Add option to disable drift fixing.

The drift fixing allows us to play content that has drift by starting
to play at the last segment in the manifest.  But some live content
specifies content in the future, so we can't just start playing at the
last segment in the manifest.

Fixes #1729

Change-Id: I3095a2d28b34ed93346933f561d77335361f1fae

externs/shaka/player.js

@@ -514,7 +514,8 @@ shaka.extern.DrmConfiguration;
  *   ignoreDrmInfo: boolean,
  *   xlinkFailGracefully: boolean,
  *   defaultPresentationDelay: number,
- *   ignoreMinBufferTime: boolean
+ *   ignoreMinBufferTime: boolean,
+ *   autoCorrectDrift: boolean
  * }}
  *
  * @property {shaka.extern.DashContentProtectionCallback} customScheme
@@ -541,6 +542,11 @@ shaka.extern.DrmConfiguration;
  *   If true will cause DASH parser to ignore minBufferTime from manifest.
  *   It allows player config to take precedence over manifest for
  *   rebufferingGoal. Defaults to false if not provided.
+ * @property {boolean} autoCorrectDrift
+ *   If true, ignore the availabilityStartTime in the manifest and instead use
+ *   the segments to determine the live edge.  This allows us to play streams
+ *   that have a lot of drift.  If false, we can't play content where the
+ *   manifest specifies segments in the future. Defaults to true.
  *
  * @exportDoc
  */

lib/dash/dash_parser.js

@@ -529,7 +529,8 @@ shaka.dash.DashParser.prototype.processManifest_ =
     let presentationDelay = suggestedPresentationDelay != null ?
         suggestedPresentationDelay : defaultPresentationDelay;
     presentationTimeline = new shaka.media.PresentationTimeline(
-        presentationStartTime, presentationDelay);
+        presentationStartTime, presentationDelay,
+        this.config_.dash.autoCorrectDrift);
   }
 
   /** @type {shaka.dash.DashParser.Context} */

lib/media/presentation_timeline.js

@@ -29,6 +29,8 @@ goog.require('shaka.media.SegmentReference');
  *   when the presentation started or will start. Only required for live.
  * @param {number} presentationDelay The delay to give the presentation, in
  *   seconds.  Only required for live.
+ * @param {boolean=} autoCorrectDrift Whether to account for drift when
+ *   determining the availability window.
  *
  * @see {shaka.extern.Manifest}
  * @see {@tutorial architecture}
@@ -38,7 +40,7 @@ goog.require('shaka.media.SegmentReference');
  * @export
  */
 shaka.media.PresentationTimeline = function(
-    presentationStartTime, presentationDelay) {
+    presentationStartTime, presentationDelay, autoCorrectDrift = true) {
   /** @private {?number} */
   this.presentationStartTime_ = presentationStartTime;
 
@@ -90,6 +92,9 @@ shaka.media.PresentationTimeline = function(
 
   /** @private {number} */
   this.userSeekStart_ = 0;
+
+  /** @private {boolean} */
+  this.autoCorrectDrift_ = autoCorrectDrift;
 };
 
 
@@ -232,7 +237,7 @@ shaka.media.PresentationTimeline.prototype.notifySegments = function(
   this.maxSegmentEndTime_ =
       Math.max(this.maxSegmentEndTime_, lastReferenceEndTime);
 
-  if (this.presentationStartTime_ != null) {
+  if (this.presentationStartTime_ != null && this.autoCorrectDrift_) {
     // Since we have explicit segment end times, calculate a presentation start
     // based on them.  This start time accounts for drift.
     // Date.now() is in milliseconds, from which we compute "now" in seconds.

lib/util/player_configuration.js

@@ -103,6 +103,7 @@ shaka.util.PlayerConfiguration = class {
         xlinkFailGracefully: false,
         defaultPresentationDelay: 10,
         ignoreMinBufferTime: false,
+        autoCorrectDrift: true,
       },
     };
 

test/media/presentation_timeline_unit.js

@@ -46,6 +46,7 @@ describe('PresentationTimeline', function() {
    * @param {number} maxSegmentDuration
    * @param {number} clockOffset
    * @param {number} presentationDelay
+   * @param {boolean=} autoCorrectDrift
    *
    * @return {shaka.media.PresentationTimeline}
    */
@@ -56,9 +57,10 @@ describe('PresentationTimeline', function() {
       segmentAvailabilityDuration,
       maxSegmentDuration,
       clockOffset,
-      presentationDelay) {
+      presentationDelay,
+      autoCorrectDrift = true) {
     let timeline = new shaka.media.PresentationTimeline(
-        presentationStartTime, presentationDelay);
+        presentationStartTime, presentationDelay, autoCorrectDrift);
     timeline.setStatic(isStatic);
     timeline.setDuration(duration || Infinity);
     timeline.setSegmentAvailabilityDuration(segmentAvailabilityDuration);
@@ -107,14 +109,15 @@ describe('PresentationTimeline', function() {
    *
    * @param {number} availability
    * @param {number=} delay
+   * @param {boolean=} autoCorrectDrift
    * @return {shaka.media.PresentationTimeline}
    */
-  function makeLiveTimeline(availability, delay) {
+  function makeLiveTimeline(availability, delay, autoCorrectDrift = true) {
     let now = Date.now() / 1000;
     let timeline = makePresentationTimeline(
         /* static */ false, /* duration */ Infinity, /* start time */ now,
         availability, /* max seg dur */ 10,
-        /* clock offset */ 0, delay || 0);
+        /* clock offset */ 0, delay || 0, autoCorrectDrift);
     expect(timeline.isLive()).toBe(true);
     expect(timeline.isInProgress()).toBe(false);
     return timeline;
@@ -212,6 +215,24 @@ describe('PresentationTimeline', function() {
       // last segment time (50) - availability (20)
       expect(timeline.getSegmentAvailabilityStart()).toBe(30);
     });
+
+    it('ignores segment times when configured to', () => {
+      const timeline = makeLiveTimeline(
+          /* availability */ 20, /* drift */ 0, /* autoCorrectDrift */ false);
+
+      const ref1 = makeSegmentReference(0, 10);
+      const ref2 = makeSegmentReference(10, 20);
+      const ref3 = makeSegmentReference(20, 30);
+      const ref4 = makeSegmentReference(30, 40);
+      const ref5 = makeSegmentReference(40, 50);
+
+      setElapsed(100);
+      timeline.notifySegments([ref1, ref2, ref3, ref4, ref5],
+                              /* periodStart */ 0);
+
+      // now (100) - max segment duration (10) - availability start time (0)
+      expect(timeline.getSegmentAvailabilityEnd()).toBe(90);
+    });
   });
 
   describe('getSegmentAvailabilityEnd', function() {