A video’s chapters are its steps. Each one is a numbered segment of the seek bar, and when a step ends the video holds its last frame, the finished result, until you say go.
Go can be a tap anywhere on the picture, the space bar, the word “next” on a computer, or two knocks on the counter on a phone. Knocks are measured on the device, and the microphone is open only while the player waits.
Counter mode fills a phone’s screen, makes the step readable from across the kitchen, and keeps the screen awake. Flip Wait off, and it is an ordinary player; a video without chapters never sees any of this.