简单粗暴，直接上图：

如果是capture的话，只需要修改：

a.  SND_PCM_STREAM_PLAYBACK      ->       SND_PCM_STREAM_CAPTURE

		if ((err = snd_pcm_open (&capture_handle, argv[1], SND_PCM_STREAM_CAPTURE, 0)) < 0) {
			fprintf (stderr, "cannot open audio device %s (%s)\n", 
				 argv[1],
				 snd_strerror (err));
			exit (1);
		}

 b.  snd_pcm_writei       ->      snd_pcm_readi

		for (i = 0; i < 10; ++i) {
			if ((err = snd_pcm_readi (capture_handle, buf, 128)) != 128) {
				fprintf (stderr, "read from audio interface failed (%s)\n",
					 snd_strerror (err));
				exit (1);
			}
		}