使用SDKv3实现音频文件格式转换

From Ffmpeg工程组

经过测试，MP3-〉MP2/MP3等没有问题，但是转换成WAV转换成功了，播放起来音乐不正常，有拖沓感。 源码如下：（VS2003编译通过，新建一个空的控制台工程，把这个CPP添加进去就可以）

// AVConvert.cpp : 定义控制台应用程序的入口点。
//
#include "stdafx.h"
#ifdef __cplusplus
extern "C"
{
#include "avcodec.h"
#include "avformat.h"
#include "avutil.h"
}
#endif //__cplusplus
#include <windows.h>
#include <excpt.h>
#pragma comment(lib,"avcodec.lib")
#pragma comment(lib,"avformat.lib")
#pragma comment(lib,"avutil.lib")

void SafeFreeCodecContext(AVCodecContext *pCodecCtx)
{
   __try
   {
       if (pCodecCtx!=NULL)
           avcodec_close(pCodecCtx);
   }
   __except (EXCEPTION_EXECUTE_HANDLER) 
   {
       // if file is rmvb, avcodec_close will raise error from internal~
       return;
   }
}

int Safe_av_find_stream_info(AVFormatContext * pFormatCtx)
{ 
   __try
   {
       return av_find_stream_info(pFormatCtx);    
   }
   __except (EXCEPTION_EXECUTE_HANDLER) 
   {
       // if file is corrupted, av_find_stream_info will raise devide zero error from internal~
       return -1;
   }
}

void SaveCloseFormatContext(AVFormatContext * pFormatCtx)
{
   __try
   {
       if (pFormatCtx!=NULL)
           av_close_input_file(pFormatCtx);
   }
   __except (EXCEPTION_EXECUTE_HANDLER) 
   {
       // if file is mov, av_close_input_file will raise error from internal~
       return;
   }
}

