diff --git a/manifest.json b/manifest.json
index 834d433..271a4d9 100644
--- a/manifest.json
+++ b/manifest.json
@@ -1,7 +1,7 @@
 {
   "manifest_version": 3,
   "name": "B站评论助手",
-  "version": "1.8.0",
+  "version": "1.8.1",
   "description": "B站网页版关键词评论助手：按搜索关键词找视频，默认模拟真人（打开视频页、滚到评论区、逐字输入、点发布），也可快速API直发；支持下载当前页视频；带防重复记录、可中断执行与页面实时进度浮层。",
   "permissions": ["storage", "tabs", "scripting", "sidePanel", "downloads", "declarativeNetRequest"],
   "host_permissions": [
diff --git a/sidepanel.js b/sidepanel.js
index 0c6df43..f9a5f8a 100644
--- a/sidepanel.js
+++ b/sidepanel.js
@@ -373,7 +373,11 @@ function refreshCustomVisibility() {
   function fmtMb(n) { return (n / 1048576).toFixed(1) + " MB"; }
 
   // 面板页自己抓文件（扩展页 fetch 免 CORS，DNR 规则注入 Referer）→ Blob → 触发保存
-  async function fetchToBlob(url, onProgress) {
+  // 取视频流并封装成 Blob。
+  // 两个必须修的坑：
+  //  1) Blob 必须带 MIME —— 不带的话 Chrome 会去嗅探内容，HTML 错误页会被存成 .txt/.html
+  //  2) 必须校验内容魔数 —— CDN 有时回 200 + HTML 验证页，不校验就会把网页存成"视频"
+  async function fetchToBlob(url, onProgress, mime) {
     const resp = await fetch(url);
     if (!resp.ok) throw new Error("HTTP " + resp.status + "（CDN拒绝，可能需要重新打开视频页）");
     const total = Number(resp.headers.get("content-length") || 0);
@@ -387,8 +391,31 @@ function refreshCustomVisibility() {
       got += value.length;
       if (onProgress) onProgress(got, total);
     }
-    return new Blob(chunks);
+    if (!chunks.length) throw new Error("CDN 返回了空内容");
+    // 魔数校验：MP4/FLV/M4S 都是二进制；返回 HTML/JSON 说明拿到的是错误页
+    const head = chunks[0];
+    const b0 = head[0], b1 = head[1], b2 = head[2], b3 = head[3];
+    const isFtyp = head.length >= 12 && b4(head,0)===0x66 && b4(head,1)===0x74 && b4(head,2)===0x79 && b4(head,3)===0x70; // "ftyp"
+    const isFlv  = head.length >= 3 && b0===0x46 && b1===0x4C && b2===0x56;                                            // "FLV"
+    const isIso  = head.length >= 8 && b0===0x00 && b1===0x00;                                                         // MP4 长度前缀
+    const isHtml = (b0===0x3C) || (b0===0xEF && b1===0xBB && b2===0xBF) ||                                               // "<" 或 BOM+"<"
+                   (b0===0x0A || b0===0x0D || b0===0x20) ||                                                             // 空白开头
+                   (b0===0x7B);                                                                                          // "{" JSON
+    if (isHtml) {
+      throw new Error("CDN 返回的不是视频（是网页/错误页），请刷新视频页后重试");
+    }
+    if (!isFtyp && !isFlv && !isIso) {
+      throw new Error("下载内容不是有效的视频格式（文件头异常），已放弃保存");
+    }
+    // MIME：优先用响应头，再按魔数判定，兜底 mp4 —— 绝不给空字符串
+    const ct = (resp.headers.get("content-type") || "").split(";")[0].trim();
+    let type = ct;
+    if (!/^video\//i.test(type) && !/^audio\//i.test(type)) {
+      type = isFtyp || isIso ? "video/mp4" : (isFlv ? "video/x-flv" : "video/mp4");
+    }
+    return new Blob(chunks, { type: type });
   }
+  function b4(u8, i) { return u8.length > i ? u8[i] : -1; }
 
   async function downloadCurrent() {
     const btn = $("btnDownload"), msg = $("dlMsg");
@@ -424,13 +451,14 @@ function refreshCustomVisibility() {
       name += "." + (f.ext || "mp4");
       try {
         let lastShow = 0;
+        const MIME_BY_EXT = { mp4: "video/mp4", flv: "video/x-flv", m4s: "video/mp4", m4a: "audio/mp4", aac: "audio/aac" };
         const blob = await fetchToBlob(f.url, (got, total) => {
           const now = Date.now();
           if (now - lastShow > 500) {
             lastShow = now;
             setText("下载中 " + fmtMb(got) + (total ? " / " + fmtMb(total) : "") + "（" + name.slice(0, 18) + "…）");
           }
-        });
+        }, MIME_BY_EXT[(f.ext || "mp4").toLowerCase()] || "video/mp4");
         const objUrl = URL.createObjectURL(blob);
         await chrome.downloads.download({
           url: objUrl, filename: "B站视频/" + name, conflictAction: "uniquify", saveAs: false