1.指定使用最新的ALSA API
#define ALSA_PCM_NEW_HW_PARAMS_API
2.包含头文件
#include <alsa/asoundlib.h>
3.定义变量
snd_pcm_t *handle; //调用snd_pcm_open打开PCM设备返回的文件句柄，后续的操作都使用是、这个句柄操作这个PCM设备
snd_pcm_hw_params_t *params; //设置流的硬件参数
snd_pcm_uframes_t frames; //snd_pcm_uframes_t其实是unsigned long类型
4.打开PCM设备
使用snd_pcm_open函数
/* Open PCM device for playback */
rc = snd_pcm_open(&handle, "defalut", SND_PCM_STREAM_PLAYBACK, 0);
if (rc < 0)
{
printf("unable to open pcm device\n");
return -1;
}
函数原型：
int snd_pcm_open(snd_pcm_t **pcm, const char *name, snd_pcm_stream_t stream, int mode);
参数说明：
pcm：即第三步声明的变量handle，用来接收返回的PCM文件句柄
name：可以是hw:0,0，或plughw:0,0
stream：可以是SND_PCM_STREAM_PLAYBACK //Playback stream
或SND_PCM_STREAM_CAPTURE //Capture stream
mode：暂时不明白是什么意思
5.分配一个硬件参数对象
/* Allocate a hardware parameters object */
snd_pcm_hw_params_alloca(¶ms);
6.向对象填充默认值
/* Fill it in with default values. */
snd_pcm_hw_params_any(handle, params);
7.设置所需的硬件参数
7.1.设置交错模式
/* Interleaved mode */
snd_pcm_hw_params_set_access(handle, params, SND_PCM_ACCESS_RW_INTERLEAVED);
可以设置的模式如下：
7.2.设置格式
/* Signed 16-bit little-endian format */
snd_pcm_hw_params_set_format(handle, params, SND_PCM_FORMAT_S16_LE);
7.3设置通道
/* Two channels (stero) */
snd_pcm_hw_params_set_channels(handle, params, 2);
7.4设置采用率
/* 44100 bits/second sampling rate */
val = 44100;
snd_pcm_hw_params_set_rate_near(handle, params, &val, &dir);
8.将上面设置的参数传给驱动，只有经过这步，上面设置的参数才有效
/* Write the parameters to the dirver */
rc = snd_pcm_hw_params(handle, params);
if (rc < 0) {
printf("unable to set hw parameters: %s\n", snd_strerror(rc));
exit(1);
}
9.获取存储采用数据buffer的大小
int dir;
snd_pcm_hw_params_get_period_size(params, &frames, &dir);
size = frames * 4;
buffer = (char *)malloc(size);
获取period time时间
snd_pcm_hw_params_get_period_time(params, &val, &dir);
10.将数据读入buffer
rc = read(0, buffer, size);
11.将buffer数据写入PCM设备
rc = snd_pcm_writei(handle, buffer, frames);
if (rc == -EPIPE) {
printf("underrun occured\n");
}
else if (rc < 0) {
printf("error from writei: %s\n", snd_strerror(rc));
}
12.将handle冲刷干净，关闭流，释放buffer
snd_pcm_drain(handle);
snd_pcm_close(handle);
free(buffer);
以下是通过alsa-lib播放wav文件的代码
/*
*作者：韦访
*CSDN:https://blog.csdn.net/rookie_wei
**/
#define ALSA_PCM_NEW_HW_PARAMS_API
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <alsa/asoundlib.h>
#define u32 unsigned int
#define u8 unsigned char
#define u16 unsigned short
#pragma pack(push)
#pragma pack(1) //1字节对齐
typedef struct {
u32 dwSize;
u16 wFormatTag;
u16 wChannels;
u32 dwSamplesPerSec;
u32 dwAvgBytesPerSec;
u16 wBlockAlign;
u16 wBitsPerSample;
} WAVEFORMAT;
typedef struct {
u8 RiffID [4];
u32 RiffSize;
u8 WaveID[4];
u8 FmtID[4];
u32 FmtSize;
u16 wFormatTag;
u16 nChannels;
u32 nSamplesPerSec; /*采样频率*/
u32 nAvgBytesPerSec; /*每秒所需字节数*/
u16 nBlockAlign; /*数据块对齐单位,每个采样需要的字节数*/
u16 wBitsPerSample;/*每个采样需要的bit数*/
u8 DataID[4];
u32 nDataBytes;
} WAVE_HEADER;
#pragma pack(pop) /* 恢复先前的pack设置 */
WAVE_HEADER g_wave_header;
snd_pcm_t *gp_handle; //调用snd_pcm_open打开PCM设备返回的文件句柄，后续的操作都使用是、这个句柄操作这个PCM设备
snd_pcm_hw_params_t *gp_params; //设置流的硬件参数
snd_pcm_uframes_t g_frames; //snd_pcm_uframes_t其实是unsigned long类型
char *gp_buffer;
u32 g_bufsize;
FILE * open_and_print_file_params(char *file_name)
{
FILE * fp = fopen(file_name, "r");
if (fp == NULL)
{
printf("can't open wav file\n");
return NULL;
}
memset(&g_wave_header, 0, sizeof(g_wave_header));
fread(&g_wave_header, 1, sizeof(g_wave_header), fp);
printf("RiffID:%c%c%c%c\n", g_wave_header.RiffID[0], g_wave_header.RiffID[1], g_wave_header.RiffID[2], g_wave_header.RiffID[3]);
printf("RiffSize:%d\n", g_wave_header.RiffSize);
