FLV封装格式

FLV包含文件头和文件体两部分，文件体由多个Tag组成，Tag的类型可以是视频、音频和Script，每个Tag只能包含以上三种类型的数据中的一种 。如下图

  • Type为0x08即音频

名称 音频编码类型 音频采样率 音频采样精度 音频类型
0 Linear PCM，platform endian 5.5kHz 8bits sndMono
1 ADPCM 11KHz 16bits sndStereo
2 MP3 22 kHz
3 Linear PCM，little endian 44 kHz
4 Nellymoser 16-kHz mono
5 Nellymoser 8-kHz mono
6 Nellymoser
7 G.711 A-law logarithmic PCM
8 G.711 mu-law logarithmic PCM
9 reserved
10 AAC
14 MP3 8-Khz
15 Device-specific sound

  • Type为0x09即视频

名称 帧类型 视频编码类型
1 keyframe （for AVC，a seekable frame） JPEG （currently unused）
2 inter frame （for AVC，a nonseekable frame） Sorenson H.263
3 disposable inter frame （H.263 only） Screen video
4 generated keyframe （reserved for server use） On2 VP6
5 video info/command frame On2 VP6 with alpha channel
6 Screen video version 2
7 AVC

  • Type为0x12即控制帧

    该类型Tag又通常被称为Metadata Tag，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File Header后面作为第一个Tag出现，而且只有一个。

    • AMF1： 第1个字节表示AMF包类型，一般总是0x02，表示字符串。第2-3个字节为UI16类型值，标识字符串的长度，一般总是0x000A（“onMetaData”长度）。后面字节为具体的字符串，一般总为“onMetaData”（6F,6E,4D,65,74,61,44,61,74,61）

    • 第1个字节表示AMF包类型，一般总是0x08，表示数组。第2-5个字节为UI32类型值，表示数组元素的个数。后面即为各数组元素的封装，数组元素为元素名称和值组成的对。

      | 值 | 含义 |
      | ————— | ———— |
      | duration | 时长 |
      | width | 视频宽度 |
      | height | 视频高度 |
      | videodatarate | 视频码率 |
      | framerate | 视频帧率 |
      | videocodecid | 视频编码方式 |
      | audiosamplerate | 音频采样率 |
      | audiosamplesize | 音频采样精度 |
      | stereo | 是否为立体 |
      | audiocodecid | 音频编码方式 |
      | filesize | 文件大小 |

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#pragma pack(1) //包大小设为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;
 
 
//大端转小端
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;
}
 
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 ==============\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 %d\n",reverse_bytes((byte *)&flv.DataOffset, sizeof(flv.DataOffset)));
	fprintf(myout,"========================================\n");
 
	//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;//-1是个迷 FirstBYteData为什么是1和减掉 
            
			if(output_a!=0){//读完TagData
				for (int i=0; i<data_size; i++)
					fputc(fgetc(ifh),afh);//将音频输出到mp3文件
			}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);//往回走一位 迷 前四位是tagdata_first_byte&0xF0 后四位是tagdata_first_byte&0x0F 不应该啊
            
			//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 //延长时间戳 变成双倍
			//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));//Timestamp只占三位 大端模式 去掉首位
#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,"\n");
 
	} while (!feof(ifh));
 
 
	_fcloseall();
 
	return 0;
}