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5 \5 B( j6 p$ M, _& o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
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3 a, E+ d6 W) s- v' o: l1 a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。
8 {. @ h2 c7 }一、HTTP网页服务器1 x9 G+ O9 a) r* T. T; K
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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- struct sockaddr_in servaddr;
' z; d1 e/ p1 ^% C - socklen_t addrsize = sizeof(struct sockaddr);$ h/ V% ?8 q/ s9 i& M% q
- bzero(&servaddr , sizeof(servaddr));
u) d: ?, H% S - servaddr.sin_family = AF_INET;
6 y; Q5 I; V9 d - servaddr.sin_addr.s_addr = inet_addr(ip);1 q) z# \) z' [; D$ u& O
- servaddr.sin_port = htons(port);
) r/ F% S. Z. B - int ret;0 H: F! T' ]1 g
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)
, x$ j" E) U2 y7 G8 b/ r - {
. \7 k5 H+ Y5 l0 Z0 v) o$ Z- y - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
+ k0 }+ N" h- F8 M) f0 q* M - return -1;
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- int on = 1;
5 }* B/ _/ i* D5 ] Y# i - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0), M0 p7 F8 L% j2 ~! Q) X. g/ R1 f. L
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- printf("setsockopt error\n");
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- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);0 Z; E( u; s1 O
- if(ret == -1)% l0 p8 w: S5 {! S( U
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- printf("Tcp bind faiLED!\n");- k5 [: H: `* E% \3 m* A2 J
- return -1;2 i. K1 Y8 a& M7 g+ A
- }
. l1 c/ `9 t4 s! b - if(listen(*socket_found , 5) == -1)+ y. h7 K( E* e& O/ b3 D
- {
0 ?/ H) @7 M. L4 x2 j% {! V% g - printf("Listen failed!\n");
2 i4 ?* j6 b1 S) l* X( t8 R% ^ - return -1;
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2 v4 e8 M+ Y" W% D% b( p - return 0;) K7 O8 X; M" _9 H$ o
- }
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);# y' l1 H4 x0 N. e; ]$ @
- void * Thread_TCP_Web_Recv(void *arg)
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- 。。。5 E. Y# K7 ?+ C [6 t5 w4 I
- while(1)# {1 A4 X5 s0 u6 R) u7 J) L
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- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
4 y' @: J2 o( W: D - printf("fd_socket_conn = accept()\n");
$ ^1 \" l1 D& @, B+ x - 。。。
. Z+ b* v& V% K8 B - recv(fd_socket_conn , recvbuf , 1000 , 0);
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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);
+ R# l, k$ @8 w0 M1 u - pic_tmpbuffer = pic.tmpbuffer;, c6 e" I: Z: I/ Y
- pic.tmpbytesused = buff.bytesused;% c. ? H! M: C
- pic_tmpbytesused = pic.tmpbytesused;4 N# Z( u/ v8 ~5 H* K+ Z9 b
- pthread_cond_broadcast(&pct);
' @- t/ j9 ^* c8 ~0 I* s, \4 p - 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;
$ [8 m3 `4 h* s" a. H - pthread_cond_t pct;
% u& ^- s0 D- P* Q$ `) b - int main(int argc, char* argv[]). _3 [* i1 g, P* w
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- TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
: m: V1 O {' J6 ?4 W& h, E3 i - pthread_mutex_init(&pmt , NULL);
8 b. p* c2 f3 S# L7 W' J - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);
3 Z# m2 V$ F' `" U6 k - pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
: P Q4 z/ M* w8 N8 ~* i4 N k - ...
% h* z+ a2 j' t/ E - while(1)
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- V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);6 m; r4 l0 @4 f+ K5 p1 N6 k% P
- ...
