本文共 4284 字,大约阅读时间需要 14 分钟。
参考雷神的代码:
/*** 最简单的SDL2播放音频的例子(SDL2播放PCM)* Simplest Audio Play SDL2 (SDL2 play PCM)** 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#include extern "C"{#include "SDL.h"};Uint32 audio_len;//音频数据大小Uint8 *audio_pos;//指向音频数据的指针/**回调函数(由系统调用)* 函数声明:typedef void (SDLCALL * SDL_AudioCallback) * (void *userdata, Uint8 * stream, int len);* This function is called when the audio device needs more data.** userdata: An application-specific parameter saved in the SDL_AudioSpec structure(SDL_AudioSpec结构中的用户自定义数据,一般情况下可以不用)* stream: A pointer to the audio data buffer.(该指针指向需要填充的音频缓冲区)* len: The length of that buffer in bytes.(音频缓冲区的大小,以字节为单位)** Once the callback returns, the buffer will no longer be valid.* Stereo samples are stored in a LRLRLR ordering.** You can choose to avoid callbacks and use SDL_QueueAudio() instead, if* you like. Just open your audio device with a NULL callback.*/void fill_audio(void *userdata, Uint8 *stream, int len){ //SDL2中必须首先使用SDL_memset()将stream中的数据设置为0 SDL_memset(stream, 0, len); if (audio_len == 0) /* Only play if we have data left */ { return; } len = (len > audio_len ? audio_len : len); /* Mix as much data as possible */ /** * 函数声明:extern DECLSPEC void SDLCALL * SDL_MixAudio(Uint8 * dst, const Uint8 * src, Uint32 len, int volume); * This takes two audio buffers of the playing audio format and mixes * them, performing addition, volume adjustment, and overflow clipping. * The volume ranges from 0 - 128, and should be set to ::SDL_MIX_MAXVOLUME * for full audio volume. Note this does not change hardware volume. * This is provided for convenience -- you can mix your own audio data. * * #define SDL_MIX_MAXVOLUME 128 */ SDL_MixAudio(stream, audio_pos, len, SDL_MIX_MAXVOLUME); audio_pos += len; audio_len -= len;}int main(int argc, char* argv[]){ //初始化SDL if (SDL_Init(SDL_INIT_AUDIO)) { printf("Could not initialize SDL - %s\n", SDL_GetError()); return -1; } //SDL_AudioSpec初始化 SDL_AudioSpec wanted_spec; wanted_spec.freq = 44100; //音频数据的采样率(常用的有48000,44100等) wanted_spec.format = AUDIO_S16SYS;//音频数据的格式 wanted_spec.channels = 2; //声道数(例如单声道取值为1,立体声取值为2) wanted_spec.silence = 0; //设置静音的值 wanted_spec.samples = 1024; //音频缓冲区中的采样个数(要求必须是2的n次方) wanted_spec.callback = fill_audio;//填充音频缓冲区的回调函数 //打开音频 if (SDL_OpenAudio(&wanted_spec, NULL) < 0) { printf("can't open audio.\n"); return -1; } FILE *fp_pcm = fopen("..\\FFmpeg_PCM\\output.pcm", "rb"); if (fp_pcm == NULL) { printf("cannot open this file\n"); return -1; } int pcm_buffer_size = 4096;//每次读取4096字节的数据,同时也是音频帧大小 char *pcm_buffer = (char *)malloc(pcm_buffer_size); int data_count = 0; //播放音频数据 SDL_PauseAudio(0); while (true) { int ret = fread(pcm_buffer, 1, pcm_buffer_size, fp_pcm); if (ret != pcm_buffer_size) { //这里有可能是会有剩余音频数据的,不知道这样改对不对? audio_pos = (Uint8 *)pcm_buffer; audio_len = ret; while (audio_len > 0) { SDL_Delay(1); } //退出 break; //循环播放 fseek(fp_pcm, 0, SEEK_SET); fread(pcm_buffer, 1, pcm_buffer_size, fp_pcm); data_count = 0; } printf("Now Playing %10d Bytes data.\n", data_count); data_count += pcm_buffer_size; audio_pos = (Uint8 *)pcm_buffer; //Audio buffer length audio_len = pcm_buffer_size; while (audio_len > 0)//Wait until finish { SDL_Delay(1); } } free(pcm_buffer); fclose(fp_pcm); SDL_Quit(); return 0;}
雷神代码中if (fread(pcm_buffer, 1, pcm_buffer_size, fp) != pcm_buffer_size){}
如果获取不到4096个字节的音频数据,就从头接着播放了,当然这意味着读到末尾了,但是剩下的音频数据没有做处理?疑问:
wanted_spec.silence = 0; //设置静音的值
wanted_spec.samples = 1024; //音频缓冲区中的采样个数(要求必须是2的n次方)int pcm_buffer_size = 4096;//每次读取4096字节的数据,同时也是音频帧大小