Detect and recover from multiple buffered ranges.

There should never be multiple buffered ranges, but if there are
then at least try to keep playing.

Issue #121

Change-Id: I562bdb194dcc1f66701ad1b5bb3246b4e2fbe431

lib/media/source_buffer_manager.js

@@ -337,12 +337,23 @@ shaka.media.SourceBufferManager.prototype.correct = function(
 
 
 /**
- * Assert correctness of SBM internal range.
+ * Emits an error message and returns true if there are multiple buffered
+ * ranges; otherwise, does nothing and returns false.
+ *
+ * @return {boolean}
  */
-shaka.media.SourceBufferManager.prototype.assertSingleRange = function() {
-  shaka.asserts.assert(this.sourceBuffer_.buffered.length <= 1,
-                       'Multiple time ranges should not be buffered!');
-  shaka.media.SegmentReference.assertCorrectReferences(this.inserted_);
+shaka.media.SourceBufferManager.prototype.detectMultipleBufferedRanges =
+    function() {
+  if (this.sourceBuffer_.buffered.length > 1) {
+    shaka.log.error(
+        'Multiple buffered ranges detected:',
+        'Either the content has gaps in it,',
+        'the content\'s segments are not aligned across bitrates,',
+        'or the browser has evicted the middle of the buffer.');
+    return true;
+  } else {
+    return false;
+  }
 };
 
 

lib/media/stream.js

@@ -352,6 +352,16 @@ shaka.media.Stream.prototype.onUpdate_ = function() {
   shaka.asserts.assert((this.updateTimer_ != null) && !this.resyncing_);
   shaka.asserts.assert(!this.fetching_);
 
+  // We should only have one buffered range at any given time, so the next
+  // segment we need is after the last one we inserted. However, non-ideal
+  // content and/or browser eviction policy may induce multiple buffered
+  // ranges in some cases.
+  if (this.sbm_.detectMultipleBufferedRanges() && this.started_) {
+    // Try to recover by clearing the buffer.
+    this.resync_(true /* clearBuffer */);
+    return;
+  }
+
   this.updateTimer_ = null;
 
   // Retain local copies since switch() may be called while fetching.
@@ -498,17 +508,6 @@ shaka.media.Stream.prototype.getBufferingGoal_ = function() {
  */
 shaka.media.Stream.prototype.getNext_ = function(
     currentTime, segmentIndex) {
-  // TODO: It's possible, depending on the browser's eviction policy, that the
-  // middle of a buffered time range is evicted, detect this and try to recover
-  // gracefully.
-
-  if (!COMPILED) {
-    // We should only have a single buffered time range at any given time,
-    // so assume that the next segment we need is after the last one we
-    // inserted.
-    this.sbm_.assertSingleRange();
-  }
-
   var last = this.sbm_.getLastInserted();
   return last != null ?
          (last.endTime != null ? segmentIndex.find(last.endTime) : null) :