fix(DASH): Fix period combining when roles are equal (#7065)

When roles exist and are equal between tracks and periods, period
combiner matches based on that instead of looking for other
similarities. This PR addresses it & adds regression test.

lib/util/periods.js

@@ -1242,7 +1242,7 @@ shaka.util.PeriodCombiner = class {
         return true;
       } else if (candidateRoleMatches.length < bestRoleMatches.length) {
         return false;
-      } else {
+      } else if (candidate.roles.length !== best.roles.length) {
         // Both streams have the same role overlap with the outputStream
         // If this is the case, choose the stream with the fewer roles overall.
         // Streams that match best together tend to be streams with the same

test/util/periods_unit.js

@@ -1369,6 +1369,74 @@ describe('PeriodCombiner', () => {
     expect(variants[3].audio.originalId).toBe('stream2,stream2');
   });
 
+  it('Matches streams based on bandwidth when roles are equal', async () => {
+    const stream1 = makeAudioStream('en');
+    stream1.bandwidth = 192000;
+    stream1.roles = ['main'];
+    stream1.originalId = 'stream1';
+
+    const stream2 = makeAudioStream('en');
+    stream2.bandwidth = 640000;
+    stream2.roles = ['main'];
+    stream2.originalId = 'stream2';
+
+    const stream3 = makeAudioStream('en');
+    stream3.bandwidth = 192000;
+    stream3.roles = ['main'];
+    stream3.originalId = 'stream3';
+
+    const stream4 = makeAudioStream('en');
+    // make slightly different bandwidth to avoid direct match by hashing.
+    stream4.bandwidth = 639000;
+    stream4.roles = ['main'];
+    stream4.originalId = 'stream4';
+
+    /** @type {!Array.<shaka.extern.Period>} */
+    const periods = [
+      {
+        id: '1',
+        videoStreams: [
+          makeVideoStream(1080),
+        ],
+        audioStreams: [
+          stream1,
+          stream2,
+        ],
+        textStreams: [],
+        imageStreams: [],
+      },
+      {
+        id: '2',
+        videoStreams: [
+          makeVideoStream(1080),
+        ],
+        audioStreams: [
+          stream3,
+          stream4,
+        ],
+        textStreams: [],
+        imageStreams: [],
+      },
+    ];
+
+    await combiner.combinePeriods(periods, /* isDynamic= */ false);
+    const variants = combiner.getVariants();
+
+    expect(variants).toEqual(jasmine.arrayWithExactContents([
+      makeAVVariant(1080, 'en', 2, ['main']),
+      makeAVVariant(1080, 'en', 2, ['main']),
+    ]));
+
+    // We can use the originalId field to see what each track is composed of.
+    const audio1 = variants[0].audio;
+    expect(audio1.bandwidth).toBe(192000);
+    expect(audio1.originalId).toBe('stream1,stream3');
+
+    const audio2 = variants[1].audio;
+    expect(audio2.bandwidth).toBe(640000);
+    expect(audio2.originalId).toBe('stream2,stream4');
+  });
+
   it('Matches streams with mismatched roles', async () => {
     /** @type {!Array.<shaka.extern.Period>} */
     const periods = [