Don't clear buffer if switching to the same stream.

Several variants may have the same audio or video stream.
When switching variants we will only update a stream if it actually
changed. This allows to keep previously buffered content if
only one of the variant's streams changed, but not the other.

Closes #693.

Change-Id: If63c9a3a95c5c48007023224457b291814f14c0c

lib/player.js

@@ -1153,6 +1153,7 @@ shaka.Player.prototype.selectVariantTrack = function(track, opt_clearBuffer) {
 
   var period = this.streamingEngine_.getCurrentPeriod();
   var variant = StreamUtils.findVariantForTrack(period, track);
+  var activeStreams = this.streamingEngine_.getActiveStreams();
   if (variant) {
     // Double check that the track is allowed to be played.
     // The track list should only contain playable variants,
@@ -1165,8 +1166,19 @@ shaka.Player.prototype.selectVariantTrack = function(track, opt_clearBuffer) {
                       '" because it is restricted.');
       return;
     }
-    if (variant.audio) streamsToSwitch[ContentType.AUDIO] = variant.audio;
-    if (variant.video) streamsToSwitch[ContentType.VIDEO] = variant.video;
+
+    if (variant.audio) {
+      // Update active streams even if we're not switching
+      // in case active streams haven't been set up yet.
+      this.updateActiveStreams_(variant.audio);
+      if (variant.audio != activeStreams[ContentType.AUDIO])
+        streamsToSwitch[ContentType.AUDIO] = variant.audio;
+    }
+    if (variant.video) {
+      this.updateActiveStreams_(variant.video);
+      if (variant.video != activeStreams[ContentType.VIDEO])
+        streamsToSwitch[ContentType.VIDEO] = variant.video;
+    }
   }
 
   // Add entries to the history.
@@ -1176,7 +1188,6 @@ shaka.Player.prototype.selectVariantTrack = function(track, opt_clearBuffer) {
 
   // Save current text stream to ensure that it doesn't get overridden
   // by a default one inside shaka.Player.configure()
-  var activeStreams = this.streamingEngine_.getActiveStreams();
   var currentTextStream = activeStreams[ContentType.TEXT];
 
   if (currentTextStream) {
@@ -1519,6 +1530,15 @@ shaka.Player.prototype.addToSwitchHistory_ = function(stream, fromAdaptation) {
     fromAdaptation: fromAdaptation
   });
 
+  this.updateActiveStreams_(stream);
+};
+
+
+/**
+ * @param {!shakaExtern.Stream} stream
+ * @private
+ */
+shaka.Player.prototype.updateActiveStreams_ = function(stream) {
   goog.asserts.assert(this.manifest_, 'Must not be destroyed');
   var periodIndex =
       shaka.util.StreamUtils.findPeriodContainingStream(this.manifest_, stream);

test/player_unit.js

@@ -879,6 +879,48 @@ describe('Player', function() {
           .toHaveBeenCalledWith(ContentType.VIDEO, variant.video, false);
     });
 
+    it('doesn\'t switch audio if old and new variants ' +
+       'have the same audio track', function() {
+          chooseStreams();
+          canSwitch();
+
+          var period = manifest.periods[0];
+          var variant1 = period.variants[0];
+          var variant2 = period.variants[1];
+          expect(variant1.audio).toEqual(variant2.audio);
+
+          player.selectVariantTrack(variantTracks[0]);
+          streamingEngine.switch.calls.reset();
+
+          player.selectVariantTrack(variantTracks[1]);
+
+          expect(streamingEngine.switch).toHaveBeenCalledWith(
+              ContentType.VIDEO, variant2.video, false);
+          expect(streamingEngine.switch).not.toHaveBeenCalledWith(
+              ContentType.AUDIO, variant2.audio, false);
+        });
+
+    it('doesn\'t switch video if old and new variants ' +
+       'have the same video track', function() {
+          chooseStreams();
+          canSwitch();
+
+          var period = manifest.periods[0];
+          var variant1 = period.variants[0];
+          var variant2 = period.variants[2];
+          expect(variant1.video).toEqual(variant2.video);
+
+          player.selectVariantTrack(variantTracks[0]);
+          streamingEngine.switch.calls.reset();
+
+          player.selectVariantTrack(variantTracks[2]);
+
+          expect(streamingEngine.switch).toHaveBeenCalledWith(
+              ContentType.AUDIO, variant2.audio, false);
+          expect(streamingEngine.switch).not.toHaveBeenCalledWith(
+              ContentType.VIDEO, variant2.video, false);
+        });
+
     it('still switches streams if called during startup', function() {
       player.selectVariantTrack(variantTracks[1]);
       expect(streamingEngine.switch).not.toHaveBeenCalled();
@@ -896,13 +938,13 @@ describe('Player', function() {
     it('still switches streams if called while switching Periods', function() {
       chooseStreams();
 
-      player.selectVariantTrack(variantTracks[1]);
+      player.selectVariantTrack(variantTracks[3]);
       expect(streamingEngine.switch).not.toHaveBeenCalled();
 
       canSwitch();
 
       var period = manifest.periods[0];
-      var variant = period.variants[1];
+      var variant = period.variants[3];
       expect(streamingEngine.switch)
           .toHaveBeenCalledWith(ContentType.AUDIO, variant.audio, false);
       expect(streamingEngine.switch)
@@ -927,9 +969,9 @@ describe('Player', function() {
 
       streamingEngine.switch.calls.reset();
 
-      var variant = period.variants[1];
-      expect(variantTracks[1].id).toBe(variant.id);
-      player.selectVariantTrack(variantTracks[1]);
+      var variant = period.variants[2];
+      expect(variantTracks[2].id).toBe(variant.id);
+      player.selectVariantTrack(variantTracks[2]);
       expect(streamingEngine.switch)
           .toHaveBeenCalledWith(ContentType.TEXT, textStream, true);
       expect(streamingEngine.switch)
@@ -1254,7 +1296,7 @@ describe('Player', function() {
       });
 
       it('includes selectVariantTrack choices', function() {
-        var track = player.getVariantTracks()[1];
+        var track = player.getVariantTracks()[3];
         player.selectVariantTrack(track);
 
         var period = manifest.periods[0];