fix(DASH): Fix precision issue on some platforms (#6258)

When recalculations of period end are made, it is possible that we will not be able to find last segment from period on low precision platforms. To mitigate it, try to use cached value of `periodEnd_` whenever possible.

Issue observed on Xbox One & Xbox Series.

lib/dash/segment_template.js

@@ -755,16 +755,10 @@ shaka.dash.TimelineSegmentIndex = class extends shaka.media.SegmentIndex {
 
     this.evict(this.periodStart_);
 
-    if (timeline.length === 0) {
-      return;
-    }
-
-    if (this.periodEnd_ !== Infinity) {
-      // Adjust the last timeline entry to match the period end
-      const lastTimePeriod = timeline[timeline.length - 1];
-      // NOTE: end should be relative to period start
-      lastTimePeriod.end = this.periodEnd_ - this.periodStart_;
-    }
+    // Do NOT adjust last range to match period end! With high precision
+    // timestamps several recalculations may give wrong results on less precise
+    // platforms. To mitigate that, we're using cached |periodEnd_| value in
+    // find/get() methods whenever possible.
   }
 
   /**
@@ -784,7 +778,7 @@ shaka.dash.TimelineSegmentIndex = class extends shaka.media.SegmentIndex {
     const timeline = this.templateInfo_.timeline;
 
     // Early exit if the time isn't within this period
-    if (time < this.periodStart_ || time > this.periodEnd_) {
+    if (time < this.periodStart_ || time >= this.periodEnd_) {
       return null;
     }
 
@@ -797,10 +791,14 @@ shaka.dash.TimelineSegmentIndex = class extends shaka.media.SegmentIndex {
       // the references by a fraction of a second. To account for this, we use
       // the start of the next segment as /end/, unless this is the last
       // reference, in which case we use the period end as the /end/
-      let end = range.end + this.periodStart_;
+      let end;
 
       if (i < lastIndex) {
         end = timeline[i + 1].start + this.periodStart_;
+      } else if (this.periodEnd_ === Infinity) {
+        end = range.end + this.periodStart_;
+      } else {
+        end = this.periodEnd_;
       }
 
       if ((time >= start) && (time < end)) {
@@ -831,6 +829,12 @@ shaka.dash.TimelineSegmentIndex = class extends shaka.media.SegmentIndex {
           .unscaledPresentationTimeOffset + range.unscaledStart;
       const timestampOffset = this.periodStart_ -
         this.templateInfo_.scaledPresentationTimeOffset;
+      const trueSegmentEnd = this.periodStart_ + range.end;
+      let segmentEnd = trueSegmentEnd;
+      if (correctedPosition === this.getNumReferences() - 1 &&
+          this.periodEnd_ !== Infinity) {
+        segmentEnd = this.periodEnd_;
+      }
 
       const partialSegmentRefs = [];
 
@@ -901,7 +905,7 @@ shaka.dash.TimelineSegmentIndex = class extends shaka.media.SegmentIndex {
 
       ref = new shaka.media.SegmentReference(
           this.periodStart_ + range.start,
-          this.periodStart_ + range.end,
+          segmentEnd,
           createUrisCb,
           /* startByte= */ 0,
           /* endByte= */ null,
@@ -916,6 +920,7 @@ shaka.dash.TimelineSegmentIndex = class extends shaka.media.SegmentIndex {
           shaka.media.SegmentReference.Status.AVAILABLE,
           this.aesKey_,
           /* allPartialSegments= */ range.partialSegments > 0);
+      ref.trueEndTime = trueSegmentEnd;
       this.references[correctedPosition] = ref;
     }
 

test/dash/dash_parser_segment_template_unit.js

@@ -786,7 +786,7 @@ describe('DashParser SegmentTemplate', () => {
         const newTemplateInfo = makeTemplateInfo(newRanges);
 
         const newEnd = newRanges[newRanges.length - 1].end;
-        index.appendTemplateInfo(newTemplateInfo, newEnd);
+        index.appendTemplateInfo(newTemplateInfo, /* periodStart= */ 0, newEnd);
         expect(index.find(newStart)).toBe(10);
         expect(index.find(newEnd - 1.0)).toBe(19);
       });