int _tmain(int argc, _TCHAR* argv[])
{
   if (argc<2)
   {
       printf("AVConvert.exe inputfile outputfile");
       return -1;
   }  
   av_register_all();
   const char * infile = argv[1];
   const char * outfile = argv[2];
   AVFormatContext *pInFmtCtx=NULL;
   if (av_open_input_file(&pInFmtCtx, infile, NULL, 0, NULL)!=0)
   {
       printf("av_open_input_file failed.\n");
       return 1; // Couldn't open file
   }
   if (pInFmtCtx==NULL)
   {
       printf("av_open_input_file OK, but FormatContext==NULL");
       return 1; // Couldn't open file
   }
   if(Safe_av_find_stream_info(pInFmtCtx)<0)
   {
       printf("av_find_stream_info failed.");
       return 2; // Couldn't find stream 
   }
   unsigned int i, audioStream;
   // Find the first audio stream
   audioStream = -1;
   for(i=0; i<pInFmtCtx->nb_streams; i++)
       if(pInFmtCtx->streams[i]->codec->codec_type==CODEC_TYPE_AUDIO)
       {
           audioStream=i;
           break;
       }
   if(audioStream==-1)
   {
       printf("input file has no audio stream");
       return 3; // Didn't find a audio stream
   }
   AVCodecContext *pInCodecCtx=NULL;    
   // Get a pointer to the codec context for the audio stream
   pInCodecCtx = pInFmtCtx->streams[audioStream]->codec;
   AVCodec *pInCodec=NULL;
   // Find the decoder for the audio stream
   pInCodec = avcodec_find_decoder(pInCodecCtx->codec_id);
   if(pInCodec==NULL)
   {
       printf("no Decoder found");
       return 4; // Codec not found
   }
   // Inform the codec that we can handle truncated bitstreams -- i.e.,
   // bitstreams where frame boundaries can fall in the middle of packets
   //if(pInCodec->capabilities & CODEC_CAP_TRUNCATED)
   //    pInCodecCtx->flags|=CODEC_FLAG_TRUNCATED;
   // Open codec
   if(avcodec_open(pInCodecCtx, pInCodec)<0)
   {
       printf("avcodec_open failed.");
       return 5; // Could not open codec
   }
   AVOutputFormat * oFormat = guess_format(NULL,outfile,NULL);
   if (oFormat==NULL)
   {
       printf("not found output file format");
       return 6;
   }
   AVFormatContext * oFmtCtx =  av_alloc_format_context();
   if (oFmtCtx==NULL)
   {
       printf("av_alloc_format_context failed");
       return 7;
   }
   oFmtCtx->oformat = oFormat;
   AVStream * oStream = av_new_stream(oFmtCtx,0);
   AVCodecContext * oCodecCtx = oStream->codec;
   oCodecCtx->codec_id = oFmtCtx->oformat->audio_codec;
   oCodecCtx->codec_type = CODEC_TYPE_AUDIO;
   oCodecCtx->sample_rate = pInFmtCtx->streams[audioStream]->codec->sample_rate;
   oCodecCtx->bit_rate = pInFmtCtx->streams[audioStream]->codec->bit_rate;
   oCodecCtx->channels = pInFmtCtx->streams[audioStream]->codec->channels;
   AVCodec * pOutCodec = avcodec_find_encoder(oStream->codec->codec_id);
   // Open codec
   if(avcodec_open(oCodecCtx, pOutCodec)<0)
   {
       printf("avcodec_open failed.");
       return 5; // Could not open codec
   }    
   if (av_set_parameters(oFmtCtx, NULL) < 0) 
   {
       printf("Invalid output format parameters\n");
       return 8;
   }
   dump_format(oFmtCtx, 0, outfile, 1);
   dump_format(pInFmtCtx, 0, infile, 0);
    if (!(oFormat->flags & AVFMT_NOFILE)) 
    {
       if (url_fopen(&oFmtCtx->pb, outfile, URL_WRONLY) < 0) 
       {
           fprintf(stderr, "Could not open '%s'\n", outfile);
           return 9;
       }
   }
   av_write_header(oFmtCtx);
   static AVPacket packet;
   int out_size = AVCODEC_MAX_AUDIO_FRAME_SIZE;
   uint8_t * inbuf = (uint8_t *)malloc(out_size);
   uint8_t * pinbuf = NULL;
   int ob_size = FF_MIN_BUFFER_SIZE;
   uint8_t * outbuf = (uint8_t *)malloc(ob_size);
   int inputSampleSize = pInCodecCtx->frame_size * 2 * pInCodecCtx->channels;//获取Sample大小
   int outputSampleSize = oCodecCtx->frame_size * 2 * oCodecCtx->channels;//获取输出Sample大小
   uint8_t * pktdata = NULL;
   int pktsize = 0;
   int len = 0;
   av_init_packet(&packet);
   while(av_read_frame(pInFmtCtx, &packet)>=0)
   {
       // Is this a packet from the audio stream?
       if(packet.stream_index==audioStream)
       {
           pktdata = packet.data;
           pktsize = packet.size;
           while (pktsize>0)
           {
               out_size = AVCODEC_MAX_AUDIO_FRAME_SIZE;
               len = avcodec_decode_audio2(pInCodecCtx,(short *)inbuf,&out_size,pktdata,pktsize);
               if (len<0)
               {
                   printf("Error while decoding.\n");
                   break;
               }
               if (out_size>0)
               {
                   pinbuf = inbuf;
                   for (i=0;i<out_size;i+=inputSampleSize)
                   {
                       AVPacket pkt;
                       av_init_packet(&pkt);
                       ob_size = FF_MIN_BUFFER_SIZE;
                       pkt.size= avcodec_encode_audio(oCodecCtx, outbuf, ob_size, (short *)pinbuf);
                       pkt.pts= av_rescale_q(oCodecCtx->coded_frame->pts, oCodecCtx->time_base, oStream->time_base);
                       pkt.flags |= PKT_FLAG_KEY;
                       pkt.stream_index= oStream->index;
                       pkt.data= outbuf;
                       /* write the compressed frame in the media file */
                       if (av_write_frame(oFmtCtx, &pkt) != 0) {
                           printf("Error while writing audio frame\n");
                           break;
                       }
                       pinbuf += inputSampleSize;
                   }
               }
               pktsize -= len;
               pktdata += len;
           }
       }
       // Free the packet that was allocated by av_read_frame
       av_free_packet(&packet);
   }
   free(inbuf);
   free(outbuf);
   av_write_trailer(oFmtCtx);
   //avcodec_close(oStream->codec);//why error here?!
   // free the streams
   for(i = 0; i < oFmtCtx->nb_streams; i++) {
       av_freep(&oFmtCtx->streams[i]->codec);
       av_freep(&oFmtCtx->streams[i]);
   }
   if (!(oFormat->flags & AVFMT_NOFILE)) {
       // close the output file
       url_fclose(&oFmtCtx->pb);
   }
   // free the stream
   av_free(oFmtCtx);
   SafeFreeCodecContext(pInCodecCtx);
   SaveCloseFormatContext(pInFmtCtx);
   printf("Convert Action is OK!\n");
   getchar();
   return 0;
}

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