refactor(player): Clean up firing of track change related events.

Issue shaka-project#3359

Change-Id: Ieffc0d0053521c9ff6c8feb9b795f3473afe3172

lib/player.js

@@ -217,6 +217,8 @@ goog.requireType('shaka.routing.Payload');
  *   <code>selectAudioLanguage()</code>, or <code>selectTextLanguage()</code>.
  * @property {string} type
  *   'adaptation'
+ * @property {shaka.extern.Track} oldTrack
+ * @property {shaka.extern.Track} newTrack
  * @exportDoc
  */
 
@@ -1866,10 +1868,8 @@ shaka.Player = class extends shaka.util.FakeEventTarget {
     // Pick the initial streams to play.
     const initialVariant = this.chooseVariant_();
     goog.asserts.assert(initialVariant, 'Must choose an initial variant!');
-    this.addVariantToSwitchHistory_(
-        initialVariant, /* fromAdaptation= */ true);
-    this.streamingEngine_.switchVariant(
-        initialVariant, /* clearBuffer= */ false, /* safeMargin= */ 0);
+    this.switchVariant_(initialVariant, /* fromAdaptation= */ true,
+        /* clearBuffer= */ false, /* safeMargin= */ 0);
 
     // Decide if text should be shown automatically.
     const initialTextStream = this.chooseTextStream_();
@@ -1907,8 +1907,10 @@ shaka.Player = class extends shaka.util.FakeEventTarget {
     this.filterManifestByCurrentVariant_();
     // Dispatch a 'trackschanged' event now that all initial filtering is done.
     this.onTracksChanged_();
+
     // Since the first streams just became active, send an adaptation event.
-    this.onAdaptation_();
+    this.onAdaptation_(null,
+        shaka.util.StreamUtils.variantToTrack(initialVariant));
 
     // Now that we've filtered out variants that aren't compatible with the
     // active one, update abr manager with filtered variants.
@@ -3575,36 +3577,34 @@ shaka.Player = class extends shaka.util.FakeEventTarget {
           new shaka.media.PreferenceBasedCriteria(language, role || '',
           /* channelCount= */ 0, /* label= */ '');
 
-      if (!this.config_.abr.enabled) {
-        const diff = (a, b) => {
-          if (!a.video && !b.video) {
-            return 0;
-          } else if (!a.video || !b.video) {
-            return Infinity;
-          } else {
-            return Math.abs((a.video.height || 0) - (b.video.height || 0)) +
+      const diff = (a, b) => {
+        if (!a.video && !b.video) {
+          return 0;
+        } else if (!a.video || !b.video) {
+          return Infinity;
+        } else {
+          return Math.abs((a.video.height || 0) - (b.video.height || 0)) +
                 Math.abs((a.video.width || 0) - (b.video.width || 0));
-          }
-        };
+        }
+      };
         // Find the variant whose size is closest to the active variant.  This
         // ensures we stay at about the same resolution when just changing the
         // language/role.
-        const active = this.streamingEngine_.getCurrentVariant();
-        const set =
+      const active = this.streamingEngine_.getCurrentVariant();
+      const set =
             this.currentAdaptationSetCriteria_.create(this.manifest_.variants);
-        let bestVariant = null;
-        for (const curVariant of set.values()) {
-          if (!bestVariant ||
+      let bestVariant = null;
+      for (const curVariant of set.values()) {
+        if (!bestVariant ||
               diff(bestVariant, active) > diff(curVariant, active)) {
-            bestVariant = curVariant;
-          }
-        }
-        if (bestVariant) {
-          const track = shaka.util.StreamUtils.variantToTrack(bestVariant);
-          this.selectVariantTrack(track, /* clearBuffer= */ true);
-          return;
+          bestVariant = curVariant;
         }
       }
+      if (bestVariant) {
+        const track = shaka.util.StreamUtils.variantToTrack(bestVariant);
+        this.selectVariantTrack(track, /* clearBuffer= */ true);
+        return;
+      }
 
       // If we haven't switched yet, just use ABR to find a new track.
       this.chooseVariantAndSwitch_();
@@ -4941,9 +4941,6 @@ shaka.Player = class extends shaka.util.FakeEventTarget {
     if (chosenVariant) {
       this.switchVariant_(chosenVariant, /* fromAdaptation= */ true,
           /* clearBuffers= */ true, /* safeMargin= */ 0);
-      // Send an adaptation event so that the UI can show the new
-      // language/tracks.
-      this.onAdaptation_();
     }
   }
 
@@ -4969,8 +4966,14 @@ shaka.Player = class extends shaka.util.FakeEventTarget {
       oldTrack = shaka.util.StreamUtils.variantToTrack(currentVariant);
     }
     const newTrack = shaka.util.StreamUtils.variantToTrack(variant);
-    // Dispatch a 'variantchanged' event
-    this.onVariantChanged_(oldTrack, newTrack);
+
+    if (fromAdaptation) {
+      // Dispatch an 'adaptation' event
+      this.onAdaptation_(oldTrack, newTrack);
+    } else {
+      // Dispatch a 'variantchanged' event
+      this.onVariantChanged_(oldTrack, newTrack);
+    }
   }
 
   /**
@@ -5108,19 +5111,23 @@ shaka.Player = class extends shaka.util.FakeEventTarget {
       return;
     }
 
-    this.addVariantToSwitchHistory_(variant, /* fromAdaptation= */ true);
-    this.streamingEngine_.switchVariant(variant, clearBuffer, safeMargin);
-    this.onAdaptation_();
+    this.switchVariant_(variant, /* fromAdaptation= */ true,
+        clearBuffer, safeMargin);
   }
 
   /**
    * Dispatches an 'adaptation' event.
+   * @param {?shaka.extern.Track} from
+   * @param {shaka.extern.Track} to
    * @private
    */
-  onAdaptation_() {
+  onAdaptation_(from, to) {
     // Delay the 'adaptation' event so that StreamingEngine has time to absorb
     // the changes before the user tries to query it.
-    const event = this.makeEvent_(shaka.Player.EventName.Adaptation);
+    const event = this.makeEvent_(shaka.Player.EventName.Adaptation, {
+      oldTrack: from,
+      newTrack: to,
+    });
     this.delayDispatchEvent_(event);
   }