code: def src_callback_new(callback, converter_type, channels):
      
      cb_data = {'callback': callback, 'channels': channels}
      handle = ffi.new_handle(cb_data)
      error = ffi.new('int*')
      state = _lib.src_callback_new(_src_input_callback, converter_type,
                                    channels, error, handle)
      if state == ffi.NULL:
          return None, handle, error[0]
      return state, handle, error[0]
docs: Initialisation for the callback based API.
  
      Parameters
      ----------
      callback : function
          Called whenever new frames are to be read. Must return a NumPy array
          of shape (num_frames, channels).
      converter_type : int
          Converter to be used.
      channels : int
          Number of channels.
  
      Returns
      -------
      state
          An anonymous pointer to the internal state of the converter.
      handle
          A CFFI handle to the callback data.
      error : int
          Error code.