A remote thumbnail as og:image is unreliable for the crawler — Facebook's signed
CDN URL expires (so an old shared link's image later vanishes) and cross-origin
hotlinking is flaky. Record a self-hosted poster for EVERY download (ensure_poster
returns the existing <base>.jpg thumbnail sidecar, or cuts a frame) and point
og:image at our own /api/public/watch/{token}/poster.jpg. Backfill now fills
poster_path for all existing downloads, not just thumbnail-less ones.
Two visual gaps for non-catalog downloads:
- Channel link: YouTube already exposes channel_url; Facebook exposes none but a
numeric uploader_id that resolves at facebook.com/<id>. `_uploader_url` derives
it so the auto-detected channel renders as a real clickable link.
- Poster: a source with no thumbnail (e.g. a direct reddit HLS URL) showed a
blank image box. The worker now cuts a representative frame with ffmpeg
(`ensure_poster`) into the `<base>.jpg` sidecar and records `poster_path`
(migration 0050). The card, the public watch page (<video poster> + og:image),
and link previews fall back to it via new authed + public poster endpoints.
Adds `app.downloads.backfill` (one-off, re-run-safe) to fill uploader_url
(re-extract YouTube/Facebook metadata) and posters for pre-existing downloads.
A shared /watch/{token} link is a client-rendered SPA, so a social crawler only
saw the generic index.html — a blank link card. The server now injects per-video
Open Graph / Twitter tags (title, channel, thumbnail) into the served HTML for
that route, so links unfurl richly in Messenger and other chat apps; real
browsers ignore the extra tags and hydrate the page as usual. Password /
expired / invalid links fall back to the generic card with no metadata leak.
Also shortens the generic site description used for search engines and link
previews.
