Castor

Castor is a Go CLI (~10,640 lines, MIT) that casts web video to smart TVs at full quality. Written by a single developer (stupside), it extracts the real video stream URL from a web page via headless Chrome, transcodes it for the target device, and serves it over the local network.

The core architecture is a read-once spool pipeline: a single ffmpeg process pulls the source, remuxes it codec-copy to MPEG-TS on disk, and optionally tees PCM audio for transcription. Everything downstream — encoding, whisper transcription, the HTTP replay server — reads from local disk. This decouples the upstream CDN (and its short-lived signed URLs) from playback: once data is spooled, the CDN can expire without killing the stream.

The pipeline uses a planner/executor split: all decisions about device type and source properties are made up front into an immutable Plan, and the executor follows it with no branching. Device discovery (SSDP + DLNA capability negotiation) runs concurrently with the upstream pull so signed URLs don't expire during the connection dance. The DLNA path is the primary, well-tested path; Chromecast support is simpler and experimental.

Notable techniques include: - Live subtitle burn-in via whisper.cpp (LocalAgreement-2 streaming policy) coordinated with ffmpeg's drawtext filter through atomic filesystem swaps — no IPC protocol, just os.Rename. - Hardware encoder auto-detection that runs a real one-frame test encode through each GPU candidate (VA-API, VideoToolbox) rather than guessing from the platform. - Replay-from-zero HTTP server that serves every TV client from byte 0, solving Samsung's HEAD → short-GET → real-GET probe dance that would otherwise consume the stream head. - Stream extraction via chromedp with 17 injected anti-detection JS scripts (WebGL, canvas, font metrics, WebRTC spoofing) and Cloudflare Turnstile bypass. - Playback gate with 60-second stall detection that surfaces ffmpeg's stderr ring buffer when the upstream dies, catching hidden CDN errors.

The puller is paced like a player (2× realtime for VOD, 1× for live) rather than a downloader, so the CDN sees a well-behaved client. Requires Chrome, ffmpeg 7.1+, and ffprobe 7.1+ on the host.