Revised check for cast namespace with try/catch rather than deal with…

… window.cast / cast namespace intermittent availability.

lib/polyfill/media_capabilities.js

@@ -105,30 +105,20 @@ shaka.polyfill.MediaCapabilities = class {
         return res;
       }
       // Use 'MediaSource.isTypeSupported' to check if the stream is supported.
+      // Cast platforms will additionally check canDisplayType(), which
+      // accepts extended MIME type parameters.
+      // See: https://github.com/shaka-project/shaka-player/issues/4726
       if (videoConfig) {
         const contentType = videoConfig.contentType;
         let isSupported = MediaSource.isTypeSupported(contentType);
         if (shaka.util.Platform.isChromecast()) {
-          // Cast platforms will additionally check canDisplayType(), which
-          // accepts extended MIME type parameters.
-          // There will be at most 2 calls:
-          // - The first call determines the stability of
-          // the API by validating a contentType input limited only to MIME type
-          // and codecs is identical to MediaSource.isTypeSupported().
-          // - If the same result is observed, a second call will be executed
-          // containing resolution, frame rate, and transfer function support.
-          // See: https://github.com/shaka-project/shaka-player/issues/4726
-          if (isSupported ===
-              shaka.polyfill.MediaCapabilities.canCastDisplayType_({
-                contentType})) {
-            isSupported = shaka.polyfill.MediaCapabilities.canCastDisplayType_({
-              contentType,
-              width: videoConfig.width,
-              height: videoConfig.height,
-              frameRate: videoConfig.framerate,
-              transferFunction: videoConfig.transferFunction,
-            });
-          }
+          isSupported = shaka.polyfill.MediaCapabilities.canCastDisplayType_({
+            contentType,
+            width: videoConfig.width,
+            height: videoConfig.height,
+            frameRate: videoConfig.framerate,
+            transferFunction: videoConfig.transferFunction,
+          });
         }
         if (!isSupported) {
           return res;
@@ -269,14 +259,6 @@ shaka.polyfill.MediaCapabilities = class {
     frameRate = undefined,
     transferFunction = undefined,
   }) {
-    if (!(window.cast && cast.__platform__ &&
-          cast.__platform__.canDisplayType)) {
-      shaka.log.error('Expected cast namespace to be available!');
-      throw new shaka.util.Error(
-          shaka.util.Error.Severity.CRITICAL,
-          shaka.util.Error.Category.CAST,
-          shaka.util.Error.Code.CAST_UNEXPECTED_PLATFORM);
-    }
     let displayType = contentType;
     if (width && height) {
       displayType += `; width=${width}; height=${height}`;
@@ -290,7 +272,18 @@ shaka.polyfill.MediaCapabilities = class {
       // this query is specifically for HDR.
       displayType += '; eotf=smpte2084';
     }
-    return cast.__platform__.canDisplayType(displayType);
+
+    let canDisplayType;
+    try {
+      canDisplayType = cast.__platform__.canDisplayType(displayType);
+    } catch (e) {
+      shaka.log.error('Expected cast namespace to be available!');
+      throw new shaka.util.Error(
+          shaka.util.Error.Severity.CRITICAL,
+          shaka.util.Error.Category.CAST,
+          shaka.util.Error.Code.CAST_UNEXPECTED_PLATFORM);
+    }
+    return canDisplayType;
   }
 
   /**

test/polyfill/media_capabilities_unit.js

@@ -6,12 +6,12 @@
 
 describe('MediaCapabilities', () => {
   const Util = shaka.test.Util;
+  const originalCast = window['cast'];
   const originalVendor = navigator.vendor;
   const originalUserAgent = navigator.userAgent;
   const originalRequestMediaKeySystemAccess =
     navigator.requestMediaKeySystemAccess;
   const originalMediaCapabilities = navigator.mediaCapabilities;
-  const originalCast = window['cast'];
 
   /** @type {MediaDecodingConfiguration} */
   let mockDecodingConfig;
@@ -182,9 +182,8 @@ describe('MediaCapabilities', () => {
           .toHaveBeenCalledTimes(1);
     });
 
-    it('fails when the cast namespace is not available', async () => {
-      // Mock Shaka throwing an error from identifying an unexpected, non-Cast
-      // platform when performing Cast logic.
+    it('throws when the cast namespace is not available', async () => {
+      // We don't set window['cast'] here to signal error.
       const isChromecastSpy =
           spyOn(shaka['util']['Platform'],
               'isChromecast').and.returnValue(true);
@@ -202,9 +201,9 @@ describe('MediaCapabilities', () => {
 
       // 1 (during install()) + 1 (for video config check).
       expect(isChromecastSpy).toHaveBeenCalledTimes(2);
-      // Called for decodingConfig.audio. This is never reached because of the
-      // error throw.
-      expect(isTypeSupportedSpy).not.toHaveBeenCalled();
+      // Called for decodingConfig.video. decodingConfig.audio is never reached
+      // due to the error thrown in canCastDisplayType().
+      expect(isTypeSupportedSpy).toHaveBeenCalledTimes(1);
     });
 
     it('should use cast.__platform__.canDisplayType for "supported" field ' +
@@ -241,10 +240,9 @@ describe('MediaCapabilities', () => {
 
       // 1 (during install()) + 1 (for video config check).
       expect(isChromecastSpy).toHaveBeenCalledTimes(2);
-      // Called once for mockDecodingConfig.audio. Resolution, frame rate, and
-      // EOTF aren't applicable for audio, so isTypeSupported() is sufficient.
-      expect(isTypeSupportedSpy).toHaveBeenCalledTimes(1);
-      // Called once for mockDecodingConfig.video.
+      // 1 (mockDecodingConfig.video) + 1 (mockDecodingConfig.audio).
+      expect(isTypeSupportedSpy).toHaveBeenCalledTimes(2);
+      // Called once in canCastDisplayType.
       expect(mockCanDisplayType).toHaveBeenCalledTimes(1);
     });
   });