How to film a piano practice video with both iPhone cameras

A keyboard fights the vertical canvas in the opposite way a guitar neck does

DualCam’s canvas is 1080 pixels wide, either 1080×1920 for standard 9:16 or 1080×2340 to fill a modern iPhone screen — a tall rectangle either way. A camera pointed straight at a keyboard produces an image that is wide and short, close to the opposite shape of the canvas it has to fit into. Back the phone up far enough to get the full keyboard in frame and the hands shrink to a fraction of the image; move in close enough to read finger placement and the ends of the keyboard run off the edges.

This is the reverse of the problem a fretboard has. A guitar neck is long and narrow, so a close shot on the fretting hand already sits fairly naturally inside a tall frame. A keyboard has no long axis to align with a tall canvas — it is wide along the one dimension the canvas is short on, which is why the layout choice that works well for guitar is not automatically the right one here.

Split top-and-bottom usually reads better than picture-in-picture for keys

A picture-in-picture layout still asks the full-frame camera to fit a wide keyboard shot into the same tall rectangle described above — putting the keys in the big frame does not solve the width problem, it just makes it the whole picture instead of a corner of it. Left-and-right split makes things worse on purpose: DualCam crops roughly a quarter of the frame off each side to fit a camera image into half the canvas’s width, and the ends of the keyboard are exactly what a crop from the sides removes first.

Top-and-bottom split is built for this shape of problem. Each half keeps the full width of the canvas and gives up height instead, which is the trade a keyboard shot actually wants — put the back camera on the keys in one half at full width, and the front camera on your face or upper body in the other half. Nothing about this is locked in before you start recording either: layout, including which split orientation is active, is free to change while DualCam is still rolling, so a first guess that crops the wrong thing is not a lost take.

Hands, pedal and posture rarely all fit in the same shot

Even with the full width of a top-and-bottom half, a shot wide enough to show the sustain pedal at your foot is a shot too wide to read individual finger placement, and a shot close enough for finger placement leaves the pedal and your posture out of frame entirely. This is the same throwaway-resolution problem a close guitar-hand shot runs into, just at the other end of the instrument: decide before you set the phone up whether this particular take is checking technique at the keys or checking the whole picture, because one camera position rarely serves both well.

Pinch-to-zoom works live on the back camera while DualCam is recording, the same as in any camera app, so nudging the framing in or out on the keys mid-take costs nothing. Switching to a different physical back lens — to a wider field of view that fits more of the keyboard in from the same distance, on iPhones where the lens picker offers one — is a heavier decision locked the moment you press record, the same as resolution, so settle on a lens before you start and check the framing in the preview first, since what the viewfinder shows is exactly what gets written to the file.

Swap which camera is the main frame between a spoken intro and playing

If the layout is picture-in-picture rather than a split for part of the take, which camera fills the frame and which sits in the small inset can be swapped while DualCam is still recording. A practical use of that: start with the front camera as the main frame for a spoken note about what you are practising, then swap to the back camera as the main frame once you start playing, so the keys get the full canvas instead of a cropped corner window.

One microphone catches the pedal along with the notes

A dual-camera recording writes a single audio track, not one per camera, and that track is whatever the phone’s one microphone actually picks up in the room — the notes, any mechanical thump from pressing the sustain pedal, and your voice if you are talking through the take, all mixed together at whatever balance the room gives you. There is no separating them afterward, so if pedal noise is a distraction, moving the phone slightly further from your feet helps more than any setting inside the app will.

There is also no pause button — recording runs straight through from the moment you press record to the moment you stop, so a passage cannot be frozen mid-run-through and picked up again later in the same file. That is not much of a limitation in practice: play through, stop, play through again. DualCam keeps every take in its own library with a thumbnail, so nothing is lost between attempts, and you can compare them afterward instead of judging a run-through in the moment it happens.