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- W# {; N* j5 E作者|donatello1996 来源 | 电子发烧友 题图|飞凌嵌入式 iMX8MPlus 核心板: https://www.forlinx.com/product/136.html& e+ J% l% j) w5 h9 p2 _
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本文采用的硬件板卡为飞凌嵌入式OKMX8MP-C开发板,系统版本Linux5.4.70+Qt5.15.0,主要介绍基于HTTP网页服务器和UDP上位机的MJPG码流传输。 MJPG格式作为一种持续传输的视频码流,在远程监控领域中应用较广,而实现这种远程监控的第三方应用最常见的有两种:浏览器HTTP网页、UDP上位机。
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两者各有优势,对比鲜明,其中: 这两种应用各有优缺点,对于嵌入式开发者来说,两者都必须掌握。
5 o( y7 R" }) w4 J一、HTTP网页服务器5 E. g5 [5 \; s3 k7 V2 m
先说下HTTP网页服务器获取MJPG码流的代码,首先是OKMX8MP-C在开发板端建立TCP服务器: - int TCP_Server_Found(socklen_t* socket_found , char* ip , int port)
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! k2 ]" N' L2 B - struct sockaddr_in servaddr;% T* h0 F( @% v: R) `
- socklen_t addrsize = sizeof(struct sockaddr);
! a5 a0 g- z3 I* U$ Q9 L - bzero(&servaddr , sizeof(servaddr));* g/ B% X3 q/ x3 u
- servaddr.sin_family = AF_INET;
8 t/ d4 p, S5 t5 _% }# \5 p - servaddr.sin_addr.s_addr = inet_addr(ip);$ P2 ?# m8 m- J# @5 D+ P5 ]
- servaddr.sin_port = htons(port);
! d. P" F7 e( G/ z+ I - int ret;6 \3 ~- w: W6 U
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)
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- printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);1 F& O0 R; T& t2 n: q
- return -1;) m8 Y0 Y$ z' Z
- }
/ r$ w# }! v1 r. s- D; \6 W - int on = 1;
0 V" T, ^# X( m8 y7 P, C - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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- printf("setsockopt error\n");' c2 l: u1 q9 P# Q+ ]7 Y0 R+ f, P
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- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
9 x" k8 x' J- z! I5 s9 i - if(ret == -1)0 B+ y1 a% v% A8 V2 Z4 G* b
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- printf("Tcp bind faiLED!\n"); U9 Q8 f- b0 _7 @
- return -1;
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# y1 j: Z- h; r3 o" Q' _& k - if(listen(*socket_found , 5) == -1)
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- printf("Listen failed!\n");
0 g! @) ~, B6 e5 k& E - return -1;
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* _, q. V2 j3 s/ }$ y" N! ^ - return 0;
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复制代码其中setsockopt()函数是可选的,一般只用于规避socket()函数的建立错误。 建立了TCP服务器后,返回的socklen_t型实参在后面的HTTP网页服务器中需要用到。 HTTP网页服务器所属的TCP操作是需要另起轮询线程来让客户端进行accept()握手操作的,accept()之前的listen()倒是只需要执行一次即可,accept()握手操作和recv()接收操作需要创建一个死循环线程: - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);
