feat: Cache mediaCapabilities.decodingInfo results

Issue shaka-project#4775

lib/util/stream_utils.js

@@ -499,6 +499,26 @@ shaka.util.StreamUtils = class {
   }
 
 
+  /**
+   * Queries mediaCapabilities for the decoding info for that decoding config.
+   * If that query has been done before, instead return a cached result.
+   * @param {!MediaDecodingConfiguration} decodingConfig
+   * @return {!Promise.<!MediaCapabilitiesDecodingInfo>}
+   * @private
+   */
+  static async getDecodingInfo_(decodingConfig) {
+    const cacheKey = JSON.stringify(decodingConfig);
+    const cache = shaka.util.StreamUtils.decodingConfigCache_;
+    if (cache[cacheKey]) {
+      return cache[cacheKey];
+    }
+    const result =
+        await navigator.mediaCapabilities.decodingInfo(decodingConfig);
+    cache[cacheKey] = result;
+    return result;
+  }
+
+
   /**
    * Get the decodingInfo results of the variants via MediaCapabilities.
    * This should be called after the DrmEngine is created and configured, and
@@ -518,11 +538,10 @@ shaka.util.StreamUtils = class {
       return;
     }
 
-    const mediaCapabilities = navigator.mediaCapabilities;
-
     const getVariantDecodingInfos = (async (variant, decodingConfig) => {
       try {
-        const result = await mediaCapabilities.decodingInfo(decodingConfig);
+        const result =
+            await shaka.util.StreamUtils.getDecodingInfo_(decodingConfig);
         variant.decodingInfos.push(result);
       } catch (e) {
         shaka.log.info('MediaCapabilities.decodingInfo() failed.',
@@ -1578,6 +1597,16 @@ shaka.util.StreamUtils = class {
 };
 
 
+/**
+ * A cache of results from mediaCapabilities.decodingInfo, indexed by the
+ * (stringified) decodingConfig.
+ *
+ * @type {Object.<(!string), (!MediaCapabilitiesDecodingInfo)>}
+ * @private
+ */
+shaka.util.StreamUtils.decodingConfigCache_ = {};
+
+
 /** @private {number} */
 shaka.util.StreamUtils.nextTrackId_ = 0;