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Recording
Where to put the phone, which frame rate to use and what to avoid, so the scan, the angles and the ball come out right.
How you film matters more than anything else for the analysis. You don’t need special gear: a phone on a tripod or clipped to the fence is enough. These are the rules that matter most.
The essentials#
- Your whole body in the picture, from your feet to the racket up high, through the whole stroke.
- A still camera. Tripod, mount or the fence. If the camera moves, the court calibration stops fitting.
- With sound. The scan finds strokes by the sound of the ball on the strings. A video without audio can’t be scanned.
- Good light. Daytime or a well-lit court. In poor light the ball gets lost and the body is tracked less well.
- The same way every time. To compare sessions, film from the same place at a similar distance. The numbers change with the camera angle.
Pick the angle#
Racketlens recognises where you filmed from (side, behind or front) and compares you with pros filmed from that same side. Each angle is best for something:
| Angle | Where the phone goes | Best for | Keep in mind |
|---|---|---|---|
| Side | On the side fence, level with where you hit | The body: your arm at contact, whether you hit in front, your finish | Only the start of the ball’s flight is visible: the net and the bounce are a projection |
| Behind | Behind your baseline, with the net and the far court in view | The ball: net margin, depth, in or out; the body works too | The best angle for measuring the ball |
| Front | Across the net, facing you | Seeing your preparation and footwork head-on | The ball flies at the camera: its speed and bounce are rough (often ±20 %) |
Distance and framing#
- Stand close enough to look big, without leaving the picture when you move. Body tracking works best when you fill a good part of the video’s height.
- If you came out small, no problem: in the app you can zoom in on yourself (mouse wheel over the video) and tracking follows the zoomed area.
- To measure the ball from behind, keep the net and the far court in view, with the lines visible. See Calibrate the court.
Frame rate#
More frames per second give smoother slow motion and better speed readings. If your phone allows it, film at 60, 120 or 240 fps.
File format#
MP4 and MOV straight from the phone work best (WebM too). If the browser says it can’t play the format, try Chrome or Safari, or convert the video to MP4 H.264.
In a group lesson#
When more than one person hits in the video, the scan asks Who are you in this video? and tells people apart by shirt colour. If you’re filming a group lesson, have everyone wear a different colour: two people dressed alike can get mixed up. See Scan session.