Add text stream sequence id

lib/media/streaming_engine.js

@@ -79,6 +79,9 @@ shaka.media.StreamingEngine = class {
     /** @private {?shaka.extern.Stream} */
     this.currentTextStream_ = null;
 
+    /** @private {number} */
+    this.textStreamSequenceId_ = 0;
+
     /** @private {boolean} */
     this.parsedPrftEventRaised_ = false;
 
@@ -235,16 +238,18 @@ shaka.media.StreamingEngine = class {
    * @param {shaka.extern.Stream} stream
    * @private
    */
-  loadNewTextStream_(stream) {
+  async loadNewTextStream_(stream) {
     const ContentType = shaka.util.ManifestParserUtils.ContentType;
     goog.asserts.assert(!this.mediaStates_.has(ContentType.TEXT),
         'Should not call loadNewTextStream_ while streaming text!');
+    this.textStreamSequenceId_++;
+    const currentSequenceId = this.textStreamSequenceId_;
 
     try {
       // Clear MediaSource's buffered text, so that the new text stream will
       // properly replace the old buffered text.
       // TODO: Should this happen in unloadTextStream() instead?
-      this.playerInterface_.mediaSourceEngine.clear(ContentType.TEXT);
+      await this.playerInterface_.mediaSourceEngine.clear(ContentType.TEXT);
     } catch (error) {
       if (this.playerInterface_) {
         this.playerInterface_.onError(error);
@@ -261,7 +266,7 @@ shaka.media.StreamingEngine = class {
     const streamText =
         textDisplayer.isTextVisible() || this.config_.alwaysStreamText;
 
-    if (streamText) {
+    if (streamText && (this.textStreamSequenceId_ == currentSequenceId)) {
       const state = this.createMediaState_(stream);
       this.mediaStates_.set(ContentType.TEXT, state);
       this.scheduleUpdate_(state, 0);