最简单的基于FFMPEG+SDL的音频播放器：拆分-解码器和播放器

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最简单的基于FFmpeg的音频播放器系列文章列表：

《最简单的基于FFMPEG+SDL的音频播放器》

《最简单的基于FFMPEG+SDL的音频播放器 ver2 （采用SDL2.0）》

《最简单的基于FFMPEG+SDL的音频播放器：拆分-解码器和播放器》

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本文补充记录《最简单的基于FFMPEG+SDL的音频播放器》中的两个例子：FFmpeg音频解码器和SDL音频采样数据播放器。这两个部分是从音频播放器中拆分出来的两个例子。FFmpeg音频解码器实现了视频数据到PCM采样数据的解码，而SDL音频采样数据播放器实现了PCM数据到音频设备的播放。简而言之，原先的FFmpeg+SDL音频播放器实现了：

音频数据->PCM->音频设备

FFmpeg音频解码器实现了：

音频数据->PCM

SDL音频采样数据播放器实现了：

PCM->音频设备

FFmpeg音频解码器

源代码

/*** 最简单的基于FFmpeg的音频解码器* Simplest FFmpeg Audio Decoder** 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** 本程序可以将音频码流（mp3，AAC等）解码为PCM采样数据。* 是最简单的FFmpeg音频解码方面的教程。* 通过学习本例子可以了解FFmpeg的解码流程。** This software decode audio streams (AAC,MP3 ...) to PCM data.* Suitable for beginner of FFmpeg.**/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>#define __STDC_CONSTANT_MACROS#ifdef _WIN32
//Windows
extern "C"
{
#include "libavcodec/avcodec.h"
#include "libavformat/avformat.h"
#include "libswresample/swresample.h"
};
#else
//Linux...
#ifdef __cplusplus
extern "C"
{
#endif
#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>
#include <libswresample/swresample.h>
#ifdef __cplusplus
};
#endif
#endif#define MAX_AUDIO_FRAME_SIZE 192000 // 1 second of 48khz 32bit audioint main(int argc, char* argv[])
{AVFormatContext    *pFormatCtx;int             i, audioStream;AVCodecContext   *pCodecCtx;AVCodec          *pCodec;AVPacket        *packet;uint8_t         *out_buffer;AVFrame         *pFrame;int ret;uint32_t len = 0;int got_picture;int index = 0;int64_t in_channel_layout;struct SwrContext *au_convert_ctx;FILE *pFile=fopen("output.pcm", "wb");char url[]="skycity1.mp3";av_register_all();avformat_network_init();pFormatCtx = avformat_alloc_context();//Openif(avformat_open_input(&pFormatCtx,url,NULL,NULL)!=0){printf("Couldn't open input stream.\n");return -1;}// Retrieve stream informationif(avformat_find_stream_info(pFormatCtx,NULL)<0){printf("Couldn't find stream information.\n");return -1;}// Dump valid information onto standard errorav_dump_format(pFormatCtx, 0, url, false);// Find the first audio streamaudioStream=-1;for(i=0; i < pFormatCtx->nb_streams; i++)if(pFormatCtx->streams[i]->codec->codec_type==AVMEDIA_TYPE_AUDIO){audioStream=i;break;}if(audioStream==-1){printf("Didn't find a audio stream.\n");return -1;}// Get a pointer to the codec context for the audio streampCodecCtx=pFormatCtx->streams[audioStream]->codec;// Find the decoder for the audio streampCodec=avcodec_find_decoder(pCodecCtx->codec_id);if(pCodec==NULL){printf("Codec not found.\n");return -1;}// Open codecif(avcodec_open2(pCodecCtx, pCodec,NULL)<0){printf("Could not open codec.\n");return -1;}packet=(AVPacket *)av_malloc(sizeof(AVPacket));av_init_packet(packet);//Out Audio Paramuint64_t out_channel_layout=AV_CH_LAYOUT_STEREO;//nb_samples: AAC-1024 MP3-1152int out_nb_samples=pCodecCtx->frame_size;AVSampleFormat out_sample_fmt=AV_SAMPLE_FMT_S16;int out_sample_rate=44100;int out_channels=av_get_channel_layout_nb_channels(out_channel_layout);//Out Buffer Sizeint out_buffer_size=av_samples_get_buffer_size(NULL,out_channels ,out_nb_samples,out_sample_fmt, 1);out_buffer=(uint8_t *)av_malloc(MAX_AUDIO_FRAME_SIZE*2);pFrame=av_frame_alloc();//FIX:Some Codec's Context Information is missingin_channel_layout=av_get_default_channel_layout(pCodecCtx->channels);//Swrau_convert_ctx = swr_alloc();au_convert_ctx=swr_alloc_set_opts(au_convert_ctx,out_channel_layout, out_sample_fmt, out_sample_rate,in_channel_layout,pCodecCtx->sample_fmt , pCodecCtx->sample_rate,0, NULL);swr_init(au_convert_ctx);while(av_read_frame(pFormatCtx, packet)>=0){if(packet->stream_index==audioStream){ret = avcodec_decode_audio4( pCodecCtx, pFrame,&got_picture, packet);if ( ret < 0 ) {printf("Error in decoding audio frame.\n");return -1;}if ( got_picture > 0 ){swr_convert(au_convert_ctx,&out_buffer, MAX_AUDIO_FRAME_SIZE,(const uint8_t **)pFrame->data , pFrame->nb_samples);printf("index:%5d\t pts:%lld\t packet size:%d\n",index,packet->pts,packet->size);//Write PCMfwrite(out_buffer, 1, out_buffer_size, pFile);index++;}}av_free_packet(packet);}swr_free(&au_convert_ctx);fclose(pFile);av_free(out_buffer);// Close the codecavcodec_close(pCodecCtx);// Close the video fileavformat_close_input(&pFormatCtx);return 0;
}