9 X2 p0 X2 ^" C' ~! p - void * Thread_TCP_Web_Recv(void *arg)% }) F" t' t2 l8 ?
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- while(1); L# b; P. U1 G- F' x; U: u
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- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
/ n+ U9 _4 R" {/ y% v7 W - printf("fd_socket_conn = accept()\n");
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- recv(fd_socket_conn , recvbuf , 1000 , 0);
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- 。。。
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复制代码MJPG帧可以使用Grab操作获取,获取到的MJPG帧需要在TCP线程中读,在Grab操作线程中写,这种被多个线程访问的资源需要加锁防止读写冲突,即资源被Grab操作写入时,需要上锁,不允许其它线程访问,操作完成时需要解锁,允许其它线程访问: - pthread_mutex_lock(&pmt);+ i/ \2 a Z; l4 p
- pic_tmpbuffer = pic.tmpbuffer;
* q2 d9 r3 T; t( i - pic.tmpbytesused = buff.bytesused;% a& f0 m1 a: f' e& b; B6 O7 s2 j
- pic_tmpbytesused = pic.tmpbytesused;
9 r) j" f* n6 ~' `4 q( p - pthread_cond_broadcast(&pct);+ ^9 B8 R. c9 r) w
- pthread_mutex_unlock(&pmt);
复制代码线程互斥锁使用之前需要初始化: - pthread_mutex_t pmt;& ~* L1 U6 A6 C1 k& {" f
- pthread_cond_t pct;
' F7 \+ W3 O3 u - int main(int argc, char* argv[])+ i4 H+ m; a( H% d
- {
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# }7 e2 L/ P5 D4 A* M - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);( W6 E4 ]0 G" O
- pthread_mutex_init(&pmt , NULL);2 _8 q2 L R% ~$ K
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);
* }' ^/ [' d3 c, X. A e - pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);) D5 v7 G9 S; R; j8 y/ e7 x4 c4 w
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- while(1)
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' Z* {0 _7 A& n$ g2 p! _ G: U - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);2 m# Y8 R) j+ S6 u7 @, k4 \" [
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- }
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- }
复制代码然后是发送的细节,发送图片文件之前,需要先发送HTTP标准头,这个相当于给发送图片或者其它类型的流数据铺路: - <p style="box-sizing: border-box; border: 0px; vertical-align: baseline; line-height: 26px;"><span style="text-indent: 32px;"># V; t( ]3 o0 d; A: ~- V0 @3 S
- </span></p><p style="box-sizing: border-box; border: 0px; vertical-align: baseline; line-height: 26px;"></p>
复制代码- #define STD_HEADER "Connection: close\r\n" \
8 i1 q3 }! z w* g: L8 x Y/ E q) S - "Server: MJPG-Streamer/0.2\r\n" \+ z1 H6 ]$ S7 {
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \. R/ h! s3 r* M8 m) F8 k; f% `( R
- "Pragma: no-cache\r\n" \
4 _4 |/ y& l6 U% { - "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
7 t3 K7 ^5 b5 O% `8 A G) ` - #define BOUNDARY "boundarydonotcross"
; \& @: h6 _+ h: b. W1 ?% \* L2 A. A - printf("preparing header\n");+ u1 `& P6 E& x4 L
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \2 r9 }$ h3 A: {5 r* P/ }
- "Access-Control-Allow-Origin: *\r\n" \
: @" p5 i; I7 x) p# X" D# N - STD_HEADER \ V+ A9 v# v0 a# S
- "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
! ]6 H- ~! ?- m. Q! h5 T% G - "\r\n" \2 j- k8 v" A ~
- "--" BOUNDARY "\r\n");
" T! p: A- f# M3 N# ]. U2 h - if(write(fd, buffer, strlen(buffer)) < 0)& s' N7 h! M7 N) y3 Q& e, p
- {
* q) Z" t& x: ^; @! r% @ - free(frame);
; u1 j3 B. P2 K8 p: P6 m - return;
5 E. I% M/ o+ n% f" E - }
复制代码发送完HTTP标准头之后,就需要发送内容头(Content-Type),这处的Content-Type为image/jpeg,同样,HTTP标准协议里面image支持的类型远不止jpeg一种,发送完内容头之后就是正文和boundary结尾,这样帧完整的HTTP头发送到指定的TCP GET地址,就会在浏览器中显示刚刚发送的图片: - <pre class="prettyprint lang-cpp" style="box-sizing: border-box; font-family: Monaco, Menlo, Consolas, "Courier New", monospace; font-size: 16px; white-space: pre-wrap; line-height: 1.38462; color: rgb(51, 51, 51); word-break: break-all; background-color: rgb(245, 245, 245); border: 0px; border-radius: 4px; vertical-align: baseline;"> sprintf(buffer, "Content-Type: image/jpeg\r\n" \
