fix(VideoPlayer): work around slow Firefox MediaCapabilities.decodingInfo

Firefox's navigator.mediaCapabilities.decodingInfo costs ~14 ms per call
(out-of-process RDD decoder probe). Shaka Player calls it once per Variant
in the DASH manifest while filtering supported variants, and YouTube
manifests routinely have 1000+ variants, so player initialization stalls
15-20 s on Gecko-based browsers before the first SourceBuffer is added.

Wrap decodingInfo to delegate "supported" checks to
MediaSource.isTypeSupported (sub-ms on Firefox) with a per-MIME cache.
DRM probes and non-media-source queries fall through to native.
Wrapper is gated to Gecko UAs so Chromium and Safari are unaffected.

Refs: https://github.com/shaka-project/shaka-player/issues/4775

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/main.js

@@ -1,3 +1,4 @@
+import "@/utils/firefoxMediaCapabilitiesFix.js";
 import { createApp } from "vue";
 import router from "@/router/router.js";
 import App from "./App.vue";

src/utils/firefoxMediaCapabilitiesFix.js

@@ -0,0 +1,49 @@
+/**
+ * Workaround for shaka-project/shaka-player#4775.
+ *
+ * Firefox's navigator.mediaCapabilities.decodingInfo() costs ~14 ms per call
+ * (out-of-process decoder probe). Shaka calls it once per Variant in the DASH
+ * manifest while filtering supported variants; YouTube manifests routinely
+ * have 1000+ variants, so player initialization stalls 15-20 s on Gecko-based
+ * browsers before any SourceBuffer is added or any segment is fetched.
+ *
+ * This module delegates the "supported" check to MediaSource.isTypeSupported
+ * (sub-ms on Firefox) and caches the result per MIME string. Smooth /
+ * powerEfficient are returned conservatively as true; Shaka's ABR will
+ * downshift if real playback isn't smooth.
+ *
+ * Active only on Gecko engines, so Chromium / Safari / Edge / iOS Firefox
+ * (WebKit) are unaffected. DRM probes (keySystemConfiguration) and non-
+ * media-source query types fall through to the native API unchanged.
+ *
+ * Remove this module (and its import in main.js) once Shaka ships a caching
+ * fix for #4775.
+ */
+if (
+    typeof navigator !== "undefined" &&
+    /Gecko\/[0-9]/.test(navigator.userAgent) &&
+    navigator.mediaCapabilities &&
+    typeof navigator.mediaCapabilities.decodingInfo === "function"
+) {
+    const orig = navigator.mediaCapabilities.decodingInfo.bind(navigator.mediaCapabilities);
+    const cache = new Map();
+    const mimeOk = mime => {
+        if (!cache.has(mime)) cache.set(mime, MediaSource.isTypeSupported(mime));
+        return cache.get(mime);
+    };
+    navigator.mediaCapabilities.decodingInfo = function (config) {
+        if (config && config.type === "media-source" && !config.keySystemConfiguration) {
+            const v = config.video;
+            const a = config.audio;
+            const supported = (!v || mimeOk(v.contentType)) && (!a || mimeOk(a.contentType));
+            return Promise.resolve({
+                supported,
+                smooth: supported,
+                powerEfficient: supported,
+                keySystemAccess: null,
+                configuration: config,
+            });
+        }
+        return orig(config);
+    };
+}