Add API to get live stream position as Date.

Closes #356

Change-Id: I5bea5906c4528313da96fd6577005b385b445a65

lib/media/presentation_timeline.js

@@ -88,6 +88,16 @@ shaka.media.PresentationTimeline.prototype.setDuration = function(duration) {
 };
 
 
+/**
+ * @return {?number} The presentation's start time in seconds.
+ * @export
+ */
+shaka.media.PresentationTimeline.prototype.getPresentationStartTime =
+    function() {
+  return this.presentationStartTime_;
+};
+
+
 /**
  * Sets the clock offset, which is the the difference between the client's clock
  * and the server's clock, in milliseconds (i.e., serverTime = Date.now() +

lib/player.js

@@ -924,6 +924,23 @@ shaka.Player.prototype.setTextTrackVisibility = function(on) {
 };
 
 
+/**
+ * Returns current playhead time as a Date.
+ *
+ * @return {Date}
+ * @export
+ */
+shaka.Player.prototype.getPlayheadTimeAsDate = function() {
+  goog.asserts.assert(this.isLive(),
+      'getPlayheadTimeInUTC should be called on a live stream!');
+  var time =
+      this.manifest_.presentationTimeline.getPresentationStartTime() * 1000 +
+      this.video_.currentTime * 1000;
+
+  return new Date(time);
+};
+
+
 /**
  * Return playback and adaptation stats.
  *

test/player_unit.js

@@ -79,7 +79,7 @@ describe('Player', function() {
       };
     }
 
-    video = createMockVideo();
+    video = createMockVideo(20);
     player = new shaka.Player(video, dependencyInjector);
 
     abrManager = new shaka.test.FakeAbrManager();
@@ -1318,6 +1318,26 @@ describe('Player', function() {
     }
   });
 
+  describe('getPlayheadTimeAsDate()', function() {
+    beforeEach(function(done) {
+      var timeline = new shaka.media.PresentationTimeline(300, 0);
+      timeline.setStatic(false);
+      manifest = new shaka.test.ManifestGenerator()
+                      .setTimeline(timeline)
+                      .addPeriod(0)
+                      .build();
+      goog.asserts.assert(manifest, 'manifest must be non-null');
+      var parser = new shaka.test.FakeManifestParser(manifest);
+      var factory = function() { return parser; };
+      player.load('', 0, factory).catch(fail).then(done);
+    });
+
+    it('gets current wall clock time in UTC', function() {
+      var liveTimeUtc = player.getPlayheadTimeAsDate();
+      expect(liveTimeUtc).toEqual(new Date(320000));
+    });
+  });
+
   /**
    * Choose streams for the given period.
    *

test/test/util/manifest_generator.js

@@ -56,6 +56,18 @@ shaka.test.ManifestGenerator.prototype.build = function() {
 };
 
 
+/**
+ * Sets a specified presentation timeline.
+ *
+ * @param {!shaka.media.PresentationTimeline} timeline
+ * @return {!shaka.test.ManifestGenerator}
+ */
+shaka.test.ManifestGenerator.prototype.setTimeline = function(timeline) {
+  this.manifest_.presentationTimeline = timeline;
+  return this;
+};
+
+
 /**
  * Sets the duration of the presentation timeline.
  *

test/test/util/simple_fakes.js

@@ -213,13 +213,15 @@ shaka.test.FakeManifestParser.prototype.configure = function() {};
 
 /**
  * Creates a fake video element.
+ * @param {number=} opt_currentTime
  * @return {!HTMLVideoElement}
  * @suppress {invalidCasts}
  */
-function createMockVideo() {
+function createMockVideo(opt_currentTime) {
   var video = {
     src: '',
     textTracks: [],
+    currentTime: opt_currentTime || 0,
     addTextTrack: jasmine.createSpy('addTextTrack'),
     addEventListener: jasmine.createSpy('addEventListener'),
     removeEventListener: jasmine.createSpy('removeEventListener'),