as standard, it would exponentially increase the bandwidth needed to support it.
Let's not forget that 8K streaming is almost certainly on the medium-term roadmap for film and TV content, and that's going to be demanding enough to deliver over the internet at 24fps, much less twice that rate.
Storing HFR Footage Is an Issue
As you've probably deduced from the points above, doubling the frame rate also greatly impacts the file sizes involved. Now, due to how video compression works, the 48fps version of a film won't be exactly twice as large, but in general they'll take up substantially more space.
Storage space in data centers is precious and video content is already one of the biggest space hogs on servers. A significant increase in movie sizes would make them more expensive to host, and therefore less profitable.
The Lowest Common Denominator Rules
Just like 30fps console games, 24fps films are likely to stick around for the foreseeable future because it's the lowest number content creators can get away with. There's no real incentive for studios to for out for HFR unless it's going to pull more people to cinemas as 3D did for a while, or if customers begin to demand it. If you're going to make the same amount of money with a 24fps film than you would with a 48fps film, why push for it?
There are always individuals such as James Cameron or Peter Jackson who break new technological ground with filmmaking, but in this case they face an uphill battle not only of public opinion, but of serious technological downsides.