如何从UPD的paquets中打开一条流?

我想使用PortAudio库来播放音频数据。此音频数据来自UDP paquets。

我看到有一个pau OpenDefaultStream()(和pau open stream()非常相似)函数来打开一个流:

PaStream *stream;
PaError err;
/* Open an audio I/O stream. */
err = Pa_OpenDefaultStream( &stream,
                            0,          /* no input channels */
                            2,          /* stereo output */
                            paFloat32,  /* 32 bit floating point output */
                            SAMPLE_RATE,
                            256,        /* frames per buffer, i.e. the number
                                               of sample frames that PortAudio will
                                               request from the callback. Many apps
                                               may want to use
                                               paFramesPerBufferUnspecified, which
                                               tells PortAudio to pick the best,
                                               possibly changing, buffer size.*/
                            patestCallback, /* this is your callback function */
                            &data ); /*This is a pointer that will be passed to
                                               your callback*/

我想我得用它来玩我的游戏,但我不知道怎么用它:

• 第一个参数是什么?
• 为什么要定义回调函数?

以下是PortAudio文档的链接: http://www.portaudio.com/trac/

任何帮助都将不胜感激:)

谢谢。