Ok, just implemented one enhancement so clients can have a better experience.
Every video upload gets a poster frame extracted at upload time (first non-black frame, scene-change detection). The upload response carries it in the NIP-94 metadata as both thumb and image tags, so you can put it straight into your imeta. This works on the NIP-96 and Blossom endpoints, and duplicate re-uploads return it as well.
The poster also has a deterministic URL, append /poster.jpg to any video URL:
On blossom.band you can also add `?poster` to any video blob URL and it will redirect you to the poster:
Older videos are not backfilled. Their poster URLs resolve to a neutral placeholder instead of a 404, so it is always safe to render whatever you construct.