fix(HLS): Don't do sequence mode workaround unless there's a text stream

lib/media/media_source_engine.js

@@ -133,6 +133,9 @@ shaka.media.MediaSourceEngine = class {
     /** @private {boolean} */
     this.ignoreManifestTimestampsInSegmentsMode_ = false;
 
+    /** @private {boolean} */
+    this.hasTextStreams_ = true;
+
     /** @private {!shaka.util.PublicPromise.<number>} */
     this.textSequenceModeOffset_ = new shaka.util.PublicPromise();
   }
@@ -369,18 +372,22 @@ shaka.media.MediaSourceEngine = class {
    *   segment durations being out of sync with segment durations. In other
    *   words, assume that there are no gaps in the segments when appending
    *   to the SourceBuffer, even if the manifest and segment times disagree.
+   * @param {string=} hasTextStreams
+   *   Indicates if the manifest has text streams.
    *
    * @return {!Promise}
    */
   async init(streamsByType, sequenceMode=false,
       manifestType=shaka.media.ManifestParser.UNKNOWN,
-      ignoreManifestTimestampsInSegmentsMode=false) {
+      ignoreManifestTimestampsInSegmentsMode=false,
+      hasTextStreams=true) {
     await this.mediaSourceOpen_;
 
     this.sequenceMode_ = sequenceMode;
     this.manifestType_ = manifestType;
     this.ignoreManifestTimestampsInSegmentsMode_ =
       ignoreManifestTimestampsInSegmentsMode;
+    this.hasTextStreams_ = hasTextStreams;
 
     for (const contentType of streamsByType.keys()) {
       const stream = streamsByType.get(contentType);
@@ -447,6 +454,13 @@ shaka.media.MediaSourceEngine = class {
             'expected \'open\'');
       }
 
+      if (this.sequenceMode_ && !this.hasTextStreams_) {
+        // There's no text streams, so we can set sequence mode early instead
+        // of setting it after the first segment is appended in appendBuffer_.
+        sourceBuffer.mode =
+            shaka.media.MediaSourceEngine.SourceBufferMode_.SEQUENCE;
+      }
+
       this.eventManager_.listen(
           sourceBuffer, 'error',
           () => this.onError_(contentType));

lib/media/streaming_engine.js

@@ -831,6 +831,7 @@ shaka.media.StreamingEngine = class {
         this.manifest_.sequenceMode,
         this.manifest_.type,
         this.manifest_.ignoreManifestTimestampsInSegmentsMode,
+        this.manifest_.textStreams.length > 0
     );
     this.destroyer_.ensureNotDestroyed();