Frames, not seconds

The software lies to you politely

Every animation tool shows a timeline in seconds, and almost everybody types in seconds. Underneath, nothing is stored in seconds. A frame is the unit, and a second is whatever number of frames you decided on before you started.

This matters the first time you specify a 300ms transition and hand it to somebody working at a different frame rate.

• At 24 fps, 300ms is 7.2 frames. You get 7, and the real duration is 292ms.
• At 25 fps, it is 7.5 frames. You get 7 or 8 depending on which way the software rounds.
• At 60 fps, it is 18 frames exactly.

None of these are wrong. They are just not the same animation, and if you approved one and shipped another, the difference is real.

The rates, and what each one is for

• 24 fps: cinema, and anything that wants to read as film. The lowest rate at which camera motion is tolerable.
• 25 fps: broadcast in India, the UK, Europe, Australia. If your work touches television anywhere on 50 Hz mains, this is the number.
• 30 fps (29.976): North American broadcast heritage, and the safest default for social video because most platforms re-encode towards it anyway.
• 50 and 60 fps: sport, screen recordings, and interface work where you want the motion to feel like the device rather than like a film.
• 12 fps: not a delivery rate, a working method. Hand-drawn animation holds each drawing for two frames inside a 24 fps timeline. Twelve distinct images a second is enough for drawn motion and nowhere near enough for a camera pan, which is why traditional animation works “on twos” and live action cannot.

29.97, and where the missing time went

When colour was added to American black-and-white television, the frame rate was slowed by exactly one part in a thousand to keep the colour subcarrier out of the audio. That 0.1% never went away. So 30 fps is usually 29.97, and 24 fps in a broadcast chain is usually 23.976.

The consequence is that a programme that runs for ten minutes of real time does not run for ten minutes of timecode. Over an hour, the gap is about 3.6 seconds. Drop-frame timecode fixes the labels by skipping two frame numbers every minute except every tenth minute: it does not drop any picture. Non-drop timecode counts honestly and drifts from the clock.

If you have ever wondered why an editor’s delivery spec says 29.97 DF and refuses anything else, that is why: a broadcast slot is measured by the clock, not by the frame count.

Set it first, and do not change it after

Pick the delivery frame rate before you place a single keyframe. Changing it later is not a neutral operation, and different tools disagree about what it means:

• After Effects keeps keyframes at their time values, so they land on fractional frames and get sampled to whichever frame is nearest. A carefully spaced move loses its spacing.
• Blender’s frame-rate change keeps the frame numbers, so the animation changes duration instead.
• Kdenlive will not let you change a project’s profile frame rate after the fact without re-interpreting every clip.

None of these is a bug. They are two reasonable answers to a question you should never have to ask.

Higher is not better, it is different

A common assumption is that 60 fps is a quality upgrade over 24. It is a different look, and the mechanism is exposure, not resolution.

With a conventional 180-degree shutter, the camera is open for half the frame interval. At 24 fps that is 1/48 of a second of blur per frame. At 60 fps it is 1/120: half as much. Less blur per frame means each frame is crisper and the strobing between them is more visible, which is exactly the “looks like a soap opera” reaction people report and cannot explain. Rendered animation has the same property: if you do not add motion blur in the render, a fast move at any frame rate will strobe.

So the honest statement is: 60 fps buys you temporal resolution and costs you the blur that hides the gaps. For interface motion, where elements are flat and travel short distances, that trade is usually good. For a camera move across a landscape, it usually is not.

What to write down

On every brief, before anything else: frame rate, resolution, and duration in frames. “Seven frames at 24” is a specification. “About a third of a second” is a conversation you will have again.