android: Select default output device based on callIntent

Add comments on existing code
Extracted a specific android controller for isolation and better testing

lint fixes

Fix device update logic and more tests

better typescript

src/controls.ts

@@ -33,12 +33,36 @@ export interface Controls {
   showNativeOutputDevicePicker?: () => void;
 }
 
+/**
+ * Output Audio device when using the controlled audio output mode (mobile).
+ */
 export interface OutputDevice {
   id: string;
   name: string;
+  /**
+   * Reverse engineered:
+   *  - on iOS always true if output is routed to speaker. In other case iOS on declare a `dummy` id device.
+   *    In that case then ElementCalls manually append a earpiece device with id `EARPIECE_CONFIG_ID` anb `{ type: "earpiece" }`
+   *  - on Android this is unused.
+   */
   forEarpiece?: boolean;
+  /**
+   * Reverse engineered:
+   * - on iOS always undefined
+   * - on Android true for the `TYPE_BUILTIN_EARPIECE`
+   */
   isEarpiece?: boolean;
+  /**
+   * Reverse engineered:
+   * - on iOS always true if output is routed to speaker. In other case iOS on declare a `dummy` id device.
+   * - on Android true for the `TYPE_BUILTIN_SPEAKER`
+   */
   isSpeaker?: boolean;
+  /**
+   * Reverse engineered:
+   * - on iOS always undefined.
+   * - on Android true for the `TYPE_BLUETOOTH_SCO`
+   */
   isExternalHeadset?: boolean;
 }
 
@@ -47,8 +71,16 @@ export interface OutputDevice {
  */
 export const setPipEnabled$ = new Subject<boolean>();
 
+/**
+ * Stores the list of available controlled audio output devices.
+ * This is set when the native code calls `setAvailableAudioDevices` with the list of available audio output devices.
+ */
 export const availableOutputDevices$ = new Subject<OutputDevice[]>();
 
+/**
+ * Stores the current audio output device id.
+ * This is set when the native code calls `setAudioDevice`
+ */
 export const outputDevice$ = new Subject<string>();
 
 /**
@@ -80,16 +112,41 @@ window.controls = {
     setPipEnabled$.next(false);
   },
 
+  /**
+   * Reverse engineered:
+   *
+   * - on iOS:
+   *  This always a list of one thing. If current route output is speaker it returns
+   *  the single `{"id":"Speaker","name":"Speaker","forEarpiece":true,"isSpeaker":true}` Notice that EC will
+   *  also manually add a virtual earpiece device with id `EARPIECE_CONFIG_ID` and `{ type: "earpiece" }`.
+   *  If the route output is not speaker then it will be `{id: 'dummy', name: 'dummy'}`
+   *
+   *
+   *  - on Android:
+   *  This is a list of all available output audio devices. The `id` is the Android AudioDeviceInfo.getId()
+   *  and the `name` is based the Android AudioDeviceInfo.productName (mapped to static strings for known types)
+   *  The `isEarpiece`, `isSpeaker` and `isExternalHeadset` are set based on the Android AudioDeviceInfo.type
+   *  matching the corresponding types for earpiece, speaker and bluetooth headset.
+   */
   setAvailableAudioDevices(devices: OutputDevice[]): void {
-    logger.info("setAvailableAudioDevices called from native:", devices);
+    logger.info(
+      "[MediaDevices controls] setAvailableAudioDevices called from native:",
+      devices,
+    );
     availableOutputDevices$.next(devices);
   },
   setAudioDevice(id: string): void {
-    logger.info("setAudioDevice called from native", id);
+    logger.info(
+      "[MediaDevices controls] setAudioDevice called from native",
+      id,
+    );
     outputDevice$.next(id);
   },
   setAudioEnabled(enabled: boolean): void {
-    logger.info("setAudioEnabled called from native:", enabled);
+    logger.info(
+      "[MediaDevices controls] setAudioEnabled called from native:",
+      enabled,
+    );
     if (!setAudioEnabled$.observed)
       throw new Error(
         "Output controls are disabled. No setAudioEnabled$ observer",

src/main.tsx

@@ -67,6 +67,6 @@ Initializer.initBeforeReact()
     );
   })
   .catch((e) => {
-    logger.error("Failed to initialize app", e);
+    logger.error(`Failed to initialize app ${e.message}`, e);
     root.render(e.message);
   });

