yup, if you trust people to pass the URL around securely with a secret in a fragment, and you trust the recipients to keep the URL secret, and you're okay for a

yup, if you trust people to pass the URL around securely with a secret in a fragment, and you trust the recipients to keep the URL secret, and you're okay for anyone who ever discovers that secret to be able to decrypt and replay recordings of your conferences... then that may be acceptable. Otherwise, you'll want a way to ensure that only devices belonging to users you've explicitly invited are able to participate (and you'll want to keep the secret evolving for forward secrecy, as amusing as it'd be for you to invite your sysadmin to a conference, only for him to go and decrypt the conversation prior to him joining to find out what you were saying before he came in...) - and this require key management to track who's who and who's trusted.