The media are usually hosted on external sites i.e. nostr.build or satellite.earth Or some clients like Primal offer their own media hosting within the client I think by default nostr relays only contain text, but there are technologies being worked on like Blossom which, as I understand, is basically like nostr relays but for (encrypted) media. PS I'm not very technical so I might off here somewhere 🙃 If I'm wrong anywhere then hopefully some more code-literate persons such as @fiatjaf, @hzrd149, @miljan, @Vitor Pamplona or @The Fishcake (nostr.build) can correct me :)