src/state/AndroidControlledAudioOutput.test.ts

@@ -0,0 +1,563 @@
+/*
+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 { it, vi, expect, beforeEach, afterEach, describe } from "vitest";
+import { firstValueFrom, of, Subject, take, toArray } from "rxjs";
+import { type RTCCallIntent } from "matrix-js-sdk/lib/matrixrtc";
+
+import { AndroidControlledAudioOutput } from "./AndroidControlledAudioOutput.ts";
+import type { Controls, OutputDevice } from "../controls";
+import { ObservableScope } from "./ObservableScope";
+import { withTestScheduler } from "../utils/test";
+
+// All the following device types are real device types that have been observed in the wild on Android devices,
+// gathered from logs.
+// There are no BT Speakers because they are currently filtered out by EXA (native layer)
+
+// A device type describing the speaker system (i.e. a mono speaker or stereo speakers) built in a device.
+const SPEAKER_DEVICE: OutputDevice = {
+  id: "3",
+  name: "Built-in speaker",
+  isEarpiece: false,
+  isSpeaker: true,
+  isExternalHeadset: false,
+};
+
+// A device type describing the attached earphone speaker.
+const EARPIECE_DEVICE: OutputDevice = {
+  id: "2",
+  name: "Built-in earpiece",
+  isEarpiece: true,
+  isSpeaker: false,
+  isExternalHeadset: false,
+};
+
+// A device type describing a Bluetooth device typically used for telephony
+const BT_HEADSET_DEVICE: OutputDevice = {
+  id: "2226",
+  name: "Bluetooth - OpenMove by Shokz",
+  isEarpiece: false,
+  isSpeaker: false,
+  isExternalHeadset: true,
+};
+
+// A device type describing a USB audio headset.
+const USB_HEADSET_DEVICE: OutputDevice = {
+  id: "29440",
+  name: "USB headset - USB-Audio - AB13X USB Audio",
+  isEarpiece: false,
+  isSpeaker: false,
+  isExternalHeadset: false,
+};
+
+// A device type describing a headset, which is the combination of a headphones and microphone
+const WIRED_HEADSET_DEVICE: OutputDevice = {
+  id: "54509",
+  name: "Wired headset - 23117RA68G",
+  isEarpiece: false,
+  isSpeaker: false,
+  isExternalHeadset: false,
+};
+
+// A device type describing a pair of wired headphones
+const WIRED_HEADPHONE_DEVICE: OutputDevice = {
+  id: "679",
+  name: "Wired headphones - TB02",
+  isEarpiece: false,
+  isSpeaker: false,
+  isExternalHeadset: false,
+};
+
+/**
+ * The base device list that is always present on Android devices.
+ * This list is ordered by the OS, the speaker is listed before the earpiece.
+ */
+const BASE_DEVICE_LIST = [SPEAKER_DEVICE, EARPIECE_DEVICE];
+
+const BT_HEADSET_BASE_DEVICE_LIST = [BT_HEADSET_DEVICE, ...BASE_DEVICE_LIST];
+
+const WIRED_HEADSET_BASE_DEVICE_LIST = [
+  WIRED_HEADSET_DEVICE,
+  ...BASE_DEVICE_LIST,
+];
+
+/**
+ * A full device list containing all the observed device types in the wild on Android devices.
+ * Ordered as they would be ordered by the OS.
+ */
+const FULL_DEVICE_LIST = [
+  BT_HEADSET_DEVICE,
+  USB_HEADSET_DEVICE,
+  WIRED_HEADSET_DEVICE,
+  WIRED_HEADPHONE_DEVICE,
+  ...BASE_DEVICE_LIST,
+];
+
+let testScope: ObservableScope;
+let mockControls: Controls;
+
+beforeEach(() => {
+  testScope = new ObservableScope();
+  mockControls = {
+    onAudioDeviceSelect: vi.fn(),
+    onOutputDeviceSelect: vi.fn(),
+  } as unknown as Controls;
+});
+
+afterEach(() => {
+  testScope.end();
+});
+
+describe("Default selection", () => {
+  it("Default to speaker for video calls", async () => {
+    const controlledAudioOutput = new AndroidControlledAudioOutput(
+      of(BASE_DEVICE_LIST),
+      testScope,
+      "video",
+      mockControls,
+    );
+
+    const emissions = await firstValueFrom(
+      controlledAudioOutput.selected$.pipe(take(1), toArray()),
+    );
+
+    expect(emissions).toEqual([
+      { id: SPEAKER_DEVICE.id, virtualEarpiece: false },
+    ]);
+
+    [
+      mockControls.onAudioDeviceSelect,
+      mockControls.onOutputDeviceSelect,
+    ].forEach((mockFn) => {
+      expect(mockFn).toHaveBeenCalledTimes(1);
+      expect(mockFn).toHaveBeenCalledWith(SPEAKER_DEVICE.id);
+    });
+  });
+
+  it("Default to earpiece for audio calls for base config", async () => {
+    const controlledAudioOutput = new AndroidControlledAudioOutput(
+      of(BASE_DEVICE_LIST),
+      testScope,
+      "audio",
+      mockControls,
+    );
+
+    const emissions = await firstValueFrom(
+      controlledAudioOutput.selected$.pipe(take(1), toArray()),
+    );
+
+    expect(emissions).toEqual([
+      { id: EARPIECE_DEVICE.id, virtualEarpiece: false },
+    ]);
+
+    [
+      mockControls.onAudioDeviceSelect,
+      mockControls.onOutputDeviceSelect,
+    ].forEach((mockFn) => {
+      expect(mockFn).toHaveBeenCalledTimes(1);
+      expect(mockFn).toHaveBeenCalledWith(EARPIECE_DEVICE.id);
+    });
+  });
+
+  ["audio", "video"].forEach((callIntent) => {
+    it(`Default to BT headset for ${callIntent} calls if present`, async () => {
+      const controlledAudioOutput = new AndroidControlledAudioOutput(
+        of(BT_HEADSET_BASE_DEVICE_LIST),
+        testScope,
+        callIntent,
+        mockControls,
+      );
+
+      const emissions = await firstValueFrom(
+        controlledAudioOutput.selected$.pipe(take(1), toArray()),
+      );
+
+      expect(emissions).toEqual([
+        { id: BT_HEADSET_DEVICE.id, virtualEarpiece: false },
+      ]);
+
+      [
+        mockControls.onAudioDeviceSelect,
+        mockControls.onOutputDeviceSelect,
+      ].forEach((mockFn) => {
+        expect(mockFn).toHaveBeenCalledTimes(1);
+        expect(mockFn).toHaveBeenCalledWith(BT_HEADSET_DEVICE.id);
+      });
+    });
+  });
+
+  ["audio", "video"].forEach((callIntent) => {
+    it(`Default to wired headset for ${callIntent} calls if present`, async () => {
+      const controlledAudioOutput = new AndroidControlledAudioOutput(
+        of(WIRED_HEADSET_BASE_DEVICE_LIST),
+        testScope,
+        callIntent,
+        mockControls,
+      );
+
+      const emissions = await firstValueFrom(
+        controlledAudioOutput.selected$.pipe(take(1), toArray()),
+      );
+
+      expect(emissions).toEqual([
+        { id: WIRED_HEADSET_DEVICE.id, virtualEarpiece: false },
+      ]);
+