运行结果

程序运行后，会解码下面的音频文件。

解码后的PCM采样数据被保存成了一个文件。使用Adobe Audition设置采样率等信息后可以查看PCM的内容。

SDL音频采样数据播放器

源代码

/*** 最简单的SDL2播放音频的例子（SDL2播放PCM）* Simplest Audio Play SDL2 (SDL2 play PCM) ** 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>
#include <tchar.h>extern "C"
{
#include "sdl/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 2.0SDL_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  */ SDL_MixAudio(stream,audio_pos,len,SDL_MIX_MAXVOLUME);audio_pos += len; audio_len -= len;
} int main(int argc, char* argv[])
{//Initif(SDL_Init(SDL_INIT_AUDIO | SDL_INIT_TIMER)) {  printf( "Could not initialize SDL - %s\n", SDL_GetError()); return -1;}//SDL_AudioSpecSDL_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;//PlaySDL_PauseAudio(0);while(1){if (fread(pcm_buffer, 1, pcm_buffer_size, fp) != pcm_buffer_size){// Loopfseek(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 lengthaudio_len =pcm_buffer_size;audio_pos = audio_chunk;while(audio_len>0)//Wait until finishSDL_Delay(1); }free(pcm_buffer);SDL_Quit();return 0;
}

运行结果

程序运行后，会读取程序文件夹下的一个PCM采样数据文件，内容如下所示。

接下来会将PCM数据输出到系统的音频设备上（音响、耳机）。

下载

Simplest FFmpeg Audio Player

SourceForge： https://sourceforge.net/projects/simplestffmpegaudioplayer/

Github：https://github.com/leixiaohua1020/simplest_ffmpeg_audio_player

开源中国：http://git.oschina.net/leixiaohua1020/simplest_ffmpeg_audio_player

CSDN下载地址：http://download.csdn.net/detail/leixiaohua1020/8924329

本程序实现了音频的解码和播放。是最简单的FFmpeg音频解码方面的教程。
通过学习本例子可以了解FFmpeg的解码流程。
项目包含3个工程：

simplest_ffmpeg_audio_player：基于FFmpeg+SDL的音频解码器
simplest_ffmpeg_audio_decoder：音频解码器。使用了libavcodec和libavformat。
simplest_audio_play_sdl2：使用SDL2播放PCM采样数据的例子。