Facebook's scraper rejected our self-hosted poster as "Corrupted Image": the poster is an
ffmpeg-produced JPEG (non-standard marker order) that browsers/iOS/Twitter decode fine but FB's
stricter processor won't. For a YouTube source, point og:image at the video's stable, non-expiring
`i.ytimg.com/vi/<id>/hqdefault.jpg` (a Google-encoded JPEG FB decodes reliably) built from the id in
the stored thumbnail — instead of the stored `sqp`-signed variant, which can expire. Non-YouTube
sources keep the poster fallback (fine everywhere but FB). Declares 480×360 so FB includes it on the
first async scrape. og.py only — no schema change.
peter
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