feat: Support for capturing audio for chrome tab. (#158)

* feat: Support for capturing audio for chrome tab.

* Update code comments.

lib/src/track/local/audio.dart

@@ -1,6 +1,7 @@
 import 'dart:async';
 
 import 'package:flutter_webrtc/flutter_webrtc.dart' as rtc;
+import 'package:meta/meta.dart';
 
 import '../../proto/livekit_models.pb.dart' as lk_models;
 import '../../types/other.dart';
@@ -15,7 +16,8 @@ class LocalAudioTrack extends LocalTrack
   covariant AudioCaptureOptions currentOptions;
 
   // private constructor
-  LocalAudioTrack._(
+  @internal
+  LocalAudioTrack(
     String name,
     TrackSource source,
     rtc.MediaStream stream,
@@ -36,7 +38,7 @@ class LocalAudioTrack extends LocalTrack
     options ??= const AudioCaptureOptions();
     final stream = await LocalTrack.createStream(options);
 
-    return LocalAudioTrack._(
+    return LocalAudioTrack(
       '',
       TrackSource.microphone,
       stream,

lib/src/track/local/local.dart

@@ -119,7 +119,9 @@ abstract class LocalTrack extends Track {
     final constraints = <String, dynamic>{
       'audio': options is AudioCaptureOptions
           ? options.toMediaConstraintsMap()
-          : false,
+          : options is ScreenShareCaptureOptions
+              ? (options).captureScreenAudio
+              : false,
       'video': options is VideoCaptureOptions
           ? options.toMediaConstraintsMap()
           : false,

lib/src/track/local/video.dart

@@ -5,6 +5,7 @@ import '../../proto/livekit_models.pb.dart' as lk_models;
 import '../../types/other.dart';
 import '../options.dart';
 import '../track.dart';
+import 'audio.dart';
 import 'local.dart';
 
 /// A video track from the local device. Use static methods in this class to create
@@ -63,6 +64,39 @@ class LocalVideoTrack extends LocalTrack with VideoTrack {
       options,
     );
   }
+
+  /// Creates a LocalTracks(audio/video) from the display.
+  ///
+  /// The current API is mainly used to capture audio when chrome captures tab,
+  /// but in the future it can also be used for flutter native to open audio
+  /// capture device when capturing screen
+  static Future<List<LocalTrack>> createScreenShareTracksWithAudio([
+    ScreenShareCaptureOptions? options,
+  ]) async {
+    options ??= const ScreenShareCaptureOptions(captureScreenAudio: true);
+
+    final stream = await LocalTrack.createStream(options);
+
+    List<LocalTrack> tracks = [
+      LocalVideoTrack._(
+        Track.screenShareName,
+        TrackSource.screenShareVideo,
+        stream,
+        stream.getVideoTracks().first,
+        options,
+      )
+    ];
+
+    if (stream.getAudioTracks().isNotEmpty) {
+      tracks.add(LocalAudioTrack(
+          Track.screenShareName,
+          TrackSource.screenShareAudio,
+          stream,
+          stream.getAudioTracks().first,
+          const AudioCaptureOptions()));
+    }
+    return tracks;
+  }
 }
 
 //