XPost: alt.comp.software.firefox   
   From: mariasophia@comprehension.com   
      
   Simon wrote:   
   > It looks like YouTube has blocked video downloads using yt-dlp. Has   
   > anybody noticed this?   
   >   
   > I've also tried using VPN and the same result. It says error 403   
   > forbidden or something like that.   
   >   
   > [download] Got error: HTTP Error 403: Forbidden. Retrying fragment 1   
   > (1/10)...   
      
   This summary below may well be wrong, but it's what I think happened.   
   And, more importantly, this contains recommended Windows solutions.   
      
   1. What changed on YouTube   
      A. YouTube added new JavaScript based proof-of-origin checks.   
      B. These checks run real browser-like JavaScript.   
      C. Python alone cannot run that JavaScript.   
      D. yt-dlp must now call an external JS engine to pass those checks.   
      
   2. What changed in yt-dlp   
      A. yt-dlp added support for external JS engines.   
      B. Without one, YouTube extraction fails or gives warnings.   
      C. This requirement became important in late 2025.   
      
   3. What Deno is   
      A. Deno is a standalone JavaScript and TypeScript runtime.   
      B. It is a single EXE on Windows, no installer needed.   
      C. yt-dlp can auto-detect deno.exe if placed next to yt-dlp.exe.   
      D. This makes Deno the easiest choice for Windows users.   
      
   4. What Node.js is   
      A. Node.js is an older, widely used JavaScript runtime.   
      B. It works with yt-dlp, but it needs a full installation.   
      C. It is not a single portable EXE on Windows.   
      D. yt-dlp supports Node, but Deno is simpler for most users.   
      E. To get and install the version that worked for me:   
      
   5. Are Deno and Node the same   
      A. No. And yes. They both run JavaScript outside a browser.   
      B. But they are separate projects with different designs.   
      C. Luckily, yt-dlp does not care which one you use.   
      
   6. Why you never needed this before   
      A. For years, yt-dlp could decode YouTube signatures in Python.   
      B. YouTube now uses JavaScript challenges Python cannot emulate.   
      C. This forced yt-dlp to rely on an external JS engine.   
      
   7. What does ffmpeg have to do with this process   
      A. ffmpeg is only used for muxing and transcoding.   
      B. The JS engine is needed only for YouTube extraction logic.   
      
   8. What are the relevant JS engines that yt-dlp can use   
      Below are the JavaScript engines that are realistically usable   
      with yt-dlp.   
      
      a. Deno   
         A. Single portable EXE.   
         B. Easiest option for Windows.   
         C. Auto detected by yt-dlp.   
         C:\> curl -LO https://github.com/denoland/deno/releases/la   
   est/download/deno-x86_64-pc-windows-msvc.zip   
      
      b. Node.js   
         A. Requires a full installer.   
         B. Widely used and reliable.   
         C. Auto detected by yt-dlp.   
         C:\> curl -O https://nodejs.org/dist/v22.11.0/node-v22.11.0-x64.msi   
         C:\> start node-v22.11.0-x64.msi   
         C:\> yt-dlp --js-runtime node https://www.youtube.com/watch?v=BY82T7Q8hiw   
      
      c. Bun   
         A. Newer JS runtime.   
         B. Has a Windows build.   
         C. Auto detected if on PATH.   
      
      d. QuickJS   
         A. Small standalone JS engine.   
         B. Windows builds exist but not common.   
         C. Auto detected if qjs is on PATH.   
      
   Summary:   
    i.   Deno is simplest.   
    ii.  Node is most common.   
    iii. Bun works but is newer.   
    iv.  QuickJS works if installed manually.   
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