fix(cast): Use cast platform APIs in MediaCapabilties polyfill

lib/polyfill/media_capabilities.js

@@ -96,37 +96,54 @@ shaka.polyfill.MediaCapabilities = class {
       return res;
     }
 
+    const videoConfig = mediaDecodingConfig['video'];
+    const audioConfig = mediaDecodingConfig['audio'];
+
     if (mediaDecodingConfig.type == 'media-source') {
       if (!shaka.util.Platform.supportsMediaSource()) {
         return res;
       }
       // Use 'MediaSource.isTypeSupported' to check if the stream is supported.
-      if (mediaDecodingConfig['video']) {
-        const contentType = mediaDecodingConfig['video'].contentType;
-        const isSupported = MediaSource.isTypeSupported(contentType);
+      // Cast platforms will instead use 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;
+        if (shaka.util.Platform.isChromecast()) {
+          isSupported = shaka.polyfill.MediaCapabilities.canDisplayType_({
+            contentType,
+            width: videoConfig.width,
+            height: videoConfig.height,
+            frameRate: videoConfig.frameRate,
+            transferFunction: videoConfig.transferFunction,
+          });
+        } else {
+          isSupported = MediaSource.isTypeSupported(contentType);
+        }
         if (!isSupported) {
           return res;
         }
       }
 
-      if (mediaDecodingConfig['audio']) {
-        const contentType = mediaDecodingConfig['audio'].contentType;
+      if (audioConfig) {
+        const contentType = audioConfig.contentType;
         const isSupported = MediaSource.isTypeSupported(contentType);
         if (!isSupported) {
           return res;
         }
       }
     } else if (mediaDecodingConfig.type == 'file') {
-      if (mediaDecodingConfig['video']) {
-        const contentType = mediaDecodingConfig['video'].contentType;
+      if (videoConfig) {
+        const contentType = videoConfig.contentType;
         const isSupported = shaka.util.Platform.supportsMediaType(contentType);
         if (!isSupported) {
           return res;
         }
       }
 
-      if (mediaDecodingConfig['audio']) {
-        const contentType = mediaDecodingConfig['audio'].contentType;
+      if (audioConfig) {
+        const contentType = audioConfig.contentType;
         const isSupported = shaka.util.Platform.supportsMediaType(contentType);
         if (!isSupported) {
           return res;
@@ -217,6 +234,51 @@ shaka.polyfill.MediaCapabilities = class {
     return res;
   }
 
+  /**
+   * Checks if the given media parameters of the video or audio streams are
+   * supported by the platform.
+   * @param {{
+   *   contentType: string,
+   *   width: (number|undefined),
+   *   height: (number|undefined),
+   *   frameRate: (number|undefined),
+   *   transferFunction: (string|undefined)
+   * }} options canDisplayType() options.
+   *     contentType: A valid MIME type and (optionally) a codecs parameter.
+   *     width: Describes the stream horizontal resolution in pixels.
+   *     height: Describes the stream vertical resolution in pixels.
+   *     frameRate: Describes the frame rate of the stream.
+   *     transferFunction: Describes the video transfer function supported by
+   *         the rendering capabilities of the user agent.
+   * @return {boolean} `true` when the stream can be displayed on a Cast device.
+   * @private
+   */
+  static canDisplayType_({
+    contentType,
+    width = undefined,
+    height = undefined,
+    frameRate = undefined,
+    transferFunction = undefined,
+  }) {
+    if (!cast.__platform__) {
+      return true;
+    }
+    let displayType = contentType;
+    if (width && height) {
+      displayType += `; width=${width}; height=${height}`;
+    }
+    if (frameRate) {
+      displayType += `; framerate=${frameRate}`;
+    }
+    if (transferFunction && transferFunction.toLowerCase() === 'pq') {
+      // A "PQ" transfer function indicates this is an HDR-capable stream;
+      // "smpte2084" is the published standard. We need to inform the platform
+      // this query is specifically for HDR.
+      displayType += '; eotf=smpte2084';
+    }
+    return cast.__platform__.canDisplayType(displayType);
+  }
+
   /**
    * A method for generating a key for the MediaKeySystemAccessRequests cache.
    *