WIP on audio route experiment

src/state/IOSNativeControlledAudioOutput.ts

@@ -0,0 +1,57 @@
+/*
+Copyright 2026 Element Corp.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { logger as rootLogger } from "matrix-js-sdk/lib/logger";
+import { map, startWith } from "rxjs";
+
+import { currentRoute$, type Controls } from "../controls.ts";
+import { type Behavior, constant } from "./Behavior.ts";
+import type { ObservableScope } from "./ObservableScope.ts";
+import {
+  type AudioOutputDeviceLabel,
+  type MediaDevice,
+  type SelectedAudioOutputDevice,
+} from "./MediaDevices.ts";
+
+/**
+ * A special implementation of audio output that allows the hosting application
+ * to have more control over the device selection process. This is used when the
+ * `controlledAudioDevices` URL parameter is set, which is currently only true on mobile.
+ */
+export class IOSNativeControlledAudioOutput implements MediaDevice<
+  AudioOutputDeviceLabel,
+  SelectedAudioOutputDevice
+> {
+  private logger = rootLogger.getChild(
+    "[MediaDevices IOSNativeControlledAudioOutput]",
+  );
+
+  public readonly available$: Behavior<Map<string, AudioOutputDeviceLabel>> =
+    constant(new Map());
+
+  public select(id: string): void {
+    this.controls.showNativeAudioDevicePicker?.();
+  }
+
+  public readonly selected$ = this.scope.behavior(
+    currentRoute$.pipe(
+      startWith(null),
+      map((route) => {
+        if (!route) return undefined;
+        this.logger.debug(`Selected ${route?.type}`);
+        return {
+          id: route.type,
+        } as SelectedAudioOutputDevice;
+      }),
+    ),
+  );
+
+  public constructor(
+    private readonly controls: Controls,
+    private readonly scope: ObservableScope,
+  ) {}
+}