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Appendix: wave.c example This is a sample application that plays back audio data: #include <errno.h> #include <fcntl.h> #include <gulliver.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <sys/ioctl.h> #include <sys/select.h> #include <sys/stat.h> #include <sys/termio.h> #include <sys/types.h> #include <unistd.h> #include <sys/asoundlib.h> const char *kRiffId = "RIFF"; const char *kWaveId = "WAVE"; typedef struct { char tag[4]; long length; } RiffTag; typedef struct { char Riff[4]; long Size; char Wave[4]; } RiffHdr; typedef struct { short FormatTag; short Channels; long SamplesPerSec; long AvgBytesPerSec; short BlockAlign; short BitsPerSample; } WaveHdr; int err (char *msg) { perror (msg); return -1; } int FindTag (FILE * fp, const char *tag) { int retVal; RiffTag tagBfr = {"", 0}; retVal = 0; // Keep reading until we find the tag or hit the EOF. while (fread ((unsigned char *) &tagBfr, sizeof (tagBfr), 1, fp)) { // If this is our tag, set the length and break. if (strncmp (tag, tagBfr.tag, sizeof tagBfr.tag) == 0) { retVal = ENDIAN_LE32(tagBfr.length); break; } // Skip ahead the specified number of bytes in the stream fseek (fp, tagBfr.length, SEEK_CUR); } // Return the result of our operation return (retVal); } int CheckHdr (FILE * fp) { RiffHdr riffHdr = {"", 0}; // Read the header and, if successful, play the file // file or WAVE file. if (fread ((unsigned char *) &riffHdr, sizeof (RiffHdr), 1, fp) == 0) return 0; if (strncmp (riffHdr.Riff, kRiffId, strlen (kRiffId)) || strncmp (riffHdr.Wave, kWaveId, strlen (kWaveId))) return -1; return 0; } int dev_raw (int fd) { struct termios termios_p; if (tcgetattr (fd, &termios_p)) return (-1); termios_p.c_cc[VMIN] = 1; termios_p.c_cc[VTIME] = 0; termios_p.c_lflag &= ~(ECHO | ICANON | ISIG | ECHOE | ECHOK | ECHONL); termios_p.c_oflag &= ~(OPOST); return (tcsetattr (fd, TCSANOW, &termios_p)); } int dev_unraw (int fd) { struct termios termios_p; if (tcgetattr (fd, &termios_p)) return (-1); termios_p.c_lflag |= (ECHO | ICANON | ISIG | ECHOE | ECHOK | ECHONL); termios_p.c_oflag |= (OPOST); return (tcsetattr (fd, TCSAFLUSH, &termios_p)); } //***************************************************************************** /* *INDENT-OFF* */ #ifdef __USAGE %C[Options] * Options: -a[card#:]<dev#> the card & device number to play out on #endif /* *INDENT-ON* */ //***************************************************************************** int main (int argc, char **argv) { int card = -1; int dev = 0; snd_pcm_t *pcm_handle; FILE *file1; WaveHdr wavHdr1; int mSamples; int mSampleRate; int mSampleChannels; int mSampleBits; char *mSampleBfr1; int rtn; snd_pcm_channel_info_t pi; snd_mixer_t *mixer_handle; snd_mixer_group_t group; snd_pcm_channel_params_t pp; snd_pcm_channel_setup_t setup; int bsize, n, N = 0, c; fd_set rfds, wfds; while ((c = getopt (argc, argv, "a:")) != EOF) { switch (c) { case 'a': if (strchr (optarg, ':')) { card = atoi (optarg); dev = atoi (strchr (optarg, ':') + 1); } else dev = atoi (optarg); printf ("Using card %d device %d \n", card, dev); break; default: return 1; } } setvbuf (stdin, NULL, _IONBF, 0); if (card == -1) { if ((rtn = snd_pcm_open_preferred (&pcm_handle, &card, &dev, SND_PCM_OPEN_PLAYBACK)) < 0) return err ("device open"); } else { if ((rtn = snd_pcm_open (&pcm_handle, card, dev, SND_PCM_OPEN_PLAYBACK)) < 0) return err ("device open"); } if (argc < 2) return err ("no file specified"); if ((file1 = fopen (argv[optind], "r")) == 0) return err ("file open #1"); if (CheckHdr (file1) == -1) return err ("CheckHdr #1"); mSamples = FindTag (file1, "fmt "); fread (&wavHdr1, sizeof (wavHdr1), 1, file1); fseek (file1, (mSamples - sizeof (WaveHdr)), SEEK_CUR); mSampleRate = ENDIAN_LE32(wavHdr1.SamplesPerSec); mSampleChannels = ENDIAN_LE16(wavHdr1.Channels); mSampleBits = ENDIAN_LE16(wavHdr1.BitsPerSample); printf ("SampleRate = %d, Channels = %d, SampleBits = %d\n", mSampleRate, mSampleChannels, mSampleBits); /* disabling mmap is not actually required in this example but it is included to * demonstrate how it is used when it is required. */ if ((rtn = snd_pcm_plugin_set_disable (pcm_handle, PLUGIN_DISABLE_MMAP)) < 0) { fprintf (stderr, "snd_pcm_plugin_set_disable failed: %s\n", snd_strerror (rtn)); return -1; } memset (&pi, 0, sizeof (pi)); pi.channel = SND_PCM_CHANNEL_PLAYBACK; if ((rtn = snd_pcm_plugin_info (pcm_handle, &pi)) < 0) { fprintf (stderr, "snd_pcm_plugin_info failed: %s\n", snd_strerror (rtn)); return -1; } memset (&pp, 0, sizeof (pp)); pp.mode = SND_PCM_MODE_BLOCK; pp.channel = SND_PCM_CHANNEL_PLAYBACK; pp.start_mode = SND_PCM_START_FULL; pp.stop_mode = SND_PCM_STOP_STOP; pp.buf.block.frag_size = pi.max_fragment_size; pp.buf.block.frags_max = 1; pp.buf.block.frags_min = 1; pp.format.interleave = 1; pp.format.rate = mSampleRate; pp.format.voices = mSampleChannels; if (mSampleBits == 8) pp.format.format = SND_PCM_SFMT_U8; else pp.format.format = SND_PCM_SFMT_S16_LE; if ((rtn = snd_pcm_plugin_params (pcm_handle, &pp)) < 0) { fprintf (stderr, "snd_pcm_plugin_params failed: %s\n", snd_strerror (rtn)); return -1; } if ((rtn = snd_pcm_plugin_prepare (pcm_handle, SND_PCM_CHANNEL_PLAYBACK)) < 0) fprintf (stderr, "snd_pcm_plugin_prepare failed: %s\n", snd_strerror (rtn)); memset (&setup, 0, sizeof (setup)); memset (&group, 0, sizeof (group)); setup.channel = SND_PCM_CHANNEL_PLAYBACK; setup.mixer_gid = &group.gid; if ((rtn = snd_pcm_plugin_setup (pcm_handle, &setup)) < 0) { fprintf (stderr, "snd_pcm_plugin_setup failed: %s\n", snd_strerror (rtn)); return -1; } printf ("Format %s \n", snd_pcm_get_format_name (setup.format.format)); printf ("Frag Size %d \n", setup.buf.block.frag_size); printf ("Rate %d \n", setup.format.rate); bsize = setup.buf.block.frag_size; if (group.gid.name[0] == 0) { printf ("Mixer Pcm Group [%s] Not Set \n", group.gid.name); exit (-1); } printf ("Mixer Pcm Group [%s]\n", group.gid.name); if ((rtn = snd_mixer_open (&mixer_handle, card, setup.mixer_device)) < 0) { fprintf (stderr, "snd_mixer_open failed: %s\n", snd_strerror (rtn)); return -1; } mSamples = FindTag (file1, "data"); mSampleBfr1 = malloc (bsize); FD_ZERO (&rfds); FD_ZERO (&wfds); n = 1; while (N < mSamples && n > 0) { FD_SET (STDIN_FILENO, &rfds); FD_SET (snd_mixer_file_descriptor (mixer_handle), &rfds); FD_SET (snd_pcm_file_descriptor (pcm_handle, SND_PCM_CHANNEL_PLAYBACK), &wfds); rtn = max (snd_mixer_file_descriptor (mixer_handle), snd_pcm_file_descriptor (pcm_handle, SND_PCM_CHANNEL_PLAYBACK)); if (select (rtn + 1, &rfds, &wfds, NULL, NULL) == -1) return err ("select"); if (FD_ISSET (STDIN_FILENO, &rfds)) { if ((rtn = snd_mixer_group_read (mixer_handle, &group)) < 0) fprintf (stderr, "snd_mixer_group_read failed: %s\n", snd_strerror (rtn)); dev_raw (fileno (stdin)); c = getc (stdin); dev_unraw (fileno (stdin)); if (c != EOF) { switch (c) { case 'q': group.volume.names.front_left += 10; break; case 'a': group.volume.names.front_left -= 10; break; case 'w': group.volume.names.front_left += 10; group.volume.names.front_right += 10; break; case 's': group.volume.names.front_left -= 10; group.volume.names.front_right -= 10; break; case 'e': group.volume.names.front_right += 10; break; case 'd': group.volume.names.front_right -= 10; break; } if (group.volume.names.front_left > group.max) group.volume.names.front_left = group.max; if (group.volume.names.front_left < group.min) group.volume.names.front_left = group.min; if (group.volume.names.front_right > group.max) group.volume.names.front_right = group.max; if (group.volume.names.front_right < group.min) group.volume.names.front_right = group.min; if ((rtn = snd_mixer_group_write (mixer_handle, &group)) < 0) fprintf (stderr, "snd_mixer_group_write failed: %s\n", snd_strerror (rtn)); } else exit (0); printf ("Volume Now at %d:%d \n", 100 * (group.volume.names.front_left - group.min) / (group.max - group.min), 100 * (group.volume.names.front_right - group.min) / (group.max - group.min)); } if (FD_ISSET (snd_mixer_file_descriptor (mixer_handle), &rfds)) { snd_mixer_callbacks_t callbacks = {0, 0, 0, 0}; snd_mixer_read (mixer_handle, &callbacks); } if (FD_ISSET (snd_pcm_file_descriptor (pcm_handle, SND_PCM_CHANNEL_PLAYBACK), &wfds)) { snd_pcm_channel_status_t status; int written = 0; if ((n = fread (mSampleBfr1, 1, min (mSamples - N, bsize), file1)) <= 0) continue; written = snd_pcm_plugin_write (pcm_handle, mSampleBfr1, n); if (written < n) { memset (&status, 0, sizeof (status)); status.channel = SND_PCM_CHANNEL_PLAYBACK; if (snd_pcm_plugin_status (pcm_handle, &status) < 0) { fprintf (stderr, "underrun: playback channel status error\n"); exit (1); } if (status.status == SND_PCM_STATUS_READY || status.status == SND_PCM_STATUS_UNDERRUN) { if (snd_pcm_plugin_prepare (pcm_handle, SND_PCM_CHANNEL_PLAYBACK) < 0) { fprintf (stderr, "underrun: playback channel prepare error\n"); exit (1); } } if (written < 0) written = 0; written += snd_pcm_plugin_write (pcm_handle, mSampleBfr1 + written, n - written); } N += written; } } n = snd_pcm_plugin_flush (pcm_handle, SND_PCM_CHANNEL_PLAYBACK); rtn = snd_mixer_close (mixer_handle); rtn = snd_pcm_close (pcm_handle); fclose (file1); return (0); }网上找了个仿制 做的音频回波例子...