Fix battery drain from Web Audio (#29203)

* Fix battery drain from Web Audio

* move suspend away from constructor

* await on resume()

* Delint

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

---------

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>
Co-authored-by: Michael Telatynski <7t3chguy@gmail.com>

src/audio/BackgroundAudio.ts

@@ -48,6 +48,12 @@ export class BackgroundAudio {
         source.buffer = this.sounds[url];
         source.loop = loop;
         source.connect(this.audioContext.destination);
+
+        await this.audioContext.resume();
+        source.onended = () => {
+            this.audioContext.suspend();
+        };
+
         source.start();
         return source;
     }

src/audio/compat.ts

@@ -15,16 +15,21 @@ import { logger } from "matrix-js-sdk/src/logger";
 import { SAMPLE_RATE } from "./VoiceRecording";
 
 export function createAudioContext(opts?: AudioContextOptions): AudioContext {
+    let ctx: AudioContext;
     if (window.AudioContext) {
-        return new AudioContext(opts);
+        ctx = new AudioContext(opts);
     } else if (window.webkitAudioContext) {
         // While the linter is correct that "a constructor name should not start with
         // a lowercase letter", it's also wrong to think that we have control over this.
         // eslint-disable-next-line new-cap
-        return new window.webkitAudioContext(opts);
+        ctx = new window.webkitAudioContext(opts);
     } else {
         throw new Error("Unsupported browser");
     }
+    // Initialize in suspended state, as Firefox starts using
+    // CPU/battery right away, even if we don't play any sound yet.
+    void ctx.suspend();
+    return ctx;
 }
 
 export function decodeOgg(audioBuffer: ArrayBuffer): Promise<ArrayBuffer> {