Fix for BLD-708: Firefox YouTube video start time.

In Firefox YouTube video with start time plays from 00:00:00.
The reason was that seekTo() could not start playing a video from
a point that hasn't been buffered yet. Why this started happening
just now, really is hard to explain.

BLD-708.

CHANGELOG.rst

@@ -5,6 +5,9 @@ These are notable changes in edx-platform.  This is a rolling list of changes,
 in roughly chronological order, most recent first.  Add your entries at or near
 the top.  Include a label indicating the component affected.
 
+Blades: Bugfix "In Firefox YouTube video with start time plays from 00:00:00".
+BLD-708.
+
 Blades: Fix bug when image response in Firefox does not retain input. BLD-711.
 
 Blades: Give numerical response tolerance as a range. BLD-25.

common/lib/xmodule/xmodule/js/spec/helper.js

@@ -16,7 +16,7 @@
             );
 
             Player.getDuration.andReturn(60);
-            Player.getAvailablePlaybackRates.andReturn(['0.50', '1.0', '1.50', '2.0']);
+            Player.getAvailablePlaybackRates.andReturn([0.50, 1.0, 1.50, 2.0]);
 
             return Player;
         },

common/lib/xmodule/xmodule/js/spec/video/general_spec.js

@@ -204,6 +204,52 @@
             });
         });
 
+        describe('YouTube video in FireFox will cue first', function () {
+            var oldUserAgent;
+
+            beforeEach(function () {
+                oldUserAgent = window.navigator.userAgent;
+                window.navigator.userAgent = 'firefox';
+
+                state = jasmine.initializePlayer('video.html', {
+                  start: 10,
+                  end: 30
+                });
+            });
+
+            afterEach(function () {
+                window.navigator.userAgent = oldUserAgent;
+            });
+
+            it('cue is called, skipOnEndedStartEndReset is set', function () {
+                state.videoPlayer.updatePlayTime(10);
+                expect(state.videoPlayer.player.cueVideoById).toHaveBeenCalledWith('cogebirgzzM', 10);
+                expect(state.videoPlayer.skipOnEndedStartEndReset).toBe(true);
+            });
+
+            it('Handling cue state', function () {
+                spyOn(state.videoPlayer, 'play');
+
+                state.videoPlayer.startTime = 10;
+                state.videoPlayer.onStateChange({data: 5});
+
+                expect(state.videoPlayer.player.seekTo).toHaveBeenCalledWith(10, true);
+                expect(state.videoPlayer.play).toHaveBeenCalled();
+            });
+
+            it('when cued, onEnded resets start and end time only the second time', function () {
+                state.videoPlayer.skipOnEndedStartEndReset = true;
+                state.videoPlayer.onEnded();
+                expect(state.videoPlayer.startTime).toBe(10);
+                expect(state.videoPlayer.endTime).toBe(30);
+
+                state.videoPlayer.skipOnEndedStartEndReset = undefined;
+                state.videoPlayer.onEnded();
+                expect(state.videoPlayer.startTime).toBe(0);
+                expect(state.videoPlayer.endTime).toBe(null);
+            });
+        });
+
         describe('checking start and end times', function () {
             var miniTestSuite = [
                 {

common/lib/xmodule/xmodule/js/src/video/03_video_player.js

@@ -447,12 +447,16 @@ function (HTML5Video, Resizer) {
             this.trigger('videoCaption.pause', null);
         }
 
-        // When only `startTime` is set, the video will play to the end
-        // starting at `startTime`. After the first time the video reaches the
-        // end, `startTime` and `endTime` are disabled. The video will play
-        // from start to the end on subsequent runs.
-        this.videoPlayer.startTime = 0;
-        this.videoPlayer.endTime = null;
+        if (this.videoPlayer.skipOnEndedStartEndReset) {
+            this.videoPlayer.skipOnEndedStartEndReset = undefined;
+        } else {
+            // When only `startTime` is set, the video will play to the end
+            // starting at `startTime`. After the first time the video reaches the
+            // end, `startTime` and `endTime` are disabled. The video will play
+            // from start to the end on subsequent runs.
+            this.videoPlayer.startTime = 0;
+            this.videoPlayer.endTime = null;
+        }
 
         // Sometimes `onEnded` events fires when `currentTime` not equal
         // `duration`. In this case, slider doesn't reach the end point of
@@ -633,12 +637,21 @@ function (HTML5Video, Resizer) {
             case this.videoPlayer.PlayerState.ENDED:
                 this.videoPlayer.onEnded();
                 break;
+            case this.videoPlayer.PlayerState.CUED:
+                this.videoPlayer.player.seekTo(this.videoPlayer.startTime, true);
+                // We need to call play() explicitly because after the call
+                // to functions cueVideoById() followed by seekTo() the video
+                // is in a PAUSED state.
+                //
+                // Why? This is how the YouTube API is implemented.
+                this.videoPlayer.play();
+                break;
         }
     }
 
     function updatePlayTime(time) {
         var duration = this.videoPlayer.duration(),
-            durationChange, tempStartTime, tempEndTime;
+            durationChange, tempStartTime, tempEndTime, youTubeId;
 
         if (
             duration > 0 &&
@@ -722,7 +735,38 @@ function (HTML5Video, Resizer) {
                 this.videoPlayer.startTime > 0 &&
                 !(tempStartTime === 0 && tempEndTime === null)
             ) {
-                this.videoPlayer.player.seekTo(this.videoPlayer.startTime);
+                // After a bug came up (BLD-708: "In Firefox YouTube video with
+                // start time plays from 00:00:00") the video refused to play
+                // from start time, and only played from the beginning.
+                //
+                // It turned out that for some reason if Firefox you couldn't
+                // seek beyond some amount of time before the video loaded.
+                // Very strange, but in Chrome there is no such bug.
+                //
+                // HTML5 video sources play fine from start time in both Chrome
+                // and Firefox.
+                if (this.browserIsFirefox && this.videoType === 'youtube') {
+                    if (this.currentPlayerMode === 'flash') {
+                        youTubeId = this.youtubeId();
+                    } else {
+                        youTubeId = this.youtubeId('1.0');
+                    }
+
+                    // When we will call cueVideoById() for some strange reason
+                    // an ENDED event will be fired. It really does no damage
+                    // except for the fact that the end time is reset to null.
+                    // We do not want this.
+                    //
+                    // The flag `skipOnEndedStartEndReset` will notify the
+                    // onEnded() callback for the ENDED event that just this
+                    // once there is no need in resetting the start and end
+                    // times
+                    this.videoPlayer.skipOnEndedStartEndReset = true;
+
+                    this.videoPlayer.player.cueVideoById(youTubeId, this.videoPlayer.startTime);
+                } else {
+                    this.videoPlayer.player.seekTo(this.videoPlayer.startTime);
+                }
             }
 
             // Reset back the actual startTime and endTime if they have been