23.976 vs 24 fps, and why films are not 24 fps

Most commercial movies are encoded at 23.976 frames per second rather than exactly 24 frames per second because of a broadcast engineering compromise made in 1953 when color was introduced to American television. To prevent high-frequency color signals from interfering with sound transmissions, broadcast engineers slowed the transmission clock by exactly 0.1 percent (1,000 ÷ 1,001), converting 24.000 fps film transfers into fractional 23.976 fps video.

While commercial cinema projectors and modern international film festivals still project at true integer 24.000 fps, nearly all Blu-ray discs, DVD releases, and streaming video platforms remain anchored to 23.976 fps. Understanding this fractional frame rate explains why video players occasionally skip frames during slow pans, why subtitles drift out of sync over time, and why macOS provides separate 47.95 Hz and 48.00 Hz display settings.

Animation

24 fps on a 60 Hz screen vs a 120 Hz screen

60 Hz screenframe held 3 refreshes

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120 Hz screen (ProMotion)frame held 3 refreshes

ABCDEF

Why did 1953 NTSC color television introduce the 0.1 percent slowdown?

To understand why a fractional frame rate exists in modern digital media, look back to the birth of color television in the United States.

When the National Television System Committee (NTSC) established the original black-and-white television standard in 1941, broadcasts operated at a field rate of exactly 60.00 Hz (30 interlaced frames per second). This was synchronized directly with the American 60 Hz AC electrical grid to avoid rolling interference lines on cathode-ray tube screens.

By 1953, RCA and NTSC engineers developed a backward-compatible method to transmit color television signals to newly manufactured color sets without rendering existing black-and-white sets obsolete:

1. They added a high-frequency color subcarrier at approximately 3.579545 MHz inside the existing 6 MHz broadcast channel spectrum.
2. However, the existing audio signal was transmitted on an FM carrier located at exactly 4.5 MHz.
3. During field testing, engineers observed an unacceptable beat frequency: harmonic intermodulation between the 4.5 MHz sound carrier and the 3.58 MHz color subcarrier produced crawling interference patterns across the viewer’s screen.
4. To eliminate the interference beat, engineers needed to make the audio carrier an exact multiple (specifically, the 286th harmonic) of half the horizontal scanline frequency.
5. Shifting the sound carrier was impossible because millions of existing black-and-white televisions were hardwired to tune to 4.5 MHz audio.

The ingenious solution was shifting the horizontal scanline frequency downward by exactly 0.1 percent, multiplying the entire transmission clock by the mathematical ratio 1,000 ÷ 1,001:

15,750 Hz × (1,000 ÷ 1,001) = 15,734.26 Hz

This slight clock shift lowered the vertical field refresh rate by the identical 0.1 percent margin:

60.00 Hz × (1,000 ÷ 1,001) = 59.940059... Hz

When theatrical 24.000 fps films were telecined and transferred to videotape for television broadcast, they were slowed down by that same 0.1 percent factor, establishing the universal fractional frame rate:

24 × (1,000 ÷ 1,001) = 24,000 ÷ 1,001 ≈ 23.976024 fps

This technical calculation was codified in international broadcasting standards, including Recommendation ITU-R BT.601 and SMPTE ST 2084.

What is the difference between 23.976, 23.98, and true 24.000 fps?

In video editing suites, technical metadata, and retail packaging, you will encounter three labels that appear interchangeable but have distinct technical meanings:

For the historical origins of why cinema adopted 24 frames per second in the first place, explore our guide on why movies are 24 fps.

Today, theatrical movies projected in commercial cinemas are delivered as Digital Cinema Packages (DCPs) operating at pure integer 24.000 fps. However, when those exact same films are packaged for consumer distribution on Blu-ray disc, 4K UHD Blu-ray, or digital streaming services, they are almost universally slowed down to 23.976 fps to maintain strict compatibility with television broadcast infrastructure and HDMI clock standards.

Why does playing 23.976 fps on a 24 Hz screen drop a frame every 41 seconds?

Many movie lovers assume that playing a movie on a screen running at 24.000 Hz or 60.000 Hz will be completely smooth. In practice, a subtle 0.1 percent clock mismatch creates a recurring visual glitch.

Consider what happens when you play a 23.976 fps movie on a display locked to an exact integer frequency of 24.000 Hz:

• In 1 second, the display expects exactly 24.000000 frames.
• In 1 second, the video file only delivers 23.976024 frames.
• The difference is a deficit of 0.023976 frames per second.

To find out how long it takes for this timing delta to accumulate into an entire missing frame:

1 frame ÷ 0.023976 frames/sec ≈ 41.71 seconds

Every 41.7 seconds, the display’s clock has outpaced the video stream by one full frame. Because the audio track must play at its natural continuous speed to preserve correct musical pitch and lip-sync, the media player cannot let video drift behind. To resynchronize audio and video, the player is forced to repeat the current frame.

During high-action scenes or static dialogue, this repeated frame is imperceptible. But if the 41st second coincides with a slow, continuous horizontal camera pan across a city skyline, the smooth movement abruptly hitches. The exact same glitch occurs in reverse when playing a true 24.000 fps theatrical master on an NTSC 59.94 Hz or 23.976 Hz display: the player must drop a frame every 41.7 seconds.

To understand how uneven cadences introduce visual stutter, read our detailed analysis of 24 fps judder on 60 Hz screens.

Why does macOS offer both 47.95 Hz and 48.00 Hz refresh rates?

If you open System Settings on a MacBook Pro with a Liquid Retina XDR display or connect an Apple Pro Display XDR, you will discover that Apple’s display engineers accounted for this exact fractional discrepancy.

As documented in Apple Support article 102297, macOS provides two separate 48 Hz timing presets in System Settings › Displays › Refresh Rate:

• 48.00 Hertz: Designed for true integer 24.000 fps cinema masters. Refreshes twice per frame (2 × 24.000 = 48.000 Hz), providing uniform 2:2 pulldown with zero frame drops.
• 47.95 Hertz: Designed for fractional 23.976 fps broadcast and streaming masters. Refreshes twice per frame (2 × 23.976024 = 47.952048 Hz), providing uniform 2:2 pulldown without the 41-second clock drift glitch.

By matching the display panel’s physical hardware oscillator to the exact mathematical rate of your media file, macOS eliminates telecine judder and periodic clock-drift stutters simultaneously. Learn how to configure these modes in our guide on how to change the refresh rate on a Mac.

How does 23.976 fps cause subtitle and audio sync drift?

The difference between 23.976 fps and other frame rates is one of the most common causes of subtitles drifting out of sync.

Subtitle files stored in plain text formats (such as SubRip .srt files) rely on absolute millisecond timecodes (hh:mm:ss,ms). If an .srt file was extracted from a 24.000 fps theatrical release and loaded alongside a 23.976 fps streaming file:

• The 0.1 percent speed difference causes subtitles to drift by approximately 3.6 seconds for every hour of playback.
• By the end of a two-hour film, dialogue appears more than 7 seconds before the subtitles display on screen.

The drift is even more extreme when crossing between European 25 fps PAL video and 23.976 fps American video due to PAL speed-up, causing subtitles to drift by 2.5 seconds every single minute (explore the full breakdown in our comparison of 50Hz vs 60Hz video).

To learn how to diagnose and correct subtitle timing drift on your Mac without re-encoding, explore our troubleshooting guide on how to fix subtitles out of sync on Mac.

How to check the exact frame rate of your video files on Mac

To verify whether your movie is true 24.000 fps or fractional 23.976 fps, you can inspect the file container using free command-line or desktop tools:

1. Using ffprobe: In Terminal, run:

   ffprobe -v error -select_streams v:0 -show_entries stream=r_frame_rate,avg_frame_rate input.mkv

   If the output reads 24000/1001, the file is 23.976 fps. If it reads 24/1, it is true 24.000 fps.
2. Using MediaInfo: Open the file in the open-source MediaInfo utility. Under the Video stream section, inspect the Frame rate field. It will explicitly display 23.976 FPS or 24.000 FPS.

Achieving steady cinema timing on your Mac

The existence of 23.976 fps is a reminder of how 20th-century analog engineering decisions continue to influence modern digital workflows. While fractional frame rates began as a clever hack to keep color television from buzzing in 1953, they remain the dominant mastering standard for consumer entertainment today.

By understanding the distinction between 23.976 fps and true 24.000 fps, you can choose the correct 47.95 Hz or 48.00 Hz cinema refresh modes in macOS, prevent the annoying 41-second pan glitch, and enjoy movies with steady, theatrical cadence.