使用alsa-lib实现录音
虽然网上已经有了很多的参考资料，但是不是很详细，而且注释也很少。有些看起来似懂非懂，所以在我这里提供了一版详细的实现代码，方便大家一起学习。
头文件的声明在 alsa_record.h
#ifndef COM_HXIONG_ALSA_RECORD_H
#define COM_HXIONG_ALSA_RECORD_H
//宏定义
#define RECORD_FAIL -1
#define RECORD_SUCCESS 0
#define RECORD_SAMPLE_RATE 8000
#define RECORD_BUFFER_TIME_MAX 500000
#define RECORD_DEVICE_NAME "hw:0,1"
//wav 格式的文件头
typedef struct{
char chunk_id[4]; /* "RIFF" */
char chunk_size[4]; /* file total size - 8(byte) */
char format[4]; /* "WAVE" */
/* sub-chunk "fmt" */
char sub_chunk_id[4]; /* "fmt " */
char sub_chunk_size[4]; /* 16 for PCM */
char audio_format[2]; /* PCM = 1*/
char audio_channels[2]; /* Mono = 1, Stereo = 2, etc. */
char samplerate[4]; /* 8000, 44100, etc. */
char byterate[4]; /* = SampleRate * NumChannels * BitsPerSample/8 */
char block_align[2]; /* = NumChannels * BitsPerSample/8 */
char bits_persample[2]; /* 8bits, 16bits, etc. */
//char fmt_chunk_end[2]; /* 附加的两个数据，值为0 */
/* sub-chunk "data" */
char sub_chunk2_id[4]; /* "data" */
char sub_chunk2_size[4]; /* data size */
} wav_format_t;
//自定义的结构体参数，目的时为了把command 中的参数最一层转换，到do_alsa_record 会再转成record_handle_t 中参数
typedef struct{
int duration; //录制的时长
int format; //录制的pcm格式
int rate; //采样率
int channel; //channel 个数
// 如有需要其他参数可以继续添加
} record_params_t;
//path 为录制的wav音频文件的保存路径
int do_alsa_record(char* path,record_params_t* params);
#endif真正实现录音功能的c文件在 alsa_record.c
#include
#include
#include
#include
#include
#include
#include //alsa-lib相关的头文件
#include "alsa_record.h"
//wav 的文件头定义，一些固定的参数先赋值
static wav_format_t wav_format={
{'R','I','F','F'}, //RIFF
{0,0,0,0}, //之所以定义成char，是因为保存int 的方式不一样，比如1，可存为00 00 00 01 ,或者01 00 00 00
{'W','A','V','E'}, //WAVE
{'f','m','t',' '}, //fmt 后面有一个空格
{16,0,0,0}, //一般为00000010H，若为00000012H则说明数据头携带附加信息,这里设成10h，如果设成12h，需要加上fmt_chunk_end
{1,0}, //PCM = 1
{2,0}, //Mono = 1, Stereo = 2
{0,0,0,0}, //samplerate
{0,0,0,0}, //byterate
{4,0}, //NumChannels * BitsPerSample/8
{16,0}, //8bits, 16bits, etc.
