Cobalt is a privacy-focused media downloader web application with a SvelteKit frontend and Node.js/Express API backend. Users paste a URL from supported platforms (YouTube, TikTok, Instagram, Twitter/X, Vimeo, Reddit, SoundCloud, Twitch, Bilibili, and 15+ others) and receive a downloadable media file. The architecture is a monorepo with three packages: @imput/cobalt-web (static frontend), @imput/cobalt-api (processing backend), and @imput/version-info (build-time version helper). The API acts as a fancy proxy - it fetches media streams from source platforms, optionally remuxes/transcodes via FFmpeg (server-side or client-side via libav.js WebAssembly), and streams results back without ever writing to disk. The frontend handles URL input, settings management (localStorage with migration), a processing queue with Web Workers for client-side FFmpeg, i18n (EN/RU), and PWA features. Key data flows: user submits URL → API validates/matches service → extracts stream URLs → returns tunnel/redirect/picker response → frontend either streams directly, proxies via API, or processes locally via Web Workers. External dependencies: FFmpeg (via ffmpeg-static), youtubei.js for YouTube, hls-parser, undici for HTTP, Redis (optional for rate limiting), Cloudflare Turnstile (optional bot protection).