How to record a great clip

Pose-based form analysis is only as good as the clip we get. A few minutes spent setting up the phone the right way is the single biggest thing you can do to improve the result.

General tips (every sport)

Keep the phone fixed — tripod, fence, water bottle on a chair, anything that doesn't move. Hand-held clips drift and break our subject tracking.
Bright, even lighting. Avoid heavy backlighting (sun directly behind the subject) — it makes the body silhouette flat and pose detection drops.
Only one person doing the activity in frame. Other people in the background are usually fine, but a second runner / lifter near the subject confuses the tracker.
5–10 seconds is the sweet spot. We cap at 10 s — anything longer just adds processing time without a real benefit.
Either landscape or portrait works, but the subject's full body must fit head-to-toe in the frame the whole time.

Running

Place the phone STILL (don't follow the runner) and run THROUGH the camera's field of view from one side to the other. Several full strides should fit in the clip.

Set the phone on a tripod / fence / chair, side-on to your run path. Roughly waist-to-chest height of the runner.
Aim the camera at the running path — start recording with the phone untouched.
Start running well before the camera (5–10 m). When you ENTER the frame you should already be at race pace.
Run all the way THROUGH the frame and a few metres past the far edge. We need ~5 strides clearly in shot.
Stop the recording AFTER the runner is fully out of frame.

Phone fixed, runner enters and fully exits the frame at running pace.

Don't

Holding the phone, panning to follow the runner, or stopping in the middle of the frame.