If pre-built media server solutions doesn’t work for your use case, then you’d need to create a custom site.
For the most part, ISPs tends to care more about:
Covering their butt legally — if they don’t know you’re engaging in anything like piracy, then it’s not really their concern; and
Ensuring their network stability — if you’re within your contractual usage limits and not using disproportionate amount of traffic causing other customers problem, then your network security is your problem.
As such, as long as the intended sharing audience are limited to only people you trust, and you put the content behind authentication w/ encryption (I.E. https), no one other than the intended recipient would know what you’re sending over the wire. That is as long as none of your users leak their credentials/report you for the content you’re sharing… which, a media server solution wouldn’t protect you from either.