These plugins are needed for some of the features of RX.Please be aware that by using these library files you as the end user you are in effect building an end user system and may be liable to pay patent licensing fees.
After downloading extract the files to the Windows\system32 directory.
MP3 licensing information here.
AAC licensing information here.
MP3 decoder is based on MAD.Download here.
AAC Plus decoder is based on FAAD2.Download here.