{'d','a','t','a'}, //data
{0,0,0,0} //data size
};
//在c文件内部定义,可以认为是录制参数的集合
typedef struct{
snd_pcm_t *pcm; //alsa pcm handle
snd_pcm_format_t format; //pcm 数据的格式
unsigned int channels; //channel
unsigned int rate; //采样率
snd_pcm_uframes_t chunk_size; //简单理解为一个channel 1秒产生的frame个数
size_t bits_per_sample; //一个sample包含的bit 数
size_t chunk_bytes; //简单理解为1秒产生的pcm数据大小
unsigned char* buffer; //用于保存录制数据的缓存buffer
} record_handle_t;
//pcm format 定义在alsa-lib/include/pcm.h
static snd_pcm_format_t get_format_from_params(record_params_t* params){
if(params!=NULL){ //传入的params不为空，
switch (params->format) { //这里只是简单的转换，后面可以根据需求制定转换规则
case 0:
return SND_PCM_FORMAT_S8;
case 1:
return SND_PCM_FORMAT_U8;
case 2:
return SND_PCM_FORMAT_S16_LE;
case 3:
return SND_PCM_FORMAT_S16_BE;
default: return SND_PCM_FORMAT_S16_LE;//默认返回
}
}
return SND_PCM_FORMAT_S16_LE; //默认返回
}
//简单的参数转换规则，可以根据需要自行修改
static unsigned int get_channel_from_params(record_params_t* params){
return (params->channel==2)?2:1; //默认返回 1
}
//这里只是简单的转换，后面可以根据需求制定转换规则
static unsigned int get_rate_from_params(record_params_t* params){
return (unsigned int)(params->raterate; //不能小于8000
}
static int init_recorder(record_handle_t* handle,record_params_t* params){
if(handle==NULL){
return RECORD_FAIL;
}
//1、打开pcm录音设备
if(snd_pcm_open(&(handle->pcm), RECORD_DEVICE_NAME, SND_PCM_STREAM_CAPTURE, 0) < 0) {
printf("snd_pcm_open fail.\n");
return RECORD_FAIL;
}
//2、录音相关参数设置
snd_pcm_hw_params_t *hwparams;
//构建参数结构体
snd_pcm_hw_params_alloca(&hwparams);
//3、获取参数
if(snd_pcm_hw_params_any(handle->pcm, hwparams) < 0) {
printf("snd_pcm_hw_params_any fail.\n");
goto init_recorder_fail;
}
//4、设置相关参数
if(snd_pcm_hw_params_set_access(handle->pcm, hwparams, SND_PCM_ACCESS_RW_INTERLEAVED) < 0) {
printf("snd_pcm_hw_params_set_access fail.\n");
goto init_recorder_fail;
}
handle->format = get_format_from_params(params);
//设置pcm数据格式
if(snd_pcm_hw_params_set_format(handle->pcm, hwparams, handle->format) < 0) {
printf("snd_pcm_hw_params_set_format fail.\n");
goto init_recorder_fail;
}
handle->channels=get_channel_from_params(params);
//设置channel
if(snd_pcm_hw_params_set_channels(handle->pcm, hwparams, handle->channels) < 0) {
printf("snd_pcm_hw_params_set_channels fail.\n");
goto init_recorder_fail;
}
handle->rate = get_rate_from_params(params);
unsigned int sample_rate = handle->rate;
//设置采样率
if(snd_pcm_hw_params_set_rate_near(handle->pcm, hwparams,&sample_rate, 0) < 0) {
printf("snd_pcm_hw_params_set_channels fail.\n");
goto init_recorder_fail;
}
if(handle->rate != sample_rate){
printf("The rate %d Hz is not supported, Using %d Hz instead.\n",handle->rate,sample_rate);
}
//
unsigned int buffer_time;
unsigned int period_time ;
if (snd_pcm_hw_params_get_buffer_time_max(hwparams, &buffer_time, 0) < 0) {
printf("snd_pcm_hw_params_get_buffer_time_max fail.\n");
goto init_recorder_fail;
}
if (buffer_time > RECORD_BUFFER_TIME_MAX){
buffer_time = RECORD_BUFFER_TIME_MAX;
}
period_time = buffer_time / 4;
if (snd_pcm_hw_params_set_buffer_time_near(handle->pcm, hwparams, &buffer_time, 0) < 0) {
printf("snd_pcm_hw_params_set_buffer_time_near fail.\n");
goto init_recorder_fail;
}
if (snd_pcm_hw_params_set_period_time_near(handle->pcm, hwparams, &period_time, 0) < 0) {
printf("snd_pcm_hw_params_set_period_time_near fail.\n");
goto init_recorder_fail;
}
//5、设置参数给alsa
if (snd_pcm_hw_params(handle->pcm, hwparams) < 0) {
printf("snd_pcm_hw_params fail.\n");
goto init_recorder_fail;
}
//获取相关参数
snd_pcm_uframes_t buffer_size;
snd_pcm_hw_params_get_period_size(hwparams, &(handle->chunk_size), 0);
snd_pcm_hw_params_get_buffer_size(hwparams, &buffer_size);
if (handle->chunk_size == buffer_size) {