+      expect(mockControls.onAudioDeviceSelect).toHaveBeenCalledExactlyOnceWith(
+        WIRED_HEADSET_DEVICE.id,
+      );
+      expect(mockControls.onOutputDeviceSelect).toHaveBeenCalledExactlyOnceWith(
+        WIRED_HEADSET_DEVICE.id,
+      );
+    });
+  });
+});
+
+describe("Test mappings", () => {
+  it("Should map output device to correct AudioDeviceLabel", async () => {
+    const controlledAudioOutput = new AndroidControlledAudioOutput(
+      of(FULL_DEVICE_LIST),
+      testScope,
+      undefined,
+      mockControls,
+    );
+
+    const availableDevices = await firstValueFrom(
+      controlledAudioOutput.available$.pipe(take(1)),
+    );
+
+    expect(availableDevices).toEqual(
+      new Map([
+        [BT_HEADSET_DEVICE.id, { type: "name", name: BT_HEADSET_DEVICE.name }],
+        [
+          USB_HEADSET_DEVICE.id,
+          { type: "name", name: USB_HEADSET_DEVICE.name },
+        ],
+        [
+          WIRED_HEADSET_DEVICE.id,
+          { type: "name", name: WIRED_HEADSET_DEVICE.name },
+        ],
+        [
+          WIRED_HEADPHONE_DEVICE.id,
+          { type: "name", name: WIRED_HEADPHONE_DEVICE.name },
+        ],
+        [SPEAKER_DEVICE.id, { type: "speaker" }],
+        [EARPIECE_DEVICE.id, { type: "earpiece" }],
+      ]),
+    );
+  });
+});
+
+describe("Test select a device", () => {
+  it(`Switch to correct device `, () => {
+    withTestScheduler(({ cold, schedule, expectObservable, flush }) => {
+      const controlledAudioOutput = new AndroidControlledAudioOutput(
+        cold("a", { a: FULL_DEVICE_LIST }),
+        testScope,
+        undefined,
+        mockControls,
+      );
+
+      schedule("-abc", {
+        a: () => controlledAudioOutput.select(EARPIECE_DEVICE.id),
+        b: () => controlledAudioOutput.select(USB_HEADSET_DEVICE.id),
+        c: () => controlledAudioOutput.select(SPEAKER_DEVICE.id),
+      });
+
+      expectObservable(controlledAudioOutput.selected$).toBe("abcd", {
+        // virtualEarpiece is always false on android.
+        // Initially the BT_HEADSET is selected.
+        a: { id: BT_HEADSET_DEVICE.id, virtualEarpiece: false },
+        b: { id: EARPIECE_DEVICE.id, virtualEarpiece: false },
+        c: { id: USB_HEADSET_DEVICE.id, virtualEarpiece: false },
+        d: { id: SPEAKER_DEVICE.id, virtualEarpiece: false },
+      });
+
+      flush();
+
+      [
+        mockControls.onOutputDeviceSelect,
+        mockControls.onAudioDeviceSelect,
+      ].forEach((mockFn) => {
+        expect(mockFn).toHaveBeenCalledTimes(4);
+        expect(mockFn).toHaveBeenNthCalledWith(1, BT_HEADSET_DEVICE.id);
+        expect(mockFn).toHaveBeenNthCalledWith(2, EARPIECE_DEVICE.id);
+        expect(mockFn).toHaveBeenNthCalledWith(3, USB_HEADSET_DEVICE.id);
+        expect(mockFn).toHaveBeenNthCalledWith(4, SPEAKER_DEVICE.id);
+      });
+    });
+  });
+
+  it(`manually switch then a bt headset is added`, () => {
+    withTestScheduler(({ cold, schedule, expectObservable, flush }) => {
+      const controlledAudioOutput = new AndroidControlledAudioOutput(
+        cold("a--b", {
+          a: BASE_DEVICE_LIST,
+          b: BT_HEADSET_BASE_DEVICE_LIST,
+        }),
+        testScope,
+        "audio",
+        mockControls,
+      );
+
+      // Default was earpiece (audio call), let's switch to speaker
+      schedule("-a--", {
+        a: () => controlledAudioOutput.select(SPEAKER_DEVICE.id),
+      });
+
+      expectObservable(controlledAudioOutput.selected$).toBe("ab-c", {
+        // virtualEarpiece is always false on android.
+        // Initially the BT_HEADSET is selected.
+        a: { id: EARPIECE_DEVICE.id, virtualEarpiece: false },
+        b: { id: SPEAKER_DEVICE.id, virtualEarpiece: false },
+        c: { id: BT_HEADSET_DEVICE.id, virtualEarpiece: false },
+      });
+
+      flush();
+
+      [
+        mockControls.onOutputDeviceSelect,
+        mockControls.onAudioDeviceSelect,
+      ].forEach((mockFn) => {
+        expect(mockFn).toHaveBeenCalledTimes(3);
+        expect(mockFn).toHaveBeenNthCalledWith(1, EARPIECE_DEVICE.id);
+        expect(mockFn).toHaveBeenNthCalledWith(2, SPEAKER_DEVICE.id);
+        expect(mockFn).toHaveBeenNthCalledWith(3, BT_HEADSET_DEVICE.id);
+      });
+    });
+  });
+
+  it(`Go back to the previously selected after the auto-switch device goes away`, () => {
+    withTestScheduler(({ cold, schedule, expectObservable, flush }) => {
+      const controlledAudioOutput = new AndroidControlledAudioOutput(
+        cold("a--b-c", {
+          a: BASE_DEVICE_LIST,
+          b: BT_HEADSET_BASE_DEVICE_LIST,
+          c: BASE_DEVICE_LIST,
+        }),
+        testScope,
+        "audio",
+        mockControls,
+      );
+
+      // Default was earpiece (audio call), let's switch to speaker
+      schedule("-a---", {
+        a: () => controlledAudioOutput.select(SPEAKER_DEVICE.id),
+      });
+
+      expectObservable(controlledAudioOutput.selected$).toBe("ab-c-d", {
+        // virtualEarpiece is always false on android.
+        // Initially the BT_HEADSET is selected.
+        a: { id: EARPIECE_DEVICE.id, virtualEarpiece: false },
+        b: { id: SPEAKER_DEVICE.id, virtualEarpiece: false },
+        c: { id: BT_HEADSET_DEVICE.id, virtualEarpiece: false },
+        d: { id: SPEAKER_DEVICE.id, virtualEarpiece: false },
+      });
+
+      flush();
+
+      [
+        mockControls.onOutputDeviceSelect,
+        mockControls.onAudioDeviceSelect,
+      ].forEach((mockFn) => {
+        expect(mockFn).toHaveBeenCalledTimes(4);
+        expect(mockFn).toHaveBeenNthCalledWith(1, EARPIECE_DEVICE.id);
+        expect(mockFn).toHaveBeenNthCalledWith(2, SPEAKER_DEVICE.id);
+        expect(mockFn).toHaveBeenNthCalledWith(3, BT_HEADSET_DEVICE.id);
+        expect(mockFn).toHaveBeenNthCalledWith(4, SPEAKER_DEVICE.id);
+      });
+    });
+  });
+});
+
+describe("Available device changes", () => {
+  let availableSource$: Subject<OutputDevice[]>;
+
+  const createAudioControlledOutput = (
+    intent: RTCCallIntent,
+  ): AndroidControlledAudioOutput => {
+    return new AndroidControlledAudioOutput(
+      availableSource$,
+      testScope,
+      intent,
+      mockControls,
+    );
+  };
+
+  beforeEach(() => {
