Frame Rates Explained: 23.976, 24, 25, 29.97 and 59.94

The frame rates at a glance

There are two families. Whole-number rates (24, 25, 30, 50, 60) are exactly what they say. Fractional rates (23.976, 29.97, 59.94) are the whole numbers multiplied by 1000/1001, a legacy of color television in North America that every 60 Hz broadcast and streaming system still uses.

Higher rates follow the same pattern: 48 and 96 for high-frame-rate cinema, 100 and 120 (or 119.88) for HFR video. The ITU's HDTV and UHDTV standards, BT.709 and BT.2100, list each fractional rate as the whole number divided by 1.001.

Where 1000/1001 came from

Black-and-white television in the US ran at 60 fields (30 frames) a second, with 525 lines per frame: a line rate of 15,750 lines a second. Color had to fit into the same channel, which already carried sound 4.5 MHz above the picture carrier. The NTSC color standard (now SMPTE ST 170) set the color subcarrier at 5 MHz × 63/88 and the line rate at 2/455 of the subcarrier, which works out to an exact fraction of that 4.5 MHz:

When film was transferred to this 59.94-field system with 3:2 pulldown, it had to slow by the same 0.1%, so "24 fps" film ran at 24000/1001 = 23.976 fps. HD and UHD standards then kept all three fractional rates so that new equipment would interoperate with existing programs, transmitters and archives, which is why cameras still offer 23.976, 29.97 and 59.94 next to 24, 30 and 60. The pulldown guide covers the cadence itself.

23.976 vs 24

The two look identical: the difference is 0.1%, one frame in every 1,001. It matters for three things.

• • Sound sync. Footage shot at 24 and played at 23.976 runs 3.6 seconds longer per hour. Sound recorded at real time against it drifts a frame out of sync after about 42 seconds, unless it is slowed by the same 0.1%. The audio sample rates guide shows how that pull-down is done.
• • Running time. A 2-hour feature at 24 fps runs 7.2 seconds longer at 23.976. Small, but it shows up in delivery paperwork that lists durations to the frame.
• • Delivery. A DCP plays at 24, not 23.976, so a 23.976 master is played 0.1% faster in the cinema and its sound has to be conformed to match. Netflix, by contrast, requires delivery at the native frame rate the show was shot and edited at.

The rule: pick one, shoot it, finish it. The camera, the sound recorder's timecode, the edit timeline and the deliverable should all name the same rate.

29.97 vs 30

The same 0.1% applies. 29.97 is the broadcast rate in North America and the other former NTSC countries, for everything from news to reality shows, and 1080i there is 59.94 interlaced fields making 29.97 frames. True 30 fps turns up in screen recordings, some phone and action-camera footage and web video. Mix them on one timeline and the NLE has to drop or repeat a frame roughly every 33 seconds to keep up.

Timecode at 29.97 counts 30 labels a second, so plain non-drop timecode drifts 3.6 seconds an hour behind the clock. Broadcast work fixes that with drop-frame timecode, explained in full in drop-frame vs non-drop-frame timecode.

25 and 50 fps

Countries with 50 Hz mains power built their television around it: 625 lines, 50 fields, 25 frames a second. HD kept the rates (the EBU lists 720p/50, 1080i/25, 1080p/25 and 1080p/50 for European production), and they are whole numbers, so there is no 1000/1001, no drop-frame and no drift against the clock.

Mains frequency also decides flicker. Lamps on 50 Hz mains pulse 100 times a second; an exposure of 1/50 s or 1/100 s averages out the pulses. At 25 fps that is a 180° shutter. A 24 fps shoot in a 50 Hz country uses 172.8° (1/50 s) to stay flicker-free under such lights; in 60 Hz countries the safe exposures are 1/60 s and 1/120 s, which is 144° at 24 fps and 180° at 30. The shutter angle guide shows the conversion.

59.94, 60 and higher

50 and 59.94 fps progressive capture fast motion with less blur and judder than 25 or 29.97, which is why sport is produced at those rates. The same rates are also the most common capture rates for slow motion on a 25 or 23.976 timeline: 59.94 played back at 23.976 is 40% speed, a 2.5× slow-down.

Rates above 60 (96, 100, 119.88, 120, 240) are almost always capture rates for slow motion rather than delivery rates. The slow motion guide works through the factors.

How to choose a frame rate

1. Start from the deliverable. The spec sheet from the broadcaster, streamer, festival or client names the frame rate. Shoot that rate, or a rate that converts cleanly to it.
2. Then the region. No spec yet: 23.976 or 29.97 in 60 Hz countries, 25 in 50 Hz countries, 24 for a cinema-first film.
3. Then the look. 24/23.976/25 for the motion blur audiences read as film; 29.97/30 for a video feel; 50/59.94 for sport and smooth motion.
4. Then the lights. Match the shutter to the mains: 1/50 s in 50 Hz countries, 1/60 s in 60 Hz countries, or check flicker-free settings on LED fixtures.
5. Write it down. Put the project frame rate on the camera report, the sound report and the dailies spec, so the recorder's timecode, the camera and editorial agree from day one.

Mixing frame rates in one edit

Every NLE lets you drop a 29.97 clip on a 23.976 timeline, but it has to invent the result. It can play the clip in real time by skipping frames (motion stutters), blend neighboring frames (soft ghosting), or build new frames with optical flow (smooth until it breaks on complex motion). Or it can conform the clip, playing every frame at the timeline rate, which changes its speed:

CineMath's Speed Change calculator gives that percentage and the change in running time for any pair of rates, including the NTSC fractional rates, and warns when you mix fractional and whole rates. The free speed change calculator runs the same sum in your browser.

Frame rate questions

Next: once the rate is set, timecode has to agree with it. Read drop-frame vs non-drop-frame timecode (the free timecode converter counts frames at any of these rates), then check any conform with the Speed Change calculator.