High frame rate

Not to be confused with slow motion.

In motion picture technology—either film or video—high frame rate (HFR) refers to higher frame rates than typical prior practice.

The frame rate for motion picture film cameras was typically 24 frames per second (fps) with multiple flashes on each frame during projection to prevent flicker. Analog television and video employed interlacing where only half of the image (known as a video field) was recorded and played back/refreshed at once but at twice the rate of what would be allowed for progressive video of the same bandwidth, resulting in smoother playback, as opposed to progressive video which is more similar to how celluloid works. The field rate of analog television and video systems was typically 50 or 60 fields per second. Usage of frame rates higher than 24 FPS for feature motion pictures and higher than 30 FPS for other applications are emerging trends in the recent past.

History of frame rates in cinema

In early cinema history, there was no standard frame rate established. Thomas Edison's early films were shot at 40 fps, while the Lumière Brothers used 16 fps. This had to do with a combination of the use of a hand crank rather than a motor, which created variable frame rates because of the inconsistency of the cranking of the film through the camera. After the introduction of synch sound recording, 24 fps became the industry standard frame rate for capture and projection of motion pictures. 24 fps was chosen because it was the minimum frame rate that would produce adequate sound quality. This was done because film was expensive, and using the lowest possible frame rate would use the least amount of film.

A few film formats have experimented with frame rates higher than the 24 fps standard. The original 3-strip Cinerama features of the 1950s ran at 26 fps. The first two Todd-AO 70mm features, Oklahoma! (1955) and Around the World in 80 Days (1956) were shot and projected at 30 fps. Douglas Trumbull's 70mm Showscan film format operated at 60 fps.

The IMAX HD (high definition in this case meaning high definition film stock, as 70mm IMAX is the highest resolution motion picture image in the world) film Momentum, presented at Seville Expo '92, was shot and projected at 48 fps. IMAX HD has also been used in film-based theme park attractions, including Disney's Soarin' Over California.

The proposed Maxivision 48 format ran 35mm film at 48 fps, but was never commercially deployed.

Digital Cinema Initiatives has published a document outlining recommended practice for high frame rate digital cinema. This document outlines the frame rates and resolutions that can be used in high frame rate digital theatrical presentations with currently available equipment.

Usage in the film industry

See also: List of films with high frame rates

Peter Jackson's The Hobbit film series, beginning with The Hobbit: An Unexpected Journey in December 2012, used a shooting and projection frame rate of 48 frames per second, becoming the first feature film with a wide release to do so. Its 2013 sequel, The Hobbit: The Desolation of Smaug and 2014 sequel, The Hobbit: The Battle of the Five Armies, followed suit. All films also have versions which are converted and projected at 24 fps.

In 2016, Ang Lee released Billy Lynn's Long Halftime Walk. Unlike The Hobbit trilogy, which used 48 frames per second, the picture shot and projected selected scenes in 120 frames per second, which is five times faster than the 24 frames per second standard used in Hollywood.

RocketJump's Video Game High School was the first web series to use HFR, and the first content shot and edited in a mixed frame rate. The series, which follows the lives of high school students in a world where gamers are revered as pro-athletes, adopted HFR in its second season, using the standard 24 frames per second for real world interactions, and 48 frames per second for "in-game" action sequences. Although the content is available on YouTube and Netflix, it can only be viewed in mixed frame rate using a special player on RocketJump's website.

Other filmmakers who intend to use the high frame rate format include James Cameron in his Avatar sequels and Andy Serkis in his adaptation of George Orwell's Animal Farm.

Out of the cinema

Frame rates higher than 24 FPS are quite common in TV drama and in-game cinematics.

Some media players are capable of showing HFR content and almost all computers and smart devices can handle this format as well. In recent years some televisions have the ability to take normal 24 fps videos and "convert" them to HFR content by interpolating the motion of the picture, effectively creating new computer generated frames between each two key frames and running them at higher refresh rate. Some computer programs allow for that as well but with higher precision and better quality as the computing power of the PC has grown.

Motion interpolation may cause some artifacts, as a result of the computer "guessing" the frames wrong.

Video encoding methods

Usually, cameras (including those in mobile phones) historically had two ways of encoding high framerate (or slow motion) video into the video file: The real-time method and the menial method.

Real-time method

The real time method treats the video as a normal video while encoding it. The output video file contains the same framerate as the sensor output framerate. The duration of the video in the output file also matches the real-life recording duration. And the output video also contains an audio track, like usual videos.

This method is used by all GoPro cameras, Apple iPhones with high framerate (slow motion) video recording functionality (starting with the iPhone 5s in late 2013), and every Samsung Galaxy flagship since 2015.

Advantages

• Video editing software (e.g. Sony Vegas, Kdenlive and precluded software in mobile phones) and video playback software (e.g. VLC media player) allow treating such videos as both usual videos and slow-motion videos.
  • During video editing and video playback, the indicated playback speed matches real life.
• Video framerate and duration matches real life.
• Includes audio track, like normal framerate videos.

These advantages make the real-time method the more useful method for power users.

Menial method

The menial method encodes recorded video files in a stretched way, and also without audio track. The framerate in the output file does not match the original sensor output framerate, and the real-life timespan of the recording does not match the length of the video in the output file

This means that the action visible inside the video runs at slower speeds than in real life, despite the indicated playback speed is ×1.

Example

An 120_FPS video whose real-life recording duration is 00h:00m:10s can be encoded in the following methods on the Samsung Galaxy Note 2, S4, Note 3, S5 and Note 4 (devices that use the menial method):

🎬 Encoding mode	📹 Sensor output framerate	Effectively encoded framerate	🎞️Output video file framerate	🕒🎥 Real-life recording duration	🕒📽️ Output video duration	🎤 Audio recorded?
🎞️ ½ (1/2)	120fps	60fps (because half truncated)	30fps (60fps if no frames truncated)	00:00:10	00:00:20	No 🔇
🎞️ ¼ (1/4)	120fps	120fps	30fps	00:00:10	00:00:40	No 🔇
🎞️ ⅛ (1/8)	120fps	120fps	15fps	00:00:10	00:01:20 (80 seconds)	No 🔇
🎞️ Real-time (as reference)	120fps	120fps	120fps	00:00:10	00:00:10	Yes 🔊

This encoding method is used by the camera software of the Panasonic Lumix DMC-FZ1000 and all Samsung Galaxy flagship devices prior from late 2012 (Galaxy Note 2) to 2014 (Galaxy S4 (including S4 Zoom), Galaxy S5, Galaxy K Zoom, Note 3, Note 4) and OnePlus phones.

Advantages

• The output video file is directly playable as slow motion in video players that do not support adjusting the playback speed (e.g. on a Galaxy S3 mini).
• The output video file is directly playable in video players and/or on devices that can only handle limited framerates (e.g. on a Galaxy S3 mini).

See also

• High-motion
• Motion interpolation