+    availableSource$ = new Subject<OutputDevice[]>();
+  });
+
+  it("When a BT headset is added, control should switch to use it", () => {
+    createAudioControlledOutput("video");
+
+    // Emit the base device list, the speaker should be selected
+    availableSource$.next(BASE_DEVICE_LIST);
+    // Initially speaker would be selected
+    [
+      mockControls.onOutputDeviceSelect,
+      mockControls.onAudioDeviceSelect,
+    ].forEach((mockFn) => {
+      expect(mockFn).toHaveBeenCalledTimes(1);
+      expect(mockFn).toHaveBeenCalledWith(SPEAKER_DEVICE.id);
+    });
+
+    // Emit a new device list with a BT device, the control should switch to it
+    availableSource$.next([BT_HEADSET_DEVICE, ...BASE_DEVICE_LIST]);
+    [
+      mockControls.onOutputDeviceSelect,
+      mockControls.onAudioDeviceSelect,
+    ].forEach((mockFn) => {
+      expect(mockFn).toHaveBeenCalledTimes(2);
+      expect(mockFn).toHaveBeenLastCalledWith(BT_HEADSET_DEVICE.id);
+    });
+  });
+
+  // Android does not set `isExternalHeadset` to true for wired headphones, so we can't test this case.'
+  it.skip("When a wired headset is added, control should switch to use it", async () => {
+    const controlledAudioOutput = createAudioControlledOutput("video");
+
+    // Emit the base device list, the speaker should be selected
+    availableSource$.next(BASE_DEVICE_LIST);
+
+    await firstValueFrom(controlledAudioOutput.selected$.pipe(take(1)));
+    // Initially speaker would be selected
+    [
+      mockControls.onOutputDeviceSelect,
+      mockControls.onAudioDeviceSelect,
+    ].forEach((mockFn) => {
+      expect(mockFn).toHaveBeenCalledTimes(1);
+      expect(mockFn).toHaveBeenCalledWith(SPEAKER_DEVICE.id);
+    });
+
+    // Emit a new device list with a wired headset, the control should switch to it
+    availableSource$.next([WIRED_HEADPHONE_DEVICE, ...BASE_DEVICE_LIST]);
+    [
+      mockControls.onOutputDeviceSelect,
+      mockControls.onAudioDeviceSelect,
+    ].forEach((mockFn) => {
+      expect(mockFn).toHaveBeenCalledTimes(2);
+      expect(mockFn).toHaveBeenLastCalledWith(WIRED_HEADPHONE_DEVICE.id);
+    });
+  });
+
+  it("When the active bt headset is removed on audio call, control should switch to earpiece", () => {
+    createAudioControlledOutput("audio");
+
+    // Emit the BT headset device list, the BT headset should be selected
+    availableSource$.next(BT_HEADSET_BASE_DEVICE_LIST);
+    // Initially speaker would be selected
+    [
+      mockControls.onOutputDeviceSelect,
+      mockControls.onAudioDeviceSelect,
+    ].forEach((mockFn) => {
+      expect(mockFn).toHaveBeenCalledTimes(1);
+      expect(mockFn).toHaveBeenCalledWith(BT_HEADSET_DEVICE.id);
+    });
+
+    // Emit a new device list without the BT headset, the control should switch to the earpiece for
+    // audio calls
+    availableSource$.next(BASE_DEVICE_LIST);
+    [
+      mockControls.onOutputDeviceSelect,
+      mockControls.onAudioDeviceSelect,
+    ].forEach((mockFn) => {
+      expect(mockFn).toHaveBeenCalledTimes(2);
+      expect(mockFn).toHaveBeenLastCalledWith(EARPIECE_DEVICE.id);
+    });
+  });
+
+  it("When the active bt headset is removed on video call, control should switch to speaker", () => {
+    createAudioControlledOutput("video");
+
+    availableSource$.next(BT_HEADSET_BASE_DEVICE_LIST);
+
+    // Initially bt headset would be selected
+    [
+      mockControls.onOutputDeviceSelect,
+      mockControls.onAudioDeviceSelect,
+    ].forEach((mockFn) => {
+      expect(mockFn).toHaveBeenCalledTimes(1);
+      expect(mockFn).toHaveBeenCalledWith(BT_HEADSET_DEVICE.id);
+    });
+
+    // Emit a new device list without the BT headset, the control should switch to speaker for video call
+    availableSource$.next(BASE_DEVICE_LIST);
+    [
+      mockControls.onOutputDeviceSelect,
+      mockControls.onAudioDeviceSelect,
+    ].forEach((mockFn) => {
+      expect(mockFn).toHaveBeenCalledTimes(2);
+      expect(mockFn).toHaveBeenLastCalledWith(SPEAKER_DEVICE.id);
+    });
+  });
+
+  it("Do not repeatidly set the same device", () => {
+    createAudioControlledOutput("video");
+
+    availableSource$.next(BT_HEADSET_BASE_DEVICE_LIST);
+    availableSource$.next(BT_HEADSET_BASE_DEVICE_LIST);
+    availableSource$.next(BT_HEADSET_BASE_DEVICE_LIST);
+    availableSource$.next(BT_HEADSET_BASE_DEVICE_LIST);
+    availableSource$.next(BT_HEADSET_BASE_DEVICE_LIST);
+
+    // Initially bt headset would be selected
+    [
+      mockControls.onOutputDeviceSelect,
+      mockControls.onAudioDeviceSelect,
+    ].forEach((mockFn) => {
+      expect(mockFn).toHaveBeenCalledTimes(1);
+      expect(mockFn).toHaveBeenCalledWith(BT_HEADSET_DEVICE.id);
+    });
+  });
+});
+
+describe("Scope management", () => {
+  it("Should stop emitting when scope ends", () => {
+    const aScope = new ObservableScope();
+    const controlledAudioOutput = new AndroidControlledAudioOutput(
+      of(BASE_DEVICE_LIST),
+      aScope,
+      undefined,
+      mockControls,
+    );
+
+    expect(mockControls.onAudioDeviceSelect).toHaveBeenCalledOnce();
+
+    aScope.end();
+
+    controlledAudioOutput.select(EARPIECE_DEVICE.id);
+
+    expect(mockControls.onAudioDeviceSelect).not.toHaveBeenCalledTimes(2);
+    expect(mockControls.onAudioDeviceSelect).toHaveBeenCalledOnce();
+  });
+
+  it("Should stop updating when scope ends", () => {
+    const aScope = new ObservableScope();
+    const availableSource$ = new Subject<OutputDevice[]>();
+    new AndroidControlledAudioOutput(
+      availableSource$,
+      aScope,
+      undefined,
+      mockControls,
+    );
+
+    availableSource$.next(BT_HEADSET_BASE_DEVICE_LIST);
+    expect(mockControls.onAudioDeviceSelect).toHaveBeenCalledOnce();
+    expect(mockControls.onAudioDeviceSelect).toHaveBeenCalledWith(
+      BT_HEADSET_DEVICE.id,
+    );
+
+    aScope.end();
+
+    availableSource$.next(BASE_DEVICE_LIST);
+
+    expect(mockControls.onAudioDeviceSelect).not.toHaveBeenCalledTimes(2);
+    // Should have been called only once with the initial BT_HEADSET_DEVICE.id
+    expect(mockControls.onAudioDeviceSelect).toHaveBeenCalledOnce();
+  });
+});

