fix(Tizen): Work around misreported AC-3 support on Tizen

Some Tizen devices seem to misreport AC-3 support.  This works around
the issue by falling back to EC-3, which seems to be supported on the
same devices and be correctly reported in all cases we have observed.

Closes #2989

Change-Id: I80f20ba796df29858728b19f8a9f6c1712c9556d

lib/media/drm_engine.js

@@ -576,12 +576,25 @@ shaka.media.DrmEngine = class {
     // first MIME type even if the others are supported.  To work around this,
     // we say that Edge supports everything.
     //
-    // See: https://bit.ly/2IcEgv0 and Issue #1495
+    // See https://github.com/google/shaka-player/issues/1495 for details.
     if (shaka.util.Platform.isEdge()) {
       return true;
     }
 
-    return this.supportedTypes_.has(contentType.toLowerCase());
+    contentType = contentType.toLowerCase();
+
+    if (shaka.util.Platform.isTizen() &&
+        contentType.includes('codecs="ac-3"')) {
+      // Some Tizen devices seem to misreport AC-3 support.  This works around
+      // the issue, by falling back to EC-3, which seems to be supported on the
+      // same devices and be correctly reported in all cases we have observed.
+      // See https://github.com/google/shaka-player/issues/2989 for details.
+      const fallback = contentType.replace('ac-3', 'ec-3');
+      return this.supportedTypes_.has(contentType) ||
+             this.supportedTypes_.has(fallback);
+    }
+
+    return this.supportedTypes_.has(contentType);
   }
 
   /**
@@ -715,6 +728,16 @@ shaka.media.DrmEngine = class {
 
         const mimeType = shaka.util.MimeUtils.getFullType(
             stream.mimeType, stream.codecs);
+        let fallbackMimeType = null;
+
+        if (stream.codecs.toLowerCase() == 'ac-3' &&
+            shaka.util.Platform.isTizen()) {
+          // Some Tizen devices seem to misreport AC-3 support, but correctly
+          // report EC-3 support.  So query EC-3 as a fallback for AC-3.
+          // See https://github.com/google/shaka-player/issues/2989 for details.
+          fallbackMimeType = shaka.util.MimeUtils.getFullType(
+              stream.mimeType, 'ec-3');
+        }
 
         for (const info of stream.drmInfos) {
           const config = configs.get(info.keySystem);
@@ -747,6 +770,22 @@ shaka.media.DrmEngine = class {
           } else {
             config.videoCapabilities.push(capability);
           }
+
+          // This is how we work around some misbehaving platforms by adding
+          // synthetic capability records using a fallback MIME type.
+          if (fallbackMimeType) {
+            /** @type {MediaKeySystemMediaCapability} */
+            const fallbackCapability = {
+              robustness: robustness || '',
+              contentType: fallbackMimeType,
+            };
+
+            if (stream.type == ContentType.AUDIO) {
+              config.audioCapabilities.push(fallbackCapability);
+            } else {
+              config.videoCapabilities.push(fallbackCapability);
+            }
+          }
         } // for (const info of stream.drmInfos)
       } // for (const stream of [audio, video])
     }  // for (const variant of variants)