ffmpeg库音频解码示例(转载)

#include <stdlib.h>
extern "C"{//
#include "avcodec.h"
#include "avformat.h"
}

int main(char arg,char *argv[])
{

    char *filename ="02.swf";

    

    av_register_all();//注册所有可解码类型

    AVFormatContext *pInFmtCtx=NULL;//文件格式

    AVCodecContext *pInCodecCtx=NULL;//编码格式 

    if (av_open_input_file(&pInFmtCtx,filename,NULL, 0, NULL)!=0)//获取文件格式

        printf("av_open_input_file error\n");

    if(av_find_stream_info(pInFmtCtx) < 0)//获取文件内音视频流的信息

        printf("av_find_stream_info error\n");

    

    unsigned int j;

    // Find the first audio stream

    int    audioStream = -1;

    for(j=0; j<pInFmtCtx->nb_streams; j++)//找到音频对应的stream

        if(pInFmtCtx->streams[j]->codec->codec_type==CODEC_TYPE_AUDIO)

        {

            audioStream=j;

            break;

        }

        if(audioStream==-1)

        {

            printf("input file has no audio stream\n");

            return 0; // Didn't find a audio stream

        }

        printf("audio stream num: %d\n",audioStream);

        pInCodecCtx = pInFmtCtx->streams[audioStream]->codec;//音频的编码上下文

        AVCodec *pInCodec=NULL;

        /* FILE *file3 = fopen("codec_private_data_size.txt","w");

        for(int i = 0; i <200000; i++)

        {

        pInCodec = avcodec_find_decoder((CodecID)i);

        if (pInCodec!=NULL)

        {

        fprintf(file3,"%s %d\n",pInCodec->name,pInCodec->priv_data_size );

        }

        }

        fclose(file3); 

        system("pause");

        */

        pInCodec = avcodec_find_decoder(pInCodecCtx->codec_id);//根据编码ID找到用于解码的结构体

        if(pInCodec==NULL)

        {

            printf("error no Codec found\n");

            return -1 ; //
Codec not found

        }

        //使用test的代替pInCodecCtx也可以完成解码，可以看出只要获取以下几个重要信息就可以实现解码和重采样

        AVCodecContext *test = avcodec_alloc_context();

        test->bit_rate = pInCodecCtx->bit_rate;//重采样用

        test->sample_rate = pInCodecCtx->sample_rate;//重采样用

        test->channels = pInCodecCtx->channels;//重采样用

        test->extradata = pInCodecCtx->extradata;//若有则必有

        test->extradata_size = pInCodecCtx->extradata_size;//若有则必要

        test->codec_type = CODEC_TYPE_AUDIO;//不必要

        test->block_align = pInCodecCtx->block_align ;//必要

        

        if(avcodec_open(test, pInCodec)<0)//将两者结合以便在下面的解码函数中调用pInCodec中的对应解码函数

        {

            printf("error avcodec_open failed.\n");

            return -1; //
Could not open codec

        }

        

        if(avcodec_open(pInCodecCtx, pInCodec)<0)

        {

            printf("error avcodec_open failed.\n");

            return -1; //
Could not open codec

        }

        

        static AVPacket packet;

        

        printf(" bit_rate = %d \r\n", pInCodecCtx->bit_rate);

        printf(" sample_rate = %d \r\n", pInCodecCtx->sample_rate);

        printf(" channels = %d \r\n", pInCodecCtx->channels);

        printf(" code_name = %s \r\n", pInCodecCtx->codec->name);

        //printf("extra data size: %d :data%x %x %x %x\n",pInCodecCtx->extradata_size,pInCodecCtx->extradata[0]

        //     ,pInCodecCtx->extradata[1],pInCodecCtx->extradata[2],pInCodecCtx->extradata[3]);

        printf(" block_align = %d\n",pInCodecCtx->block_align);

        

        //system("pause");

        //////////////////////////////////////////////////////////////////////////

        uint8_t *pktdata;

        int pktsize;

        int out_size = AVCODEC_MAX_AUDIO_FRAME_SIZE*100;

        uint8_t * inbuf = (uint8_t *)malloc(out_size);

        FILE* pcm,*packetinfo;

        packetinfo = fopen("packetinfo.txt","w");

        pcm = fopen("result.pcm","wb");

        long start = clock();

        while(av_read_frame(pInFmtCtx, &packet)>=0)//pInFmtCtx中调用对应格式的packet获取函数

        {

            //fprintf(packetinfo," packet { pts=%d; dts =%d;%x,%x,%x,%x; size=%d; stream_index=%d; pos=%d;}\n",

            // packet.pts,packet.dts,packet.data[0],packet.data[1],packet.data[2],packet.data[3],packet.size,packet.stream_index,packet.pos);

            if(packet.stream_index==audioStream)//如果是音频

            {

                pktdata = packet.data;

                pktsize = packet.size;

                while(pktsize>0)

                {

                    //fprintf(packetinfo,"packet data:%x %x %x %x %x\n",pktdata[0],pktdata[1],pktdata[2],pktdata[3],pktdata[4]);

                    //fprintf(packetinfo,"packet size:%d\n\n",pktsize);

                    out_size = AVCODEC_MAX_AUDIO_FRAME_SIZE*100;

                    //解码

                    int len = avcodec_decode_audio2(pInCodecCtx,(short*)inbuf,&out_size,pktdata,pktsize);

                    if (len<0)

                    {

                        printf("Error while decoding.\n");

                        break;

                    }

                    if(out_size>0)

                    {

                        fwrite(inbuf,1,out_size,pcm);//pcm记录

                        fflush(pcm);

                    }

                    pktsize -= len;

                    pktdata += len;

                }

            } 

            av_free_packet(&packet);

        }

        long end = clock();

        printf("cost time :%f\n",double(end-start)/(double)CLOCKS_PER_SEC);

        free(inbuf);

        fclose(pcm);

        fclose(packetinfo);

        if (pInCodecCtx!=NULL)

        {

            avcodec_close(pInCodecCtx);

        }

        if (test!=NULL)

        {

            avcodec_close(test);

        }

        av_free(test);

        av_close_input_file(pInFmtCtx);

        return 0;
}

转自：http://blog.chinaunix.net/u3/108358/showart_2132123.html