fix(player): Fix resolution changes with lang change.

Now, when changing audio languages, we'll try to stick with the same
resolution we were at before.  This only happens with ABR disabled
since ABR will switch resolutions anyway.

Fixes shaka-project#3262
Closes shaka-project#3288

Change-Id: Ie4e529ad4ab942d74ae46318c605b45b8a07123b

lib/player.js

@@ -3541,6 +3541,38 @@ 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)) +
+                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 =
+            this.currentAdaptationSetCriteria_.create(this.manifest_.variants);
+        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;
+        }
+      }
+
+      // If we haven't switched yet, just use ABR to find a new track.
       this.chooseVariantAndSwitch_();
     } else if (this.video_ && this.video_.audioTracks) {
       const audioTracks = Array.from(this.video_.audioTracks);

test/player_unit.js

@@ -1727,6 +1727,22 @@ describe('Player', () => {
       expect(getActiveVariantTrack().audioRoles).toEqual([]);
     });
 
+    // https://github.com/google/shaka-player/issues/3262
+    it('selectAudioLanguage() doesn\'t change resolution', () => {
+      player.configure('abr.enabled', false);
+      abrManager.chooseIndex = 1;
+      const lowResEn =
+          variantTracks.filter((t) => t.language == 'en' && t.height == 200)[0];
+      player.selectVariantTrack(lowResEn);
+
+      // Switching to 'es' should keep the low-res stream and not choose the
+      // high-res version.
+      player.selectAudioLanguage('es');
+      const lowResEs =
+          variantTracks.filter((t) => t.language == 'es' && t.height == 200)[0];
+      expect(getActiveVariantTrack().id).toBe(lowResEs.id);
+    });
+
     it('selectTextLanguage() does not change selected variant track', () => {
       // This came up in a custom application that allows to select
       // from all tracks regardless of selected language.