% a2 H$ \) K' t; X- ~) r9 ^9 y% V - "Content-Length: %d\r\n" \6 a% Y6 n* ^ W& u4 B1 M' F
- "X-Timestamp: %d.%06d\r\n" \
% b0 o, m& f" y3 z/ _ - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
$ S/ I4 s* p6 ^/ _3 \& B! `6 }2 F" ^ - printf("sending intemdiate header\n");7 @, @& r' o7 g% ?1 [$ ^7 C
- if(write(fd, buffer, strlen(buffer)) < 0)- l n) z2 Y4 Q
- break;
% h9 I; S& z! @6 z" x# U3 p. V7 }4 X4 B - printf("sending frame\n");
/ c0 g5 R) |9 p' ^6 Y4 e) o# Q0 t. X - if(write(fd, frame, frame_size) < 0)' `7 E' | Y7 \: C0 k2 c
- break;( M! ~5 Z" |6 s) a
- printf("sending boundary\n");
& x. c3 }. o! q3 ? - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
3 Z9 i8 `$ @0 ?" T, _5 o' F+ d - if(write(fd, buffer, strlen(buffer)) < 0): [8 V2 I* C5 w4 Z2 U0 @9 t
- break;</pre><p style="box-sizing: border-box; border: 0px; font-size: 16px; vertical-align: baseline; line-height: 26px; color: rgb(51, 51, 51); font-family: " helvetica="" neue",="" helvetica,="" tahoma,="" arial,="" "microsoft="" yahei",="" "hiragino="" sans="" gb",="" "wenquanyi="" micro="" hei",="" sans-serif;"=""></p>
复制代码另外需要说明的是,TCP服务器线程在发送MJPEG流的时候是死循环发送的,因此TCP客户端在发送完GET指令之后,就会收到TCP服务器循环发送的图像缓存,TCP客户端会陷入忙等待状态无法再对外发送任何GET或者POST指令,从客户端使用者角度来看的效果就是网页一直在等待。 
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# `: B8 a8 {! t二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:# T# W* E5 A2 {1 y3 H7 _
- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port). l8 ^* W( s- B8 Z2 q- w' C6 E
- {
8 F" F3 `! D- A' o4 c - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);
Y8 Z2 r' [; T* G k, Q) u - if(*socket_found == (~0))
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+ e/ r4 e5 ^7 e5 h" c! Z - printf("Create udp send socket failed!\n");0 Z) F- {2 @6 ?; S
- return -1;
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; U) h0 x6 g' T8 M& q2 A, f' t - addr->sin_family = AF_INET;
9 R8 ^1 Y4 B, W8 x, y - addr->sin_addr.s_addr = inet_addr(ip);
7 a! U* I @+ C) { - addr->sin_port = htons(port);
4 P1 N) z1 t+ y - memset(addr->sin_zero, 0, 8);
5 A6 M/ ~% P1 r. ~0 ?: O - return 0;
0 C& \1 l- `, W/ h# G3 j" H3 c - }
复制代码
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& T; K1 D3 H$ b而UDP文件发送则要比HTTP发送简单得多,只需要将文件切片,每一片为固定长度的UDP帧长度,逐帧发送即可:
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- while(fend > 0)! S5 P' T h# x/ ^
- {2 k- {; q$ h% X8 }% q
- memset(picture.data , 0 , sizeof(picture.data));0 ?0 R5 _) A: e! R' T2 m
- fread(picture.data , UDP_FRAME_LEN , 1, fp);; J; c1 l% t8 r$ Q, y3 K
- if(fend >= UDP_FRAME_LEN)3 }8 c/ G7 w6 I& ^! [
- {' C! }+ z& x" p% l" U- C$ c! H# W
- picture.length = UDP_FRAME_LEN;! c/ W. u9 m: x
- picture.fin = 0;
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2 O9 ^3 ^+ w# Z5 |! R3 @% o - else, F7 o. s% [% A5 g! t- P# A: Z, o
- {
& d l4 A ]; r; i2 d: h8 l. i ? - picture.length = fend;
* e7 o: R7 A! L+ {! j, U - picture.fin = 1;
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- //printf("sendbytes = %d \n",sendbytes);
x7 T$ n4 c7 `& T: k% J0 { - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
8 L5 t1 j8 Z6 K9 P% G4 I0 M9 p - if(sendbytes == -1)% U6 R, I- Y% ^# U5 E
- {
2 M. \5 k5 S2 p* U - printf("Send Picture Failed!d\n");/ J" s# y$ ~% b! _7 x
- return -1;
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- else
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- fend -= UDP_FRAME_LEN;
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- }
复制代码
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$ R9 f& s* v/ i6 t* PiMX8MPlus 核心板: https://www.forlinx.com/product/136.html |