[video_player_avfoundation] fix playback speed resetting (#7657)

Calling play is the same as setting the rate to 1.0 (or to `defaultRate` depending on ios version, *documentation in this first link is clearly not updated because it does not mention `defaultRate`*):

https://developer.apple.com/documentation/avfoundation/avplayer/1386726-play?language=objc
https://developer.apple.com/documentation/avfoundation/avplayer/3929373-defaultrate?language=objc

*The second link contains a note about not starting playback by setting the rate to 1.0. I assume this is because of the introduction of `defaultRate` (which can be different than 1.0) and not because `play` may do something more than just setting `rate` as that wording is explicit about setting rate to 1.0, it says nothing about any other value.*

This is also why flutter/plugins#4331 did not work well. It was setting `rate` to 1.0 (through `play`) then immediately to the value set by `setPlaybackSpeed`. One of them or both caused change to `playbackLikelyToKeepUp` which triggered `observeValueForKeyPath` with `playbackLikelyToKeepUpContext` which in turn called again `updatePlayingState` where was `rate` again changed first to 1.0 then to another value and so on. In this PR the rate is changed only once and then to the same value, seems when `rate` is assigned but not really changed it does not trigger anything.

In issues below `seekTo` can trigger `playbackLikelyToKeepUp` change which will call `updatePlayingState` and reset `rate` to 1.0 through `play`. When the speed is set in dart before initialization then the dart side will set it right after calling `play` but even some time after initialization there is still a flood of events calling `updatePlayingState` and it is likely that some of them will call it after `setPlaybackSpeed`. Actually even when `setPlaybackSpeed` was not called on dart side it (dart side) will always change speed after play to 1.0 so it ignores this new `defaultRate` feature.

- fixes flutter/flutter#71264
- fixes flutter/flutter#73643

packages/video_player/video_player_avfoundation/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 2.6.7
+
+* Fixes playback speed resetting.
+
 ## 2.6.6
 
 * Fixes changing global audio session category to be collision free across plugins.

packages/video_player/video_player_avfoundation/darwin/RunnerTests/VideoPlayerTests.m

@@ -672,6 +672,8 @@ - (void)testSeekToleranceWhenSeekingToEnd {
   // Change playback speed.
   [videoPlayerPlugin setPlaybackSpeed:2 forPlayer:textureId.integerValue error:&error];
   XCTAssertNil(error);
+  [videoPlayerPlugin playPlayer:textureId.integerValue error:&error];
+  XCTAssertNil(error);
   XCTAssertEqual(avPlayer.rate, 2);
   XCTAssertEqual(avPlayer.timeControlStatus, AVPlayerTimeControlStatusWaitingToPlayAtSpecifiedRate);
 
@@ -839,6 +841,41 @@ - (void)testFailedToLoadVideoEventShouldBeAlwaysSent {
   [self waitForExpectationsWithTimeout:10.0 handler:nil];
 }
 
+- (void)testUpdatePlayingStateShouldNotResetRate {
+  NSObject<FlutterPluginRegistrar> *registrar =
+      [GetPluginRegistry() registrarForPlugin:@"testUpdatePlayingStateShouldNotResetRate"];
+
+  FVPVideoPlayerPlugin *videoPlayerPlugin = [[FVPVideoPlayerPlugin alloc]
+       initWithAVFactory:[[StubFVPAVFactory alloc] initWithPlayer:nil output:nil]
+      displayLinkFactory:nil
+               registrar:registrar];
+
+  FlutterError *error;
+  [videoPlayerPlugin initialize:&error];
+  XCTAssertNil(error);
+  FVPCreationOptions *create = [FVPCreationOptions
+      makeWithAsset:nil
+                uri:@"https://flutter.github.io/assets-for-api-docs/assets/videos/bee.mp4"
+        packageName:nil
+         formatHint:nil
+        httpHeaders:@{}];
+  NSNumber *textureId = [videoPlayerPlugin createWithOptions:create error:&error];
+  FVPVideoPlayer *player = videoPlayerPlugin.playersByTextureId[textureId];
+
+  XCTestExpectation *initializedExpectation = [self expectationWithDescription:@"initialized"];
+  [player onListenWithArguments:nil
+                      eventSink:^(NSDictionary<NSString *, id> *event) {
+                        if ([event[@"event"] isEqualToString:@"initialized"]) {
+                          [initializedExpectation fulfill];
+                        }
+                      }];
+  [self waitForExpectationsWithTimeout:10 handler:nil];
+
+  [videoPlayerPlugin setPlaybackSpeed:2 forPlayer:textureId.integerValue error:&error];
+  [videoPlayerPlugin playPlayer:textureId.integerValue error:&error];
+  XCTAssertEqual(player.player.rate, 2);
+}
+
 #if TARGET_OS_IOS
 - (void)testVideoPlayerShouldNotOverwritePlayAndRecordNorDefaultToSpeaker {
   NSObject<FlutterPluginRegistrar> *registrar = [GetPluginRegistry()

packages/video_player/video_player_avfoundation/darwin/video_player_avfoundation/Sources/video_player_avfoundation/FVPVideoPlayer.m