src/state/AndroidControlledAudioOutput.ts

@@ -0,0 +1,358 @@
+/*
+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 {
+  distinctUntilChanged,
+  map,
+  merge,
+  type Observable,
+  scan,
+  startWith,
+  Subject,
+  tap,
+} from "rxjs";
+
+import {
+  type AudioOutputDeviceLabel,
+  type MediaDevice,
+  type SelectedAudioOutputDevice,
+} from "./MediaDevices.ts";
+import type { ObservableScope } from "./ObservableScope.ts";
+import type { RTCCallIntent } from "matrix-js-sdk/lib/matrixrtc";
+import { type Controls, type OutputDevice } from "../controls.ts";
+import { type Behavior } from "./Behavior.ts";
+
+type ControllerState = {
+  /**
+   * The list of available output devices, ordered by preference order (most preferred first).
+   */
+  devices: OutputDevice[];
+  /**
+   * Explicit user preference for the selected device.
+   */
+  preferredDeviceId: string | undefined;
+  /**
+   * The effective selected device, always valid against available devices.
+   */
+  selectedDeviceId: string | undefined;
+};
+
+/**
+ * The possible actions that can be performed on the controller,
+ * either by the user or by the system.
+ */
+type ControllerAction =
+  | { type: "selectDevice"; deviceId: string | undefined }
+  | { type: "deviceUpdated"; devices: OutputDevice[] };
+/**
+ * The implementation of the audio output media device for Android when using the controlled audio output mode.
+ *
+ * In this mode, the hosting application (e.g. Element Mobile) is responsible for providing the list of available audio output devices.
+ * There are some android specific logic compared to others:
+ *  - AndroidControlledAudioOutput is the only one responsible for selecting the best output device.
+ *  - On android, we don't listen to the selected device from native code (control.setAudioDevice).
+ *  - If a new device is added or removed, this controller will determine the new selected device based
+ *    on the available devices (that is ordered by preference order) and the user's selection (if any).
+ *
+ * Given the differences in how the native code is handling the audio routing on Android compared to iOS,
+ * we have this separate implementation. It allows us to have proper testing and avoid side effects
+ * from platform specific logic breaking the other platform's implementation.
+ */
+export class AndroidControlledAudioOutput implements MediaDevice<
+  AudioOutputDeviceLabel,
+  SelectedAudioOutputDevice
+> {
+  private logger = rootLogger.getChild(
+    "[MediaDevices AndroidControlledAudioOutput]",
+  );
+
+  // STATE stream: the current state of the controller, including the list of available devices and the selected device.
+  private readonly controllerState$: Behavior<ControllerState>;
+
+  /**
+   * @inheritdoc
+   */
+  public readonly available$: Behavior<Map<string, AudioOutputDeviceLabel>>;
+
+  /**
+   * Effective selected device, always valid against available devices.
+   *
+   * On android, we don't listen to the selected device from native code (control.setAudioDevice).
+   * Instead, we determine the selected device ourselves based on the available devices and the user's selection (if any).
+   */
+  public readonly selected$: Behavior<SelectedAudioOutputDevice | undefined>;
+
+  // COMMAND stream: user asks to select a device
+  private readonly selectDeviceCommand$ = new Subject<string | undefined>();
+
+  public select(id: string): void {
+    this.logger.info(`select device: ${id}`);
+    this.selectDeviceCommand$.next(id);
+  }
+
+  /**
+   * Creates an instance of AndroidControlledAudioOutput.
+   *
+   * @constructor
+   * @param controlledDevices$ - The list of available output devices coming from the hosting application, ordered by preference order (most preferred first).
+   * @param scope - The ObservableScope to create the Behaviors in.
+   * @param initialIntent - The initial call intent (e.g. "audio" or "video") that can be used to determine the default audio routing (e.g. default to earpiece for audio calls and speaker for video calls).
+   * @param controls - The controls provided by the hosting application to control the audio routing and notify of user actions.
+   */
+  public constructor(
+    private readonly controlledDevices$: Observable<OutputDevice[]>,
+    private readonly scope: ObservableScope,
+    private initialIntent: RTCCallIntent | undefined = undefined,
+    controls: Controls,
+  ) {
+    this.controllerState$ = this.startObservingState$();
+
+    this.selected$ = this.effectiveSelectionFromState$(this.controllerState$);
+
+    this.available$ = scope.behavior(
+      this.controllerState$.pipe(
+        map((state) => {
+          this.logger.info("available devices updated:", state.devices);
+
+          return new Map<string, AudioOutputDeviceLabel>(
+            state.devices.map((outputDevice) => {
+              return [outputDevice.id, mapDeviceToLabel(outputDevice)];
+            }),
+          );
+        }),
+      ),
+    );
+
+    // Effect 1: notify host when effective selection changes
+    this.selected$
+      // It is a behavior so it has built-in distinct until change
+      .pipe(scope.bind())
+      .subscribe((device) => {
+        // Let the hosting application know which output device has been selected.
+        if (device !== undefined) {
+          this.logger.info("onAudioDeviceSelect called:", device);
+          controls.onAudioDeviceSelect?.(device.id);
+          // Also invoke the deprecated callback for backward compatibility
+          // TODO: it appears that on Android the hosting application is only using the deprecated callback (onOutputDeviceSelect)
+          // and not the new one (onAudioDeviceSelect), we should clean this up and only have one callback for audio device selection.
+          controls.onOutputDeviceSelect?.(device.id);
+        }
+      });
+  }
+
+  private startObservingState$(): Behavior<ControllerState> {
+    const initialState: ControllerState = {
+      devices: [],
+      preferredDeviceId: undefined,
+      selectedDeviceId: undefined,
+    };
+
+    // Merge the two possible inputs observable as a single
+    // stream of actions that will update the state of the controller.
+    const actions$: Observable<ControllerAction> = merge(
+      this.controlledDevices$.pipe(
+        map(
+          (devices) =>
+            ({ type: "deviceUpdated", devices }) satisfies ControllerAction,
+        ),
+      ),
+      this.selectDeviceCommand$.pipe(
+        map(
+          (deviceId) =>
+            ({ type: "selectDevice", deviceId }) satisfies ControllerAction,
+        ),
+      ),
+    );
+
+    const initialAction: ControllerAction = {
+      type: "deviceUpdated",
+      devices: [],
+    };
+
+    return this.scope.behavior(
+      actions$.pipe(
+        startWith(initialAction),
+        scan((state, action): ControllerState => {
