Placeholders for MSE on Chromium too.

src/content/media.js

@@ -1,28 +1,5 @@
-if (typeof exportFunction === "function" && "MediaSource" in window) ns.on("capabilities", event => {
-  debug("Media Hook", document.URL, document.documentElement && document.documentElement.innerHTML, ns.capabilities); // DEV_ONLY
-  let mediaBlocker = !ns.allows("media");
-  let unpatched = new Map();
-  function patch(obj, methodName, replacement) {
-     let methods = unpatched.get(obj) || {};
-     methods[methodName] = obj[methodName];
-     exportFunction(replacement, obj, {defineAs: methodName});
-     unpatched.set(obj, methods);
-  }
-  let urlMap = new WeakMap();
-  patch(window.URL, "createObjectURL",  function(o, ...args) {
-    let url = unpatched.get(window.URL).createObjectURL.call(this, o, ...args);
-    if (o instanceof MediaSource) {
-      let urls = urlMap.get(o);
-      if (!urls) urlMap.set(o, urls = new Set());
-      urls.add(url);
-    }
-    return url;
-  });
-
-  patch(window.MediaSource.prototype, "addSourceBuffer", function(mime, ...args) {
-    let ms = this;
-    let urls = urlMap.get(ms);
-
+if ("MediaSource" in window) {
+  let notify = allowed => {
     let request = {
       id: "noscript-media",
       type: "media",
@@ -30,26 +7,77 @@ if (typeof exportFunction === "function" && "MediaSource" in window) ns.on("capa
       documentUrl: document.URL,
       embeddingDocument: true,
     };
-    seen.record({policyType: "media", request, allowed: false});
+    seen.record({policyType: "media", request, allowed});
+    debug("MSE notification", document.URL); // DEV_ONLY
     notifyPage();
-
-    if (mediaBlocker) {
-      let exposedMime = `${mime} (MSE)`;
-      setTimeout(() => {
-        let me = Array.from(document.querySelectorAll("video,audio"))
-          .find(e => e.srcObject === ms || urls && urls.has(e.src));
-        if (!me) return;
-        try {
-          let ph = PlaceHolder.create("media", request);
-          ph.replace(me);
-          PlaceHolder.listen();
-        } catch (e) {
-          error(e);
-        }
-      }, 0);
-      throw new Error(`${exposedMime} blocked by NoScript`);
+    return request;
+  };
+  let createPlaceholder = (mediaElement, request) => {
+    try {
+      let ph = PlaceHolder.create("media", request);
+      ph.replace(mediaElement);
+      PlaceHolder.listen();
+      debug("MSE placeholder for %o", mediaElement); // DEV_ONLY
+    } catch (e) {
+      error(e);
     }
+  };
 
-    return unpatched.get(window.MediaSource.prototype).addSourceBuffer.call(ms, mime, ...args);
-  });
-});
+  if (typeof exportFunction === "function") {
+    // Mozilla
+    let mediablocker = true;
+    ns.on("capabilities", e => {
+      mediaBlocker = !ns.allows("media");
+    });
+
+    let unpatched = new Map();
+    function patch(obj, methodName, replacement) {
+       let methods = unpatched.get(obj) || {};
+       methods[methodName] = obj[methodName];
+       exportFunction(replacement, obj, {defineAs: methodName});
+       unpatched.set(obj, methods);
+    }
+    let urlMap = new WeakMap();
+    patch(window.URL, "createObjectURL",  function(o, ...args) {
+      let url = unpatched.get(window.URL).createObjectURL.call(this, o, ...args);
+      if (o instanceof MediaSource) {
+        let urls = urlMap.get(o);
+        if (!urls) urlMap.set(o, urls = new Set());
+        urls.add(url);
+      }
+      return url;
+    });
+
+    patch(window.MediaSource.prototype, "addSourceBuffer", function(mime, ...args) {
+      let ms = this;
+      let urls = urlMap.get(ms);
+      let request = notify(!mediaBlocker);
+      if (mediaBlocker) {
+        let exposedMime = `${mime} (MSE)`;
+        setTimeout(() => {
+          let me = Array.from(document.querySelectorAll("video,audio"))
+            .find(e => e.srcObject === ms || urls && urls.has(e.src));
+          if (me) createPlaceholder(me, request);
+        }, 0);
+        throw new Error(`${exposedMime} blocked by NoScript`);
+      }
+
+      return unpatched.get(window.MediaSource.prototype).addSourceBuffer.call(ms, mime, ...args);
+    });
+
+  } else if ("SecurityPolicyViolationEvent" in window) {
+    // Chromium
+    addEventListener("securitypolicyviolation", e => {
+      if (!e.isTrusted || ns.allows("media")) return;
+      let {blockedURI, violatedDirective} = e;
+      if (blockedURI.startsWith("blob") && violatedDirective.startsWith("media-src")) {
+        let request = notify(false);
+        for (let me of document.querySelectorAll("video,audio")) {
+          if (!(me.src || me.currentSrc) || me.src.startsWith("blob")) {
+            createPlaceholder(me, request);
+          }
+        }
+      }
+    }, true);
+  }
+}