How do I filter by SIP/SDP Protocol

edit

sip and sdp or frame.protocols contains "sip:sdp"

packet-sdp.c:

    /*
     * As RFC 2327 says, "SDP is purely a format for session
     * description - it does not incorporate a transport protocol,
     * and is intended to use different transport protocols as
     * appropriate including the Session Announcement Protocol,
     * Session Initiation Protocol, Real-Time Streaming Protocol,
     * electronic mail using the MIME extensions, and the
     * Hypertext Transport Protocol."
     *
     * We therefore don't set the protocol or info columns;
     * instead, we append to them, so that we don't erase
     * what the protocol inside which the SDP stuff resides
     * put there.
     */
    col_append_str(pinfo->cinfo, COL_PROTOCOL, "/SDP");