The opcodes that receive audio signals are:
Synchronous input: in, in32, inch, inh, ino, inq, inrg, ins and inx
File streaming: diskin, diskin2 soundin and hdf5read
User defined channel input: invalue
Streaming input: soundin
Websocket input: websocket
Direct to zak input: inz
See the section Software Bus for input and output through the API.
The mp3in allows reading of mp3 files, which are currently not supported by ordinary reading methods inside Csound.