+          switch (action.type) {
+            case "deviceUpdated": {
+              const chosenDevice = this.chooseEffectiveSelection({
+                previousDevices: state.devices,
+                availableDevices: action.devices,
+                currentSelectedId: state.selectedDeviceId,
+                preferredDeviceId: state.preferredDeviceId,
+              });
+
+              return {
+                ...state,
+                devices: action.devices,
+                selectedDeviceId: chosenDevice,
+              };
+            }
+            case "selectDevice": {
+              const chosenDevice = this.chooseEffectiveSelection({
+                previousDevices: state.devices,
+                availableDevices: state.devices,
+                currentSelectedId: state.selectedDeviceId,
+                preferredDeviceId: action.deviceId,
+              });
+
+              return {
+                ...state,
+                preferredDeviceId: action.deviceId,
+                selectedDeviceId: chosenDevice,
+              };
+            }
+          }
+        }, initialState),
+      ),
+    );
+  }
+
+  private effectiveSelectionFromState$(
+    state$: Observable<ControllerState>,
+  ): Behavior<SelectedAudioOutputDevice | undefined> {
+    return this.scope.behavior(
+      state$
+        .pipe(
+          map((state) => {
+            if (state.selectedDeviceId) {
+              return {
+                id: state.selectedDeviceId,
+                /** This is an iOS thing, always false for android*/
+                virtualEarpiece: false,
+              };
+            }
+            return undefined;
+          }),
+          distinctUntilChanged((a, b) => a?.id === b?.id),
+        )
+        .pipe(
+          tap((selected) => {
+            this.logger.debug(`selected device: ${selected?.id}`);
+          }),
+        ),
+    );
+  }
+
+  private chooseEffectiveSelection(args: {
+    previousDevices: OutputDevice[];
+    availableDevices: OutputDevice[];
+    currentSelectedId: string | undefined;
+    preferredDeviceId: string | undefined;
+  }): string | undefined {
+    const {
+      previousDevices,
+      availableDevices,
+      currentSelectedId,
+      preferredDeviceId,
+    } = args;
+
+    this.logger.debug(`chooseEffectiveSelection with args:`, args);
+
+    // Take preferredDeviceId in priority or default to the last effective selection.
+    const activeSelectedDeviceId = preferredDeviceId || currentSelectedId;
+    const isAvailable = availableDevices.some(
+      (device) => device.id === activeSelectedDeviceId,
+    );
+
+    // If there is no current device, or it is not available anymore,
+    // choose the default device selection logic.
+    if (activeSelectedDeviceId === undefined || !isAvailable) {
+      this.logger.debug(
+        `No current device or it is not available, using default selection logic.`,
+      );
+      // use the default selection logic
+      return this.chooseDefaultDeviceId(availableDevices);
+    }
+
+    // Is there a new added device?
+    // If a device is added, we might want to switch to it if it's more preferred than the currently selected device.
+    const newDeviceWasAdded = availableDevices.some(
+      (device) => !previousDevices.some((d) => d.id === device.id),
+    );
+
+    if (newDeviceWasAdded) {
+      // TODO only want to check from the added device, not all devices.?
+      // check if the currently selected device is the most preferred one, if not switch to the most preferred one.
+      const mostPreferredDevice = availableDevices[0];
+      this.logger.debug(
+        `A new device was added, checking if we should switch to it.`,
+        mostPreferredDevice,
+      );
+      if (mostPreferredDevice.id !== activeSelectedDeviceId) {
+        // Given this is automatic switching, we want to be careful and only switch to a more private device
+        // (e.g. from speaker to a BT headset) but not switch from a more private device to a less private one
+        // (e.g. from a BT headset to the speaker), as that can be disruptive for the user if it happens unexpectedly.
+        if (mostPreferredDevice.isExternalHeadset == true) {
+          this.logger.info(
+            `The currently selected device ${mostPreferredDevice.id} is not the most preferred one, switching to the most preferred one ${activeSelectedDeviceId} instead.`,
+          );
+          // Let's switch as it is a more private device.
+          return mostPreferredDevice.id;
+        }
+      }
+    }
+
+    // no changes
+    return activeSelectedDeviceId;
+  }
+
+  /**
+   *   The logic for the default is different based on the call type.
+   *   For example for a voice call we want to default to the earpiece if it's available,
+   *   but for a video call we want to default to the speaker.
+   *   If the user is using a BT headset we want to default to that, as it's likely what they want to use for both video and voice calls.
+   *
+   *   @param available the available audio output devices to choose from, keyed by their id, sorted by likelihood of it being used for communication.
+   *
+   */
+  private chooseDefaultDeviceId(available: OutputDevice[]): string | undefined {
+    this.logger.debug(
+      `Android routing logic intent: ${this.initialIntent} finding best default...`,
+    );
+    if (this.initialIntent === "audio") {
+      const systemProposed = available[0];
+      // If no headset is connected, android will route to the speaker by default,
+      // but for a voice call we want to route to the earpiece instead,
+      // so override the system proposed routing in that case.
+      if (systemProposed?.isSpeaker == true) {
+        // search for the earpiece
+        const earpieceDevice = available.find(
+          (device) => device.isEarpiece == true,
+        );
+        if (earpieceDevice) {
+          this.logger.debug(
+            `Android routing: Switch to earpiece instead of speaker for voice call`,
+          );
+          return earpieceDevice.id;
+        } else {
+          this.logger.debug(
+            `Android routing: no earpiece found, cannot switch, use system proposed routing`,
+          );
+          return systemProposed.id;
+        }
+      } else {
+        this.logger.debug(
+          `Android routing: Use system proposed routing `,
+          systemProposed,
+        );
+        return systemProposed?.id;
+      }
+    } else {
+      // Use the system best proposed best routing.
+      return available[0]?.id;
+    }
+  }
+}
+
+// Utilities
+function mapDeviceToLabel(device: OutputDevice): AudioOutputDeviceLabel {
+  const { name, isEarpiece, isSpeaker } = device;
+  if (isEarpiece) return { type: "earpiece" };
+  else if (isSpeaker) return { type: "speaker" };
+  else return { type: "name", name };
+}

