C++使用alsa库实现播放声音文件

前言

平常读麦克风的场景居多，有时候也需要播放一个声音文件，这里就介绍怎么处理。

一、命令行

1.ffmpeg

ffmpeg -i <filename.wav> -f alsa default

2.aplay

aplay -i <filename.wav>

如果提示找不到aplay就安装工具：

sudo apt install alsa-utils

二、代码实现

main.cpp

#include <alsa/asoundlib.h>
#include <iostream>
#include <fstream>

#define PCM_DEVICE "default"//默认的播放设备,你可以在settings里面调换

int main(int argc, char *argv[]) {
    const char *audioFilename = "../wakeup.wav";

    // 配置ALSA参数
    snd_pcm_t *pcmHandle;
    if (snd_pcm_open(&pcmHandle, PCM_DEVICE, SND_PCM_STREAM_PLAYBACK, 0) < 0) {
        std::cerr << "Error: Failed to open PCM device" << std::endl;
        return 1;
    }

    snd_pcm_hw_params_t *params;
    snd_pcm_hw_params_alloca(&params);
    snd_pcm_hw_params_any(pcmHandle, params);
    snd_pcm_hw_params_set_access(pcmHandle, params, SND_PCM_ACCESS_RW_INTERLEAVED);
    snd_pcm_hw_params_set_format(pcmHandle, params, SND_PCM_FORMAT_S16_LE);
    snd_pcm_hw_params_set_channels(pcmHandle, params, 2);
    unsigned int sampleRate = 48000;
    snd_pcm_hw_params_set_rate_near(pcmHandle, params, &sampleRate, nullptr);
    snd_pcm_uframes_t bufferSize = 512;
    snd_pcm_hw_params_set_buffer_size_near(pcmHandle, params, &bufferSize);
    snd_pcm_hw_params(pcmHandle, params);

    std::ifstream ifs("../wakeup.wav");
    if (ifs.is_open()) {
        std::string data;
        size_t size;
        char buffer[8192];
        while ((size = ifs.readsome(buffer, 8192)) > 0) {
            data.append(buffer, size);
        }
        snd_pcm_sframes_t err = snd_pcm_writei(pcmHandle, (const void *) data.c_str(),
                                               data.size()); 
        if (err < 0) {
            std::cerr << "Error: Failed to write PCM device" << std::endl;
        }
        ifs.close();
    }

    // 关闭PCM设备和文件
    snd_pcm_close(pcmHandle);
    return 0;
}

CMakeLists.txt

cmake_minimum_required(VERSION 3.10)
project(write_speaker)

set(CMAKE_CXX_STANDARD 11)

add_executable(${PROJECT_NAME} main.cpp)
target_link_libraries(${PROJECT_NAME} asound)

三、知识补充

C++使用Alsa采集linux音频

1、运行时前先装库,sudo apt-get install libalsa

2遍tab自动提示出库文件，选择库，alsa-ocaml-dev，最终的命令行为：sudo apt-get install libalsa-ocaml-dev

2、编译执行脚本，gcc -o main main.c -lasound;

3、执行 ./main

以下是代码

#include <stdlib.h>
#include <stdio.h>
#include <alsa/asoundlib.h>
#include <signal.h>
static int recording;

void stop_record(int param)
{
recording = 0;
}
void InitCapture(snd_pcm_t ** handle,snd_pcm_hw_params_t ** params,snd_pcm_uframes_t* frames,char ** buffer,int* size)
{
int ret;
unsigned int val;
int dir;
//打开设备
ret = snd_pcm_open(handle, “default”, SND_PCM_STREAM_CAPTURE, 0);
printf(“after open file\n”);
if (ret < 0)
{
fprintf(stderr, “unable to open device:%s\n”, snd_strerror(ret));
exit(1);
}
//分配一个硬件参数结构体
snd_pcm_hw_params_alloca(params);

//使用默认参数
snd_pcm_hw_params_any(*handle, *params);

//翻译
    snd_pcm_hw_params_set_access(*handle, *params, SND_PCM_ACCESS_RW_INTERLEAVED);

//S16小端
snd_pcm_hw_params_set_format(*handle, *params, SND_PCM_FORMAT_S16_LE);

//双通道，立体声
snd_pcm_hw_params_set_channels(*handle, *params, 2);

//采样率
val = 44100;
snd_pcm_hw_params_set_rate_near(*handle, *params,&val,&dir);

*frames = 32;
snd_pcm_hw_params_set_period_size_near(*handle, *params,frames,&dir);

//参数生效
ret = snd_pcm_hw_params(*handle, *params);
if (ret<0)
{
	fprintf(stderr, "unable to set hw parameters:%s\n", snd_strerror(ret));
		exit(1);
}
//得到一个周期的数据大小
snd_pcm_hw_params_get_period_size(*params, frames, &dir);

//16位双通道，16位为2字节，2字节*2通道=4，假如frames=1024，则size是1024*4 = 4096
*size = *frames * 4;
*buffer = (char*)malloc(*size); 

//设置一个周期的时间长度
snd_pcm_hw_params_get_period_time(*params, &val, &dir);
}

void CaptureAudio(snd_pcm_t ** handle,snd_pcm_uframes_t* frames,char ** buffer,int* size,FILE ** pFile)
{
int ret;

recording = 1;
while (recording)
{
	ret = snd_pcm_readi(*handle, *buffer,*frames);
	if (ret == -EPIPE )
	{
		fprintf(stderr, "overrun occurred\n");
		snd_pcm_prepare(*handle);
	}
	else if (ret < 0)
	{
		fprintf(stderr, "error from read\n");
		snd_strerror(ret);
	}
	else if (ret != (int)(*frames))
	{
		fprintf(stderr, "short read %d frames\n",ret);
	}
	printf("write to file......%d\n", *size);
	//写到标准输出中去
	ret = fwrite(*buffer, sizeof(char), *size, *pFile);
	if (ret != *size)
	{
		fprintf(stderr, "short write :write %d bytes\n", ret);
	}
	if (signal(SIGINT, stop_record)==SIG_ERR)
	{
		fprintf(stderr, "signal failed\n");
	}
}
}

void CloseCaptureDevice(FILE ** pFile,snd_pcm_t ** handle,char ** buffer)
{
printf(“write file exit\n”);
snd_pcm_drain(*handle);
snd_pcm_close(*handle);
free(*buffer);
fclose(*pFile);
}

int main()
{
FILE * pFile;
pFile = fopen(“test.pcm”, “wb”);
int size;
//给文件操作分配一个句柄
snd_pcm_t * handle;
//硬件参数
snd_pcm_hw_params_t * params;
//
snd_pcm_uframes_t frames;
char * buffer;
printf(“before open file\n”);
InitCapture(&handle,&params,&frames,&buffer,&size);
CaptureAudio(&handle,&frames,&buffer,&size,&pFile);
CloseCaptureDevice(&pFile,&handle,&buffer);
printf(“write file exit\n”);

return 0;
}