printf("Can't use period equal to buffer size (%lu == %lu).\n",handle->chunk_size,buffer_size);
goto init_recorder_fail;
}
//根据设置计算出audio 的chunk 大小
handle->bits_per_sample = snd_pcm_format_physical_width(handle->format);
handle->chunk_bytes = (handle->chunk_size*handle->bits_per_sample * handle->channels)/8;
//申请所需的内存
handle->buffer = (unsigned char*)malloc(handle->chunk_bytes);
if(!handle->buffer){
printf("malloc buffer fail.\n");
goto init_recorder_fail;
}
return RECORD_SUCCESS;
init_recorder_fail:
snd_pcm_close(handle->pcm); //参数设置失败，就关闭
return RECORD_FAIL;
}
static int destroy_recorder(record_handle_t* handle){
if(handle==NULL){
printf("destroy_recorder handle is null.\n");
return RECORD_FAIL;
}
free(handle->buffer); //释放内存
snd_pcm_drain(handle->pcm);
snd_pcm_close(handle->pcm);
return RECORD_SUCCESS;
}
static int create_path(const char *path)
{
char *start;
mode_t mode = S_IRWXU | S_IRGRP | S_IXGRP | S_IROTH | S_IXOTH;
if (path[0] == '/')
start = strchr(path + 1, '/');
else
start = strchr(path, '/');
while (start) {
char *buffer = strdup(path);
buffer[start-path] = 0x00;
if (mkdir(buffer, mode) == -1 && errno != EEXIST) {
printf("creating directory %s fail.\n", buffer);
free(buffer);
return -1;
}
free(buffer);
start = strchr(start + 1, '/');
}
return 0;
}
static int safe_open(const char *name)
{
int fd;
fd = open(name, O_WRONLY | O_CREAT, 0644);
if (fd == -1) {
if (errno != ENOENT)
return -1;
if (create_path(name) == 0)
fd = open(name, O_WRONLY | O_CREAT, 0644);
}
return fd;
}
static int number_to_string(char* dest,size_t src,int len){
if(dest==NULL)
return RECORD_FAIL;
int index=0;
while(index>8; //右移
index++; //下标加1
}
return RECORD_SUCCESS;
}
static int do_record(record_handle_t* handle,int fd,int duration){
//计算音频数据长度（秒数 * 采样率 * 帧长度）
size_t total_size =duration*handle->rate*handle->bits_per_sample*handle->channels/8;
printf("do_record total_size is %d.\n",total_size);
snd_pcm_t* pcm=handle->pcm;
unsigned char* buffer=handle->buffer;
size_t size = handle->chunk_size;
size_t frame_byte = handle->bits_per_sample*handle->channels/8;
size_t count = 0;
int ret = 0;
//封装好wav的文件头
count = sizeof(wav_format_t);
size_t tmp=count+total_size -8; //计算chunk size大小
number_to_string(wav_format.chunk_size,tmp,4);
number_to_string(wav_format.audio_channels,handle->channels,2);
number_to_string(wav_format.samplerate,handle->rate,4);
tmp=handle->rate*frame_byte;
number_to_string(wav_format.byterate,tmp,4);
number_to_string(wav_format.block_align,frame_byte,2);
number_to_string(wav_format.bits_persample,handle->bits_per_sample,2);
number_to_string(wav_format.sub_chunk2_size,total_size,4);
//写入wav 文件头
if(write(fd,&wav_format,count)!=count){
printf("write count(%d) fail.\n",count);
return RECORD_FAIL;
}
while (total_size>0) { //写入的数据超过total size就结束
ret = snd_pcm_readi(pcm, buffer, size);
if (ret == -EAGAIN ) {
snd_pcm_wait(pcm, 1000);
} else if (ret == -EPIPE) {
snd_pcm_prepare(pcm);
printf("snd_pcm_readi return EPIPE.\n");
} else if (ret == -ESTRPIPE) {
printf("snd_pcm_readi return ESTRPIPE.\n");
} else if (ret < 0) {
printf("snd_pcm_readi return fail.\n");
return RECORD_FAIL;
}
if(ret>0){
count = ret*frame_byte;
if(write(fd,buffer,count)!=count){
printf("write count(%d) fail.\n",count);
return RECORD_FAIL;
}
total_size -= count;
}
}
return RECORD_SUCCESS;
}
int do_alsa_record(char* path,record_params_t* params){
record_handle_t record_handle={0};
if(init_recorder(&record_handle,params)==RECORD_FAIL){
printf("init_recorder fail.\n");
return RECORD_FAIL;
}
int fd = safe_open(path);
if(fd>0){
do_record(&record_handle,fd,params->duration);
close(fd); //at last,we must close fd
}else{
printf("file(%s) open fail.\n",path);
}
destroy_recorder(&record_handle);
return RECORD_SUCCESS;
}