Tutorials Sports

Slow Motion and Replay for Sports

Intermediate · ~18 min

Overview

Slow motion is the shot sports coverage is judged on, and most amateur attempts look wrong for two specific and fixable reasons: the frame rate was not high enough, and the shutter was left where it would be for normal speed. Both are decided at capture and cannot be corrected afterwards. This guide covers the arithmetic of frame rate and playback speed, the shutter rule that changes for slow motion, and how replay works when you do not have a dedicated replay system.

What You Need

A camera that shoots at higher frame rates at your delivery resolution
Considerably more light than normal-speed shooting requires
The frame rate calculator, for working out capture rate against target speed
Storage, because high frame rates consume it quickly
A recording of each camera feed if you intend to recut replays
A clear decision about your project frame rate before you shoot

Steps

Decide the playback speed first, then derive the capture rate

Capture rate divided by project frame rate gives you the slowdown factor. Shooting 120 fps for a 30 fps timeline plays at quarter speed. 60 fps for 30 plays at half. Work backwards from how slow you want it rather than shooting at the highest rate available and deciding later, because the highest rate usually costs resolution and light.

Set shutter relative to the capture rate, not the project rate

The double-the-frame-rate rule still applies, but to the rate you are capturing at. Shooting 120 fps means roughly 1/240, not 1/60. This is the single most common slow-motion mistake, leaving the shutter at a normal-speed value produces smeared, mushy motion that defeats the entire purpose of shooting high frame rate.

Budget for the light you are about to lose

A faster shutter means less light per frame, and slow motion demands a much faster shutter. Combined with the fact that high frame rates sometimes restrict maximum aperture or force a sensor crop, slow motion is a light-hungry format. Outdoors in daylight it is straightforward. In an indoor venue it is frequently the constraint that decides whether it is possible at all.

Check what high frame rate costs on your camera

Many cameras reduce resolution, crop the sensor, disable autofocus, limit recording duration, or drop audio at their highest frame rates. Find out which applies to yours before the event rather than discovering mid-match that your slow-motion camera cannot autofocus.

Conform in the edit deliberately

Interpret the high-frame-rate clip to your project rate so it plays slow at full quality, rather than applying a speed change to a normal-rate clip, which invents frames and produces artefacts. If your camera already flags the footage for conform, check it landed at the speed you expected.

Build replay from recorded isolated feeds

Without a dedicated replay system, the workable approach is recording every camera feed separately alongside the switched output, plus a live marker log of significant moments. An operator can then pull the marked moment from the best angle during a stoppage, which covers most of the value of a replay system at a fraction of the cost.

Pro Tips

Shutter at roughly double your capture rate. Leaving it at the normal-speed value is why most amateur slow motion looks smeared.
Shoot slow motion outdoors where you can. Light is the constraint that most often makes it impossible indoors.
Check for flicker at high frame rates under artificial light. The safe shutter values change with the capture rate.
High frame rate consumes storage fast. Budget cards accordingly and offload between periods.
Not everything benefits from slow motion. Use it on the decisive moment, not throughout, or it stops meaning anything.

Knowledge Base

What You'll Learn

Slow motion is entirely determined at capture, which is why it cannot be fixed later. Below: the arithmetic, and why shutter is the setting that ruins most attempts.

The Arithmetic, and Why It Has to Be Decided in Advance

Slow motion works by capturing more frames per second than you play back, so the same action occupies more time on the timeline while every frame remains a real photograph.

The relationship is straightforward: capture rate divided by project rate equals the slowdown factor. Capturing at 120 fps for a 30 fps project gives quarter speed. Capturing at 100 for a 25 fps project gives the same. Capturing at 60 for 30 gives half speed, which is gentle and often the right choice for team sport.

This cannot be achieved after the fact. Slowing down normal-rate footage means the software must invent the missing frames, either by duplicating them, which produces visible judder, or by interpolating, which produces smeared artefacts around fast-moving edges. Both are obvious on exactly the fast motion you wanted to slow down.

So the decision belongs at capture, and it costs something: higher frame rates need more light, more storage, and frequently a resolution or autofocus compromise. Choosing the slowdown you actually need rather than the maximum available is usually the better trade.

Why Shutter Ruins Most Slow Motion

The most common slow-motion failure is not frame rate, people generally get that right, it is leaving the shutter where normal-speed shooting put it.

The motion blur rule says shutter should sit near double the frame rate. At 25 or 30 fps that means around 1/50 or 1/60, which produces the blur audiences read as natural.

When you capture at 120 fps, the rule still applies to the capture rate, so the shutter should be near 1/240. Leaving it at 1/60 means each frame is exposed four times longer than it should be, capturing four times as much motion blur per frame.

At normal speed that blur is invisible because the frames pass quickly. Played back at quarter speed, every frame is on screen four times longer and its blur becomes plainly visible, producing the soft, smeared look that makes amateur slow motion recognisable.

The consequence is a light problem: a shutter four times faster admits far less light, which is why slow motion is comfortable in daylight and difficult in a sports hall. That constraint is real and is the reason to choose the slowdown you need rather than the maximum available.

Where This Fits

This guide covers one specific part of sports production. The wider picture, camera positions, switching discipline, comms, replay and highlights, and the sync problems that break multicamera setups, is in Multi-Camera Coverage for Live Sports: Positions and Switching, which frames the discipline as a whole and links out to the detailed guides underneath it, including this one. If you are starting from scratch rather than solving a specific problem, read that first and come back here.

FAQ

Q: What frame rate should I shoot for slow motion?
A: Work backwards from the playback speed you want: capture rate divided by project rate is your slowdown factor. 60 fps into a 30 fps timeline gives half speed, 120 gives quarter. Higher is not automatically better, since high rates cost light, storage, and often resolution or autofocus.

Q: Why does my slow motion look smeared rather than crisp?
A: Your shutter was set for normal speed rather than for the capture rate. The double-the-frame-rate rule applies to what you are capturing at, so 120 fps wants roughly 1/240. Leaving it at 1/60 records four times too much motion blur per frame, which becomes obvious when each frame is on screen four times longer.

Q: Can I add slow motion to normal-speed footage in the edit?
A: Only by inventing frames, which produces either judder from duplication or smearing artefacts from interpolation. Both most visible on exactly the fast motion you wanted to slow. Frame-rate decisions have to be made at capture. Nothing in post recovers frames that were never recorded.

Q: How do I do replays without a dedicated replay system?
A: Record every camera feed separately alongside the switched programme output, and keep a live marker log of significant moments with timecode. During a stoppage an operator can pull the marked moment from whichever angle was best, which covers most of the value at a small fraction of the cost.