lwyd-back

YouTube video/audio downloader backend for lwyd.

Stack

• Python 3.14 + FastAPI + pytubefix + yt-dlp + ffmpeg
• uv + PEP 517 (uv_build), Nix dev shell (flake.nix)
• Logging via reger (default level INFO)

Setup

cp .env.example .env   # then edit SERVER_* / DOWNLOAD_DIR
uv sync
uv run lwyd-back

Requires ffmpeg on PATH.

API

Method	Path	Description
POST	/api/info/{video_id}	Video metadata + available video/audio streams
POST	/api/predownload/{video_id}	Start a download task, returns task_id
GET	/api/task/{task_id}	Task status / progress polling
GET	/api/download/{task_id}	Download the finished file

predownload body: mode (video | audio | both), video_resolution, video_codec, audio_bitrate, audio_codec, container (mp4 | webm | mkv | mov | mp3 | wav | flac | ogg | m4a).

Download pipeline

1. pytubefix (sync YouTube) — streams fetched with client fallback WEB → IOS → TV → WEB_EMBED → ANDROID_VR; downloads run in threads, ffmpeg merge/convert runs as a subprocess, so the event loop stays free.
2. yt-dlp fallback — when pytubefix fails (e.g. SABR-only videos blocked by PoToken INVALID), the task automatically retries with yt-dlp, which handles SABR/po_token streams.

/api/info uses AsyncYouTube for non-blocking metadata lookups.