printf("WaveID:%c%c%c%c\n", g_wave_header.WaveID[0], g_wave_header.WaveID[1], g_wave_header.WaveID[2], g_wave_header.WaveID[3]);
printf("FmtID:%c%c%c%c\n", g_wave_header.FmtID[0], g_wave_header.FmtID[1], g_wave_header.FmtID[2], g_wave_header.FmtID[3]);
printf("FmtSize:%d\n", g_wave_header.FmtSize);
printf("wFormatTag:%d\n", g_wave_header.wFormatTag);
printf("nChannels:%d\n", g_wave_header.nChannels);
printf("nSamplesPerSec:%d\n", g_wave_header.nSamplesPerSec);
printf("nAvgBytesPerSec:%d\n", g_wave_header.nAvgBytesPerSec);
printf("nBlockAlign:%d\n", g_wave_header.nBlockAlign);
printf("wBitsPerSample:%d\n", g_wave_header.wBitsPerSample);
printf("DataID:%c%c%c%c\n", g_wave_header.DataID[0], g_wave_header.DataID[1], g_wave_header.DataID[2], g_wave_header.DataID[3]);
printf("nDataBytes:%d\n", g_wave_header.nDataBytes);
return fp;
}
int set_hardware_params()
{
int rc;
/* Open PCM device for playback */
rc = snd_pcm_open(&gp_handle, "hw:0,0", SND_PCM_STREAM_PLAYBACK, 0);
if (rc < 0)
{
printf("unable to open pcm device\n");
return -1;
}
/* Allocate a hardware parameters object */
snd_pcm_hw_params_alloca(&gp_params);
/* Fill it in with default values. */
rc = snd_pcm_hw_params_any(gp_handle, gp_params);
if (rc < 0)
{
printf("unable to Fill it in with default values.\n");
goto err1;
}
/* Interleaved mode */
rc = snd_pcm_hw_params_set_access(gp_handle, gp_params, SND_PCM_ACCESS_RW_INTERLEAVED);
if (rc < 0)
{
printf("unable to Interleaved mode.\n");
goto err1;
}
snd_pcm_format_t format;
if (8 == g_wave_header.FmtSize)
{
format = SND_PCM_FORMAT_U8;
}
else if (16 == g_wave_header.FmtSize)
{
format = SND_PCM_FORMAT_S16_LE;
}
else if (24 == g_wave_header.FmtSize)
{
format = SND_PCM_FORMAT_U24_LE;
}
else if (32 == g_wave_header.FmtSize)
{
format = SND_PCM_FORMAT_U32_LE;
}
else
{
printf("SND_PCM_FORMAT_UNKNOWN.\n");
format = SND_PCM_FORMAT_UNKNOWN;
goto err1;
}
/* set format */
rc = snd_pcm_hw_params_set_format(gp_handle, gp_params, format);
if (rc < 0)
{
printf("unable to set format.\n");
goto err1;
}
/* set channels (stero) */
snd_pcm_hw_params_set_channels(gp_handle, gp_params, g_wave_header.nChannels);
if (rc < 0)
{
printf("unable to set channels (stero).\n");
goto err1;
}
/* set sampling rate */
u32 dir, rate = g_wave_header.nSamplesPerSec;
rc = snd_pcm_hw_params_set_rate_near(gp_handle, gp_params, &rate, &dir);
if (rc < 0)
{
printf("unable to set sampling rate.\n");
goto err1;
}
/* Write the parameters to the dirver */
rc = snd_pcm_hw_params(gp_handle, gp_params);
if (rc < 0) {
printf("unable to set hw parameters: %s\n", snd_strerror(rc));
goto err1;
}
snd_pcm_hw_params_get_period_size(gp_params, &g_frames, &dir);
g_bufsize = g_frames * 4;
gp_buffer = (u8 *)malloc(g_bufsize);
if (gp_buffer == NULL)
{
printf("malloc failed\n");
goto err1;
}
return 0;
err1:
snd_pcm_close(gp_handle);
return -1;
}
int main(int argc, char *argv[])
{
if (argc < 2)
{
printf("usage: %s filename.wav\n", argv[0]);
return -1;
}
FILE * fp = open_and_print_file_params(argv[1]);
int fd = open(argv[1], O_RDONLY);
if (fp == NULL)
{
printf("open_and_print_file_params error\n");
return -1;
}
int ret = set_hardware_params();
if (ret < 0)
{
printf("set_hardware_params error\n");
return -1;
}
size_t rc;
while (1)
{
rc = fread(gp_buffer, g_bufsize, 1, fp);
if (rc <1)
{
break;
}
ret = snd_pcm_writei(gp_handle, gp_buffer, g_frames);
if (ret == -EPIPE) {
printf("underrun occured\n");
break;
}
else if (ret < 0) {
printf("error from writei: %s\n", snd_strerror(ret));
break;
}
}
snd_pcm_drain(gp_handle);
snd_pcm_close(gp_handle);
free(gp_buffer);
fclose(fp);
return 0;
}
编译命令：
gcc wavplayer.c -o wavplayer -lasound -ldl -lm