@@ -29,6 +29,8 @@ @interface FVPVideoPlayer ()
 @property(nonatomic) CGAffineTransform preferredTransform;
 /// Indicates whether the video player is currently playing.
 @property(nonatomic, readonly) BOOL isPlaying;
+/// The target playback speed requested by the plugin client.
+@property(nonatomic, readonly) NSNumber *targetPlaybackSpeed;
 /// Indicates whether the video player has been initialized.
 @property(nonatomic, readonly) BOOL isInitialized;
 /// The updater that drives callbacks to the engine to indicate that a new frame is ready.
@@ -323,7 +325,15 @@ - (void)updatePlayingState {
     return;
   }
   if (_isPlaying) {
-    [_player play];
+    // Calling play is the same as setting the rate to 1.0 (or to defaultRate depending on iOS
+    // version) so last set playback speed must be set here if any instead.
+    // https://github.com/flutter/flutter/issues/71264
+    // https://github.com/flutter/flutter/issues/73643
+    if (_targetPlaybackSpeed) {
+      [self updateRate];
+    } else {
+      [_player play];
+    }
   } else {
     [_player pause];
   }
@@ -332,6 +342,32 @@ - (void)updatePlayingState {
   _displayLink.running = _isPlaying || self.waitingForFrame;
 }
 
+/// Synchronizes the player's playback rate with targetPlaybackSpeed, constrained by the playback
+/// rate capabilities of the player's current item.
+- (void)updateRate {
+  // See https://developer.apple.com/library/archive/qa/qa1772/_index.html for an explanation of
+  // these checks.
+  // If status is not AVPlayerItemStatusReadyToPlay then both canPlayFastForward
+  // and canPlaySlowForward are always false and it is unknown whether video can
+  // be played at these speeds, updatePlayingState will be called again when
+  // status changes to AVPlayerItemStatusReadyToPlay.
+  float speed = _targetPlaybackSpeed.floatValue;
+  BOOL readyToPlay = _player.currentItem.status == AVPlayerItemStatusReadyToPlay;
+  if (speed > 2.0 && !_player.currentItem.canPlayFastForward) {
+    if (!readyToPlay) {
+      return;
+    }
+    speed = 2.0;
+  }
+  if (speed < 1.0 && !_player.currentItem.canPlaySlowForward) {
+    if (!readyToPlay) {
+      return;
+    }
+    speed = 1.0;
+  }
+  _player.rate = speed;
+}
+
 - (void)sendFailedToLoadVideoEvent {
   if (_eventSink == nil) {
     return;
@@ -473,27 +509,8 @@ - (void)setVolume:(double)volume {
 }
 
 - (void)setPlaybackSpeed:(double)speed {
-  // See https://developer.apple.com/library/archive/qa/qa1772/_index.html for an explanation of
-  // these checks.
-  if (speed > 2.0 && !_player.currentItem.canPlayFastForward) {
-    if (_eventSink != nil) {
-      _eventSink([FlutterError errorWithCode:@"VideoError"
-                                     message:@"Video cannot be fast-forwarded beyond 2.0x"
-                                     details:nil]);
-    }
-    return;
-  }
-
-  if (speed < 1.0 && !_player.currentItem.canPlaySlowForward) {
-    if (_eventSink != nil) {
-      _eventSink([FlutterError errorWithCode:@"VideoError"
-                                     message:@"Video cannot be slow-forwarded"
-                                     details:nil]);
-    }
-    return;
-  }
-
-  _player.rate = speed;
+  _targetPlaybackSpeed = @(speed);
+  [self updatePlayingState];
 }
 
 - (CVPixelBufferRef)copyPixelBuffer {

packages/video_player/video_player_avfoundation/pubspec.yaml

@@ -2,7 +2,7 @@ name: video_player_avfoundation
 description: iOS and macOS implementation of the video_player plugin.
 repository: https://github.com/flutter/packages/tree/main/packages/video_player/video_player_avfoundation
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+video_player%22
-version: 2.6.6
+version: 2.6.7
 
 environment:
   sdk: ^3.4.0