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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;">
$ a5 n, n0 D) o; N; k* r - </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" \
- k) `7 R+ m, q8 G) r) M ^ - "Server: MJPG-Streamer/0.2\r\n" \* I2 q/ ]( F$ F5 ?* G6 k
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \, X( _& e8 f M4 H$ R0 `) `2 J' A
- "Pragma: no-cache\r\n" \
- J, T9 H5 |; @+ U1 ]$ z. H - "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"/ m, W" a W% Y3 M
- #define BOUNDARY "boundarydonotcross"* H7 |; L6 e1 `% m% d9 y }, K
- printf("preparing header\n");$ A0 i4 ^. m9 ]( l! S' u* r
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \5 ]- W4 r1 G5 M J0 I: ~
- "Access-Control-Allow-Origin: *\r\n" \
/ I) t' X! R0 h. J. ]' X. [6 q - STD_HEADER \
6 v$ D5 v- x6 Y* c) b! k ]4 a - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \9 M" i# I. A4 r
- "\r\n" \
0 \8 j* k& H5 W& T: j) H$ |3 h - "--" BOUNDARY "\r\n");7 n0 o& O! e* v6 ?% g
- if(write(fd, buffer, strlen(buffer)) < 0)
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- free(frame);
# O+ u2 |* r% z4 E, [6 S - return;
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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" \
& h4 D9 d' h! q" I& P - "Content-Length: %d\r\n" \
9 N! h" }3 d2 z0 r. Q2 u j - "X-Timestamp: %d.%06d\r\n" \
; S8 [& [) d8 B8 P - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);0 j7 x7 p; j2 n- W+ G. t
- printf("sending intemdiate header\n");& [2 `: M4 J9 X% Q
- if(write(fd, buffer, strlen(buffer)) < 0)
( f) p3 g# P2 f" d7 B$ j - break;4 T* {) R" U2 W+ Z% O
- printf("sending frame\n");
% c; v6 Q. Z6 d! n7 ]7 ^: A! D - if(write(fd, frame, frame_size) < 0)
# P* t6 l# M+ ~; ?$ r& l - break;
K- D9 { Q4 j: ~9 g% y* e - printf("sending boundary\n");
8 ~1 g3 X5 X% b0 G } - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");0 b/ U/ o# I% q, ^! r
- if(write(fd, buffer, strlen(buffer)) < 0)( u! d3 p: q. w, g
- 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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二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:' K H M, f/ n7 i' B
- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)
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- *socket_found = socket(AF_INET, SOCK_DGRAM, 0);7 J! s; D. c6 p9 w
- if(*socket_found == (~0))
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7 ?' m1 D% ]+ H4 q; ? - printf("Create udp send socket failed!\n");
6 Z/ K9 r. y8 K, t2 A - return -1;
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- addr->sin_family = AF_INET;- t. h" A6 q2 L; H4 d- z: L# P8 a
- addr->sin_addr.s_addr = inet_addr(ip);
, c, L7 R" b) [5 f; U - addr->sin_port = htons(port);8 ^ O8 \4 Z- _$ [0 s
- memset(addr->sin_zero, 0, 8);
- b# k G/ o6 [( d - return 0;9 ?; N4 K; q" |3 z2 a$ \
- }
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" m6 t) G) e% K2 Z1 F/ V$ m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:; U/ D, v' O- F( D' U r4 W+ s! ^
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' R3 Q* O1 ^5 j1 l% b- while(fend > 0)
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1 R1 V6 _ S2 V) ]6 i; v - memset(picture.data , 0 , sizeof(picture.data));
: I4 h' j( K0 S6 g0 J Y G - fread(picture.data , UDP_FRAME_LEN , 1, fp);
6 Q( Y' {; @9 S& m+ d - if(fend >= UDP_FRAME_LEN): C$ a: M. _* G0 i. S0 B/ @+ [2 N/ x
- {
: h' O7 O, @* u) K3 m5 G7 M - picture.length = UDP_FRAME_LEN;( [) ]9 V& Q, J0 a- g% s! o
- picture.fin = 0;
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% P0 Y$ f! V/ d4 j - else0 Z) V/ \1 x4 W9 E; B4 b
- {
* u1 o' k) Y, U1 `- `% \& C - picture.length = fend;
9 j( p4 x+ z" d: D0 I+ x+ G: [& b - picture.fin = 1;
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0 u* h! ^, W7 }, Y2 O' w/ O# p2 j - //printf("sendbytes = %d \n",sendbytes);' i) \6 C6 c6 i+ Y8 E6 @, e8 a
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
3 ?4 q0 J( o- E, o1 m - if(sendbytes == -1)
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' Z4 f& z, ^$ p - printf("Send Picture Failed!d\n");
. F7 ?1 v6 z/ P, i6 C - return -1; B# C( y e v! Y! s; _
- }
% ]( k$ ^( I& u( v9 W6 f - else
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3 ~+ M2 Z% ^3 c- O* j* R - fend -= UDP_FRAME_LEN;
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- }
复制代码 / d* R; z5 ]1 U, N3 z2 I6 {
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iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |