RTP －视频流广播

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RTP －视频流广播

分类：学习之路2008-09-03 10:15 10191人阅读评论(19) 收藏举报

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 "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();

//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：tinnal@163.com

#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();

{

/* 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。

RTP － 视频流广播