fix: fix reference searching when search time = segment.endTime

Fixes #3191

Backported to v2.5.x

Change-Id: I4f2c6b3e2e67a6db1bfb71815a5ce80a3584e41e

lib/media/segment_index.js

@@ -71,10 +71,18 @@ shaka.media.SegmentIndex.prototype.find = function(time) {
   // For live streams, searching from the end is faster.  For VOD, it balances
   // out either way.  In both cases, references_.length is small enough that the
   // difference isn't huge.
-  for (let i = this.references_.length - 1; i >= 0; --i) {
-    let r = this.references_[i];
+  const lastReferenceIndex = this.references_.length - 1;
+  for (let i = lastReferenceIndex; i >= 0; --i) {
+    const r = this.references_[i];
+    const start = r.startTime;
+    // A rounding error can cause /time/ to equal e.endTime or fall in between
+    // 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 its end time as /end/.
+    const end = i < lastReferenceIndex ?
+        this.references_[i + 1].startTime : r.endTime;
     // Note that a segment ends immediately before the end time.
-    if ((time >= r.startTime) && (time < r.endTime)) {
+    if ((time >= start) && (time < end)) {
       return r.position;
     }
   }

test/media/segment_index_unit.js

@@ -85,13 +85,26 @@ describe('SegmentIndex', /** @suppress {accessControls} */ function() {
       expect(pos).toBeNull();
     });
 
-    it('returns null if time is within a gap', function() {
-      let actual1 = makeReference(1, 10, 20, uri(10));
-      let actual2 = makeReference(2, 25, 30, uri(25));
-      let index = new shaka.media.SegmentIndex([actual1, actual2]);
+    it('works with two references if time == first end time', () => {
+      const actual1 = makeReference(1, 10, 20.12, uri(10));
+      const actual2 = makeReference(2, 20.13, 30, uri(20));
+      const index = new shaka.media.SegmentIndex([actual1, actual2]);
+
+      const pos = index.find(20.12);
+      goog.asserts.assert(pos != null, 'Null position!');
+      const ref = index.get(pos);
+      expect(ref).toBe(actual1);
+    });
 
-      let pos = index.find(23);
-      expect(pos).toBeNull();
+    it('works with time is between first endTime and second startTime', () => {
+      const actual1 = makeReference(1, 10, 20.12111, uri(10));
+      const actual2 = makeReference(2, 20.12113, 30, uri(20));
+      const index = new shaka.media.SegmentIndex([actual1, actual2]);
+
+      const pos = index.find(20.12112);
+      goog.asserts.assert(pos != null, 'Null position!');
+      const ref = index.get(pos);
+      expect(ref).toBe(actual1);
     });
   });