本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑
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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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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。 % a! R2 h& a7 B" {3 V8 c
一、HTTP网页服务器
' w2 g j4 y" v) j6 B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) S5 _. w U' U+ i. Y
- {
* r3 H, q( t; ]0 k% ^ - struct sockaddr_in servaddr;
4 @; b+ |5 w" h' T* q& ` - socklen_t addrsize = sizeof(struct sockaddr);" M* F$ G0 s; W# P
- bzero(&servaddr , sizeof(servaddr));
o2 F) j4 O. c! D0 M& J/ h - servaddr.sin_family = AF_INET;
2 W3 d# I5 P; |# ^$ N# S - servaddr.sin_addr.s_addr = inet_addr(ip);' q0 b ~ o- n; R
- servaddr.sin_port = htons(port);
' ^/ ?- d, D/ A# ^, i0 ? - int ret;
+ m' C( b; w5 d& P8 K1 G9 }% G - IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)/ v2 k2 g$ S1 e/ O# A
- {) _7 d5 K i) W+ t& }0 d) ]
- printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
1 U$ H# i: L/ }5 z - return -1;' }7 q& I4 ~; _7 z9 P" L% P. `' }
- }
- G: x' w1 U8 L( V - int on = 1;
% |' w9 F& z8 A# s - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)) c, e P7 s) e& C. m
- {
5 T3 ^# k+ L* ?, A$ V# b- F* Q4 } - printf("setsockopt error\n");
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- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
& ]6 q0 I+ _; _% |: i. i/ e - if(ret == -1)# `# _# D! V6 d) C Q) P+ D
- {$ w" l3 @% `/ V0 S$ `$ [
- printf("Tcp bind faiLED!\n");7 g# E* U* A+ F2 _* q$ N, E) `5 `
- return -1;
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- if(listen(*socket_found , 5) == -1), I- E5 D/ e# a4 ^: ~- f
- {
" W5 h/ g2 ] N, o - printf("Listen failed!\n");
6 R+ S, l! \: x$ p5 w8 e6 q* d - return -1;
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- return 0;5 M) l! f5 t5 v, v* ]
- }
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);; l& r4 U$ b" t' G
- void * Thread_TCP_Web_Recv(void *arg)8 [) `$ A: l/ q% Y( k
- {
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1 e3 Z9 y% r6 [9 X0 O3 a* R$ E - while(1)$ t# ~# q! u# o$ K& W! H
- {
e) _+ r, _3 `; D& Z7 E - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
( \' ~% t3 \4 }! w - printf("fd_socket_conn = accept()\n");
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- recv(fd_socket_conn , recvbuf , 1000 , 0);& W- \+ s/ E( W+ L
- }
# `( |" C" g' X4 e - 。。。
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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);
# Q" f) b8 w+ s5 z - pic_tmpbuffer = pic.tmpbuffer;/ J5 Y' ^* n9 s& }& m
- pic.tmpbytesused = buff.bytesused;
. T& b, { r$ t: h - pic_tmpbytesused = pic.tmpbytesused;: k" v' y$ u. u9 ]* Y+ {5 f6 x
- pthread_cond_broadcast(&pct);; W" q0 q$ ~: v& l& A3 e
- 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; B& ]& Z* {) E- h! t- l) A3 q- L
- pthread_cond_t pct;% C' a: c8 F" h3 Q% f
- int main(int argc, char* argv[])
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- TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
' b1 U, R9 \5 w5 W+ R a - pthread_mutex_init(&pmt , NULL);
' O9 v$ F. @+ T# v, ] I0 F - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);8 J, Z+ t6 S- A. D! s' [: c6 ~: c
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
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, P2 z7 c4 T6 L; s - while(1)
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- V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);! S s4 t+ L; W; m( ?/ ]
- ...
