Filming guide

How to film a delivery

Two minutes of set-up gives the most accurate numbers. Here is where to stand, how to set up slo-mo, and what each choice lets StumpSage measure.

Where to put the phone

Walk the phone round the bowler

Drag it, tap a spot, or use the buttons. The readout says which view that is, and what one phone there can measure and what it can’t.

The essentials

Four things decide most of what a clip can give. Two more help.

Side-on, square to the pitch
Stand level with the bowling crease, on the side of the bowling arm, so the run-up crosses the frame.
One phone measures best in the plane it faces. Side-on, that plane is the delivery stride itself, so the knee, trunk and stride angles are read true; from anywhere else, a 2D angle is distorted.
Tripod at hip height
A steady phone at about 1 m keeps angles true. Lean it on a kit bag if you have no tripod.
A moving camera blurs the picture and shifts the background the angles are read against. If it moves too much, the capture check says: “The camera moved too much. Use a tripod, or rest the phone on a kit bag.”
Slo-mo at 240 fps
Switch the camera to Slo-mo. At 240 fps the arm and the landing foot stay sharp; 120 fps works too.
Slo-mo is what turns key moments into measurements: timings and the knee’s change after landing need 60 or 120 frames a second. The next section has the detail.
Run-up to follow-through in frame
Start recording before the run-up and stop after the follow-through. Keep the whole body in view.
The analysis looks for the run-up, the jump, both foot contacts and release. If part of it is missing: “Part of the body left the frame. Keep the whole action in view.”

12–15 m from the crease: Far enough to fit the last strides, the jump and the follow-through without zooming.
Good light, plain background: Film with the sun behind you if you can, and avoid other players walking through the shot.

Frame rates, and what they change

Every measurement has a slowest frame rate it can be read from, and a rate for full confidence. Filmed side-on, it adds up like this.

Frame rate	Adds	Full confidence from here
Normal speed, 30 fps	The key moments, and Delivery stride length Front knee at landing Trunk bend at release Release height Front arm at back-foot contact Back hip at back-foot landing	—
60 fps	Run-up speed Pre-delivery stride Jump height Back-knee bend after landing Front knee after landing Run-up rhythm Front arm at front-foot contact	Front arm at front-foot contact
Slo-mo, 120 fps	Back foot to front foot Front foot to release Braking at landing Arm speed (approx.)	Run-up speed Pre-delivery stride Jump height Back-knee bend after landing Delivery stride length Front knee at landing Front knee after landing Trunk bend at release Release height Run-up rhythm Front arm at back-foot contact Back hip at back-foot landing
Slo-mo, 240 fps	Sharper pictures of the fastest moments	Back foot to front foot Front foot to release Braking at landing Arm speed (approx.)

Below 60 fps, an angle read at one moment is approximate: the nearest frame can be up to 17 ms from the moment. It shows as ≈ and a whole number, its confidence is capped and it never turns red. The card says: “Filmed at normal speed, so this number is approximate. Switch your camera to slo-mo (120 or 240 fps) for an accurate reading.”

A clip that was already slowed down when it was exported is a different case. When StumpSage can estimate the slow-down: “Exported already slowed down. StumpSage estimated how much, so the frame rate and times are approximate. Use the original file from the phone that filmed it for exact numbers.” When it can’t: “Exported already slowed down, by an amount we couldn’t work out, so no times or speeds are shown. Use the original file from the phone that filmed it instead.”

Setting up slo-mo

Angles and timings need 120 to 240 frames a second. Film with your phone’s own camera app in slo-mo, then upload the clip here.

iPhone

Set Slo-mo to 240 fpsSettings › Camera › Record Slo-mo › 1080p at 240 fps.
Film in SLO-MOOpen Camera and swipe to SLO-MO. Side-on, phone on a tripod at hip height, run-up to follow-through.
Upload the originalChoose the clip from Photos on the Analyse a delivery page. Moving it to a Mac first? AirDrop keeps the original 240 fps file, but exporting it from Photos bakes the slow motion into a 30 fps file.

Android

Open your camera in Slow motionIn the camera app, choose Slow motion (often under More). Pick 240 fps if your phone offers it; 120 works too.
Film side-onPhone on a tripod at hip height, 12–15 m from the crease, run-up to follow-through in frame.
Upload the originalChoose the clip from your videos on the Analyse a delivery page.

Clips sent through WhatsApp or Instagram lose their slow motion. Upload the original file from the phone that filmed it.

Light, background, one bowler

Film with the sun behind you if you can, and avoid other players walking through the shot.

Light: Too dark: “Too dark. Film in brighter, even light.” Too bright: “Too bright in places. Keep the sun behind the camera, not behind the bowler.”
One bowler: “No bowler found. Keep one bowler in frame from run-up to follow-through.”
Size in frame: “The bowler is a little small. Move closer or zoom in slightly.”

What each view measures

The view each measurement needs, the frame rate, and whether it needs your height. A phone measures only what its view can see.

Side-on

17 from one phone

Tripod level with the crease and square to the pitch, whole body in frame from run-up to follow-through.

Run-up speed60 fps or more · Full confidence from 120 fps · Needs your height
Pre-delivery stride60 fps or more · Full confidence from 120 fps · Needs your height
Jump height60 fps or more · Full confidence from 120 fps · Needs your height
Back foot to front foot120 fps or more · Full confidence from 240 fps
Back-knee bend after landing60 fps or more · Full confidence from 120 fps
Delivery stride lengthNormal speed works · Full confidence from 120 fps · Needs your height
Front foot to release120 fps or more · Full confidence from 240 fps
Front knee at landingNormal speed works: approx. below 60 fps · Full confidence from 120 fps
Front knee after landing60 fps or more · Full confidence from 120 fps
Trunk bend at releaseNormal speed works: approx. below 60 fps · Full confidence from 120 fps
Braking at landing120 fps or more · Full confidence from 240 fps · Needs your height · Always approx. from one phone
Release heightNormal speed works: approx. below 60 fps · Full confidence from 120 fps · Needs your height
Arm speed (approx.)120 fps or more · Full confidence from 240 fps · Always approx. from one phone
Run-up rhythm60 fps or more · Full confidence from 120 fps
Front arm at back-foot contactNormal speed works: approx. below 60 fps · Full confidence from 120 fps · Always approx. from one phone
Front arm at front-foot contact60 fps or more · Always approx. from one phone
Back hip at back-foot landingBody LoadNormal speed works: approx. below 60 fps · Full confidence from 120 fps

Not yet: Ball speed (needs ball tracking), Take-off contact time (needs heel and toe tracking).

From behind

3 from one phone

Phone behind the run-up, in line with the stumps.

Head stability60 fps or more · Full confidence from 120 fps · Needs your height
Action type60 fps or more · Full confidence from 120 fps · Always approx. from one phone
Hip drop at landingNormal speed works: approx. below 60 fps · Full confidence from 60 fps

Not yet: Front-foot direction (needs heel and toe tracking), Back-foot direction (needs heel and toe tracking).

Front-on

1 from one phone

Phone behind the batter’s stumps, safely outside the net.

Head stability60 fps or more · Full confidence from 120 fps · Needs your height

The demo analysis is a nets clip filmed from behind. It shows the key moments, but no measurements: knee, trunk and stride numbers need a side-on clip. Open the demo analysis (filmed from behind)

Lab mode: two phones

Coming, not in the beta yet.

One phone can’t measure rotation: the shoulders and hips turn across its line of sight. Lab mode films side-on and from behind at once, syncs the two clips with a clap or a flash, and calibrates them from the pitch markings, so these can be measured in 3D:

Side bend at release
Shoulder counter-rotation
Hip–shoulder separation
Hip turn at release

Even then they stay approximate, and as Body Load indicators they are a watch point at most, never a verdict: the research on them is mixed or early.

Common mistakes

What the capture checks catch most often, and what they tell you to do.

Filmed from too far: The bowler is too small. Move closer so they fill about half the frame height.
Part of the action out of frame: Part of the body left the frame. Keep the whole action in view.
Holding the phone: The camera moved too much. Use a tripod, or rest the phone on a kit bag.
Too dark: Too dark. Film in brighter, even light.
The sun behind the bowler: Too bright in places. Keep the sun behind the camera, not behind the bowler.
Nobody, or more than one bowler: No bowler found. Keep one bowler in frame from run-up to follow-through.
A clip of a whole session: A long clip. Trim it to one delivery, run-up to follow-through.
Started too late, stopped too early: Too short for the whole action. Record from the start of the run-up to the end of the follow-through.
A forwarded or exported clip: Exported already slowed down, by an amount we couldn’t work out, so no times or speeds are shown. Use the original file from the phone that filmed it instead.
HDR video: Filmed in HDR10, which looks washed out here. Turn off HDR video in the camera settings.
A converted file: Converted from another frame rate, so some frames repeat. Use the camera app’s own file.