Add simple play/pause controls

src/voice/Playback.ts

@@ -0,0 +1,97 @@
+/*
+Copyright 2021 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import EventEmitter from "events";
+import {UPDATE_EVENT} from "../stores/AsyncStore";
+
+export enum PlaybackState {
+    Decoding = "decoding",
+    Stopped = "stopped", // no progress on timeline
+    Paused = "paused", // some progress on timeline
+    Playing = "playing", // active progress through timeline
+}
+
+export class Playback extends EventEmitter {
+    private context: AudioContext;
+    private source: AudioBufferSourceNode;
+    private state = PlaybackState.Decoding;
+    private audioBuf: AudioBuffer;
+
+    constructor(private buf: ArrayBuffer) {
+        super();
+        this.context = new AudioContext();
+    }
+
+    public emit(event: PlaybackState, ...args: any[]): boolean {
+        this.state = event;
+        super.emit(event, ...args);
+        super.emit(UPDATE_EVENT, event, ...args);
+        return true; // we don't ever care if the event had listeners, so just return "yes"
+    }
+
+    public async prepare() {
+        this.audioBuf = await this.context.decodeAudioData(this.buf);
+        this.emit(PlaybackState.Stopped); // signal that we're not decoding anymore
+    }
+
+    public get currentState(): PlaybackState {
+        return this.state;
+    }
+
+    public get isPlaying(): boolean {
+        return this.currentState === PlaybackState.Playing;
+    }
+
+    private onPlaybackEnd = async () => {
+        await this.context.suspend();
+        this.emit(PlaybackState.Stopped);
+    };
+
+    public async play() {
+        // We can't restart a buffer source, so we need to create a new one if we hit the end
+        if (this.state === PlaybackState.Stopped) {
+            if (this.source) {
+                this.source.disconnect();
+                this.source.removeEventListener("ended", this.onPlaybackEnd);
+            }
+
+            this.source = this.context.createBufferSource();
+            this.source.connect(this.context.destination);
+            this.source.buffer = this.audioBuf;
+            this.source.start(); // start immediately
+            this.source.addEventListener("ended", this.onPlaybackEnd);
+        }
+
+        // We use the context suspend/resume functions because it allows us to pause a source
+        // node, but that still doesn't help us when the source node runs out (see above).
+        await this.context.resume();
+        this.emit(PlaybackState.Playing);
+    }
+
+    public async pause() {
+        await this.context.suspend();
+        this.emit(PlaybackState.Paused);
+    }
+
+    public async stop() {
+        await this.onPlaybackEnd();
+    }
+
+    public async toggle() {
+        if (this.isPlaying) await this.pause();
+        else await this.play();
+    }
+}