Sports Video Analysis Glossary: 35 Terms

Capture

Rolling buffer: A recording loop that keeps only the last few seconds of video in memory and discards everything older. Nothing is written to storage until you tap save, so a two-hour session costs you the storage of the clips you actually kept. This is the mechanism behind every instant replay app.
Pre-record (retroactive capture): Saving the seconds that happened before you pressed the button. The camera was already buffering, so the tap reaches backwards in time. It is why you can film a whole training block without watching the phone.
Trigger: The action that commits the buffer to a file: a screen tap, a volume button, a widget, or a timer. On a sideline the trigger has to work without looking at the screen, which is why physical buttons matter more than they sound.
Frame rate (fps): Frames captured per second. 30 fps is fine for tactics, 60 fps for most technique work, 120 or 240 fps for a bat, club or racket at contact. Work out what your sport needs with the frame rate calculator.
Shutter speed: How long each frame is exposed. Slow shutter blurs a fast limb into a smear, which ruins frame-by-frame review even at high fps. The rule of thumb outdoors: shutter at least double your frame rate.
Rolling shutter: Most phone sensors read the image line by line rather than all at once, so a fast bat or club can appear bent in a still frame. It is a sensor artifact, not a technique fault, and it shows up most at high zoom and low light.
Resolution: 1080p or 4K, the pixel count per frame. 4K buys you the ability to crop in later; it also multiplies file size and heat. For buffer maths at your setting see the storage and buffer time calculator.
Bitrate: Data spent per second of video, in Mbps. Two clips at the same resolution can differ three times over in file size and detail because of bitrate. Low bitrate shows first as mush around fast-moving edges.
Low light capture: Indoor courts and evening pitches force the camera to choose between a slow shutter, a high ISO, or a dark image. All three hurt slow-motion review, so gyms and evening sessions usually need a lower frame rate than daylight.

Timing and delay

Instant replay: Playback of the action within seconds of it happening, while the athlete still remembers the attempt. The sideline workflow is set out in capturing instant replay on the sideline.
Delayed mirror: A screen that shows what the camera saw a fixed number of seconds ago, running continuously with no taps at all. The athlete performs, turns around, and watches themselves. Common in gymnastics, dance and throwing. See delayed mirror mode.
Capture delay: The gap you set between the live action and what the mirror screen shows, typically 5 to 30 seconds. Long enough to walk back to the screen, short enough that the attempt is still fresh. Per-sport values in optimal replay delay by sport.
Latency: Time from the real event to it appearing on screen, including encoding and display. Distinct from capture delay: latency is unwanted lag, capture delay is a setting you chose.
Clip length: How many seconds a saved replay holds, counted backwards from the trigger. Ten seconds covers a serve or a lift; thirty covers a rally or a play. Longer clips cost storage and review time.
Feedback window: The period after an attempt in which feedback still changes the next attempt. Motor learning research puts the useful window in seconds to a couple of minutes, which is the whole argument for sideline replay over evening film study.

Playback and review

Slow motion: Playback below real speed. True slow motion comes from capturing extra frames; slowing 30 fps footage just repeats frames and looks stuttery. See slow motion analysis apps.
Frame-by-frame scrubbing: Stepping through a clip one frame at a time to find the exact moment of contact, foot strike or release. The core review action for technique work, explained in frame-by-frame video analysis.
Telestration: Drawing on a paused frame: lines, angles, circles. Named after the broadcast tool, now standard in coaching apps. See drawing on video frames.
Side-by-side comparison: Two clips played together, usually a current attempt against an earlier one or a model. Useful only when both clips share camera position and frame rate.
Overlay (ghosting): Two clips stacked semi-transparently so body positions line up. Sensitive to framing: a half-metre difference in camera position makes the overlay lie.
Camera angle: Where the camera sits relative to the movement. Down-the-line and face-on answer different questions, and swapping angles mid-session breaks comparison. Placement maths in the camera placement calculator.
Key position: The single frame a coach checks first: contact, release, foot plant, catch. Naming key positions before filming turns review from browsing into checking.

Device and storage

Local-only storage: Video that never leaves the device: no upload, no account, no cloud copy. It removes the consent and data-retention problem that comes with uploading footage of minors. Background in ethics of recording in sports facilities.
Offline capture: Recording and reviewing with no network at all. Most pitches, pools and rural courts have no usable signal, which is the case made in video review without wifi.
Thermal throttling: The phone reducing frame rate or resolution because it is too hot. Shows up in long 4K buffer sessions in sun, and it is the usual reason a session degrades an hour in.
Battery drain: Continuous capture is one of the heaviest loads a phone takes. Screen off and lower resolution both buy substantial run time; estimate yours with the battery life estimator.
Storage headroom: Free space left for saved clips. A rolling buffer needs far less than continuous recording, but 4K clips still add up across a season.
Codec (H.264 / HEVC): The compression format for the video file. HEVC halves file size at equal quality but is slower to encode and less portable when sharing to older devices. Sharing trade-offs in sharing slow motion clips.

Coaching practice

Augmented feedback: Information about a movement that the athlete could not get from their own senses, video being the clearest example. Contrast with intrinsic feedback, what they felt themselves.
Knowledge of performance: Feedback about how the movement was executed, for example elbow position at release. Distinct from knowledge of results, which is only whether the ball went in.
Knowledge of results: Feedback about the outcome alone. Athletes usually already have it; the coaching value of video is that it supplies knowledge of performance instead.
Motor learning: The lasting change in movement capability that comes from practice, as opposed to the temporary change during a session. Evidence on video and motor learning is collected in visual feedback and motor learning.
Self-modeling: Showing athletes their own best attempts rather than an expert model. Works well with a rolling buffer because the good attempt was already captured.
Feedback frequency: How often you give feedback per set of attempts. Constant feedback speeds up the session and slows down retention; fading it as the skill lands is the standard recommendation.
Filming consent: Permission to record, especially with minors on a club pitch. Local-only capture narrows the question but does not remove it; clubs need a written policy, covered in clubs and academies.

Where to go next

Definitions follow the motor learning literature on augmented feedback (Schmidt & Lee, Motor Control and Learning), Android CameraX capture documentation, and the sport-specific numbers used across our ReplayR guides. Last verified 12 August 2026.

Sports video analysis glossary: 35 terms in plain English