diff --git a/src/hooks/json-stringify.ts b/src/hooks/json-stringify.ts
index 1919aec5..bce3705a 100644
--- a/src/hooks/json-stringify.ts
+++ b/src/hooks/json-stringify.ts
@@ -18,10 +18,33 @@ function stringify(
     // TODO: add below to a dump-level logger
     // console.debug('JSON.stringify', value, replacer, space);
 
-    // @ts-expect-error TS doesn't allow optional chaining on `unknown`. See: https://github.com/microsoft/TypeScript/issues/37700
-    const ctx = value?.playbackContext?.contentPlaybackContext as unknown;
-    if (!isPrimitive(ctx)) {
-      (ctx as Record<string, unknown>).isInlinePlaybackNoAd = true;
+    const holder = value as Record<string, any>;
+    const pbCtx = holder.playbackContext as Record<string, any> | undefined;
+    const ctx = pbCtx?.contentPlaybackContext as
+      | Record<string, unknown>
+      | undefined;
+
+    if (!isPrimitive(ctx) && ctx!.isInlinePlaybackNoAd !== true) {
+      // Setting `isInlinePlaybackNoAd` tells InnerTube not to serve ads, which
+      // avoids the server-side SABR "backoff" that otherwise stalls playback
+      // after a few seconds. YouTube has shipped a "locker" script that defines
+      // this property as non-writable/non-configurable via Object.defineProperty,
+      // so a direct assignment (`ctx.isInlinePlaybackNoAd = true`) silently fails.
+      //
+      // Instead of mutating YouTube's object in place, rebuild the holder chain
+      // with fresh plain objects. `JSON.stringify` only serializes own enumerable
+      // properties, so spreading reproduces exactly what would be serialized while
+      // dropping any locked property descriptors, letting our flag stick.
+      value = {
+        ...holder,
+        playbackContext: {
+          ...pbCtx,
+          contentPlaybackContext: {
+            ...ctx,
+            isInlinePlaybackNoAd: true
+          }
+        }
+      };
       console.info(`[JSON.stringify] Set isInlinePlaybackNoAd`);
     }
   }