Frame rate: 24, 30 or 60 fps?

Common frame rates and where they come from

Why 24 looks like film and 60 looks like video

Each frame of a moving subject is a short exposure, and the blur within it is what tells the eye that the subject moved. Cinema's convention is a shutter open for half the frame interval, called the 180-degree rule. At 24 fps that is 1/48 of a second. That is long enough for motion to smear slightly, so the brain joins the frames into smooth movement. At 60 fps the same rule gives 1/120 of a second, so each frame is crisper and there are more of them, and motion looks smooth rather than fluid. Neither is wrong. Sport, gameplay and interfaces benefit from seeing each moment clearly; drama benefits from the softness that lets the eye fill in the gaps.

The look people call the soap-opera effect is exactly this. High-frame-rate footage feels like video because the blur cue is gone. So does 24 fps footage that a television's motion smoothing has stretched to 60. It is a matter of association and taste rather than quality, but the association is strong enough that most narrative work stays at 24 or 25.

Frame rate and bitrate

Doubling the frame rate doubles the pictures per second, so at a fixed bitrate each frame gets half the bits. In practice the cost is less than double. Frames next to each other at 60 fps are more alike than at 30, so the encoder can describe them more cheaply. But it is far from free. A 60 fps file at a 30 fps bitrate will show softening in fast motion, which is the very thing 60 fps was chosen for. When you export a high-frame-rate master, raise the bitrate above the figures in the bitrate guide, using the high end of each range as a starting point.

Hosting ladders publish targets for a baseline rate, and VideoBB's are stated per resolution. Transcoders do not invent frames. The rate you upload is the rate viewers receive. A 60 fps upload produces 60 fps renditions, and a 24 fps upload produces 24 fps renditions. Decide the rate at the shoot, not at the export.

30 fps or 60 fps?

Variable frame rate: the problem nobody warns you about

Phones, screen recorders and video-call tools often save files with a variable frame rate. The recorder writes a frame whenever it has one. The rate then wanders between, say, 24 and 60 as the device gets busier or quieter. Players cope by reading each frame's timestamp. Editors and transcoders usually assume a constant rate. When they meet a variable one, the symptoms are familiar: audio that drifts out of sync, a duration that does not match the source, or a file that reports 60 fps and plays like 20.

Check before you upload. ffprobe shows two rates for a stream, r_frame_rate and avg_frame_rate; if they differ, the file is variable. The fix is to convert to a constant frame rate once, cleanly. The command ffmpeg -i in.mp4 -fps_mode cfr -r 30 -c:v libx264 -crf 18 -c:a copy out.mp4 resamples the video to a steady 30 fps. It leaves the audio untouched. Choose the rate closest to what the recorder was aiming for, then send the result through upload. The upload failures guide lists this among the causes of processing errors, and preparing video for upload includes it in the export checklist.

Choosing a frame rate for a project

1. Start from the region and the delivery. Web-only content can use 24, 30 or 60. Content that also goes to broadcast should follow the local standard: 25 or 50 in PAL regions, and 29.97 or 59.94 in NTSC regions.
2. Match the rate to the motion. Fast, detailed motion wants 50 or 60; conversation and narrative are fine at 24, 25 or 30.
3. Set the shutter to roughly half the frame interval unless you want a deliberate look; 1/48 at 24 fps, 1/60 at 30 fps, 1/120 at 60 fps.
4. Keep every source clip at the same rate, and set the timeline to match before importing.
5. Export at the timeline rate, constant, with the bitrate raised for 50 or 60 fps.
6. Confirm with ffprobe that the exported file reports the rate you intended and that it is constant.

Displays and judder

Where the frames end up matters too.

• Most computer displays refresh at 60 Hz. 30 and 60 fps divide evenly, but 24 fps does not. Some frames are shown for three refreshes and some for two. That slight unevenness is called judder.
• 120 Hz displays, common on newer phones and monitors, divide evenly by 24, 30 and 60 and show all three cleanly.
• Televisions often switch refresh rate to match a 24 fps source. Browsers on computers do not. So a 24 fps web video has mild judder on a 60 Hz screen, and the player can do nothing about it.
• Motion-smoothing settings on televisions interpolate to the panel rate and are the main cause of the soap-opera effect on film content.