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视音频数据处理入门系列文章：

视音频数据处理入门：RGB、YUV像素数据处理

视音频数据处理入门：PCM音频采样数据处理

视音频数据处理入门：H.264视频码流解析

视音频数据处理入门：AAC音频码流解析

视音频数据处理入门：FLV封装格式解析

视音频数据处理入门：UDP-RTP协议解析

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前两篇文章介绍了音频码流处理程序和视频码流处理程序，本文介绍将他们打包到一起后的数据——封装格式数据的处理程序。封装格式数据在视频播放器中的位置如下所示。

本文中的程序是一个FLV封装格式解析程序。该程序可以从FLV中分析得到它的基本单元Tag，并且可以简单解析Tag首部的字段。通过修改该程序可以实现不同的FLV格式数据处理功能。

原理

FLV封装格式是由一个FLV Header文件头和一个一个的Tag组成的。Tag中包含了音频数据以及视频数据。FLV的结构如下图所示。

有关FLV的格式本文不再做记录。可以参考文章《 视音频编解码学习工程：FLV封装格式分析器》。本文的程序实现了FLV中的FLV Header和Tag的解析，并可以分离出其中的音频流。

代码

整个程序位于simplest_flv_parser()函数中，如下所示。

/*** 最简单的视音频数据处理示例* Simplest MediaData Test** 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** 本项目包含如下几种视音频测试示例：*  (1)像素数据处理程序。包含RGB和YUV像素格式处理的函数。*  (2)音频采样数据处理程序。包含PCM音频采样格式处理的函数。*  (3)H.264码流分析程序。可以分离并解析NALU。*  (4)AAC码流分析程序。可以分离并解析ADTS帧。*  (5)FLV封装格式分析程序。可以将FLV中的MP3音频码流分离出来。*  (6)UDP-RTP协议分析程序。可以将分析UDP/RTP/MPEG-TS数据包。** This project contains following samples to handling multimedia data:*  (1) Video pixel data handling program. It contains several examples to handle RGB and YUV data.*  (2) Audio sample data handling program. It contains several examples to handle PCM data.*  (3) H.264 stream analysis program. It can parse H.264 bitstream and analysis NALU of stream.*  (4) AAC stream analysis program. It can parse AAC bitstream and analysis ADTS frame of stream.*  (5) FLV format analysis program. It can analysis FLV file and extract MP3 audio stream.*  (6) UDP-RTP protocol analysis program. It can analysis UDP/RTP/MPEG-TS Packet.**/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>//Important!
#pragma pack(1)#define TAG_TYPE_SCRIPT 18
#define TAG_TYPE_AUDIO  8
#define TAG_TYPE_VIDEO  9typedef unsigned char byte;
typedef unsigned int uint;typedef struct {byte Signature[3];byte Version;byte Flags;uint DataOffset;
} FLV_HEADER;typedef struct {byte TagType;byte DataSize[3];byte Timestamp[3];uint Reserved;
} TAG_HEADER;//reverse_bytes - turn a BigEndian byte array into a LittleEndian integer
uint reverse_bytes(byte *p, char c) {int r = 0;int i;for (i=0; i<c; i++) r |= ( *(p+i) << (((c-1)*8)-8*i));return r;
}/*** Analysis FLV file* @param url    Location of input FLV file.*/int simplest_flv_parser(char *url){//whether output audio/video streamint output_a=1;int output_v=1;//-------------FILE *ifh=NULL,*vfh=NULL, *afh = NULL;//FILE *myout=fopen("output_log.txt","wb+");FILE *myout=stdout;FLV_HEADER flv;TAG_HEADER tagheader;uint previoustagsize, previoustagsize_z=0;uint ts=0, ts_new=0;ifh = fopen(url, "rb+");if ( ifh== NULL) {printf("Failed to open files!");return -1;}//FLV file headerfread((char *)&flv,1,sizeof(FLV_HEADER),ifh);fprintf(myout,"============== FLV Header ==============\n");fprintf(myout,"Signature:  0x %c %c %c\n",flv.Signature[0],flv.Signature[1],flv.Signature[2]);fprintf(myout,"Version:    0x %X\n",flv.Version);fprintf(myout,"Flags  :    0x %X\n",flv.Flags);fprintf(myout,"HeaderSize: 0x %X\n",reverse_bytes((byte *)&flv.DataOffset, sizeof(flv.DataOffset)));fprintf(myout,"========================================\n");//move the file pointer to the end of the headerfseek(ifh, reverse_bytes((byte *)&flv.DataOffset, sizeof(flv.DataOffset)), SEEK_SET);//process each tagdo {previoustagsize = _getw(ifh);fread((void *)&tagheader,sizeof(TAG_HEADER),1,ifh);//int temp_datasize1=reverse_bytes((byte *)&tagheader.DataSize, sizeof(tagheader.DataSize));int tagheader_datasize=tagheader.DataSize[0]*65536+tagheader.DataSize[1]*256+tagheader.DataSize[2];int tagheader_timestamp=tagheader.Timestamp[0]*65536+tagheader.Timestamp[1]*256+tagheader.Timestamp[2];char tagtype_str[10];switch(tagheader.TagType){case TAG_TYPE_AUDIO:sprintf(tagtype_str,"AUDIO");break;case TAG_TYPE_VIDEO:sprintf(tagtype_str,"VIDEO");break;case TAG_TYPE_SCRIPT:sprintf(tagtype_str,"SCRIPT");break;default:sprintf(tagtype_str,"UNKNOWN");break;}fprintf(myout,"[%6s] %6d %6d |",tagtype_str,tagheader_datasize,tagheader_timestamp);//if we are not past the end of file, process the tagif (feof(ifh)) {break;}//process tag by typeswitch (tagheader.TagType) {case TAG_TYPE_AUDIO:{ char audiotag_str[100]={0};strcat(audiotag_str,"| ");char tagdata_first_byte;tagdata_first_byte=fgetc(ifh);int x=tagdata_first_byte&0xF0;x=x>>4;switch (x){case 0:strcat(audiotag_str,"Linear PCM, platform endian");break;case 1:strcat(audiotag_str,"ADPCM");break;case 2:strcat(audiotag_str,"MP3");break;case 3:strcat(audiotag_str,"Linear PCM, little endian");break;case 4:strcat(audiotag_str,"Nellymoser 16-kHz mono");break;case 5:strcat(audiotag_str,"Nellymoser 8-kHz mono");break;case 6:strcat(audiotag_str,"Nellymoser");break;case 7:strcat(audiotag_str,"G.711 A-law logarithmic PCM");break;case 8:strcat(audiotag_str,"G.711 mu-law logarithmic PCM");break;case 9:strcat(audiotag_str,"reserved");break;case 10:strcat(audiotag_str,"AAC");break;case 11:strcat(audiotag_str,"Speex");break;case 14:strcat(audiotag_str,"MP3 8-Khz");break;case 15:strcat(audiotag_str,"Device-specific sound");break;default:strcat(audiotag_str,"UNKNOWN");break;}strcat(audiotag_str,"| ");x=tagdata_first_byte&0x0C;x=x>>2;switch (x){case 0:strcat(audiotag_str,"5.5-kHz");break;case 1:strcat(audiotag_str,"1-kHz");break;case 2:strcat(audiotag_str,"22-kHz");break;case 3:strcat(audiotag_str,"44-kHz");break;default:strcat(audiotag_str,"UNKNOWN");break;}strcat(audiotag_str,"| ");x=tagdata_first_byte&0x02;x=x>>1;switch (x){case 0:strcat(audiotag_str,"8Bit");break;case 1:strcat(audiotag_str,"16Bit");break;default:strcat(audiotag_str,"UNKNOWN");break;}strcat(audiotag_str,"| ");x=tagdata_first_byte&0x01;switch (x){case 0:strcat(audiotag_str,"Mono");break;case 1:strcat(audiotag_str,"Stereo");break;default:strcat(audiotag_str,"UNKNOWN");break;}fprintf(myout,"%s",audiotag_str);//if the output file hasn't been opened, open it.if(output_a!=0&&afh == NULL){afh = fopen("output.mp3", "wb");}//TagData - First Byte Dataint data_size=reverse_bytes((byte *)&tagheader.DataSize, sizeof(tagheader.DataSize))-1;if(output_a!=0){//TagData+1for (int i=0; i<data_size; i++)fputc(fgetc(ifh),afh);}else{for (int i=0; i<data_size; i++)fgetc(ifh);}break;}case TAG_TYPE_VIDEO:{char videotag_str[100]={0};strcat(videotag_str,"| ");char tagdata_first_byte;tagdata_first_byte=fgetc(ifh);int x=tagdata_first_byte&0xF0;x=x>>4;switch (x){case 1:strcat(videotag_str,"key frame  ");break;case 2:strcat(videotag_str,"inter frame");break;case 3:strcat(videotag_str,"disposable inter frame");break;case 4:strcat(videotag_str,"generated keyframe");break;case 5:strcat(videotag_str,"video info/command frame");break;default:strcat(videotag_str,"UNKNOWN");break;}strcat(videotag_str,"| ");x=tagdata_first_byte&0x0F;switch (x){case 1:strcat(videotag_str,"JPEG (currently unused)");break;case 2:strcat(videotag_str,"Sorenson H.263");break;case 3:strcat(videotag_str,"Screen video");break;case 4:strcat(videotag_str,"On2 VP6");break;case 5:strcat(videotag_str,"On2 VP6 with alpha channel");break;case 6:strcat(videotag_str,"Screen video version 2");break;case 7:strcat(videotag_str,"AVC");break;default:strcat(videotag_str,"UNKNOWN");break;}fprintf(myout,"%s",videotag_str);fseek(ifh, -1, SEEK_CUR);//if the output file hasn't been opened, open it.if (vfh == NULL&&output_v!=0) {//write the flv header (reuse the original file's hdr) and first previoustagsizevfh = fopen("output.flv", "wb");fwrite((char *)&flv,1, sizeof(flv),vfh);fwrite((char *)&previoustagsize_z,1,sizeof(previoustagsize_z),vfh);}
#if 0//Change Timestamp//Get Timestampts = reverse_bytes((byte *)&tagheader.Timestamp, sizeof(tagheader.Timestamp));ts=ts*2;//Writeback Timestampts_new = reverse_bytes((byte *)&ts, sizeof(ts));memcpy(&tagheader.Timestamp, ((char *)&ts_new) + 1, sizeof(tagheader.Timestamp));
#endif//TagData + Previous Tag Sizeint data_size=reverse_bytes((byte *)&tagheader.DataSize, sizeof(tagheader.DataSize))+4;if(output_v!=0){//TagHeaderfwrite((char *)&tagheader,1, sizeof(tagheader),vfh);//TagDatafor (int i=0; i<data_size; i++)fputc(fgetc(ifh),vfh);}else{for (int i=0; i<data_size; i++)fgetc(ifh);}//rewind 4 bytes, because we need to read the previoustagsize again for the loop's sakefseek(ifh, -4, SEEK_CUR);break;}default://skip the data of this tagfseek(ifh, reverse_bytes((byte *)&tagheader.DataSize, sizeof(tagheader.DataSize)), SEEK_CUR);}fprintf(myout,"\n");} while (!feof(ifh));_fcloseall();return 0;
}

