fix(DASH): Evict empty indexes in MetaSegmentIndex

lib/media/segment_index.js

@@ -698,25 +698,29 @@ shaka.media.MetaSegmentIndex = class extends shaka.media.SegmentIndex {
 
     /** @private {!Array.<!shaka.media.SegmentIndex>} */
     this.indexes_ = [];
+
+    /**
+     * Represents the number of evicted segments from segment indexes that have
+     * been evicted out of the indexes array.
+     * @private {number}
+     */
+    this.numEvicted_ = 0
   }
 
   /** Evicts all old SegmentIndexes in this MetaSegmentIndex that are empty. */
   evictEmpty() {
-    // If we hypothetically have a segment index that is empty but comes after
-    // one that has references, assume it's new and leave it in.
-    const newIndexes = [];
-    let include = false;
-    for (const index of this.indexes_) {
-      if (!index.isEmpty()) {
-        include = true;
-      }
-      if (include) {
-        newIndexes.push(index);
-      } else {
-        index.release();
-      }
+    if (this.indexes_.length == 0) {
+      return;
     }
-    this.indexes_ = newIndexes;
+    const prevNewestIndex = this.indexes_[this.indexes_.length - 1];
+    while (this.indexes_.length > 0 && this.indexes_[0].isEmpty()) {
+      const index = this.indexes_.shift();
+      this.numEvicted_ += index.getNumEvicted();
+      index.release();
+    }
+    goog.asserts.assert(
+        this.indexes_[this.indexes_.length - 1] == prevNewestIndex,
+        'The newest segment index should never be evicted.');
   }
 
   /**
@@ -743,6 +747,7 @@ shaka.media.MetaSegmentIndex = class extends shaka.media.SegmentIndex {
     // Be careful to clone the Array.  We don't want to share the reference with
     // our clone and affect each other accidentally.
     clone.indexes_ = this.indexes_.slice();
+    clone.numEvicted_ = this.numEvicted_;
     return clone;
   }
 
@@ -773,7 +778,7 @@ shaka.media.MetaSegmentIndex = class extends shaka.media.SegmentIndex {
    * @export
    */
   find(time) {
-    let numPassedInEarlierIndexes = 0;
+    let numPassedInEarlierIndexes = this.numEvicted_;
 
     for (const index of this.indexes_) {
       const position = index.find(time);
@@ -794,7 +799,7 @@ shaka.media.MetaSegmentIndex = class extends shaka.media.SegmentIndex {
    * @export
    */
   get(position) {
-    let numPassedInEarlierIndexes = 0;
+    let numPassedInEarlierIndexes = this.numEvicted_;
     let sawSegments = false;
 
     for (const index of this.indexes_) {

lib/media/streaming_engine.js

@@ -2502,6 +2502,11 @@ shaka.media.StreamingEngine = class {
    * @private
    */
   async evict_(mediaState, presentationTime) {
+    const segmentIndex = mediaState.stream.segmentIndex;
+    if (segmentIndex instanceof shaka.media.MetaSegmentIndex) {
+      segmentIndex.evictEmpty();
+    }
+
     const logPrefix = shaka.media.StreamingEngine.logPrefix_(mediaState);
     shaka.log.v2(logPrefix, 'checking buffer length');
 

lib/util/periods.js

@@ -622,7 +622,6 @@ shaka.util.PeriodCombiner = class {
           outputStream.segmentIndex.appendSegmentIndex(match.segmentIndex);
         }
       }
-      outputStream.segmentIndex.evictEmpty();
     }
   }