Allow switching between Periods with and without text

We don't allow switching between Periods that are video+audio to
video-only because it is incompatible with MSE.  When the browser
gets to the transition, it will pause waiting for the audio buffer.

However, we should allow switching between Periods that do and do not
have text streams.

Issue #715

Change-Id: I77f3bf92681d8181c90169b8f4a15857b7d9e66d

lib/media/streaming_engine.js

@@ -207,7 +207,8 @@ shaka.media.StreamingEngine = function(
  *   waitingToFlushBuffer: boolean,
  *   clearingBuffer: boolean,
  *   recovering: boolean,
- *   hasError: boolean
+ *   hasError: boolean,
+ *   resumeAt: number
  * }}
  *
  * @description
@@ -250,6 +251,10 @@ shaka.media.StreamingEngine = function(
  * @property {boolean} hasError
  *   True indicates that the stream has encountered an error and has stopped
  *   updates.
+ * @property {number} resumeAt
+ *   An override for the time to start performing updates at.  If the playhead
+ *   is behind this time, update_() will still start fetching segments from
+ *   this time.  If the playhead is ahead of the time, this field is ignored.
  */
 shaka.media.StreamingEngine.MediaState_;
 
@@ -632,10 +637,12 @@ shaka.media.StreamingEngine.prototype.seeked = function() {
  *
  * @param {!Object.<shaka.util.ManifestParserUtils.ContentType,
                     shakaExtern.Stream>} streamsByType
+ * @param {number=} opt_resumeAt
  * @return {!Promise}
  * @private
  */
-shaka.media.StreamingEngine.prototype.initStreams_ = function(streamsByType) {
+shaka.media.StreamingEngine.prototype.initStreams_ = function(
+    streamsByType, opt_resumeAt) {
   var MapUtils = shaka.util.MapUtils;
   goog.asserts.assert(this.config_,
       'StreamingEngine configure() must be called before init()!');
@@ -678,7 +685,8 @@ shaka.media.StreamingEngine.prototype.initStreams_ = function(streamsByType) {
           waitingToFlushBuffer: false,
           clearingBuffer: false,
           recovering: false,
-          hasError: false
+          hasError: false,
+          resumeAt: opt_resumeAt || 0
         };
         this.scheduleUpdate_(this.mediaStates_[type], 0);
       }
@@ -904,6 +912,7 @@ shaka.media.StreamingEngine.prototype.update_ = function(mediaState) {
   // Get the next timestamp we need.
   var timeNeeded = this.getTimeNeeded_(mediaState, playheadTime);
   shaka.log.v2(logPrefix, 'timeNeeded=' + timeNeeded);
+  mediaState.resumeAt = 0;
 
   var currentPeriodIndex = this.findPeriodContainingStream_(mediaState.stream);
   var needPeriodIndex = this.findPeriodContainingTime_(timeNeeded);
@@ -1013,7 +1022,7 @@ shaka.media.StreamingEngine.prototype.getTimeNeeded_ = function(
   //      of the timestamps in the manifest), but we need drift free times when
   //      comparing times against presentation and Period boundaries.
   if (!mediaState.lastStream || !mediaState.lastSegmentReference) {
-    return playheadTime;
+    return Math.max(playheadTime, mediaState.resumeAt);
   }
 
   var lastPeriodIndex =
@@ -1703,7 +1712,7 @@ shaka.media.StreamingEngine.prototype.handlePeriodTransition_ = function(
 
