fix(DASH): Fix bad error on DASH DAI (#6047)

Fixes #6010

lib/util/periods.js

@@ -790,11 +790,34 @@ shaka.util.PeriodCombiner = class {
         for (const codec of match.codecs.split(',')) {
           codecs.add(codec);
         }
-        outputStream.codecs = Array.from(codecs).join(',');
+        const PeriodCombiner = shaka.util.PeriodCombiner;
+        outputStream.codecs = PeriodCombiner.filterDuplicateCodecs_(
+            Array.from(codecs)).join(',');
       }
     }
   }
 
+  /**
+   * @param {!Array.<string>} codecs
+   * @return {!Array.<string>} codecs
+   * @private
+   */
+  static filterDuplicateCodecs_(codecs) {
+    // Filter out duplicate codecs.
+    const seen = new Set();
+    const ret = [];
+    for (const codec of codecs) {
+      const shortCodec = shaka.util.MimeUtils.getCodecBase(codec);
+      if (!seen.has(shortCodec)) {
+        ret.push(codec);
+        seen.add(shortCodec);
+      } else {
+        shaka.log.debug('Ignoring duplicate codec');
+      }
+    }
+    return ret;
+  }
+
   /**
    * Clone a Stream to make an output Stream for combining others across
    * periods.