rtp_secure_media=mandatory
rtp_secure_media=optional
rtp_secure_media=mandatory:AES_CM_256_HMAC_SHA1_80,AES_CM_256_HMAC_SHA1_32
rtp_secure_media=optional:AES_CM_256_HMAC_SHA1_80
rtp_secure_media=forbidden

true implies mandatory
false implies forbidden
not set implies optional

rtp_secure_media_inbound or rtp_secure_media_outbound take precedence and are treated the same way based on leg direction