kbuilt

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A public, zero-install browser video downloader powered by a self-hosted cobalt engine.

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What Is This

kbuilt is meant to be a website anyone can open and use directly:

1. Open the public kbuilt site.
2. Paste a public video URL from YouTube, Bilibili, Douyin, TikTok, X/Twitter, Instagram, Reddit, Vimeo, SoundCloud, and other cobalt-supported sites.
3. Pick quality and mode.
4. Click download and save the file in the browser.

There is no desktop app, no browser extension, no local yt-dlp, and no user login. The public web app talks directly to a public Hugging Face Spaces engine that runs imputnet/cobalt.

Public URLs

Surface	URL
Web app	https://kbuilt.vercel.app/
Engine health	https://weipingapple-kbuilt-engine.hf.space/
Source	https://github.com/appleweiping/kbuilt

The production web app is live on Vercel and uses the public HF Spaces engine below.

Architecture

Browser user
  |
  | opens kbuilt and posts a media URL
  v
Vercel static front-end
  |
  | direct API call, no video bytes through Vercel
  v
HF Spaces Docker engine running cobalt
  |
  | tunnel / redirect / picker result
  v
Browser saves the media file

Important boundaries:

• Vercel only serves the static UI and tiny optional AI text endpoints.
• The download stream is produced by the HF Spaces cobalt engine and goes directly to the browser.
• kbuilt does not cache media, store user links, or proxy video through Vercel.
• The front-end asks cobalt for localProcessing: "disabled" so the public site stays zero-install and avoids local remux/transcode flows.

What Works

• Public-link downloads through cobalt-supported services: YouTube, Bilibili, Douyin, TikTok, X/Twitter, Instagram, Reddit, Twitch, Vimeo, SoundCloud, Pinterest, Tumblr, and more.
• Quality selection: max / 2160p / 1080p / 720p / 480p.
• Modes: video+audio, audio only, mute.
• Four UI languages: Chinese, English, Japanese, Korean.
• Light/dark terminal-style UI.
• Optional AI summary based on page metadata only. Subtitle translation is not advertised as automatic unless caption text is provided later.

Honest YouTube Note

YouTube often blocks datacenter IPs. HF Spaces runs from datacenter infrastructure, so YouTube may fail intermittently or require cookies/proxy support on the engine. This is a platform limitation shared by free cloud downloaders, not a kbuilt-specific extraction bug.

For production validation, prefer non-YouTube public links such as TikTok, SoundCloud, X/Twitter, Instagram, Reddit, Twitch, Vimeo, Douyin, and Bilibili when cobalt upstream currently supports that service. Service reliability follows cobalt and each platform's anti-bot rules.

Deployment

Full deployment instructions are in docs/DEPLOY.md.

Production shape:

• Engine: public Hugging Face Docker Space weipingapple/kbuilt-engine
• Front-end: public Vercel project kbuilt, root directory web
• Engine URL: https://weipingapple-kbuilt-engine.hf.space/

License And Credits

• This repository's front-end, API glue, docs, and assets are released under the MIT License.
• The download engine is imputnet/cobalt, licensed AGPL-3.0. kbuilt uses the official container image and does not modify cobalt source code.

No warranty. Use kbuilt only for content you are allowed to download.