FLV (Flash Video) 是由 Adobe 公司推出的一种封装格式，主要用于流媒体系统。
FLV 封装的媒体文件具有体积轻巧、封装播放简单等特点，很适合网络应用。
目前各浏览器普遍使用 Flash Player 作为网页播放器，使得安装有浏览器的计算机终端不需要另外安装播放器，
这也是 FLV 格式广为流行的原因之一。
FLV 文件主要由一个 Header 加上由多个 Tag 组成的 Body 构成。
一、FLV Header（UI8表示无符号8位，也就是一个字节；UB[5]表示一个字节中的5位）
二、FLV Body（Flv Body由一个一个Tag组成，每个Tag前都有一个PerviousTagSize字段，标记着前面一个Tag的大小。）
Tag有三种类型，Audio Tag（音频Tag），Video Tag（视频Tag），script Tag（又称Metadata Tag）
每个Tag由Tag Header和Tag Data组成，对于不同类型的Tag，Tag Header的格式都是相同的（都是11byte的长度），Tag Body的格式就不一样了。
综上所述FLV整体的结构如下图：
1、AudioTag Data
如果SoundFormat=10，那么音频数据就是AACAUDIODATA。
2、Video Tag Data
对于H.264数据来说，CodecID = 7。
当CodecID = 7时，视频数据就是AVCVIDEOPACKET格式。
3、Script Tag Data
该类型Tag又通常被称为MetadataTag，会放一些关于FLV视频和音频的元数据信息
如：duration、width、height等。通常该类型Tag会跟在FileHeader后面作为第一个Tag出现，而且只有一个。
第一个AMF包：
第一个字节一般为0x02，表示字符串，第2-3个字节表示字符串的长度，一般为0x000A，后面跟的就是字符串，一般为"onMetaData"。
第二AMF包：
第一个字节为0x08，表示数组，第2-5个字节表示数组元素个数，后面跟着就是数组的元素，格式为：元素名长度（UI16） + 元素名（UI8[n]） + 元素的值(double)，最后以“009”结尾
原文链接：https://blog.csdn.net/weixin_42462202/article/details/88661883
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。
#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 9 typedef 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 stream int 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 header fread((char *)&flv,1,sizeof(FLV_HEADER),ifh); fprintf(myout,"============== FLV Header ============== "); fprintf(myout,"Signature: 0x %c %c %c ",flv.Signature[0],flv.Signature[1],flv.Signature[2]); fprintf(myout,"Version: 0x %X ",flv.Version); fprintf(myout,"Flags : 0x %X ",flv.Flags); fprintf(myout,"HeaderSize: 0x %X ",reverse_bytes((byte *)&flv.DataOffset, sizeof(flv.DataOffset))); fprintf(myout,"======================================== "); //move the file pointer to the end of the header fseek(ifh, reverse_bytes((byte *)&flv.DataOffset, sizeof(flv.DataOffset)), SEEK_SET); //process each tag do { 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 tag if (feof(ifh)) { break; } //process tag by type switch (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 Data int data_size=reverse_bytes((byte *)&tagheader.DataSize, sizeof(tagheader.DataSize))-1; if(output_a!=0){ //TagData+1 for (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 previoustagsize vfh = 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 Timestamp ts = reverse_bytes((byte *)&tagheader.Timestamp, sizeof(tagheader.Timestamp)); ts=ts*2; //Writeback Timestamp ts_new = reverse_bytes((byte *)&ts, sizeof(ts)); memcpy(&tagheader.Timestamp, ((char *)&ts_new) + 1, sizeof(tagheader.Timestamp)); #endif //TagData + Previous Tag Size int data_size=reverse_bytes((byte *)&tagheader.DataSize, sizeof(tagheader.DataSize))+4; if(output_v!=0){ //TagHeader fwrite((char *)&tagheader,1, sizeof(tagheader),vfh); //TagData for (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 sake fseek(ifh, -4, SEEK_CUR); break; } default: //skip the data of this tag fseek(ifh, reverse_bytes((byte *)&tagheader.DataSize, sizeof(tagheader.DataSize)), SEEK_CUR); } fprintf(myout," "); } while (!feof(ifh)); _fcloseall(); return 0; }
原文链接：https://blog.csdn.net/leixiaohua1020/article/details/50535082