Fix fast quality change for alternate audio (#1046)

* Fix fast quality change for alternate audio
* Don't reset audio loader in fast quality change as it resets on media change

src/master-playlist-controller.js

@@ -725,9 +725,7 @@ export class MasterPlaylistController extends videojs.EventTarget {
       this.masterPlaylistLoader_.media(media);
 
       this.mainSegmentLoader_.resetLoader();
-      if (this.audiosegmentloader_) {
-        this.audioSegmentLoader_.resetLoader();
-      }
+      // don't need to reset audio as it is reset when media changes
     }
   }
 

test/master-playlist-controller.test.js

@@ -214,6 +214,49 @@ QUnit.test('does not resync the segmentLoader when no fast quality change occurs
     assert.equal(this.player.tech_.hls.stats.bandwidth, 4194304, 'default bandwidth');
   });
 
+QUnit.test('fast quality change resyncs audio segment loader', function(assert) {
+  this.requests.length = 0;
+  this.player = createPlayer();
+  this.player.src({
+    src: 'alternate-audio-multiple-groups.m3u8',
+    type: 'application/vnd.apple.mpegurl'
+  });
+
+  const masterPlaylistController = this.player.tech_.hls.masterPlaylistController_;
+
+  masterPlaylistController.selectPlaylist = () => {
+    return masterPlaylistController.master().playlists[0];
+  };
+
+  // master
+  this.standardXHRResponse(this.requests.shift());
+  // media
+  this.standardXHRResponse(this.requests.shift());
+
+  masterPlaylistController.mediaSource.trigger('sourceopen');
+
+  this.player.audioTracks()[0].enabled = true;
+
+  let resets = 0;
+
+  masterPlaylistController.audioSegmentLoader_.resetLoader = () => resets++;
+  masterPlaylistController.fastQualityChange_();
+  assert.equal(resets, 0, 'does not reset the audio segment loader when media same');
+
+  // force different media
+  masterPlaylistController.selectPlaylist = () => {
+    return masterPlaylistController.master().playlists[1];
+  };
+
+  assert.equal(this.requests.length, 1, 'one request');
+  masterPlaylistController.fastQualityChange_();
+  assert.equal(this.requests.length, 2, 'added a request for new media');
+  assert.equal(resets, 0, 'does not reset the audio segment loader yet');
+  // new media request
+  this.standardXHRResponse(this.requests[1]);
+  assert.equal(resets, 1, 'resets the audio segment loader when media changes');
+});
+
 QUnit.test('if buffered, will request second segment byte range', function(assert) {
   this.requests.length = 0;
   this.player.src({

utils/manifest/alternate-audio-multiple-groups.m3u8

@@ -0,0 +1,8 @@
+#EXTM3U
+#EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID="audio",LANGUAGE="eng",NAME="English",AUTOSELECT=YES, DEFAULT=YES,URI="eng/prog_index.m3u8"
+#EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID="audio-hi",LANGUAGE="eng",NAME="English",AUTOSELECT=YES, DEFAULT=YES,URI="eng/prog_index.m3u8"
+
+#EXT-X-STREAM-INF:PROGRAM-ID=1,BANDWIDTH=195023,CODECS="avc1.42e00a,mp4a.40.2",AUDIO="audio"
+lo/prog_index.m3u8
+#EXT-X-STREAM-INF:PROGRAM-ID=1,BANDWIDTH=591680,CODECS="avc1.42e01e,mp4a.40.2",AUDIO="audio-hi"
+hi/prog_index.m3u8