RTP － 视频流广播
这是用RTP（RFC3350）按RFC2550封装MPEG ES流数据的发送程序。学习RTP的路真的辛苦。在网上收集的有关RTP的程序都是那种只负责RTP数据包发送的库，如jrtplib等，他们的DEMO程序都只是用来发发字符串，编编聊天程序，无论是国内还是国外，都没有结合真正的应用的DEMO。其实我的目的很简单，就是写发个视频流服务器，不用复杂，只用把基本原理弄懂，因为这样你才能有的放矢。与网上和RTP相关的库没有应用不一让，当你尝试以流媒体服务器、linux来baidu或google时，你搜出来完非就那么几类：
1.FFSERVER
FFMPEG2的DEMO,说它有名只是因为这类程序太少了。FFMPEG2是很好用，我现在还在用，但这个DEMO就有很多“炒作”的嫌疑了。好像在做着FFMPEG2库的演示而不是真的视频流服务器。后来想想，这不正是作者想要的吗，但这不是我想要的。编解码部分我会很偏向FFMPEG这个“大杂会”，其它部分我会选择其它的“强者”
2.Darwin、Helix
两个都是非常有名软件，也只能称之为软件了，因为就算Darwin有源码，这种代码规模，也不适合用于嵌入式。说回软件本身，真的很有名。它们都是很真真拿来商业化运行的软件，但我是研发人员，不是视频流服务商，对不起，Apple，对不起，Microsoft。
3.LIVE555
如果说上面两个和我都相关性为零（当然了，也是困扰了N周以后痛苦得出的结论），那LIVE555真的给了我一条出路，它是一个代码规模非常合适，又非常强大的媒体解决方案（称之为方案是因为它功能非常的丰富）。有长一段时间，我想去弄懂它的源码，不过和网上的很多人一样，最后软下来了，毕竟，去把这么多东西揉在一起，框架会弄得很复杂，因为我们要把这些完全不同的东西不断一层一层的抽像，最后抽像成一样（哲学呀）。它结构复杂是我中断分析它原来的其中一个原因，但不是主要原因。它结构的复杂程度也没胡像很多人网上说的那样严重，如果你是一个C++的热忱爱好者，你反而会迷上这段代码，当然了，对C的爱好都来说，当然是一种折磨了。暂时把我自己归类在C++爱好者范畴吧，呵呵，我很欣赏这段原码。主要原因是我不希望被某一个库绑死。LIVE555是有编解码能力，但我更希望它只做服务器的工作。
因此，最终后回来的老路上来，没有帮助，就得自己帮自己，从最基础的RFC看起。经过了N天（周）的英文，终于领会了如果在RTP承载MPEG数据包。在这个过程中很得到了一些LIVE555的帮助（通过对Ethereal捕捉的LIVE555数据包进行分析）。先把程序弄上来，原理性的以后有空再写，程序只有一个.cpp文件，在vs.net 2003下编译通过，播放的视频文件在http://www.cnitblog.com/Files/tinnal/ES流解释程序.rar 内，播放的客户端采用VLC，其下载地址为http://www.videolan.org/。选择打开网络串流，然后选择“UDP/RTP”端口，输入程序的输出端口1000，然后才运行程序，你将在VLC内看到测试的广播视频，IP不一样的话自己改改就行。其它所谓的原理性的，也就是看RFC 3350、RFC2550以及iso13818－2的一些重点地方。
// MPEG2RTP.h
#include
<
stdio.h
>
#include
<
stdlib.h
>
#include
<
conio.h
>
#include
<
string
.h
>
#include
<
winsock2.h
>
#include
<
winsock2.h
>
//
#include "mem.h"
//
#define PACK_STARTCODE (unsigned int)0x000001ba
#define SYSTEM_HEADER_STARTCODE (unsigned int)0x000001bb
#define PICTURE_START_CODE (unsigned int)0x00000100
#define GROUP_START_CODE (unsigned int)0x000000B8
#define ISO_11172_ENDCODE (unsigned int)0x000001b9
#define SEQUENCE_HEADER_CODE (unsigned int)0x000001b3
#define PACKET_BUFFER_END (unsigned int)0x00000000
#define MAX_RTP_PKT_LENGTH 1440
#define HEADER_LENGTH 16
#define DEST_IP "192.168.0.98"
#define DEST_PORT 1000
#define MPA 14 /*MPEG PAYLOAD TYPE */
#define MPV 32
typedef struct
{
/**//* byte 0 */
unsigned char csrc_len:4; /**//* expect 0 */
unsigned char extension:1; /**//* expect 1, see RTP_OP below */
unsigned char padding:1; /**//* expect 0 */
unsigned char version:2; /**//* expect 2 */
/**//* byte 1 */
unsigned char payload:7; /**//* RTP_PAYLOAD_RTSP */
unsigned char marker:1; /**//* expect 1 */
/**//* bytes 2, 3 */
unsigned short seq_no;
/**//* bytes 4-7 */
unsigned long timestamp;
/**//* bytes 8-11 */
unsigned long ssrc; /**//* stream number is used here. */
} RTP_FIXED_HEADER;
typedef struct {
//byte 0
unsigned char TR_high2:2; /**//* Temporal Reference high 2 bits*/
unsigned char T:1; /**//* video specific head extension flag */
unsigned char MBZ:5; /**//* unused */
//byte1
