Don't change start time in SegmentIndex.fit().

Since we have gap jumping, we don't need to worry about a gap at the
beginning of the segment index.  By changing the start time of the
first segment, it makes merging complicated since the pre-fit and
post-fit times are different.  This difference can cause duplicate
entries in the index.

Issue shaka-project#1464
Closes shaka-project#1486

Change-Id: Ib3521e186cd8e256366a3c3e922e0764bd58bbd9

lib/media/segment_index.js

@@ -21,7 +21,6 @@ goog.require('goog.asserts');
 goog.require('shaka.log');
 goog.require('shaka.media.SegmentReference');
 goog.require('shaka.util.IDestroyable');
-goog.require('shaka.util.ManifestParserUtils');
 
 
 
@@ -254,9 +253,6 @@ shaka.media.SegmentIndex.prototype.evict = function(time) {
  * @param {?number} periodDuration
  */
 shaka.media.SegmentIndex.prototype.fit = function(periodDuration) {
-  const tolerance =
-      shaka.util.ManifestParserUtils.GAP_OVERLAP_TOLERANCE_SECONDS;
-
   goog.asserts.assert(periodDuration != null,
                       'Period duration must be known for static content!');
   goog.asserts.assert(periodDuration != Infinity,
@@ -284,20 +280,6 @@ shaka.media.SegmentIndex.prototype.fit = function(periodDuration) {
     return;
   }
 
-  // Adjust the first SegmentReference if the start time is smaller than the gap
-  // tolerance (including negative).
-  let firstReference = this.references_[0];
-  if (firstReference.startTime < tolerance) {
-    this.references_[0] =
-        new shaka.media.SegmentReference(
-            firstReference.position,
-            /* startTime */ 0,
-            firstReference.endTime,
-            firstReference.getUris,
-            firstReference.startByte,
-            firstReference.endByte);
-  }
-
   // Adjust the last SegmentReference.
   let lastReference = this.references_[this.references_.length - 1];
   this.references_[this.references_.length - 1] =

lib/media/streaming_engine.js

@@ -1367,6 +1367,10 @@ shaka.media.StreamingEngine.prototype.getSegmentReferenceNeeded_ = function(
     let optimalPosition = Math.max(0, position - 1);
     reference = this.getSegmentReferenceIfAvailable_(
         mediaState, currentPeriodIndex, optimalPosition);
+    let drift = (reference.endTime - reference.startTime) / 3;
+    if (playheadTime > reference.endTime + drift)
+      reference = this.getSegmentReferenceIfAvailable_(
+          mediaState, currentPeriodIndex, optimalPosition + 1);
   }
   return reference ||
       this.getSegmentReferenceIfAvailable_(
@@ -1504,7 +1508,6 @@ shaka.media.StreamingEngine.prototype.fetchAndAppend_ = function(
   // We may set |needInitSegment| to true in switch(), so set it to false here,
   // since we want it to remain true if switch() is called.
   mediaState.needInitSegment = false;
-
   shaka.log.v2(logPrefix, 'fetching segment');
   let fetchSegment = this.fetch_(reference, mediaState.type);
 

lib/player.js

@@ -2073,7 +2073,7 @@ shaka.Player.prototype.defaultConfig_ = function() {
       ignoreTextStreamFailures: false,
       startAtSegmentBoundary: false,
       smallGapLimit: 0.5,
-      jumpLargeGaps: false,
+      jumpLargeGaps: true,
       durationBackoff: 1
     },
     abrFactory: shaka.abr.SimpleAbrManager,

test/media/segment_index_unit.js

@@ -166,7 +166,7 @@ describe('SegmentIndex', /** @suppress {accessControls} */ function() {
       index.fit(/* periodDuration */ 15);
       let newReferences = [
         /* ref 0 dropped because it ends before the period starts */
-        makeReference(1, 0, 4, uri(1)),  // start time clamped to 0
+        makeReference(1, -3, 4, uri(1)),
         makeReference(2, 4, 11, uri(2)),
         makeReference(3, 11, 15, uri(3))  // end time clamped to period
         /* ref 4 dropped because it starts after the period ends */