本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑 * K8 ?4 l% j3 t2 Z+ z% k# m# J
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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- F8 U& \5 G, z4 `; ?, s. r
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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。 2 @) d1 J1 V* k/ m8 E$ z9 I
一、HTTP网页服务器
* a' V9 u$ r# a9 A3 K( g- d( _: E9 j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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9 N/ b0 k6 M. w3 }- y - struct sockaddr_in servaddr;
# J$ z6 \) p$ R S; c" y* Q - socklen_t addrsize = sizeof(struct sockaddr);
* j) a0 I/ t2 T' w, E& R - bzero(&servaddr , sizeof(servaddr));, `( H0 O2 U4 _3 c$ m! V# f
- servaddr.sin_family = AF_INET;
) X1 }& ?$ g6 X. o4 ] - servaddr.sin_addr.s_addr = inet_addr(ip);& u0 J- N/ A4 c" l! g8 `
- servaddr.sin_port = htons(port);
' V/ O7 N; B& F% i. Y - int ret;+ H9 g/ f+ U4 w4 z7 Y) @! [
- 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);
2 y+ d) h* y0 m) {) W+ g - return -1;% k, k H% r$ C7 F
- }
8 ?* H9 n8 k) n w5 P& A1 T - int on = 1;/ J2 R$ Q4 ~( r/ j. c, X8 j
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0), E( F; L6 E/ \; S
- {
! u% ]8 l. U8 [. M, ], b* b - printf("setsockopt error\n");
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- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
2 E, G. o# C# t3 s - if(ret == -1)
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- printf("Tcp bind faiLED!\n");
1 T7 V2 r3 E1 S4 ~ - return -1;
2 `& h4 ~9 G7 D2 d- U/ n% ~ - }
( q1 | j D8 u- \( M4 i - if(listen(*socket_found , 5) == -1) C5 k( S+ l# ^3 n- F$ p
- {
1 A' V7 |+ l# E3 B3 R& J: D7 a* ^( u% m - printf("Listen failed!\n");& c2 w6 Y, g& M+ e0 N: y
- return -1;
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- return 0;0 M* w: ?' C$ b% \: g1 y
- }
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);
* k! i# c- ^2 ?) g% U* _* j; o - void * Thread_TCP_Web_Recv(void *arg)
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- 。。。; H$ a1 n) {5 p! g" M0 l
- while(1)
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- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
. J2 _ |: F# r5 J - printf("fd_socket_conn = accept()\n");
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: L8 D3 D1 P( e2 F1 [0 { - 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);
0 B% q3 {. i" x! S9 r+ ^: x7 C6 r; b - pic_tmpbuffer = pic.tmpbuffer;
: m% F8 X9 f7 W% M! b+ `! B - pic.tmpbytesused = buff.bytesused;1 e* {- N# P- a3 E6 ?5 G
- pic_tmpbytesused = pic.tmpbytesused;
. N4 k5 Q. V, y7 } - pthread_cond_broadcast(&pct);
) g$ f; u$ e8 V - 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;
( d/ \& e, M: ^& Z - pthread_cond_t pct;/ m& n/ M+ l @. I+ q
- int main(int argc, char* argv[]) O% q! W8 E5 t
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- TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
5 J. s1 L( c i7 c/ ] - pthread_mutex_init(&pmt , NULL);
6 u) n4 |7 z, C) A* c7 I4 H! f# ^ - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);" z" B h; Y* j6 z+ e) J
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
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- while(1)8 ]4 ~% V% [" E% A7 [1 P
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- V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);
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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;">
+ A! [2 H: G) a6 X - </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" \& Z# e$ g' p; ]& ? M, n
- "Server: MJPG-Streamer/0.2\r\n" \