src/state/MediaDevices.ts

@@ -15,6 +15,7 @@ import {
   Subject,
   switchMap,
   type Observable,
+  tap,
 } from "rxjs";
 import { createMediaDeviceObserver } from "@livekit/components-core";
 import { type Logger, logger as rootLogger } from "matrix-js-sdk/lib/logger";
@@ -34,6 +35,7 @@ import { getUrlParams } from "../UrlParams";
 import { platform } from "../Platform";
 import { switchWhen } from "../utils/observable";
 import { type Behavior, constant } from "./Behavior";
+import { AndroidControlledAudioOutput } from "./AndroidControlledAudioOutput.ts";
 
 // This hardcoded id is used in EX ios! It can only be changed in coordination with
 // the ios swift team.
@@ -49,10 +51,18 @@ export type AudioOutputDeviceLabel =
   | { type: "earpiece" }
   | { type: "default"; name: string | null };
 
+/**
+ * Base selected-device value shared by all media kinds.
+ *
+ * `id` is the effective device identifier used by browser media APIs.
+ */
 export interface SelectedDevice {
   id: string;
 }
 
+/**
+ * Selected audio input value with audio-input-specific metadata.
+ */
 export interface SelectedAudioInputDevice extends SelectedDevice {
   /**
    * Emits whenever we think that this audio input device has logically changed
@@ -61,6 +71,9 @@ export interface SelectedAudioInputDevice extends SelectedDevice {
   hardwareDeviceChange$: Observable<void>;
 }
 
+/**
+ * Selected audio output value with output-routing-specific metadata.
+ */
 export interface SelectedAudioOutputDevice extends SelectedDevice {
   /**
    * Whether this device is a "virtual earpiece" device. If so, we should output
@@ -69,23 +82,42 @@ export interface SelectedAudioOutputDevice extends SelectedDevice {
   virtualEarpiece: boolean;
 }
 
+/**
+ * Common reactive contract for selectable input/output media devices (mic, speaker, camera).
+ *
+ * `Label` is the type used to represent a device in UI lists.
+ * `Selected` is the type used to represent the active selection for a device kind.
+ */
 export interface MediaDevice<Label, Selected> {
   /**
-   * A map from available device IDs to labels.
+   * Reactive map of currently available devices keyed by device ID.
+   *
+   * `Label` defines the UI-facing label data structure for each device type.
    */
   available$: Behavior<Map<string, Label>>;
+
   /**
-   * The selected device.
+   * The active device selection.
+   * Can be `undefined` when no device is yet selected.
+   *
+   * When defined, `Selected` contains the selected device ID plus any
+   * type-specific metadata.
    */
   selected$: Behavior<Selected | undefined>;
+
   /**
-   * Selects a new device.
+   * Requests selection of a device by ID.
+   *
+   * Implementations typically persist this preference and let `selected$`
+   * converge to the effective device (which may differ if the requested ID is
+   * unavailable).
    */
   select(id: string): void;
 }
 
