Function soundio::outstream_write_callback

pub extern "C" fn outstream_write_callback(
    stream: *mut SoundIoOutStream, 
    frame_count_min: c_int, 
    frame_count_max: c_int
)

This is called when an outstream needs to be written to. The OutStreamUserData struct is obtained from the stream.userdata, then the user-supplied callback is called with an OutStreamWriter object.