Enable preferred audio input device selection on Android

[jfversluis]

Problem

On Android, AudioRecorder and AudioStreamer hardcode AudioSource.Mic as the audio source, which always uses the system default microphone. There is no way to route recording through a Bluetooth headset, USB microphone, or other external input device.

Changes

1. New PreferredDevice property on BaseOptions (Android)

A new AudioDeviceInfo? PreferredDevice property (in BaseOptions.android.cs) allows consumers to select a specific input device:

var audioManager = (AudioManager)context.GetSystemService(Context.AudioService);
var btDevice = audioManager.GetDevices(GetDevicesTargets.Inputs)
    .FirstOrDefault(d => d.Type == AudioDeviceType.BluetoothSco);

var recorder = audioMgr.CreateRecorder(new AudioRecorderOptions
{
    PreferredDevice = btDevice
});

2. Apply SetPreferredDevice on AudioRecord and MediaRecorder

Both the AudioRecord (WAV) and MediaRecorder (AAC) recording paths now call SetPreferredDevice() when a preferred device is specified:

• AudioRecord: API 23+ (Marshmallow)
• MediaRecorder: API 28+ (Pie), called before Prepare()

Return values are checked and failures are logged via Trace.

3. AudioStreamer support

The AudioStream class (used by AudioStreamer) now also applies SetPreferredDevice() on its AudioRecord instance, so Bluetooth streaming works too.

4. Documentation

Added Android device selection section to audio-recorder.md with:

• Code example for enumerating devices and setting PreferredDevice
• API level requirements
• BLUETOOTH_CONNECT permission note for Android 12+

Design: Opt-in only

PreferredDevice defaults to null — no behavioral change for existing users. The system default microphone is used unless the consumer explicitly sets a preferred device.

Closes #198

Companion PRs

• #208 — iOS/macCatalyst Bluetooth recording support
• #210 — Windows audio device selection

[Copilot]

Pull request overview

Adds an Android-facing options API to allow callers to specify a preferred audio input device (e.g., Bluetooth/USB mic) and wires that preference into the Android recording implementations.

Changes:

• Introduces BaseOptions.PreferredDevice (Android-only) for selecting an AudioDeviceInfo as the recording input.
• Applies the preferred device to the AudioRecord (WAV) path via SetPreferredDevice.
• Applies the preferred device to the MediaRecorder (AAC) path via SetPreferredDevice.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/Plugin.Maui.Audio/BaseOptions.android.cs	Adds Android-only PreferredDevice option to the shared options base type.
src/Plugin.Maui.Audio/AudioRecorder/AudioRecorder.android.cs	Attempts to route recording to the preferred device for both WAV (AudioRecord) and AAC (MediaRecorder).

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[jfversluis]

@copilot resolve the merge conflicts in this pull request

[Copilot]

@copilot resolve the merge conflicts in this pull request

Resolved in 27712a3 by merging the latest main branch changes and reconciling the docs/sample conflicts while keeping the Android device-selection work intact.