1. Display Some PCM Types and Formats
2. Opening PCM Device and Setting Parameters
/* This example opens the default PCM device, sets some parameters, and then displays the value of most of the hardware parameters. It does not perform any sound playback or recording. */ /* Use the newer ALSA API */ #define ALSA_PCM_NEW_HW_PARAMS_API /* All of the ALSA library API is defined * in this header */ #include <alsa/asoundlib.h> int main() { int rc; snd_pcm_t *handle; snd_pcm_hw_params_t *params; unsigned int val, val2; int dir; snd_pcm_uframes_t frames; /* Open PCM device for playback. */ rc = snd_pcm_open(&handle, "default", SND_PCM_STREAM_PLAYBACK, 0); if (rc < 0) { fprintf(stderr, "unable to open pcm device: %s ", snd_strerror(rc)); exit(1); } /* Allocate a hardware parameters object. */ snd_pcm_hw_params_alloca(¶ms); /* Fill it in with default values. */ snd_pcm_hw_params_any(handle, params); /* Set the desired hardware parameters. */ /* Interleaved mode */ snd_pcm_hw_params_set_access(handle, params, SND_PCM_ACCESS_RW_INTERLEAVED); /* Signed 16-bit little-endian format */ snd_pcm_hw_params_set_format(handle, params, SND_PCM_FORMAT_S16_LE); /* Two channels (stereo) */ snd_pcm_hw_params_set_channels(handle, params, 2); /* 44100 bits/second sampling rate (CD quality) */ val = 44100; snd_pcm_hw_params_set_rate_near(handle, params, &val, &dir); /* Write the parameters to the driver */ rc = snd_pcm_hw_params(handle, params); if (rc < 0) { fprintf(stderr, "unable to set hw parameters: %s ", snd_strerror(rc)); exit(1); } /* Display information about the PCM interface */ printf("PCM handle name = '%s' ", snd_pcm_name(handle)); printf("PCM state = %s ", snd_pcm_state_name(snd_pcm_state(handle))); snd_pcm_hw_params_get_access(params, (snd_pcm_access_t *) &val); printf("access type = %s ", snd_pcm_access_name((snd_pcm_access_t)val)); snd_pcm_hw_params_get_format(params, &val); printf("format = '%s' (%s) ", snd_pcm_format_name((snd_pcm_format_t)val), snd_pcm_format_description( (snd_pcm_format_t)val)); snd_pcm_hw_params_get_subformat(params, (snd_pcm_subformat_t *)&val); printf("subformat = '%s' (%s) ", snd_pcm_subformat_name((snd_pcm_subformat_t)val), snd_pcm_subformat_description( (snd_pcm_subformat_t)val)); snd_pcm_hw_params_get_channels(params, &val); printf("channels = %d ", val); snd_pcm_hw_params_get_rate(params, &val, &dir); printf("rate = %d bps ", val); snd_pcm_hw_params_get_period_time(params, &val, &dir); printf("period time = %d us ", val); snd_pcm_hw_params_get_period_size(params, &frames, &dir); printf("period size = %d frames ", (int)frames); snd_pcm_hw_params_get_buffer_time(params, &val, &dir); printf("buffer time = %d us ", val); snd_pcm_hw_params_get_buffer_size(params, (snd_pcm_uframes_t *) &val); printf("buffer size = %d frames ", val); snd_pcm_hw_params_get_periods(params, &val, &dir); printf("periods per buffer = %d frames ", val); snd_pcm_hw_params_get_rate_numden(params, &val, &val2); printf("exact rate = %d/%d bps ", val, val2); val = snd_pcm_hw_params_get_sbits(params); printf("significant bits = %d ", val); snd_pcm_hw_params_get_tick_time(params, &val, &dir); printf("tick time = %d us ", val); val = snd_pcm_hw_params_is_batch(params); printf("is batch = %d ", val); val = snd_pcm_hw_params_is_block_transfer(params); printf("is block transfer = %d ", val); val = snd_pcm_hw_params_is_double(params); printf("is double = %d ", val); val = snd_pcm_hw_params_is_half_duplex(params); printf("is half duplex = %d ", val); val = snd_pcm_hw_params_is_joint_duplex(params); printf("is joint duplex = %d ", val); val = snd_pcm_hw_params_can_overrange(params); printf("can overrange = %d ", val); val = snd_pcm_hw_params_can_mmap_sample_resolution(params); printf("can mmap = %d ", val); val = snd_pcm_hw_params_can_pause(params); printf("can pause = %d ", val); val = snd_pcm_hw_params_can_resume(params); printf("can resume = %d ", val); val = snd_pcm_hw_params_can_sync_start(params); printf("can sync start = %d ", val); snd_pcm_close(handle); return 0; }
