Fix playback of multi-Period embedded text content.

Since embedded text tracks are not "real" tracks, we need to ignore them
when handling Period transitions.  This ensures that the other streams
will handle the transition instead of waiting for the text stream to get
updated.

Fixes #2075
Fixes #2094

Change-Id: I2c7c92cb04795edb3f7695677ee6745bad3f4471

lib/media/streaming_engine.js

@@ -1339,11 +1339,7 @@ shaka.media.StreamingEngine.prototype.update_ = function(mediaState) {
   // If it's a text stream and the original id starts with 'CC', it's CEA
   // closed captions. Do not schedule update for closed captions text
   // mediastate, since closed captions are embedded in video streams.
-  const isCaptionState = (state) => {
-    return state.type == ContentType.TEXT &&
-        state.stream.mimeType == shaka.util.MimeUtils.CLOSED_CAPTION_MIMETYPE;
-  };
-  if (isCaptionState(mediaState)) {
+    if (shaka.media.StreamingEngine.isEmbeddedText_(mediaState)) {
     this.playerInterface_.mediaSourceEngine.setSelectedClosedCaptionId(
         mediaState.stream.originalId || '');
     return null;
@@ -1443,7 +1439,9 @@ shaka.media.StreamingEngine.prototype.update_ = function(mediaState) {
   mediaStates.forEach((otherState) => {
     // Do not consider embedded captions in this calculation.  It could lead
     // to hangs in streaming.
-    if (isCaptionState(otherState)) return;
+      if (shaka.media.StreamingEngine.isEmbeddedText_(otherState)) {
+        return;
+      }
 
     const timeNeeded = this.getTimeNeeded_(otherState, presentationTime);
     minTimeNeeded = Math.min(minTimeNeeded, timeNeeded);
@@ -2199,13 +2197,15 @@ shaka.media.StreamingEngine.prototype.handlePeriodTransition_ = function(
   goog.asserts.assert(
       mediaStates.every(function(ms) {
         return ms.needPeriodIndex == needPeriodIndex || ms.hasError ||
-            !shaka.media.StreamingEngine.isIdle_(ms);
+            !shaka.media.StreamingEngine.isIdle_(ms) ||
+            shaka.media.StreamingEngine.isEmbeddedText_(ms);
       }),
       'All MediaStates should need the same Period or be performing updates.');
 
   // Only call onChooseStreams() when all MediaStates need the same Period.
   let needSamePeriod = mediaStates.every(function(ms) {
-    return ms.needPeriodIndex == needPeriodIndex;
+    return ms.needPeriodIndex == needPeriodIndex ||
+        shaka.media.StreamingEngine.isEmbeddedText_(ms);
   });
   if (!needSamePeriod) {
     shaka.log.debug(
@@ -2239,6 +2239,10 @@ shaka.media.StreamingEngine.prototype.handlePeriodTransition_ = function(
     let allReady = mediaStates.every(function(ms) {
       let isIdle = shaka.media.StreamingEngine.isIdle_(ms);
       let currentPeriodIndex = this.findPeriodContainingStream_(ms.stream);
+      if (shaka.media.StreamingEngine.isEmbeddedText_(ms)) {
+        // Embedded text tracks don't do Period transitions.
+        return true;
+      }
       return isIdle && ms.needPeriodIndex == needPeriodIndex &&
           currentPeriodIndex != needPeriodIndex;
     }.bind(this));
@@ -2325,6 +2329,18 @@ shaka.media.StreamingEngine.prototype.handlePeriodTransition_ = function(
 };
 
 
+/**
+ * @param {shaka.media.StreamingEngine.MediaState_} mediaState
+ * @return {boolean}
+ * @private
+ */
+shaka.media.StreamingEngine.isEmbeddedText_ = function(mediaState) {
+  const MimeUtils = shaka.util.MimeUtils;
+  return mediaState.type == shaka.util.ManifestParserUtils.ContentType.TEXT &&
+      mediaState.stream.mimeType == MimeUtils.CLOSED_CAPTION_MIMETYPE;
+};
+
+
 /**
  * @param {shaka.media.StreamingEngine.MediaState_} mediaState
  * @return {boolean} True if the given MediaState is idle; otherwise, return