     // Vet |streamsByType| before switching.
     for (var type in this.mediaStates_) {
-      if (streamsByType[type]) continue;
+      if (streamsByType[type] || type == ContentType.TEXT) continue;
 
       shaka.log.error(logPrefix,
                       'invalid Streams chosen: missing ' + type + ' Stream');
@@ -1714,8 +1723,12 @@ shaka.media.StreamingEngine.prototype.handlePeriodTransition_ = function(
     }
 
     for (var type in streamsByType) {
-      if (this.mediaStates_[type] ||
-          (type == ContentType.TEXT && this.config_.ignoreTextStreamFailures)) {
+      if (this.mediaStates_[type]) continue;
+      if (type == ContentType.TEXT) {
+        // initStreams_ will switch streams and schedule an update.
+        this.initStreams_(
+            {text: streamsByType[ContentType.TEXT]}, needPeriod.startTime);
+        delete streamsByType[type];
         continue;
       }
 
@@ -1729,8 +1742,13 @@ shaka.media.StreamingEngine.prototype.handlePeriodTransition_ = function(
 
     for (var type in this.mediaStates_) {
       var stream = streamsByType[type];
-      this.switch(type, stream, /* clearBuffer */ false);
-      this.scheduleUpdate_(this.mediaStates_[type], 0);
+      if (stream) {
+        this.switch(type, stream, /* clearBuffer */ false);
+        this.scheduleUpdate_(this.mediaStates_[type], 0);
+      } else {
+        goog.asserts.assert(type == ContentType.TEXT, 'Invalid streams chosen');
+        delete this.mediaStates_[type];
+      }
     }
 
     // We've already set up the Period so call onCanSwitch_() right now.

lib/util/error.js

@@ -504,6 +504,11 @@ shaka.util.Error.Code = {
   /**
    * The StreamingEngine called onChooseStreams() but the callback receiver
    * did not return the correct number or type of Streams.
+   *
+   * This can happen when there is multi-Period content where one Period is
+   * video+audio and another is video-only or audio-only.  We don't support this
+   * case because it is incompatible with MSE.  When the browser reaches the
+   * transition, it will pause, waiting for the audio stream.
    */
   'INVALID_STREAMS_CHOSEN': 5005,
 

test/media/streaming_engine_unit.js

@@ -712,6 +712,60 @@ describe('StreamingEngine', function() {
     expect(onStartupComplete).toHaveBeenCalled();
   });
 
+  it('plays when 1st Period doesn\'t have text streams', function() {
+    setupVod();
+    manifest.periods[0].textStreams = [];
+
+    mediaSourceEngine = new shaka.test.FakeMediaSourceEngine(segmentData);
+    createStreamingEngine();
+
+    playhead.getTime.and.returnValue(0);
+    onStartupComplete.and.callFake(setupFakeGetTime.bind(null, 0));
+    onChooseStreams.and.callFake(function(period) {
+      var chosen = defaultOnChooseStreams(period);
+      if (period == manifest.periods[0])
+        delete chosen[ContentType.TEXT];
+      return chosen;
+    });
+
+    // Here we go!
+    streamingEngine.init();
+    runTest();
+
+    expect(mediaSourceEngine.segments).toEqual({
+      audio: [true, true, true, true],
+      video: [true, true, true, true],
+      text: [false, false, true, true]
+    });
+  });
+
+  it('plays when 2nd Period doesn\'t have text streams', function() {
+    setupVod();
+    manifest.periods[1].textStreams = [];
+
+    mediaSourceEngine = new shaka.test.FakeMediaSourceEngine(segmentData);
+    createStreamingEngine();
+
+    playhead.getTime.and.returnValue(0);
+    onStartupComplete.and.callFake(setupFakeGetTime.bind(null, 0));
+    onChooseStreams.and.callFake(function(period) {
+      var chosen = defaultOnChooseStreams(period);
+      if (period == manifest.periods[1])
+        delete chosen[ContentType.TEXT];
+      return chosen;
+    });
+
+    // Here we go!
+    streamingEngine.init();
+    runTest();
+
+    expect(mediaSourceEngine.segments).toEqual({
+      audio: [true, true, true, true],
+      video: [true, true, true, true],
+      text: [true, true, false, false]
+    });
+  });
+
   describe('handles seeks (VOD)', function() {
     var onTick;
     var stub = function() {};