scan-subread/src/play-clock.ts

src/play-clock.ts (722 bytes)
1 // What a media player said about its position, and when it said it. Pure.
2 //
3 // A player does not report each millisecond. It reports a position, the
4 // time of the report, and the speed. The position now is computed from
5 // these three. This is a port of PlayClock.kt from SubRead Overlay.
6 
7 export interface PlayClock {
8   positionMs: number;
9   /** The time of the report, on the same clock as the `nowMs` parameters. */
10   reportedAtMs: number;
11   speed: number;
12   playing: boolean;
13 }
14 
15 /** The position in the media at `nowMs`. */
16 export function positionAt(clock: PlayClock, nowMs: number): number {
17   if (!clock.playing) return clock.positionMs;
18   return clock.positionMs + (nowMs - clock.reportedAtMs) * clock.speed;
19 }