Allow AbrManager to clear ahead of the playhead

SimpleAbrManager will now leave 5s of video ahead of the playhead and
clear the rest when upgrading to a higher resolution.

Also smooths transitions for overlapping segments by scheduling an
abort() call to reset MediaSource internals after removing content or
changing the append window.

Related to issue #435

Change-Id: Ie036515388e1e7e4b3b8f3ab9922e3d5e7ed2627

externs/shaka/abr_manager.js

@@ -29,11 +29,25 @@
 shakaExtern.AbrManager = function() {};
 
 
+/**
+ * @typedef {function(!Object.<string, !shakaExtern.Stream>, number=)}
+ *   A callback which implementations call to switch streams.
+ *
+ *   The first argument is a map of content types to chosen streams.
+ *
+ *   The second argument is an optional number of seconds of content to leave in
+ *   the buffer ahead of the playhead.  Anything beyond that will be cleared.
+ *   This is used to make a resolution change take effect sooner, at the cost of
+ *   wasting previously downloaded segments.  If undefined, nothing will be
+ *   cleared.
+ */
+shakaExtern.AbrManager.SwitchCallback;
+
+
 /**
  * Initializes the AbrManager.
  *
- * @param {function(!Object.<string, !shakaExtern.Stream>)} switchCallback
- *     A callback which implementations call to switch streams.
+ * @param {shakaExtern.AbrManager.SwitchCallback} switchCallback
  * @exportDoc
  */
 shakaExtern.AbrManager.prototype.init = function(switchCallback) {};

lib/abr/simple_abr_manager.js

@@ -32,7 +32,7 @@ goog.require('shaka.log');
  * @export
  */
 shaka.abr.SimpleAbrManager = function() {
-  /** @private {?function(!Object.<string, !shakaExtern.Stream>)} */
+  /** @private {?shakaExtern.AbrManager.SwitchCallback} */
   this.switch_ = null;
 
   /** @private {boolean} */
@@ -105,6 +105,16 @@ shaka.abr.SimpleAbrManager.BANDWIDTH_UPGRADE_TARGET_ = 0.85;
 shaka.abr.SimpleAbrManager.BANDWIDTH_DOWNGRADE_TARGET_ = 0.95;
 
 
+/**
+ * The number of seconds of content to leave in buffer ahead of the playhead
+ * when upgrading video.  This makes video upgrades visible sooner.
+ *
+ * @private
+ * @const {number}
+ */
+shaka.abr.SimpleAbrManager.UPGRADE_LEAVE_IN_BUFFER_ = 5;
+
+
 /** @override */
 shaka.abr.SimpleAbrManager.prototype.stop = function() {
   this.switch_ = null;
@@ -206,12 +216,18 @@ shaka.abr.SimpleAbrManager.prototype.suggestStreams_ = function() {
   var oldVideo = this.streamsByType_['video'];
   var chosen = this.chooseStreams_();
   if (chosen['audio'] != oldAudio || chosen['video'] != oldVideo) {
+    var opt_leaveInBuffer = undefined;
+    if (oldVideo && chosen.video &&
+        chosen.video.bandwidth > oldVideo.bandwidth) {
+      opt_leaveInBuffer = shaka.abr.SimpleAbrManager.UPGRADE_LEAVE_IN_BUFFER_;
+    }
     var currentBandwidthKbps =
         Math.round(this.bandwidthEstimator_.getBandwidthEstimate() / 1000.0);
     shaka.log.debug(
         'Calling switch_()...',
-        'bandwidth=' + currentBandwidthKbps + ' kbps');
-    this.switch_(chosen);
+        'bandwidth=' + currentBandwidthKbps + ' kbps',
+        'opt_leaveInBuffer=', opt_leaveInBuffer);
+    this.switch_(chosen, opt_leaveInBuffer);
   }
 };
 

lib/media/media_source_engine.js

@@ -379,9 +379,17 @@ shaka.media.MediaSourceEngine.prototype.remove =
   if (contentType == 'text') {
     return this.textEngine_.remove(startTime, endTime);
   }
-  return this.enqueueOperation_(
-      contentType,
-      this.remove_.bind(this, contentType, startTime, endTime));
+  return Promise.all([
+    this.enqueueOperation_(
+        contentType,
+        this.remove_.bind(this, contentType, startTime, endTime)),
+    // Queue an abort() to help MSE splice together overlapping segments.
+    // We may have overlap if part of an already-decoded segment is removed
+    // and replaced by another representation, as happens during adaptation.
+    this.enqueueOperation_(
+        contentType,
+        this.abort_.bind(this, contentType))
+  ]);
 };
 
 
@@ -437,9 +445,17 @@ shaka.media.MediaSourceEngine.prototype.setAppendWindowEnd = function(
     this.textEngine_.setAppendWindowEnd(appendWindowEnd);
     return Promise.resolve();
   }
-  return this.enqueueOperation_(
-      contentType,
-      this.setAppendWindowEnd_.bind(this, contentType, appendWindowEnd));
+  return Promise.all([
+    // Queue an abort() to help MSE splice together overlapping segments.
+    // We set appendWindowEnd when we change periods in DASH content, and the
+    // period transition may result in overlap.
+    this.enqueueOperation_(
+        contentType,
+        this.abort_.bind(this, contentType)),
+    this.enqueueOperation_(
+        contentType,
+        this.setAppendWindowEnd_.bind(this, contentType, appendWindowEnd))
+  ]);
 };
 
 
@@ -483,6 +499,16 @@ shaka.media.MediaSourceEngine.prototype.setDuration = function(duration) {
 };
 
 
+/**
+ * Get the current MediaSource duration.
+ *
+ * @return {number}
+ */
+shaka.media.MediaSourceEngine.prototype.getDuration = function() {
+  return this.mediaSource_.duration;
+};
+
+
 /**
  * Append data to the SourceBuffer.
  * @param {string} contentType
@@ -506,11 +532,41 @@ shaka.media.MediaSourceEngine.prototype.append_ =
  */
 shaka.media.MediaSourceEngine.prototype.remove_ =
     function(contentType, startTime, endTime) {
+  if (endTime <= startTime) {
+    // Ignore removal of inverted or empty ranges.
+    // Fake 'updateend' event to resolve the operation.
+    this.onUpdateEnd_(contentType);
+    return;
+  }
+
   // This will trigger an 'updateend' event.
   this.sourceBuffers_[contentType].remove(startTime, endTime);
 };
 
 
+/**
+ * Call abort() on the SourceBuffer.
+ * This resets MSE's last_decode_timestamp on all track buffers, which should
+ * trigger the splicing logic for overlapping segments.
+ * @param {string} contentType
+ * @private
+ */
+shaka.media.MediaSourceEngine.prototype.abort_ = function(contentType) {
+  // Save the append window end, which is reset on abort().
+  var appendWindowEnd = this.sourceBuffers_[contentType].appendWindowEnd;
+
+  // This will not trigger an 'updateend' event, since nothing is happening.
+  // This is only to reset MSE internals, not to abort an actual operation.
+  this.sourceBuffers_[contentType].abort();
+
+  // Restore the append window end.
+  this.sourceBuffers_[contentType].appendWindowEnd = appendWindowEnd;
+
+  // Fake 'updateend' event to resolve the operation.
+  this.onUpdateEnd_(contentType);
+};
+
+
 /**
  * Set the SourceBuffer's timestamp offset.
  * @param {string} contentType