Add player.isAudioOnly()

This simplifies detection of audio-only content and makes the process
a little more obvious.

Closes #942

Backported to v2.1.x for issue #969

Change-Id: I89b599fb8c8915c9e1b45d2f9b81a3ac7193e5ef

demo/asset_section.js

@@ -206,13 +206,8 @@ shakaDemo.load = function() {
 
     shakaDemo.hashShouldChange_();
 
-    // Audio-only tracks have no width/height.
-    var videoTracks = player.getVariantTracks().filter(function(t) {
-      return t.videoCodec;
-    });
-
     // Set a different poster for audio-only assets.
-    if (videoTracks.length == 0) {
+    if (player.isAudioOnly()) {
       shakaDemo.localVideo_.poster = shakaDemo.audioOnlyPoster_;
     }
 

demo/receiver_app.js

@@ -127,13 +127,8 @@ ShakaReceiver.prototype.checkIdle_ = function() {
     this.idle_.style.display = 'none';
     this.cancelIdleTimer_();
 
-    // Audio-only tracks have no width/height.
-    var videoTracks = this.player_.getVariantTracks().filter(function(t) {
-      return t.videoCodec;
-    });
-
     // Set a special poster for audio-only assets.
-    if (videoTracks.length == 0) {
+    if (this.player_.isAudioOnly()) {
       this.video_.poster =
           '//shaka-player-demo.appspot.com/assets/audioOnly.gif';
     } else {

lib/player.js

@@ -988,6 +988,26 @@ shaka.Player.prototype.isInProgress = function() {
 };
 
 
+/**
+ * @return {boolean} True for audio-only content.  False otherwise.
+ * @export
+ */
+shaka.Player.prototype.isAudioOnly = function() {
+  if (!this.manifest_ || !this.manifest_.periods.length)
+    return false;
+
+  var variants = this.manifest_.periods[0].variants;
+  if (!variants.length)
+    return false;
+
+  // Note that if there are some audio-only variants and some audio-video
+  // variants, the audio-only variants are removed during filtering.
+  // Therefore if the first variant has no video, that's sufficient to say it
+  // is audio-only content.
+  return !variants[0].video;
+};
+
+
 /**
  * Get the seekable range for the current stream.
  * @return {{start: number, end: number}}

test/player_unit.js

@@ -2328,6 +2328,55 @@ describe('Player', function() {
     }).then(done);
   });
 
+  describe('isAudioOnly', function() {
+    it('detects audio-only content', function(done) {
+      // This factory recreates the parser each time, so updates to |manifest|
+      // affect the next load() call.
+      var parserFactory = function() {
+        return new shaka.test.FakeManifestParser(manifest);
+      };
+
+      // False before we've loaded anything.
+      expect(player.isAudioOnly()).toEqual(false);
+
+      manifest = new shaka.test.ManifestGenerator()
+              .addPeriod(0)
+                .addVariant(0).bandwidth(100)
+                  .addVideo(0).mime('video/mp4', 'good')
+                  .addAudio(1).mime('audio/mp4', 'good')
+              .build();
+      player.load('', 0, parserFactory).then(function() {
+        // We have audio & video tracks, so this is not audio-only.
+        expect(player.isAudioOnly()).toEqual(false);
+
+        manifest = new shaka.test.ManifestGenerator()
+                .addPeriod(0)
+                  .addVariant(0).bandwidth(100)
+                    .addVideo(0).mime('video/mp4', 'good')
+                .build();
+        return player.load('', 0, parserFactory);
+      }).then(function() {
+        // We have video-only tracks, so this is not audio-only.
+        expect(player.isAudioOnly()).toEqual(false);
+
+        manifest = new shaka.test.ManifestGenerator()
+                .addPeriod(0)
+                  .addVariant(0).bandwidth(100)
+                    .addAudio(1).mime('audio/mp4', 'good')
+                .build();
+        return player.load('', 0, parserFactory);
+      }).then(function() {
+        // We have audio-only tracks, so this is audio-only.
+        expect(player.isAudioOnly()).toEqual(true);
+
+        return player.unload();
+      }).then(function() {
+        // When we have nothing loaded, we go back to not audio-only status.
+        expect(player.isAudioOnly()).toEqual(false);
+      }).catch(fail).then(done);
+    });
+  });
+
   describe('load', function() {
     it('tolerates bandwidth of NaN, undefined, or 0', function(done) {
       // Regression test for https://github.com/google/shaka-player/issues/938