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• Keep the camera still. Use a tripod and let the athlete run through the shot. StrideLab finds ground contacts by looking for a planted foot standing still in the picture, so a phone that pans to follow the runner breaks it. The app warns you when it sees the camera moving.
• Pick the angle for what you're filming. Film starts and runs on the straight side-on. Film the bend from behind or in front, where the lean into the bend shows.
• Whole body in frame, reasonably large, in good, even light.
• Use 120 fps. The in-app recorder records at 120 fps by default (60 is offered too). Slower video is still measured, but contact times are less precise, and the report marks those numbers.
• On the 0.5x lens, keep the key strides toward the middle of the frame: straight lines bend slightly near the edges.

Yes. Record once, do several block starts, then stop. StrideLab looks through the recording for starts (a set position with hands on the track, then the push away) and lists them for you to check. Adjust where each begins and ends, uncheck or remove any that are wrong, use Add a start for one it missed, or Search for more starts. Each confirmed start becomes its own clip, and the full recording stays in your library.

Standing starts aren't found automatically in long recordings; place them with Add a start. If a recording has no start in it (strides or the bend), StrideLab offers to analyse the whole clip or to mark the run.

From the movement of the body. Hands down and still followed by a drive away is a start. Feet trading places in a steady rhythm from the first frame, with no set position, is running. A bend shows as the body leaning to one side stride after stride, which is visible from behind or in front, and as the hips following a curved path.

StrideLab shows what it found and how sure it is as a small label under the phase badge in the player. Tap it, or open the ••• menu and choose What's in this clip, to see why and to change it. When it isn't sure, it asks you before showing any coaching.

From the side, a bend and a straight run look almost the same, so StrideLab can't tell them apart there: it asks "stride, or curve?" instead of deciding. A 200 m start (blocks on the bend) looks the same as a 100 m start from the side; mark it yourself in What's in this clip.

In the player, tap the kind label or use What's in this clip and choose Start, Stride or Curve. In the library, a clip's menu has Analyze as…. Your choice is saved with the clip and always wins over the automatic answer. Choose Let StrideLab tell to go back to automatic.

That's coach mode: playback runs to the next moment worth talking about and waits on that frame, with the tip beside the runner. Tap Continue to go on. To play straight through instead, turn off Stop at each tip in the player's corner menu.

• Press and hold the video on a frame to mark what it is: a foot landing and leaving, the set position or the launch.
• If the skeleton is on someone else, press and hold, choose "This isn't me" and tap the athlete.
• Tap the pencil to edit the skeleton and drag a joint into place.

The measurements and tips are rebuilt from your corrections. Undo walks back the last edit, and clearing your corrections returns to the automatic result.

That number is less precise than usual, for example because the frame rate is low or the tracker was less sure of a joint on that frame. Tap it to see why and by roughly how much. The rating shown is still the one the measured value earns.

A phone video with no calibration can't measure distances like "21 cm ahead" reliably. So foot placement is shown as zones (behind, under or ahead of the hips), and the app measures what video can support: angles and times.

In Profile (the person icon in the library), turn on Beginner coaching to see how to fix each tip, with the target drawn on the body. Reference level sets the level you're compared against; a lower level widens the bands so "on target" is reachable.

Tap Import and pick the video. When StrideLab asks to read your photo library, allow it: for a Slo-mo, StrideLab then copies the original high-frame-rate file, so every frame the camera filmed is measured.

If you decline, the video still imports, but Photos hands over a slowed-down 30 fps copy with nothing in the file saying it's slowed. Timing on that copy is far less precise, and starts may not be found. You can change the permission in Settings > Apps > StrideLab > Photos.

If the video is stored in iCloud (Optimize iPhone Storage), Photos downloads it first, and StrideLab shows the progress. You need a connection for that step.

StrideLab measures every frame on your device, so the time grows with the number of frames: a 240 fps clip has twice as many as a 120 fps one. Recording at 120 fps keeps contact timing precise and the analysis quicker. Opening a clip again later is instant, because the analysis is saved.

Free: the two demo starts (with the full player, coaching and report), browsing your library, deleting clips, and sharing the original video of a clip.

StrideLab Pro: recording and importing, analysing your own clips (start, stride and curve), and saving a video with the skeleton drawn in. It's $9.99 a month or $99.99 a year in the U.S. (the app shows your local price), and eligible new subscribers get a 7-day free trial.

Sign in with the same Apple Account, open StrideLab, tap the person icon in the library, then Subscription > Restore purchases. The paywall also has a Restore Purchases button.

Go to Settings > Apple Account > Subscriptions on your iPhone or iPad, choose StrideLab Pro and cancel, at least 24 hours before the end of the current period to avoid the next charge. You keep access until the period ends. You can also get there from StrideLab: Profile > Subscription > Manage subscription. Refunds are handled by Apple at reportaproblem.apple.com.

Nothing is deleted. Your clips stay in your library, and you can still share their original videos or delete them. Opening their analysis needs StrideLab Pro again.

The prices come from the App Store, so StrideLab needs a connection to show them. Check your connection and tap Try again. An active subscription keeps working offline until its end date.

Everything stays on your device: your videos, their analyses, your corrections and settings. Nothing is uploaded, and there are no accounts, ads or analytics. Videos and analyses are kept out of iCloud Backup because of their size. See the privacy policy for details.

Delete clips you no longer need from the library (a clip's menu has Delete). That removes the video and its analysis from StrideLab. Recordings saved to your camera roll are separate copies; delete those in Photos. Deleting the app removes everything StrideLab stored.