When calling the codec_* functions as part of textops, they do not pick up the codecs unless they are specified as an rtpmap parameter.
e.g. codec_delete("PCMA") will only succeed if an rtpmap line exists defining the PCMA codec.
According to SDP RFC it is legal to specify known codecs by number only on the m= line, without an rtpmap entry.
My expectation of opensips is to know these common codec numbers abd be able to manipulate the sdp even without the rtpmap entry present.