[camera]Fix CameraPreview freezes during startVideoRecording on iOS (flutter#1023)

Author: cvolzke4

CHANGELOG.md

@@ -1,3 +1,7 @@
+## 0.4.3
+
+* Add capability to prepare the capture session for video recording on iOS.
+
 ## 0.4.2
 
 * Add sensor orientation value to `CameraDescription`.

android/src/main/java/io/flutter/plugins/camera/CameraPlugin.java

@@ -205,6 +205,12 @@ public void onMethodCall(MethodCall call, final Result result) {
           camera.takePicture((String) call.argument("path"), result);
           break;
         }
+      case "prepareForVideoRecording":
+        {
+          // This optimization is not required for Android.
+          result.success(null);
+          break;
+        }
       case "startVideoRecording":
         {
           final String filePath = call.argument("filePath");

ios/Classes/CameraPlugin.m

@@ -467,9 +467,7 @@ - (void)startVideoRecordingAtPath:(NSString *)path result:(FlutterResult)result
       _eventSink(@{@"event" : @"error", @"errorDescription" : @"Setup Writer Failed"});
       return;
     }
-    [_captureSession stopRunning];
     _isRecording = YES;
-    [_captureSession startRunning];
     result(nil);
   } else {
     _eventSink(@{@"event" : @"error", @"errorDescription" : @"Video is already recording!"});
@@ -726,6 +724,9 @@ - (void)handleMethodCallAsync:(FlutterMethodCall *)call result:(FlutterResult)re
       [_camera close];
       _dispatchQueue = nil;
       result(nil);
+    } else if ([@"prepareForVideoRecording" isEqualToString:call.method]) {
+      [_camera setUpCaptureSessionForAudio];
+      result(nil);
     } else if ([@"startVideoRecording" isEqualToString:call.method]) {
       [_camera startVideoRecordingAtPath:call.arguments[@"filePath"] result:result];
     } else if ([@"stopVideoRecording" isEqualToString:call.method]) {

lib/camera.dart

@@ -256,6 +256,24 @@ class CameraController extends ValueNotifier<CameraValue> {
     return _creatingCompleter.future;
   }
 
+  /// Prepare the capture session for video recording.
+  ///
+  /// Use of this method is optional, but it may be called for performance
+  /// reasons on iOS.
+  ///
+  /// Preparing audio can cause a minor delay in the CameraPreview view on iOS.
+  /// If video recording is intended, calling this early eliminates this delay
+  /// that would otherwise be experienced when video recording is started.
+  /// This operation is a no-op on Android.
+  ///
+  /// Throws a [CameraException] if the prepare fails.
+  Future<void> prepareForVideoRecording() async {
+    // TODO(amirh): remove this on when the invokeMethod update makes it to stable Flutter.
+    // https://github.com/flutter/flutter/issues/26431
+    // ignore: strong_mode_implicit_dynamic_method
+    await _channel.invokeMethod('prepareForVideoRecording');
+  }
+
   /// Listen to events from the native plugins.
   ///
   /// A "cameraClosing" event is sent when the camera is closed automatically by the system (for example when the app go to background). The plugin will try to reopen the camera automatically but any ongoing recording will end.

pubspec.yaml

@@ -2,7 +2,7 @@ name: camera
 description: A Flutter plugin for getting information about and controlling the
   camera on Android and iOS. Supports previewing the camera feed, capturing images, capturing video,
   and streaming image buffers to dart.
-version: 0.4.2
+version: 0.4.3
 authors:
   - Flutter Team <[email protected]>
   - Luigi Agosti <[email protected]>