alsa学习--4.用alsa播放wav文件

一. 
1.用alsa播放wav文件的过程
  a. 打开snd_pcm_open
  b. 为param分配空间，并初始化参数
      b.1 这儿为了确认参数需要读取wav文件的头,并根据wav文件来确认参数
            需要确认的参数有三个: format(即SND_PCM_FORMAT_S16_LE类似) channels rate
  c. snd_pcm_hw_params将参数设到driver中去
  d. 循环读取wav文件中的数据,并把数据snd_pcm_writei写到驱动中进行播放
2.代码

#include "utils.h"

//#define ALSA_PCM_NEW_HW_PARAMS_API

#include <alsa/asoundlib.h>

#include <stdlib.h>

//需要从wav文件中读取的三个参数

typedef struct {

    snd_pcm_format_t format;

    unsigned int channels;

    unsigned int rate;

}HWParams; 

//下面这四个结构体是为了分析wav头的

typedef struct {

    u_int magic;   /* 'RIFF' */

    u_int length;  /* filelen */

    u_int type;    /* 'WAVE' */

} WaveHeader;

typedef struct {

    u_short format;       /* see WAV_FMT_* */

    u_short channels;

    u_int sample_fq;     /* frequence of sample */

    u_int byte_p_sec;

    u_short byte_p_spl;  /* samplesize; 1 or 2
bytes */

    u_short bit_p_spl;   /* 8, 12 or 16
bit */

} WaveFmtBody;

typedef struct {

    WaveFmtBody format;

    u_short ext_size;

    u_short bit_p_spl;

    u_int channel_mask;

    u_short guid_format; /* WAV_FMT_* */

    u_char guid_tag[14]; /* WAV_GUID_TAG */

} WaveFmtExtensibleBody;

typedef struct {

    u_int type; /* 'data' */

    u_int length; /* samplecount */

} WaveChunkHeader;

#define COMPOSE_ID(a,b,c,d) ((a) | ((b)<<8) | ((c)<<16) | ((d)<<24))

#define WAV_RIFF COMPOSE_ID('R','I','F','F')

#define WAV_WAVE COMPOSE_ID('W','A','V','E')

#define WAV_FMT COMPOSE_ID('f','m','t',' ')

#define WAV_DATA COMPOSE_ID('d','a','t','a')

//分析wav的头，并解析出alsa的param需要的三个参数

int check_wavfile(int fd, HWParams* hw_params)

{

    int ret;

    int i, len;

    WaveHeader* header;

    WaveFmtBody* fmt;

    WaveChunkHeader* chunk_header;

    unsigned char* pbuf = (unsigned char*)malloc(128); 

    if(NULL == pbuf)

    {

        dbmsg("pbuf malloc error");

        return -1;

    }

    //1. check Wave Header

    len = sizeof(WaveHeader);

    if( (ret=read(fd, pbuf, len)) != len)

    {

        dbmsg("read error");

        return -1;

    }

    header = (WaveHeader*)pbuf;

    if( (header->magic!=WAV_RIFF) || (header->type!=WAV_WAVE))

    {

        dbmsg("not a wav file");

        return -1;

    }

    //2. check Wave Fmt

    len = sizeof(WaveChunkHeader)+sizeof(WaveFmtBody);

    if( (ret=read(fd, pbuf, len)) != len)

    {

        dbmsg("read error");

        return -1;

    }

    chunk_header = (WaveChunkHeader*)pbuf;

    if( chunk_header->type!=WAV_FMT)

    {

        dbmsg("fmt body error");

        return -1;

    }

    fmt = (WaveFmtBody*)(pbuf+sizeof(WaveChunkHeader));

    if(fmt->format != 0x0001) //WAV_FMT_PCM

    {

        dbmsg("format is not pcm");

        return -1;

    }

    dbmsg("format=0x%x, channels=0x%x,sample_fq=%d,byte_p_sec=%d,byte_p_sample=%d,bit_p_sample=%d",

            fmt->format, fmt->channels,fmt->sample_fq, fmt->byte_p_sec,

            fmt->byte_p_spl, fmt->bit_p_spl);

    //copy params

    hw_params->channels = fmt->channels;

    hw_params->rate = fmt->sample_fq;

    switch(fmt->bit_p_spl)

