This is what I've done, and it's worked well for me:

1) Make a dedicated "Nostr 101" video that's tailor-made for your audience. It should walk through what Nostr is, why your audience should care about it, and how they can make an account and follow you

Here's mine I did with  @Derek Ross: https://youtu.be/_jrkUXDReqI

2) In all future videos that you want to funnel your subscribers to Nostr (I do it in as many as I can), just give a very brief "follow me on Nostr" in the video, and tell them that to learn more, "go watch that 'Nostr 101' video linked in the description", and plunk your npub right under it