 /**
  * An observable that represents if we should display the devices menu for iOS.
+ *
  * This implies the following
  *  - hide any input devices (they do not work anyhow on ios)
  *  - Show a button to show the native output picker instead.
@@ -143,19 +175,29 @@ function buildDeviceMap(
 function selectDevice$<Label>(
   available$: Observable<Map<string, Label>>,
   preferredId$: Observable<string | undefined>,
+  defaultPicker: (available: Map<string, Label>) => string | undefined = (
+    available,
+  ) => available.keys().next().value,
 ): Observable<string | undefined> {
   return combineLatest([available$, preferredId$], (available, preferredId) => {
     if (available.size) {
-      // If the preferred device is available, use it. Or if every available
-      // device ID is falsy, the browser is probably just being paranoid about
-      // fingerprinting and we should still try using the preferred device.
-      // Worst case it is not available and the browser will gracefully fall
-      // back to some other device for us when requesting the media stream.
-      // Otherwise, select the first available device.
-      return (preferredId !== undefined && available.has(preferredId)) ||
-        (available.size === 1 && available.has(""))
-        ? preferredId
-        : available.keys().next().value;
+      if (preferredId !== undefined && available.has(preferredId)) {
+        // If the preferred device is available, use it.
+        return preferredId;
+      } else if (available.size === 1 && available.has("")) {
+        // In some cases the enumerateDevices will list the devices with empty string details:
+        // `{deviceId:'', kind:'audiooutput|audioinput|videoinput', label:'', groupId:''}`
+        // This can happen when:
+        //     1. The user has not yet granted permissions to microphone/devices
+        //     2. The page is not running in a secure context (e.g. localhost or https)
+        //     3. In embedded WebViews, restrictions are often tighter, need active capture..
+        //     3. The browser is blocking access to device details for privacy reasons (?)
+        // This is most likely transitional, so keep the current device selected until we get a more accurate enumerateDevices.
+        return preferredId;
+      } else {
+        // No preferred, so pick a default.
+        return defaultPicker(available);
+      }
     }
     return undefined;
   });
@@ -251,14 +293,16 @@ class AudioOutput implements MediaDevice<
 
   public readonly selected$ = this.scope.behavior(
     selectDevice$(this.available$, audioOutputSetting.value$).pipe(
-      map((id) =>
-        id === undefined
-          ? undefined
-          : {
+      map((id) => {
+        if (id === undefined) {
+          return undefined;
+        } else {
+          return {
             id,
             virtualEarpiece: false,
-            },
-      ),
+          };
+        }
+      }),
     ),
   );
   public select(id: string): void {
@@ -275,6 +319,11 @@ class AudioOutput implements MediaDevice<
   }
 }
 
+/**
+ * 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.
+ */
 class ControlledAudioOutput implements MediaDevice<
   AudioOutputDeviceLabel,
   SelectedAudioOutputDevice
@@ -309,8 +358,12 @@ class ControlledAudioOutput implements MediaDevice<
 
         // Create a virtual earpiece device in case a non-earpiece device is
         // designated for this purpose
-        if (iosDeviceMenu && availableRaw.some((d) => d.forEarpiece))
+        if (iosDeviceMenu && availableRaw.some((d) => d.forEarpiece)) {
+          this.logger.info(
+            `IOS Add virtual earpiece device with id ${EARPIECE_CONFIG_ID}`,
+          );
           available.set(EARPIECE_CONFIG_ID, { type: "earpiece" });
+        }
 
         return available;
       },
@@ -320,6 +373,7 @@ class ControlledAudioOutput implements MediaDevice<
   private readonly deviceSelection$ = new Subject<string>();
 
   public select(id: string): void {
+    this.logger.info(`select device: ${id}`);
     this.deviceSelection$.next(id);
   }
 
@@ -338,6 +392,10 @@ class ControlledAudioOutput implements MediaDevice<
           ? undefined
           : { id, virtualEarpiece: id === EARPIECE_CONFIG_ID };
       },
+    ).pipe(
+      tap((selected) => {
+        this.logger.debug(`selected device: ${selected?.id}`);
+      }),
     ),
   );
 
@@ -351,23 +409,17 @@ class ControlledAudioOutput implements MediaDevice<
       // been selected - for example, Element X iOS listens to this to determine
       // whether it should enable the proximity sensor.
       if (device !== undefined) {
-        this.logger.info(
-          "[controlled-output] onAudioDeviceSelect called:",
-          device,
-        );
+        this.logger.info("onAudioDeviceSelect called:", device);
         window.controls.onAudioDeviceSelect?.(device.id);
         // Also invoke the deprecated callback for backward compatibility
         window.controls.onOutputDeviceSelect?.(device.id);
       }
     });
     this.available$.subscribe((available) => {
-      this.logger.info("[controlled-output] available devices:", available);
+      this.logger.debug("available devices:", available);
     });
     this.availableRaw$.subscribe((availableRaw) => {
-      this.logger.info(
-        "[controlled-output] available raw devices:",
-        availableRaw,
-      );
+      this.logger.debug("available raw devices:", availableRaw);
     });
   }
 }
@@ -434,7 +486,14 @@ export class MediaDevices {
     AudioOutputDeviceLabel,
     SelectedAudioOutputDevice
   > = getUrlParams().controlledAudioDevices
-    ? new ControlledAudioOutput(this.usingNames$, this.scope)
+    ? platform == "android"
+      ? new AndroidControlledAudioOutput(
+          controlledAvailableOutputDevices$,
+          this.scope,
+          getUrlParams().callIntent,
+          window.controls,
+        )
+      : new ControlledAudioOutput(this.usingNames$, this.scope)
     : new AudioOutput(this.usingNames$, this.scope);
 
   public readonly videoInput: MediaDevice<DeviceLabel, SelectedDevice> =