@ffi.callback('<STR_LIT>')<EOL>def _src_input_callback(cb_data, data):
cb_data = ffi.from_handle(cb_data)<EOL>ret = cb_data['<STR_LIT>']()<EOL>if ret is None:<EOL><INDENT>cb_data['<STR_LIT>'] = None<EOL>return <NUM_LIT:0>  <EOL><DEDENT>input_data = _np.require(ret, requirements='<STR_LIT:C>', dtype=_np.float32)<EOL>input_frames, channels = _check_data(input_data)<EOL>if cb_data['<STR_LIT>'] != channels:<EOL><INDENT>raise ValueError('<STR_LIT>')<EOL><DEDENT>cb_data['<STR_LIT>'] = input_data<EOL>data[<NUM_LIT:0>] = ffi.cast('<STR_LIT>', ffi.from_buffer(input_data))<EOL>return input_frames<EOL>
Internal callback function to be used with the callback API.

    Pulls the Python callback function from the handle contained in `cb_data`
    and calls it to fetch frames. Frames are converted to the format required by
    the API (float, interleaved channels). A reference to these data is kept
    internally.

    Returns
    -------
    frames : int
        The number of frames supplied.