fix: exclude "future" segments from presentation timeline auto correc…

…t drift calculations (#4945)

Resolves #4944

lib/media/presentation_timeline.js

@@ -236,7 +236,16 @@ shaka.media.PresentationTimeline = class {
 
     let firstReferenceStartTime = references[0].startTime;
     let lastReferenceEndTime = references[0].endTime;
+
+    // Date.now() is in milliseconds, from which we compute "now" in seconds.
+    const now = (Date.now() + this.clockOffset_) / 1000.0;
+
     for (const reference of references) {
+      // Exclude segments that are in the "future".
+      if (now < reference.startTime) {
+        continue;
+      }
+
       firstReferenceStartTime = Math.min(
           firstReferenceStartTime, reference.startTime);
       lastReferenceEndTime = Math.max(lastReferenceEndTime, reference.endTime);
@@ -251,8 +260,6 @@ shaka.media.PresentationTimeline = class {
         !this.startTimeLocked_) {
       // 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.
-      const now = (Date.now() + this.clockOffset_) / 1000.0;
       this.presentationStartTime_ =
           now - this.maxSegmentEndTime_ - this.maxSegmentDuration_;
     }

test/dash/dash_parser_live_unit.js

@@ -194,7 +194,8 @@ describe('DashParser Live', () => {
           template, {updateTime: updateTime, contents: basicLines.join('\n')});
 
       fakeNetEngine.setResponseText('dummy://foo', text);
-      Date.now = () => 0;
+      const baseTime = new Date(2015, 11, 30);
+      Date.now = () => baseTime.getTime();
       const manifest = await parser.start('dummy://foo', playerInterface);
 
       expect(manifest).toBeTruthy();
@@ -211,7 +212,7 @@ describe('DashParser Live', () => {
       // seconds long in all of these cases.  So 11 seconds after the
       // manifest was parsed, the first segment should have fallen out of
       // the availability window.
-      Date.now = () => 11 * 1000;
+      Date.now = () => baseTime.getTime() + (11 * 1000);
       await updateManifest();
       // The first reference should have been evicted.
       expect(stream.segmentIndex.find(0)).toBe(firstPosition + 1);