and also even for an appview it's relevant only if you want to do something with those blobs, afaik appviewlite just fetches them directly from the PDS iirc
Depending on how you configure it, it can fetch the blobs lazily from the PDSes (and possibly cache the thumbnails to disk), or it can reuse an existing CDN (https://cdn.bsky.app)
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for the relay it's just a few terabytes
but there might be some appview-side processing involved with videos
then apart from the CDN nothing needs the aforementioned petabyte i guess