Feat(player): Add updateStartTime method to play (shaka-project#3491)

This provides a way to decide on a start time after the manifestparsed event,
but before the load process ends.

lib/cast/cast_utils.js

@@ -388,6 +388,7 @@ shaka.cast.CastUtils.PlayerVoidMethods = [
   'selectVariantsByLabel',
   'setTextTrackVisibility',
   'trickPlay',
+  'updateStartTime',
   'goToLive',
 ];
 

lib/player.js

@@ -533,6 +533,15 @@ shaka.Player = class extends shaka.util.FakeEventTarget {
     /** @private {!Array.<function():(!Promise|undefined)>} */
     this.cleanupOnUnload_ = [];
 
+    /**
+     * This playback start position will be used when
+     * <code>updateStartTime()</code> has been called to provide an updated
+     * start position during the media loading process.
+     *
+     * @private {?number}
+     */
+    this.updatedStartTime_ = null;
+
     if (dependencyInjector) {
       dependencyInjector(this);
     }
@@ -1046,6 +1055,19 @@ shaka.Player = class extends shaka.util.FakeEventTarget {
     return this.wrapWalkerListenersWithPromise_(events);
   }
 
+  /**
+   * Provides a way to update the stream start position during the media loading
+   * process. Can for example be called from the <code>manifestparsed</code>
+   * event handler to update the start position based on information in the
+   * manifest.
+   *
+   * @param {number} startTime
+   * @export
+   */
+  updateStartTime(startTime) {
+    this.updatedStartTime_ = startTime;
+  }
+
   /**
    * Tell the player to load the content at <code>assetUri</code> and start
    * playback at <code>startTime</code>. Before calling <code>load</code>,
@@ -1066,6 +1088,8 @@ shaka.Player = class extends shaka.util.FakeEventTarget {
    * @export
    */
   load(assetUri, startTime, mimeType) {
+    this.updatedStartTime_ = null;
+
     // Do not allow the player to be used after |destroy| is called.
     if (this.loadMode_ == shaka.Player.LoadMode.DESTROYED) {
       return Promise.reject(this.createAbortLoadError_());
@@ -1804,6 +1828,13 @@ shaka.Player = class extends shaka.util.FakeEventTarget {
     // something we are now depending on.
     has.startTime = wants.startTime;
 
+    // If updateStartTime() has been called since load() was invoked use the
+    // requested startTime
+    if (this.updatedStartTime_ != null) {
+      has.startTime = this.updatedStartTime_;
+      this.updatedStartTime_ = null;
+    }
+
     // Store a reference to values in |has| after asserting so that closure will
     // know that they will still be non-null between calls to await.
     const mediaElement = has.mediaElement;

test/player_integration.js

@@ -87,6 +87,41 @@ describe('Player', () => {
     });
   });  // describe('attach')
 
+  describe('updateStartTime() in manifestparsed event handler', () => {
+    it('does not get segments prior to startTime', async () => {
+      player.addEventListener('manifestparsed', () => {
+        player.updateStartTime(24);
+      });
+      const results = {
+        requestedVideoSegment0: false,
+        requestedVideoSegment1: false,
+        requestedVideoSegment2: false,
+      };
+      const expected = {
+        requestedVideoSegment0: false,
+        requestedVideoSegment1: false,
+        requestedVideoSegment2: true,
+      };
+      player.getNetworkingEngine().registerRequestFilter(
+          (type, request) => {
+            if (request.uris[0] == 'test:sintel/video/0') {
+              results.requestedVideoSegment0 = true;
+            }
+            if (request.uris[0] == 'test:sintel/video/1') {
+              results.requestedVideoSegment1 = true;
+            }
+            if (request.uris[0] == 'test:sintel/video/2') {
+              results.requestedVideoSegment2 = true;
+            }
+          });
+      await player.load('test:sintel_compiled');
+      video.play();
+      await waiter.waitUntilPlayheadReachesOrFailOnTimeout(video, 25, 30);
+      expect(results).toEqual(expected);
+    });
+  });
+
+
   describe('getStats', () => {
     it('gives stats about current stream', async () => {
       // This is tested more in player_unit.js.  This is here to test the public