上文中的函数调用方法如下所示。

simplest_flv_parser("cuc_ieschool.flv");

结果

本程序的输入为一个FLV的文件路径，输出为FLV的统计数据，如下图所示。

此外本程序还可以分离FLV中的视频码流和音频码流。需要注意的是本程序并不能分离一些特定类型的音频（例如AAC）和视频，这一工作有待以后有时间再完成。

下载

Simplest mediadata test

项目主页

SourceForge：https://sourceforge.net/projects/simplest-mediadata-test/

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

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

CSDN下载地址： http://download.csdn.net/detail/leixiaohua1020/9422409

本项目包含如下几种视音频数据解析示例：
 (1)像素数据处理程序。包含RGB和YUV像素格式处理的函数。
 (2)音频采样数据处理程序。包含PCM音频采样格式处理的函数。
 (3)H.264码流分析程序。可以分离并解析NALU。
 (4)AAC码流分析程序。可以分离并解析ADTS帧。
 (5)FLV封装格式分析程序。可以将FLV中的MP3音频码流分离出来。
 (6)UDP-RTP协议分析程序。可以将分析UDP/RTP/MPEG-TS数据包。

雷霄骅 (Lei Xiaohua)
leixiaohua1020@126.com
http://blog.csdn.net/leixiaohua1020