feat: Seek bar smooth seeking (#8287)

* refactor(player): decrease the indentation level in the currentTime method

* fix(player): cache_.currentTime is not updated when the current time is set

Updating cache_.currentTime as soon as the currentTime is set avoids having to wait for the timeupdate event, which results in:

- making cache_.currentTime more reliable
- updating the progress bar on mouse up after dragging when the media is paused.

See also: #6232, #6234, #6370, #6372

* feat: add an option to handle smooth seeking

Adds a player option called enableSmoothSeeking, which is false by default,
to provide a smoother seeking experience on mobile and desktop devices.

Usage:
```javascript
// Enables the smooth seeking
const player = videojs('player', {enableSmoothSeeking: true});

// Disable the smooth seeking
player.options({enableSmoothSeeking: false});
```

- **player.js** add an `option` called `enableSmoothSeeking`
- **time-display.js** add a listener to the `seeking` event if `enableSmoothSeeking` is `true` allowing to update the `CurrentTimeDisplay` and `RemainingTimeDisplay` in real time
- **seek-bar.js** `update` the seek bar on `mousemove` event  if `enableSmoothSeeking` is `true`
- add test cases

src/js/control-bar/progress-control/seek-bar.js

@@ -324,6 +324,10 @@ class SeekBar extends Slider {
 
     // Set new time (tell player to seek to new time)
     this.userSeek_(newTime);
+
+    if (this.player_.options_.enableSmoothSeeking) {
+      this.update();
+    }
   }
 
   enable() {

src/js/control-bar/time-controls/time-display.js

@@ -26,7 +26,7 @@ class TimeDisplay extends Component {
   constructor(player, options) {
     super(player, options);
 
-    this.on(player, ['timeupdate', 'ended'], (e) => this.updateContent(e));
+    this.on(player, ['timeupdate', 'ended', 'seeking'], (e) => this.update(e));
     this.updateTextNode_();
   }
 
@@ -71,6 +71,20 @@ class TimeDisplay extends Component {
     super.dispose();
   }
 
+  /**
+   * Updates the displayed time according to the `updateContent` function which is defined in the child class.
+   *
+   * @param {Event} [event]
+   *          The `timeupdate`, `ended` or `seeking` (if enableSmoothSeeking is true) event that caused this function to be called.
+   */
+  update(event) {
+    if (!this.player_.options_.enableSmoothSeeking && event.type === 'seeking') {
+      return;
+    }
+
+    this.updateContent(event);
+  }
+
   /**
    * Updates the time display text node with a new time
    *

src/js/player.js

@@ -5413,7 +5413,9 @@ Player.prototype.options_ = {
   breakpoints: {},
   responsive: false,
   audioOnlyMode: false,
-  audioPosterMode: false
+  audioPosterMode: false,
+  // Default smooth seeking to false
+  enableSmoothSeeking: false
 };
 
 TECH_EVENTS_RETRIGGER.forEach(function(event) {

test/unit/player.test.js

@@ -3423,3 +3423,66 @@ QUnit.test('should not reset the error when the tech triggers an error that is n
   errorStub.restore();
   log.error.restore();
 });
+
+QUnit.test('smooth seeking set to false should not update the display time components or the seek bar', function(assert) {
+  const player = TestHelpers.makePlayer({});
+  const {
+    currentTimeDisplay,
+    remainingTimeDisplay,
+    progressControl: {
+      seekBar
+    }
+  } = player.controlBar;
+  const currentTimeDisplayUpdateContent = sinon.spy(currentTimeDisplay, 'updateContent');
+  const remainingTimeDisplayUpdateContent = sinon.spy(remainingTimeDisplay, 'updateContent');
+  const seekBarUpdate = sinon.spy(seekBar, 'update');
+
+  assert.false(player.options().enableSmoothSeeking, 'enableSmoothSeeking is false by default');
+
+  player.trigger('seeking');
+
+  assert.ok(currentTimeDisplayUpdateContent.notCalled, 'currentTimeDisplay updateContent was not called');
+  assert.ok(remainingTimeDisplayUpdateContent.notCalled, 'remainingTimeDisplay updateContent was not called');
+
+  seekBar.trigger('mousedown');
+  seekBar.trigger('mousemove');
+
+  assert.ok(seekBarUpdate.notCalled, 'seekBar update was not called');
+
+  currentTimeDisplayUpdateContent.restore();
+  remainingTimeDisplayUpdateContent.restore();
+  seekBarUpdate.restore();
+  player.dispose();
+});
+
+QUnit.test('smooth seeking set to true should update the display time components and the seek bar', function(assert) {
+  const player = TestHelpers.makePlayer({enableSmoothSeeking: true});
+  const {
+    currentTimeDisplay,
+    remainingTimeDisplay,
+    progressControl: {
+      seekBar
+    }
+  } = player.controlBar;
+  const currentTimeDisplayUpdateContent = sinon.spy(currentTimeDisplay, 'updateContent');
+  const remainingTimeDisplayUpdateContent = sinon.spy(remainingTimeDisplay, 'updateContent');
+  const seekBarUpdate = sinon.spy(seekBar, 'update');
+
+  assert.true(player.options().enableSmoothSeeking, 'enableSmoothSeeking is true');
+
+  player.duration(1);
+  player.trigger('seeking');
+
+  assert.ok(currentTimeDisplayUpdateContent.called, 'currentTimeDisplay updateContent was called');
+  assert.ok(remainingTimeDisplayUpdateContent.called, 'remainingTimeDisplay updateContent was called');
+
+  seekBar.trigger('mousedown');
+  seekBar.trigger('mousemove');
+
+  assert.ok(seekBarUpdate.called, 'seekBar update was called');
+
+  currentTimeDisplayUpdateContent.restore();
+  remainingTimeDisplayUpdateContent.restore();
+  seekBarUpdate.restore();
+  player.dispose();
+});