Click: the jump, the hug, the laugh you caught at exactly the right second. Your video plays through a camera view until the shutter fires, and the moment drops out as a print.
Exports a silent video, so you can add your song when you post. Everything stays on your device.
At least six seconds, with the best bit about two seconds in. Trim it so the shutter lands right.
A still works too: it becomes the print.