unsigned char TR_low8:8; /**//* Temporal Reference low 8 bits*/
//byte3
unsigned char P:3; /**//* picture type; 1=I,2=P,3=B,4=D */
unsigned char E:1; /**//* set if last byte of payload is slice end code */
unsigned char B:1; /**//* set if start of payload is slice start code */
unsigned char S:1; /**//* sequence header present flag */
unsigned char N:1; /**//* N bit; used in MPEG 2 */
unsigned char AN:1; /**//* Active N bit */
//byte4
unsigned char FFC:3; /**//* forward_f_code */
unsigned char FFV:1; /**//* full_pel_forward_vector */
unsigned char BFC:3; /**//* backward_f_code */
unsigned char FBV:1; /**//* full_pel_backward_vector */
} MPEG_VID_SPECIFIC_HDR; /**//* 4 BYTES */
enum reading_status {
SLICE_AGAIN,
SLICE_BREAK,
UNKNOWN,
SLICE,
SEQUENCE_HEADER,
GROUP_START,
PICTURE
};
void validate_file();
float frame_rate(int buffer_index);
unsigned int read_picture_type(int buffer_index);
unsigned int read_FBV(int buffer_index);
unsigned int read_BFC(int buffer_index);
unsigned int read_FFV(int buffer_index);
unsigned int read_FFC(int buffer_index);
unsigned int extract_temporal_reference(int buffer_index);
unsigned int find_next_start_code(unsigned int *buffer_index);
void reset_buffer_index(void);
BOOL InitWinsock();
#include
<
stdio.h
>
#include
<
stdlib.h
>
#include
<
conio.h
>
#include
<
string
.h
>
#include
<
winsock2.h
>
#include
<
winsock2.h
>
//
#include "mem.h"
//
#define PACK_STARTCODE (unsigned int)0x000001ba#define SYSTEM_HEADER_STARTCODE (unsigned int)0x000001bb#define PICTURE_START_CODE (unsigned int)0x00000100#define GROUP_START_CODE (unsigned int)0x000000B8#define ISO_11172_ENDCODE (unsigned int)0x000001b9#define SEQUENCE_HEADER_CODE (unsigned int)0x000001b3#define PACKET_BUFFER_END (unsigned int)0x00000000#define MAX_RTP_PKT_LENGTH 1440#define HEADER_LENGTH 16#define DEST_IP "192.168.0.98"#define DEST_PORT 1000#define MPA 14 /*MPEG PAYLOAD TYPE */#define MPV 32typedef struct { /**//* byte 0 */ unsigned char csrc_len:4; /**//* expect 0 */ unsigned char extension:1; /**//* expect 1, see RTP_OP below */ unsigned char padding:1; /**//* expect 0 */ unsigned char version:2; /**//* expect 2 */ /**//* byte 1 */ unsigned char payload:7; /**//* RTP_PAYLOAD_RTSP */ unsigned char marker:1; /**//* expect 1 */ /**//* bytes 2, 3 */ unsigned short seq_no; /**//* bytes 4-7 */ unsigned long timestamp; /**//* bytes 8-11 */ unsigned long ssrc; /**//* stream number is used here. */} RTP_FIXED_HEADER;typedef struct { //byte 0 unsigned char TR_high2:2; /**//* Temporal Reference high 2 bits*/ unsigned char T:1; /**//* video specific head extension flag */ unsigned char MBZ:5; /**//* unused */ //byte1 unsigned char TR_low8:8; /**//* Temporal Reference low 8 bits*/ //byte3 unsigned char P:3; /**//* picture type; 1=I,2=P,3=B,4=D */ unsigned char E:1; /**//* set if last byte of payload is slice end code */ unsigned