3. Simple Sound Playback
/* This example reads standard from input and writes to the default PCM device for 5 seconds of data. */ /* Use the newer ALSA API */ #define ALSA_PCM_NEW_HW_PARAMS_API #include <alsa/asoundlib.h> int main() { long loops; int rc; int size; snd_pcm_t *handle; snd_pcm_hw_params_t *params; unsigned int val; int dir; snd_pcm_uframes_t frames; char *buffer; /* Open PCM device for playback. */ rc = snd_pcm_open(&handle, "default", SND_PCM_STREAM_PLAYBACK, 0); if (rc < 0) { fprintf(stderr, "unable to open pcm device: %s ", snd_strerror(rc)); exit(1); } /* Allocate a hardware parameters object. */ snd_pcm_hw_params_alloca(¶ms); /* Fill it in with default values. */ snd_pcm_hw_params_any(handle, params); /* Set the desired hardware parameters. */ /* Interleaved mode */ snd_pcm_hw_params_set_access(handle, params, SND_PCM_ACCESS_RW_INTERLEAVED); /* Signed 16-bit little-endian format */ snd_pcm_hw_params_set_format(handle, params, SND_PCM_FORMAT_S16_LE); /* Two channels (stereo) */ snd_pcm_hw_params_set_channels(handle, params, 2); /* 44100 bits/second sampling rate (CD quality) */ val = 44100; snd_pcm_hw_params_set_rate_near(handle, params, &val, &dir); /* Set period size to 32 frames. */ frames = 32; snd_pcm_hw_params_set_period_size_near(handle, params, &frames, &dir); /* Write the parameters to the driver */ rc = snd_pcm_hw_params(handle, params); if (rc < 0) { fprintf(stderr, "unable to set hw parameters: %s ", snd_strerror(rc)); exit(1); } /* Use a buffer large enough to hold one period */ snd_pcm_hw_params_get_period_size(params, &frames, &dir); size = frames * 4; /* 2 bytes/sample, 2 channels */ buffer = (char *) malloc(size); /* We want to loop for 5 seconds */ snd_pcm_hw_params_get_period_time(params, &val, &dir); /* 5 seconds in microseconds divided by * period time */ loops = 5000000 / val; while (loops > 0) { loops--; rc = read(0, buffer, size); if (rc == 0) { fprintf(stderr, "end of file on input "); break; } else if (rc != size) { fprintf(stderr, "short read: read %d bytes ", rc); } rc = snd_pcm_writei(handle, buffer, frames); if (rc == -EPIPE) { /* EPIPE means underrun */ fprintf(stderr, "underrun occurred "); snd_pcm_prepare(handle); } else if (rc < 0) { fprintf(stderr, "error from writei: %s ", snd_strerror(rc)); } else if (rc != (int)frames) { fprintf(stderr, "short write, write %d frames ", rc); } } snd_pcm_drain(handle); snd_pcm_close(handle); free(buffer); return 0; }
编译之后，可以用下面的命令来测试：
./example3 < /dev/urandom
4. Simple Sound Recording
/* This example reads from the default PCM device and writes to standard output for 5 seconds of data. */ /* Use the newer ALSA API */ #define ALSA_PCM_NEW_HW_PARAMS_API #include <alsa/asoundlib.h> int main() { long loops; int rc; int size; snd_pcm_t *handle; snd_pcm_hw_params_t *params; unsigned int val; int dir; snd_pcm_uframes_t frames; char *buffer; /* Open PCM device for recording (capture). */ rc = snd_pcm_open(&handle, "default", SND_PCM_STREAM_CAPTURE, 0); if (rc < 0) { fprintf(stderr, "unable to open pcm device: %s ", snd_strerror(rc)); exit(1); } /* Allocate a hardware parameters object. */ snd_pcm_hw_params_alloca(¶ms); /* Fill it in with default values. */ snd_pcm_hw_params_any(handle, params); /* Set the desired hardware parameters. */ /* Interleaved mode */ snd_pcm_hw_params_set_access(handle, params, SND_PCM_ACCESS_RW_INTERLEAVED); /* Signed 16-bit little-endian format */ snd_pcm_hw_params_set_format(handle, params, SND_PCM_FORMAT_S16_LE); /* Two channels (stereo) */ snd_pcm_hw_params_set_channels(handle, params, 2); /* 44100 bits/second sampling rate (CD quality) */ val = 44100; snd_pcm_hw_params_set_rate_near(handle, params, &val, &dir); /* Set period size to 32 frames. */ frames = 32; snd_pcm_hw_params_set_period_size_near(handle, params, &frames, &dir); /* Write the parameters to the driver */ rc = snd_pcm_hw_params(handle, params); if (rc < 0) { fprintf(stderr, "unable to set hw parameters: %s ", snd_strerror(rc)); exit(1); } /* Use a buffer large enough to hold one period */ snd_pcm_hw_params_get_period_size(params, &frames, &dir); size = frames * 4; /* 2 bytes/sample, 2 channels */ buffer = (char *) malloc(size); /* We want to loop for 5 seconds */ snd_pcm_hw_params_get_period_time(params, &val, &dir); loops = 5000000 / val; while (loops > 0) { loops--; rc = snd_pcm_readi(handle, buffer, frames); if (rc == -EPIPE) { /* EPIPE means overrun */ fprintf(stderr, "overrun occurred "); snd_pcm_prepare(handle); } else if (rc < 0) { fprintf(stderr, "error from read: %s ", snd_strerror(rc)); } else if (rc != (int)frames) { fprintf(stderr, "short read, read %d frames ", rc); } rc = write(1, buffer, size); if (rc != size) fprintf(stderr, "short write: wrote %d bytes ", rc); } snd_pcm_drain(handle); snd_pcm_close(handle); free(buffer); return 0; }
录音使用下面的命令测试：
./listing4 > sound.raw
./listing3 < sound.raw
5. wav格式文件播放测试
这个例子是我根据例子3修改而来的，用来播放wav格式音频文件，注意wav文件格式必须是44100、16bit, 2通道。
#include <alsa/asoundlib.h> int main(int argc, char *argv[]) { int rc; int size; snd_pcm_t *handle; snd_pcm_hw_params_t *params; unsigned int val; int dir; snd_pcm_uframes_t frames; char *buffer; FILE *fp; fp = fopen(argv[1], "rb"); if (!fp) { fprintf(stderr, "can't open sound file "); exit(1); } /* Open PCM device for playback. */ rc = snd_pcm_open(&handle, "default", SND_PCM_STREAM_PLAYBACK, 0); if (rc < 0) { fprintf(stderr, "unable to open pcm device: %s ", snd_strerror(rc)); exit(1); } /* Allocate a hardware parameters object. */ snd_pcm_hw_params_alloca(¶ms); /* Fill it in with default values. */ snd_pcm_hw_params_any(handle, params); /* Set the desired hardware parameters. */ /* Interleaved mode */ snd_pcm_hw_params_set_access(handle, params, SND_PCM_ACCESS_RW_INTERLEAVED); /* Signed 16-bit little-endian format */ snd_pcm_hw_params_set_format(handle, params, SND_PCM_FORMAT_S16_LE); /* Two channels (stereo) */ snd_pcm_hw_params_set_channels(handle, params, 2); /* 44100 bits/second sampling rate (CD quality) */ val = 44100; snd_pcm_hw_params_set_rate_near(handle, params, &val, &dir); /* Set period size to 32 frames. */ frames = 32; snd_pcm_hw_params_set_period_size_near(handle, params, &frames, &dir); /* Write the parameters to the driver */ rc = snd_pcm_hw_params(handle, params); if (rc < 0) { fprintf(stderr, "unable to set hw parameters: %s ", snd_strerror(rc)); exit(1); } /* Use a buffer large enough to hold one period */ snd_pcm_hw_params_get_period_size(params, &frames, &dir); size = frames * 4; /* 2 bytes/sample, 2 channels */ buffer = (char *)malloc(size); fseek(fp, 44, SEEK_SET); while (1) { rc = fread(buffer, 1, size, fp); if (rc == 0) { fprintf(stderr, "end of file on input "); break; } else if (rc != size) { fprintf(stderr, "short read: read %d bytes ", rc); } rc = snd_pcm_writei(handle, buffer, frames); if (rc == -EPIPE) { /* EPIPE means underrun */ fprintf(stderr, "underrun occurred "); snd_pcm_prepare(handle); } else if (rc < 0) { fprintf(stderr, "error from writei: %s ", snd_strerror(rc)); } else if (rc != (int)frames) { fprintf(stderr, "short write, write %d frames ", rc); } } snd_pcm_drain(handle); snd_pcm_close(handle); fclose(fp); free(buffer); return 0; }