    {

        case 8:

            hw_params->format = SND_PCM_FORMAT_U8;

            break;

        case 16:

            hw_params->format = SND_PCM_FORMAT_S16_LE;

            break;

        default:

            dbmsg("FIXME: add more format");

            break;

    }

    //3. check data chunk

    len = sizeof(WaveChunkHeader);

    if( (ret=read(fd, pbuf, len)) != len)

    {

        dbmsg("read error");

        return -1;

    }

    chunk_header = (WaveChunkHeader*)pbuf;

    if(chunk_header->type != WAV_DATA)

    {

        dbmsg("not data chunk");

        return -1;

    }

    dbmsg("pcm_data_size=0x%x",chunk_header->length);

    free(pbuf);

    pbuf = NULL;

    return -1;

}

int main ( int argc, char *argv[] )

{

    int i, fd;

    int ret, dir, size;

    unsigned int val, val2;

    char* buffer;

    snd_pcm_t* handle;

    snd_pcm_hw_params_t* params;

    snd_pcm_uframes_t periodsize;

    snd_pcm_uframes_t frames;

    HWParams hw_params;

    if(argc<2)

    {

        dbmsg("usage ./play ");

        return -1;

    }

    fd = open(argv[1], O_RDWR);

    if(fd<0)

    {

        dbmsg("file open error");

        return -1;

    }

    check_wavfile(fd, &hw_params);  
//从wav头中分析出的参数，保存在hw_param中

    //1. 打开alsa

    if( (ret = snd_pcm_open(&handle, "default", SND_PCM_STREAM_PLAYBACK, 0)) < 0)

    {

        dbmsg("open pcm device error:%s", snd_strerror(ret));

        return -1;

    }

    //2. 给参数分配空间,并用hw_param(从wav头中分析出的参数)初始化

    snd_pcm_hw_params_alloca(¶ms);

    snd_pcm_hw_params_any(handle, params);

    snd_pcm_hw_params_set_access(handle, params, SND_PCM_ACCESS_RW_INTERLEAVED);

    //snd_pcm_hw_params_set_format(handle, params, SND_PCM_FORMAT_S16_LE); //last
param get from wav file

    snd_pcm_hw_params_set_format(handle, params, hw_params.format); 

    //snd_pcm_hw_params_set_channels(handle, params, 2);

    snd_pcm_hw_params_set_channels(handle, params, hw_params.channels); //last
param get from wav file

    dbmsg("hw_params: format=%d, channels=%d", hw_params.format, hw_params.channels);

    val = 44100; 

    snd_pcm_hw_params_set_rate_near(handle,params, &val, &dir);

    frames = 32*4; 

    snd_pcm_hw_params_set_period_size_near(handle, params, &frames, &dir);

    //3. set param to driver

    if((ret=snd_pcm_hw_params(handle, params)) < 0)

    {

        dbmsg("set hw params error:%s", snd_strerror(ret));

        return -1;

    }

    snd_pcm_hw_params_get_period_size(params, &frames, &dir);

    size = frames*4; //2byte/smaple, 2
channels

    buffer = (char*)malloc(size);

    snd_pcm_hw_params_get_period_time(params, &val, &dir);

    while(1)

    {

        ret = read(fd, buffer, size);                //3.从wav文件中读取数据

        if(ret==0)

        {

            dbmsg("end of file");

            return 0;

        }else if (ret!=size)

        {

            dbmsg("short read");

        }

        ret = snd_pcm_writei(handle, buffer, frames);   //4.将读取数据写到driver中进行播放

        if(ret == -EPIPE)

        {

            //dbmsg("-EPIPE");

            snd_pcm_prepare(handle);

        }

    }

    snd_pcm_drain(handle);

    snd_pcm_close(handle);

    free(buffer);

    return EXIT_SUCCESS;

}

3. 运行结果

cong@msi:/work/ffmpeg/test/alsa/testalsa/4player$
make run

export LD_LIBRARY_PATH=/work/ffmpeg/out/lib/ \

    && ./play /work/ffmpeg/test/resource//test.wav

play.c:check_wavfile[94]: format=0x1, channels=0x2,sample_fq=44100,byte_p_sec=176400,byte_p_sample=4,bit_p_sample=16

play.c:check_wavfile[123]: pcm_data_size=0x25c9b20

play.c:main[168]: hw_params: format=2, channels=2

4.代码打包


4player.rar(下载后改名为4player.tar.gz)