Only use mediaPresentationDuration to detect IPR.

We shouldn't use the sum of Period durations to detect the duration of
live streams.  It is possible for Periods to be added or the duration
to change, so the sum of Period durations is only valid for VOD.

Closes #1148

Change-Id: I53846807d18b97b0127eb75bb83be526eb7095ee

lib/dash/dash_parser.js

@@ -525,7 +525,10 @@ shaka.dash.DashParser.prototype.processManifest_ =
   var periods = periodsAndDuration.periods;
 
   presentationTimeline.setStatic(mpdType == 'static');
-  presentationTimeline.setDuration(duration || Infinity);
+  if (mpdType == 'static' || !periodsAndDuration.durationDerivedFromPeriods) {
+    // Ignore duration calculated from Period lengths if this is dynamic.
+    presentationTimeline.setDuration(duration || Infinity);
+  }
   presentationTimeline.setSegmentAvailabilityDuration(
       segmentAvailabilityDuration != null ?
       segmentAvailabilityDuration :
@@ -570,7 +573,11 @@ shaka.dash.DashParser.prototype.processManifest_ =
  * @param {shaka.dash.DashParser.Context} context
  * @param {!Array.<string>} baseUris
  * @param {!Element} mpd
- * @return {{periods: !Array.<shakaExtern.Period>, duration: ?number}}
+ * @return {{
+ *   periods: !Array.<shakaExtern.Period>,
+ *   duration: ?number,
+ *   durationDerivedFromPeriods: boolean
+ * }}
  * @private
  */
 shaka.dash.DashParser.prototype.parsePeriods_ = function(
@@ -676,12 +683,14 @@ shaka.dash.DashParser.prototype.parsePeriods_ = function(
     }
     return {
       periods: periods,
-      duration: presentationDuration
+      duration: presentationDuration,
+      durationDerivedFromPeriods: false
     };
   } else {
     return {
       periods: periods,
-      duration: prevEnd
+      duration: prevEnd,
+      durationDerivedFromPeriods: true
     };
   }
 };