[camera_web] Add video recording functionality (flutter#4210)

* feat: Add Support for Video Recording in Camera Web
* docs: add video recording documentation

Co-authored-by: Bartosz Selwesiuk <bselwesiuk@gmail.com>

Author: ABausG

packages/camera/camera/lib/src/camera_controller.dart

@@ -335,7 +335,7 @@ class CameraController extends ValueNotifier<CameraValue> {
   /// 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.
+  /// This operation is a no-op on Android and Web.
   ///
   /// Throws a [CameraException] if the prepare fails.
   Future<void> prepareForVideoRecording() async {

packages/camera/camera_web/CHANGELOG.md

@@ -1,5 +1,6 @@
-## NEXT
+## 0.2.1
 
+* Add video recording functionality.
 * Fix cameraNotReadable error that prevented access to the camera on some Android devices.
 
 ## 0.2.0

packages/camera/camera_web/README.md

@@ -83,11 +83,24 @@ if (kIsWeb) {
 }
 ```
 
+### Video recording 
+
+The video recording implementation is backed by [MediaRecorder Web API](https://developer.mozilla.org/en-US/docs/Web/API/MediaRecorder) with the following [browser support](https://caniuse.com/mdn-api_mediarecorder):
+
+![Data on support for the MediaRecorder feature across the major browsers from caniuse.com](https://caniuse.bitsofco.de/image/mediarecorder.png).
+
+A video is recorded in one of the following video MIME types: 
+- video/webm (e.g. on Chrome or Firefox)
+- video/mp4 (e.g. on Safari)
+
+Pausing, resuming or stopping the video recording throws a `PlatformException` with the `videoRecordingNotStarted` error code if the video recording was not started.
+
+For the browsers that do not support the video recording:
+- `CameraPlatform.startVideoRecording` throws a `PlatformException` with the `notSupported` error code.
+
 ## Missing implementation
 
 The web implementation of [`camera`][camera] is missing the following features:
-
-- Video recording ([in progress](https://github.com/flutter/plugins/pull/4210))
 - Exposure mode, point and offset
 - Focus mode and point
 - Sensor orientation

packages/camera/camera_web/example/integration_test/camera_error_code_test.dart

@@ -113,6 +113,13 @@ void main() {
         );
       });
 
+      testWidgets('videoRecordingNotStarted', (tester) async {
+        expect(
+          CameraErrorCode.videoRecordingNotStarted.toString(),
+          equals('videoRecordingNotStarted'),
+        );
+      });
+
       testWidgets('unknown', (tester) async {
         expect(
           CameraErrorCode.unknown.toString(),