main.cpp

/**
 * 最简单的SDL2播放音频的例子（SDL2播放PCM）
 * Simplest Audio Play SDL2 (SDL2 play PCM) 
 *
 * 雷霄骅 Lei Xiaohua
 * leixiaohua1020@126.com
 * 中国传媒大学/数字电视技术
 * Communication University of China / Digital TV Technology
 * http://blog.csdn.net/leixiaohua1020
 *
 * 本程序使用SDL2播放PCM音频采样数据。SDL实际上是对底层绘图
 * API（Direct3D，OpenGL）的封装，使用起来明显简单于直接调用底层
 * API。
 *
 * 函数调用步骤如下: 
 *
 * [初始化]
 * SDL_Init(): 初始化SDL。
 * SDL_OpenAudio(): 根据参数（存储于SDL_AudioSpec）打开音频设备。
 * SDL_PauseAudio(): 播放音频数据。
 *
 * [循环播放数据]
 * SDL_Delay(): 延时等待播放完成。
 *
 * This software plays PCM raw audio data using SDL2.
 * SDL is a wrapper of low-level API (DirectSound).
 * Use SDL is much easier than directly call these low-level API.
 *
 * The process is shown as follows:
 *
 * [Init]
 * SDL_Init(): Init SDL.
 * SDL_OpenAudio(): Opens the audio device with the desired 
 *					parameters (In SDL_AudioSpec).
 * SDL_PauseAudio(): Play Audio.
 *
 * [Loop to play data]
 * SDL_Delay(): Wait for completetion of playback.
 */

#include <stdio.h>

extern "C"
{
#include "SDL2/SDL.h"
};

//Buffer:
//|-----------|-------------|
//chunk-------pos---len-----|
static  Uint8  *audio_chunk; 
static  Uint32  audio_len; 
static  Uint8  *audio_pos; 

/* Audio Callback
 * The audio function callback takes the following parameters: 
 * stream: A pointer to the audio buffer to be filled 
 * len: The length (in bytes) of the audio buffer 
 * 
*/ 
void  fill_audio(void *udata,Uint8 *stream,int len){ 
	//SDL 2.0
	SDL_memset(stream, 0, len);
	if(audio_len==0)
			return; 
	len=(len>audio_len?audio_len:len);

	SDL_MixAudio(stream,audio_pos,len,SDL_MIX_MAXVOLUME);
	audio_pos += len; 
	audio_len -= len; 
} 

int main(int argc, char* argv[])
{
	//Init
	if(SDL_Init(SDL_INIT_AUDIO | SDL_INIT_TIMER)) {  
		printf( "Could not initialize SDL - %s\n", SDL_GetError()); 
		return -1;
	}
	//SDL_AudioSpec
	SDL_AudioSpec wanted_spec;
	wanted_spec.freq = 44100; 
	wanted_spec.format = AUDIO_S16SYS; 
	wanted_spec.channels = 2; 
	wanted_spec.silence = 0; 
	wanted_spec.samples = 1024; 
	wanted_spec.callback = fill_audio; 

	if (SDL_OpenAudio(&wanted_spec, NULL)<0){ 
		printf("can't open audio.\n"); 
		return -1; 
	} 

	FILE *fp=fopen("./NocturneNo2inEflat_44.1k_s16le.pcm","rb+");
	if(fp==NULL){
		printf("cannot open this file\n");
		return -1;
	}
	int pcm_buffer_size=4096;
	char *pcm_buffer=(char *)malloc(pcm_buffer_size);
	int data_count=0;

	//Play
	SDL_PauseAudio(0);

	while(1){
		if (fread(pcm_buffer, 1, pcm_buffer_size, fp) != pcm_buffer_size){
			// Loop
			fseek(fp, 0, SEEK_SET);
			fread(pcm_buffer, 1, pcm_buffer_size, fp);
			data_count=0;
		}
		printf("Now Playing %10d Bytes data.\n",data_count);
		data_count+=pcm_buffer_size;
		//Set audio buffer (PCM data)
		audio_chunk = (Uint8 *) pcm_buffer; 
		//Audio buffer length
		audio_len =pcm_buffer_size;
		audio_pos = audio_chunk;
		
		while(audio_len>0)//Wait until finish
			SDL_Delay(1); 
	}
	free(pcm_buffer);
	SDL_Quit();

	return 0;
}