MP4v2 基本使用（二）

MP4转H264文件

本文最目标是基本的MP4v2接口的使用，并且实现一个简单的提取mp4文件里面264流的功能；

1.264文件基本知识

下看看H264文件的基本常识 
NAL 头 0x00 0x00 0x00 0x01 
sps ：nal+0x67开头 
pps ：nal+0x68开头

I帧 0x65 开头 
P帧… 
具体的参考别人的解析 
http://blog.****.net/jefry_xdz/article/details/8461343

2.mp4v2提取264文件的代码

 #include <stdlib.h>
 #include <stdio.h>
 #include <string.h>
 #include <sys/types.h>
 #include <dirent.h>
 #include <time.h>
 #include <sys/time.h>
 #include <mp4v2/mp4v2.h>

 unsigned char sps[],pps[];
 int spslen = ,ppslen = ;

 int get264stream(MP4FileHandle oMp4File,int VTrackId,int totalFrame)
 {
     if(!oMp4File) return -;
     char NAL[] = {0x00,0x00,0x00,0x01};
     unsigned char *pData = NULL;
     unsigned int nSize = ;
     MP4Timestamp pStartTime;
     MP4Duration pDuration;
     MP4Duration pRenderingOffset;
     bool pIsSyncSample = ;

     int nReadIndex = ;
     FILE *pFile = NULL;
     pFile = fopen("out.h264","wb"); 

     while(nReadIndex < totalFrame)
     {
         nReadIndex ++;
         //printf("nReadIndex:%d\n",nReadIndex);
         MP4ReadSample(oMp4File,VTrackId,nReadIndex,&pData,&nSize,&pStartTime,&pDuration,&pRenderingOffset,&pIsSyncSample);

         //IDR֡ 帧，写入sps pps先
         if(pIsSyncSample)
         {
             fwrite(NAL,,,pFile);
             fwrite(sps,spslen,,pFile);

             fwrite(NAL,,,pFile);
             fwrite(pps,ppslen,,pFile);

         }
         //264frame
         if(pData && nSize > )
         {
             //标准的264帧，前面几个字节就是frame的长度.
             //需要替换为标准的264 nal 头.
             pData[] = 0x00;
             pData[] = 0x00;
             pData[] = 0x00;
             pData[] = 0x01;
             fwrite(pData,nSize,,pFile);
         }

         //如果传入MP4ReadSample的视频pData是null
         // 它内部就会new 一个内存
         //如果传入的是已知的内存区域，
         //则需要保证空间bigger then max frames size.
         free(pData);
         pData = NULL;
     }
     fflush(pFile);
     fclose(pFile);  

     return ;
 }
 int openmp4file(char *sMp4file)
 {
     MP4FileHandle oMp4File;
     int i;

     //unsigned int oStreamDuration;
     unsigned int oFrameCount;

     oMp4File = MP4Read(sMp4file);
     int videoindex = -,audioindex = -;
     uint32_t numSamples;
     //uint32_t timescale;
     //uint64_t duration;        

     if (!oMp4File)
     {
         printf("Read error....%s\r\n",sMp4file);
         return -;
     }

     MP4TrackId trackId = MP4_INVALID_TRACK_ID;
     uint32_t numTracks = MP4GetNumberOfTracks(oMp4File,NULL,);
     printf("numTracks:%d\n",numTracks);

     for (i = ; i < numTracks; i++)
     {
         trackId = MP4FindTrackId(oMp4File, i,NULL,);
         const char* trackType = MP4GetTrackType(oMp4File, trackId);
         if (MP4_IS_VIDEO_TRACK_TYPE(trackType))
         {
             //printf("[%s %d] trackId:%d\r\n",__FUNCTION__,__LINE__,trackId);
             videoindex= trackId;

             //duration = MP4GetTrackDuration(oMp4File, trackId );
             numSamples = MP4GetTrackNumberOfSamples(oMp4File, trackId);
             //timescale = MP4GetTrackTimeScale(oMp4File, trackId);
             //oStreamDuration = duration/(timescale/1000);
             oFrameCount = numSamples;

             // read sps/pps
             uint8_t **seqheader;
             uint8_t **pictheader;
             uint32_t *pictheadersize;
             uint32_t *seqheadersize;
             uint32_t ix;
             MP4GetTrackH264SeqPictHeaders(oMp4File, trackId, &seqheader, &seqheadersize, &pictheader, &pictheadersize);

             for (ix = ; seqheadersize[ix] != ; ix++)
             {
                 memcpy(sps, seqheader[ix], seqheadersize[ix]);
                 spslen = seqheadersize[ix];
                 free(seqheader[ix]);
             }
             free(seqheader);
             free(seqheadersize);

             for (ix = ; pictheadersize[ix] != ; ix++)
             {
                 memcpy(pps, pictheader[ix], pictheadersize[ix]);
                 ppslen = pictheadersize[ix];
                 free(pictheader[ix]);
             }
　　　　　　　　　 free(pictheader);
                free(pictheadersize);
         }

         else if (MP4_IS_AUDIO_TRACK_TYPE(trackType))
         {
             audioindex = trackId;
             printf("audioindex:%d\n",audioindex);
         }
     }

     //解析完了mp4，主要是为了获取sps pps 还有video的trackID
     if(videoindex >= )
         get264stream(oMp4File,videoindex,oFrameCount);  

     //需要mp4close 否则在嵌入式设备打开mp4上多了会内存泄露挂掉.
     MP4Close(oMp4File,);
     return ;
 }

 int main(void)
 {
     openmp4file("test.mp4");
     return ;
 }

3.测试文件ffproe的信息如下.

测试的mp4文件和生成的264文件信息如下，用播放器播放可以正常显示图像.