0 ]/ f. c" c6 a, o) ` - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \! R1 z4 r! v' I4 u2 \
- "Pragma: no-cache\r\n" \
' d6 u0 t* B: } - "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"0 J" m E! p! d* d+ l
- #define BOUNDARY "boundarydonotcross"
3 @: Z7 C/ R4 @3 `& {0 X - printf("preparing header\n");) v& N, g) f9 K0 r i2 m; \
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
% L! p6 Y* S1 A0 N* i - "Access-Control-Allow-Origin: *\r\n" \+ `5 D# ~) Y t
- STD_HEADER \9 `7 c& z3 \. w% @" y& f/ Z
- "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
% x1 P. i# ?7 K - "\r\n" \0 A) ?5 V+ w! o# N
- "--" BOUNDARY "\r\n");+ l7 l1 h+ C) A/ `
- if(write(fd, buffer, strlen(buffer)) < 0)
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- free(frame);# v( K! }( R+ z
- return;: l) D' 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" \
3 o' Q( Q( j' G# W" s5 a" h. J - "Content-Length: %d\r\n" \
' }4 o: d, ]7 w1 k$ d9 I# Q, X - "X-Timestamp: %d.%06d\r\n" \
: ^. w# }$ e, f# ]& b - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec); `9 k" o/ x% N7 U1 ~
- printf("sending intemdiate header\n");& s/ `$ x% a+ C* z1 P& ]0 J3 l
- if(write(fd, buffer, strlen(buffer)) < 0)+ o y8 U% u& o
- break;4 B! o1 M+ z7 ^) B5 J
- printf("sending frame\n");
2 l7 x. I3 q2 { - if(write(fd, frame, frame_size) < 0)
/ ?/ B8 C! G0 o; ?* u0 a - break;
" d* g) ?: I _; T' [2 s - printf("sending boundary\n");
& }7 s/ s O1 g4 L$ u$ P& t - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
3 r# {" X6 S& G - if(write(fd, buffer, strlen(buffer)) < 0)
! d( z# \% w- i; p# N1 v - 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:" ]% {9 ?$ ]( w- \1 J" t
- 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);
/ c% ], H% l/ C" j% @ - if(*socket_found == (~0))
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- printf("Create udp send socket failed!\n");6 m/ U. l ~3 r" S) f: T% P. Z
- return -1;
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7 }; I" B6 F& ?% w8 A9 N' K. [ - addr->sin_family = AF_INET;4 L. l0 _+ Q) S* i
- addr->sin_addr.s_addr = inet_addr(ip);0 Q& d9 {7 n3 i6 T1 s# v
- addr->sin_port = htons(port);' C# z4 D, a; I0 n
- memset(addr->sin_zero, 0, 8);+ R: ~: \- ~# H9 g |. X* T
- return 0;
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复制代码
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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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& k" Y; |1 l) u6 J- while(fend > 0)$ a! C) `0 ^6 B/ k8 ~$ w# g- D4 s
- {
& G1 i" C k) I& Q$ Q - memset(picture.data , 0 , sizeof(picture.data));
% O- }& n$ I+ z: c - fread(picture.data , UDP_FRAME_LEN , 1, fp);
4 X: }" ]8 V1 d1 w - if(fend >= UDP_FRAME_LEN)9 X3 W f0 M: T4 F; U" L: _# D+ v0 u
- {) M$ q8 w& D, z7 l! W' F
- picture.length = UDP_FRAME_LEN;' ?4 ]" @) p. c( E: o7 \1 A$ G) q
- picture.fin = 0;& e+ m" k7 P2 t; V
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- else% v: X1 J! ?, n" z# M
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- picture.length = fend;
2 g' v! _! _2 @ - picture.fin = 1;
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! B" u: u# }6 g% p, \5 B - //printf("sendbytes = %d \n",sendbytes);
$ K0 [( C& ~1 I5 E3 A - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);, l& @& \# I* Z$ A
- if(sendbytes == -1)) C, N% _& ]3 ?. m3 z
- {
Z3 }" z/ g7 w - printf("Send Picture Failed!d\n");" j9 |# T9 c) E0 b: M& G
- 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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iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |