How to select/change bitrate for AMR codec

[tesk_terrus@xxxxxxxxxxxxxxxxx (Yuri Maliy)]

Hi All, i want to use AMR codec with pjsip for Symbian VAS.
 
aud_param.flags = PJMEDIA_AUD_DEV_CAP_EXT_FORMAT;
aud_param.ext_fmt.bitrate = 4750;
aud_param.ext_fmt.vad = 0;