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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;">
8 @3 V: I. _( C - </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 m+ w8 P% s5 i w7 v r - "Server: MJPG-Streamer/0.2\r\n" \
: a& R/ O% t3 m% @; r* y; f3 T - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
) ?! [! x* `+ B: Y2 v3 p - "Pragma: no-cache\r\n" \6 N0 I6 f* u1 X6 `
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n": g- _- F( s; J5 D) A, C
- #define BOUNDARY "boundarydonotcross"
4 l8 l/ d; a: @ h5 x* q, w - printf("preparing header\n");7 v6 {' Z( D+ [# K5 [+ b8 C! _
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \/ m' h% N: \: g0 ^( V4 K
- "Access-Control-Allow-Origin: *\r\n" \
7 N( m1 W. E8 B4 j% I: Z2 u - STD_HEADER \
8 x# `% n, v' i9 x& t" q" p - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \% s+ o; v8 Z$ k& @) `
- "\r\n" \: c: f6 O2 {8 M2 W! n4 [
- "--" BOUNDARY "\r\n");
# q" o; @$ Q* w- X$ y7 g - if(write(fd, buffer, strlen(buffer)) < 0)
& ?$ e8 d2 j9 K4 P% T1 L - {
: U) R6 b2 Y/ m& S6 c. g% F0 y o" ` - free(frame);
7 E1 d4 m p T0 s) ? - return;! m+ ]( ~( L5 J- x g: [
- }
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" \3 h, l+ n# _8 b7 z
- "Content-Length: %d\r\n" \+ q6 ~+ ^$ l9 G" M4 E
- "X-Timestamp: %d.%06d\r\n" \* f7 b2 f7 T7 [ h0 c4 H
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);! V4 m+ n0 S% Q/ H8 J% U! q
- printf("sending intemdiate header\n");, c, Z0 t$ L0 K& S C8 @' @
- if(write(fd, buffer, strlen(buffer)) < 0)* P- z& c! ^7 ~
- break;9 m8 t3 J c' z" g7 S: _6 W
- printf("sending frame\n");
8 Q% ^/ y3 @$ q - if(write(fd, frame, frame_size) < 0)4 J8 r2 f- v6 G9 r! b
- break; Z2 [7 y @6 \
- printf("sending boundary\n");$ R' [4 r5 {7 j# w
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");1 q1 i* w" y2 s: L1 l
- if(write(fd, buffer, strlen(buffer)) < 0)6 V+ k$ j7 L) Z
- 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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3 I: f# W1 Z& C/ I二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:5 _+ W6 {& `* E% U* R7 `
- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)
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; Z" {, t# B+ r7 L7 b9 { - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);0 L2 D! L, J) _) W$ x: y
- if(*socket_found == (~0))3 H$ [+ \" a3 ?& n) ~+ C
- {+ p& R# [9 h' ^/ u1 V# X! Q! W m
- printf("Create udp send socket failed!\n");( T2 R7 X9 U/ w0 ~8 {
- return -1;4 P. x E5 q5 m' O
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- addr->sin_family = AF_INET;$ R5 |( s1 h7 c6 t9 x) D
- addr->sin_addr.s_addr = inet_addr(ip);
- o, ^' T' w9 ?: C - addr->sin_port = htons(port);
/ o0 @9 E! L+ K1 m: \% `. h, \2 i - memset(addr->sin_zero, 0, 8);" t; J `* @8 @/ Q$ p
- return 0;
* x& \/ \" p4 L i - }
复制代码
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) ?3 b% O8 }% a+ V% g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)
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- memset(picture.data , 0 , sizeof(picture.data));/ e. @/ `. m- V. u# e& ?
- fread(picture.data , UDP_FRAME_LEN , 1, fp);( v6 O$ y! ], A3 c- R |
- if(fend >= UDP_FRAME_LEN) l3 t5 n( ~5 |2 c9 c7 Z6 y. `
- {
8 W1 V' U# y! v0 a) k - picture.length = UDP_FRAME_LEN;
1 F) g! L6 c0 v' M$ U W) L - picture.fin = 0;; R2 w5 s$ T. _& n& v
- }
4 \+ m# `4 |! n/ P2 s3 Q" b7 P - else m+ P" K5 W; i" Y4 }0 u0 ]! X5 e
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- picture.length = fend;, i' e6 I9 n7 F! [* o* o2 O
- picture.fin = 1;$ I5 _+ f* J$ _, L7 g
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- //printf("sendbytes = %d \n",sendbytes);
' A# Q! l2 i5 u6 x. x3 S0 l( n - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);& `" h6 t c/ N4 g
- if(sendbytes == -1)4 D/ B( M8 k' f7 D* a
- {/ I- k) {' A' o' ]( R
- printf("Send Picture Failed!d\n");
' s) d% |+ g) x3 k9 e5 T9 M - return -1;& F, }; P4 n' U" t% e
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- else
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- fend -= UDP_FRAME_LEN;; W4 s: n; ^7 h2 t4 ?+ a
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- }
复制代码
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/ N" B& Z7 a2 J, t5 x. e& o- f/ ]iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |