rtp_secure_media=true
--inbound: Accept the srongest supported offered crypto suite, MUST result in a negotiated crypto or aborts.

--outbound: offer all supported crypto suites, MUST result in a negotiated crypto or aborts.

rtp_secure_media=optional
--inbound: Accept the srongest supported offered crypto suite, fall back to no crypto if no valid ones accepted.

--outbound: offer all supported crypto suites, OPTIONAL result in a negotiated crypto falls back to no crypto.

rtp_secure_media=<suite1>,<suiteN>
--inbound:  same behaviour as rtp_secure_media=true with smaller set of acceptable suites.
--outbound: offer supplied crypto suites, same behaviour as rtp_secure_media=true with smaller set of suites.