char B:1; /**//* set if start of payload is slice start code */ unsigned char S:1; /**//* sequence header present flag */ unsigned char N:1; /**//* N bit; used in MPEG 2 */ unsigned char AN:1; /**//* Active N bit */ //byte4 unsigned char FFC:3; /**//* forward_f_code */ unsigned char FFV:1; /**//* full_pel_forward_vector */ unsigned char BFC:3; /**//* backward_f_code */ unsigned char FBV:1; /**//* full_pel_backward_vector */} MPEG_VID_SPECIFIC_HDR; /**//* 4 BYTES */enum reading_status { SLICE_AGAIN, SLICE_BREAK, UNKNOWN, SLICE, SEQUENCE_HEADER, GROUP_START, PICTURE };void validate_file();float frame_rate(int buffer_index);unsigned int read_picture_type(int buffer_index);unsigned int read_FBV(int buffer_index);unsigned int read_BFC(int buffer_index);unsigned int read_FFV(int buffer_index);unsigned int read_FFC(int buffer_index);unsigned int extract_temporal_reference(int buffer_index);unsigned int find_next_start_code(unsigned int *buffer_index);void reset_buffer_index(void);BOOL InitWinsock();
//MPEG2RTP.cpp
// 这个程序主要用于RTP封装MPEG2数据的学习和测试，不作任何其它用途
//
软件在VS.net 2003中编译通过，但在linux下作小量修改也应编译通过。
//
通过VLC测试，VLC能正确接收和解码由本程序发送的TEST.MPV编码流。
//
//
作者：冯富秋 Tinnal
//
邮箱：[email protected]
#include
"
MPEG2RTP.h
"
#pragma comment(lib,
"
Ws2_32
"
)unsigned
char
buf[MAX_RTP_PKT_LENGTH
+
4
];
//
input buffer
enum
reading_status state
=
SEQUENCE_HEADER;unsigned
int
g_index_in_packet_buffer
=
HEADER_LENGTH;
static
unsigned
long
g_time_stamp
=
0
;
static
unsigned
long
g_time_stamp_current
=
0
;
static
float
g_frame_rate
=
0
;
static
unsigned
int
g_delay_time
=
0
;
static
unsigned
int
g_timetramp_increment
=
0
;FILE
*
mpfd;SOCKET socket1;RTP_FIXED_HEADER
*
rtp_hdr;MPEG_VID_SPECIFIC_HDR
*
mpeg_hdr;
#if
0
void
Send_RTP_Packet(unsigned
char
*
buf,
int
bytes)
{ int i = 0; int count = 0; printf("/nPacket length %d/n",bytes); printf("RTP Header: [M]:%s [sequence number]:0x%lx [timestamp]:0x%lx/n", rtp_hdr->marker == 1?"TRUE":"FALSE", rtp_hdr->seq_no, rtp_hdr->timestamp); printf(" [TR]:%d [AN]:%d [N]:%d [Sequence Header]:%s / /n [Begin Slice]:%s [End Slice]:%s / /n [Pictute Type]:%d / /n [FBV]:%d [BFC]:%d [FFV]:%d [FFC]:%d/n", (mpeg_hdr->TR_high2 << 8 | mpeg_hdr->TR_low8), mpeg_hdr->AN, mpeg_hdr->N, mpeg_hdr->S == 1?"TRUE":"FALSE", mpeg_hdr->B ==1?"TRUE":"FALSE", mpeg_hdr->E ==1?"TRUE":"FALSE", mpeg_hdr->P, mpeg_hdr->FBV, mpeg_hdr->BFC, mpeg_hdr->FFV, mpeg_hdr->FFC); while(bytes --) { printf("%02x ",buf[count++]); if(++i == 16) { i=0; printf("/n");
} } printf("/n");}
#else
Send_RTP_Packet(unsigned
char
*
buf,
int
bytes)
{ return send( socket1, (char*) buf, bytes, 0 );}
#endif
void
main(
int
argc,
char
*
argv[])
{ unsigned int next_start_code; unsigned int next_start_code_index; unsigned int sent_bytes; unsigned short seq_num =0; unsigned short stream_num = 10; struct sockaddr_in server; int len =sizeof(server);#if 0 mpfd = fopen("E://tinnal//live555//vc_proj//es//Debug//test.mpv", "rb"); #else if (argc < 2) { printf("/nUSAGE: %s mpegfile/nExiting../n/n",argv[0]); exit(0); } mpfd = fopen(argv[1], "rb");#endif if (mpfd == NULL ) { printf("/nERROR: could not open input file %s/n/n",argv[1]); exit(0); } rtp_hdr = (RTP_FIXED_HEADER*)&buf[0]; mpeg_hdr = (MPEG_VID_SPECIFIC_HDR*)&buf[12]; memset((void *)rtp_hdr,0,12); //zero-out the rtp fixed hdr memset((void *)mpeg_hdr,0,4); //zero-out the video specific hdr memset((void *)buf,0,MAX_RTP_PKT_LENGTH + 4); InitWinsock(); server.sin_family=AF_INET; server.sin_port=htons(DEST_PORT); //server的监听端口 server.sin_addr.s_addr=inet_addr(DEST_IP); //server的地址 socket1=socket(AF_INET,SOCK_DGRAM,0); connect(socket1, (const sockaddr *)&server, len) ; //read the first packet from the mpeg file //always read 4 extra bytes in (in case there's a startcode there) //but dont send more than MAX_RTP_PKT_LENGTH in one packet fread(&(buf[HEADER_LENGTH]), MAX_RTP_PKT_LENGTH-HEADER_LENGTH+4, 1,mpfd); validate_file(); do { /**//* initialization of the two RTP headers */ rtp_hdr->seq_no = htons(seq_num ++); rtp_hdr->payload = MPV; rtp_hdr->version = 2; rtp_hdr->marker = 0; rtp_hdr->ssrc = htonl(stream_num); mpeg_hdr->S = mpeg_hdr->E = mpeg_hdr->B= 0; do{ next_start_code = find_next_start_code(&next_start_code_index); if ((next_start_code >0x100) && (next_start_code<0x1b0) ) { // // if(state == SEQUENCE_HEADER || state ==GROUP_START || state ==PICTURE || state == UNKNOWN) { state = SLICE; mpeg_hdr->B = 1; } // // // else if (state == SLICE ||state == SLICE_AGAIN) { state = SLICE_AGAIN; sent_bytes = next_start_code_index; mpeg_hdr->E = 1; } // // // // else if (state == SLICE_BREAK) { state = UNKNOWN; sent_bytes = next_start_code_index; mpeg_hdr->E = 1; goto Sent_Packet; } } switch(next_start_code) { case SEQUENCE_HEADER_CODE: // // // if(state == SLICE || state == SLICE_AGAIN) { state = SEQUENCE_HEADER; sent_bytes = next_start_code_index; // // rtp_hdr->marker = 1; goto Sent_Packet; } state = SEQUENCE_HEADER; g_frame_rate = frame_rate(next_start_code_index); g_delay_time = (unsigned int)(1000.0 / g_frame_rate +0.5); //ms g_timetramp_increment = (unsigned int)(90000.0 / g_frame_rate +0.5); //90K Hz mpeg_hdr->S=1; break; case GROUP_START_CODE: // // // if(state == SLICE || state == SLICE_AGAIN) { state = GROUP_START; sent_bytes = next_start_code_index; // // rtp_hdr->marker = 1; goto Sent_Packet; } state = GROUP_START; case PICTURE_START_CODE: // // // if(state == SLICE || state == SLICE_AGAIN) { state = PICTURE; sent_bytes = next_start_code_index; // // rtp_hdr->marker = 1; goto Sent_Packet; } state = PICTURE; mpeg_hdr->TR_high2 = (extract_temporal_reference(next_start_code_index) & 0x300 )>> 8; mpeg_hdr->TR_low8 = extract_temporal_reference(next_start_code_index) & 0xff; mpeg_hdr->P = read_picture_type(next_start_code_index); //now read the motion vectors information if( (mpeg_hdr->P==2) || (mpeg_hdr->P==3)) { //if B- or P-type picture, need forward mv mpeg_hdr->FFV = read_FFV(next_start_code_index); mpeg_hdr->FFC = read_FFC(next_start_code_index); } if( mpeg_hdr->P==3) { // if B-type pictue, need backward mv mpeg_hdr->FBV = read_FBV(next_start_code_index); mpeg_hdr->BFC = read_BFC(next_start_code_index); } // // if( mpeg_hdr->P== 1 || mpeg_hdr->P == 2 ){ g_time_stamp += g_timetramp_increment; g_time_stamp_current = g_time_stamp; }else{ g_time_stamp += g_timetramp_increment; } break; case PACKET_BUFFER_END: // // if(state == SLICE_AGAIN) { state = UNKNOWN; goto Sent_Packet; } // // if(state == SLICE) { state = SLICE_BREAK; sent_bytes = next_start_code_index; goto Sent_Packet; } // // // if(state == SLICE_BREAK ) { state = SLICE_BREAK; sent_bytes = next_start_code_index; goto Sent_Packet; } break; } }while(next_start_code != PACKET_BUFFER_END);Sent_Packet: rtp_hdr->timestamp = htonl(g_time_stamp_current); Send_RTP_Packet(buf, sent_bytes); //copy the tail data to the head of the packet buffer memmove(&buf[HEADER_LENGTH], &buf[sent_bytes], MAX_RTP_PKT_LENGTH-sent_bytes); //reset the buffer index to zero reset_buffer_index(); //reading data into buffer again fread(&(buf[(MAX_RTP_PKT_LENGTH-sent_bytes)+HEADER_LENGTH]), sent_bytes -HEADER_LENGTH , 1,mpfd); // sleep g_delay_time msec for sending next picture data if(rtp_hdr->marker ==1) Sleep( g_delay_time ); }while(!feof(mpfd)); closesocket(socket1); fclose(mpfd); printf("stream end./n");}//==================================================================unsigned int find_next_start_code(unsigned int *next_start_code_index) //NOTE: all start codes ARE byte-aligned{ unsigned int byte0=0,byte1=0,byte2=0,byte3=0,startcode=0; //while not startcode and have not exceeded max packet length while (g_index_in_packet_buffer < MAX_RTP_PKT_LENGTH) { if (buf[g_index_in_packet_buffer+0] == 0 && buf[g_index_in_packet_buffer+1] == 0 && buf[g_index_in_packet_buffer+2] ==1) { //printf("FOUND startcode %d/n",indx); byte0=(int)buf[g_index_in_packet_buffer+0]; byte1=(int)buf[g_index_in_packet_buffer+1]; byte2=(int)buf[g_index_in_packet_buffer+2]; byte3=(int)buf[g_index_in_packet_buffer+3]; startcode=(byte0 << 24) + (byte1 << 16) + (byte2 << 8) + byte3; *next_start_code_index = g_index_in_packet_buffer; g_index_in_packet_buffer = g_index_in_packet_buffer+4; return(startcode); } else g_index_in_packet_buffer++; } // if (g_index_in_packet_buffer >= (MAX_RTP_PKT_LENGTH)) { *next_start_code_index = g_index_in_packet_buffer -1; g_index_in_packet_buffer = HEADER_LENGTH; return PACKET_BUFFER_END; } printf("Error reading buffer../n"); exit(-1); return -1;}void reset_buffer_index(void){ g_index_in_packet_buffer = HEADER_LENGTH;}//========================================================float frame_rate(int buffer_index){ unsigned char frame_rate_code; frame_rate_code = (unsigned char)buf[buffer_index +7] & 0xf; switch(frame_rate_code) { case 0x1: return 23.976; case 0x2: return 24.0; case 0x3: return 25.0; case 0x4: return 29.97; case 0x5: return 30.0; case 0x6: return 50.0; case 0x7: return 59.94; case 0x8: return 60.0; default: return 0; }}//========================================================unsigned int extract_temporal_reference(int buffer_index) // 10 bits{ unsigned int low2bits=0,TR=0; // TR = temporal reference; TR = (unsigned int) (buf[buffer_index+4]); TR <<= 2; low2bits = (unsigned int) (buf[buffer_index+5]); TR |= (low2bits >> 6); return(TR);}//========================================================unsigned int read_picture_type(int buffer_index){ unsigned int pictype=0; pictype = (unsigned int) buf[buffer_index+5]; pictype = (pictype >> 3) & (0x7); return (pictype);}//=======================================================unsigned int read_FFV(int buffer_index) // 1 bit{ return( (int) ((buf[buffer_index+7] & (0x4)) >> 2));}//=======================================================unsigned int read_FFC(int buffer_index) // 3 bits{ unsigned int FFC=0,lowbit=0; FFC = (int) (buf[buffer_index+7] & (0x3)); FFC <<= 1; lowbit = (int) ((buf[buffer_index+8]) & (0x80)); FFC = FFC | (lowbit >> 7 ); return(FFC);}//=======================================================unsigned int read_FBV(int buffer_index) // 1 bit{ return( (int) ((buf[buffer_index+8] & (0x40))>>6) );}//=======================================================unsigned int read_BFC(int buffer_index) // 3 bits{ return( (int) ( (buf[buffer_index+8] & (0x38) ) >> 3 ) );}void validate_file(){ /**//* to validate the file, ensure the existance of a startcode */ int j=0,valid=0; while ((j++<MAX_RTP_PKT_LENGTH) && (!valid)) { if (!((int)buf[j+0] + (int)buf[j+1]) && (((int)buf[j+2])==1)) valid=1; } if (!valid) { printf("/nERROR: start code not found. / /nInput file must be a valid MPEG I file./n"); exit(0); } }BOOL InitWinsock(){ int Error; WORD VersionRequested; WSADATA WsaData; VersionRequested=MAKEWORD(2,2); Error=WSAStartup(VersionRequested,&WsaData); //启动WinSock2 if(Error!=0) { return FALSE; } else { if(LOBYTE(WsaData.wVersion)!=2||HIBYTE(WsaData.wHighVersion)!=2) { WSACleanup(); return FALSE; } } return TRUE;}
完成这个测试程序后，我有了很大的信心，又重复看了RFC3550几编，其实，如果你真看了程序，你发现我只发送了RTP，并没有发送RTCP数据包，因此，我们是不能同步多个RTP流的。我没去编码下去，因为我觉得已经够了。这里强调，没用说的RTP没有了RTCP就不行！接下来的工作，就是把这个程序的下层发包函数去掉，采用RTP库JRTPLIB，我觉得这才应该是JRTPLIB的DEMO！如果有人问，就这样的一个程序就能完成任务了，要JRTPLIB干嘛，其实，我不写RTCP相关代码的原因为多个：
1.RTCP里头有很多关于RTCP发送简隔的时间计算，RTP信息的统计，这种操作不是难，而是烦，我不想去写
2.RTCP和RTP一开始出来的时候并不是因为视频的点播等应用的，而是视频会议。RTCP有管理与会者的层面含义，这一功能在很多场合并不会用到。
3.我想简单，没有写多个流间的同步，如一个影片的视频和音频流。这些其实是RTCP来完成的。
我懒得去写，因为这些功作RTP的各个库类都做得很好。我觉得用库的最大优点就在这吧。