4kvm-downloader

# 4kvm.net Video Downloader Automatically download videos from 4kvm.net, defeating 8 layers of anti-scraping protection. ## Anti-scraping layers | Layer | Mechanism | Defeat | |-------|-----------|--------| | 1. WASM-signed API | `build_play_url()` in `nbmovie_wasm` reads DOM meta tags and generates time-sensitive signed URLs | Headless browser (Playwright) executes WASM in real browser context | | 2. Extensionless segments | CDN URLs have no `.ts` extension, breaking ffmpeg HLS parser | Manual URL extraction from m3u8 | | 3. PNG-disguised segments | Each `.ts` segment has a fake PNG header (~110 bytes) prepended | Strip bytes before IEND marker + 8 bytes | | 4. No-referrer policy | `referrerPolicy: 'no-referrer'` on video element; CDN rejects requests with Referer header | Omit Referer header from segment downloads | | 5. Cross-domain CDN | m3u8 on `oss.douyinbit.com`, segments on `sns-open-qc.xhscdn.com` (Tencent COS) | Follow redirect chain | | 6. Connection-level rate limiting | CDN throttles when >2-4 parallel connections hit from same IP | Use 2 workers, fall back to curl (uses system proxy) for failures | | 7. HEAD 404 misdirection | CDN returns HTTP 404 to HEAD requests even when GET works | Use GET only for m3u8 liveness checks | | 8. Base64-encoded relative URLs | Some segments have `/ets/{hash}/{base64}` paths; base64 may be truncated in m3u8 | Use the full URL from the CDN's redirect response, not the truncated base64 | ## Prerequisites Before running, ensure...