本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑 . c" X( }+ v- q8 G
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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.html9 N& Q& w7 F3 J$ X# i- V
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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。 % X- h% n0 ^. d

x1 A! x3 p& V! F3 A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 w- X; [6 N+ S& B( D. W( ~一、HTTP网页服务器3 g* M5 q' X 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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; U: O: L+ h, G - struct sockaddr_in servaddr;8 E8 Q+ ^. c& c2 s9 J
- socklen_t addrsize = sizeof(struct sockaddr);
3 r; n: O" o+ t; P ^ - bzero(&servaddr , sizeof(servaddr));
0 H" w2 r; T% j4 e+ g - servaddr.sin_family = AF_INET;0 k- s f* h% h5 ^5 a5 L4 k
- servaddr.sin_addr.s_addr = inet_addr(ip);
: u$ R" w' d$ v - servaddr.sin_port = htons(port);% q, ?# c6 _5 t p7 N: w
- int ret;/ }% J3 g u/ m* L
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)& {2 R$ U. o+ h% T
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- printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
$ } l) G$ x: a# M - return -1;- [8 c; K; M2 r
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- int on = 1; o) h/ Z, ]) e5 ~
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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- printf("setsockopt error\n");
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+ y" C4 H$ g! Q( X/ ?* @9 U& f @! Z - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
( [; P) `4 O, n; h5 W3 ^) g - if(ret == -1)/ ?% F" u& j( Y/ n% ]
- {
' U: t2 X* @9 F0 W& ]! M$ u - printf("Tcp bind faiLED!\n");% m& |# p: E( p) S) J2 L- ?- n
- return -1;
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- if(listen(*socket_found , 5) == -1)( f, A5 A4 s: _7 C4 d8 @
- {
1 p2 @4 u% {; s/ u/ X6 Y' ~ - printf("Listen failed!\n");, {% w7 L$ K* y
- return -1;
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- 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);4 |$ q0 s' b2 C& i/ O
- void * Thread_TCP_Web_Recv(void *arg)1 [5 f' q" y4 t
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- 。。。, ]& ^# B+ ]5 { o! ?8 Z1 g7 S9 I
- while(1)
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- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
6 E. g: E7 m* l$ S% b! o" e* o+ W } - printf("fd_socket_conn = accept()\n");
& s4 o c1 ]5 c# S - 。。。
; b1 Y; ~1 W) ]: @5 D - 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);
4 ^) b) O, M1 Y" j5 v& f - pic_tmpbuffer = pic.tmpbuffer;
- u3 Z8 Y$ i( \) }; ~5 ? - pic.tmpbytesused = buff.bytesused;- e5 r" c$ s: f3 i& i
- pic_tmpbytesused = pic.tmpbytesused;
. h1 [, k* j0 G9 S. n2 n5 L - pthread_cond_broadcast(&pct);
- Y" a' I8 ^$ h7 J1 o% q9 k - 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;; y% P: E8 h/ h% W, ~
- pthread_cond_t pct;
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- TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);! p2 _- d/ d# q4 o& j# R4 ?
- pthread_mutex_init(&pmt , NULL);6 W- ?# H. Z: P4 ^$ _1 U: e
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);1 n+ N; L$ C- c4 Y; [
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);4 p9 j$ {' s1 u Y2 p! Y
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- while(1)7 P% @( C ^1 z" E z; i) n1 H$ A
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- V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);9 r4 B" h3 {0 V: ~" b
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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# p% D' x, u
- </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" \
* j% T o7 C0 \" ? - "Server: MJPG-Streamer/0.2\r\n" \ Y W/ J$ O! C8 G* C( T1 ~; {
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
/ E4 X$ D# E( V" c) [- r0 r - "Pragma: no-cache\r\n" \9 @8 I V- C! z' c. ?& M: h
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"3 C/ i, D4 `' _- g5 {; r% E1 Y+ w
- #define BOUNDARY "boundarydonotcross"9 w6 Y v8 q9 s, y- ~
- printf("preparing header\n");
3 [6 I. O4 H$ K& A1 G - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \3 q5 z) B' `: _2 j
- "Access-Control-Allow-Origin: *\r\n" \
9 N! Z! C8 @4 q$ _3 I" e! g - STD_HEADER \
4 P7 n( a/ P. T) k w9 S - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
% G; B7 c+ f$ h' Q - "\r\n" \
! N9 o" {% K: F. j3 m, G) E5 t - "--" BOUNDARY "\r\n");
?0 R7 M: q. W3 @2 M - if(write(fd, buffer, strlen(buffer)) < 0)
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- free(frame);
9 m2 _' ^( k# w- P' T - return;: e7 ?& s- s" I7 s# b6 F
- }
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" \7 [% e* F- F) q5 ~7 q
- "Content-Length: %d\r\n" \
* B/ L. A: }8 v% L, Q& K, s - "X-Timestamp: %d.%06d\r\n" \
/ c% x4 b7 u! \ - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
8 S3 n0 n6 p- h - printf("sending intemdiate header\n");
6 w. O( ?& B7 j, o- \( d - if(write(fd, buffer, strlen(buffer)) < 0); l4 `9 w! h! I0 m) M' b
- break;
# b2 o3 w3 O; Q# c# Y - printf("sending frame\n");
/ d4 m& L1 n# L B* ~ - if(write(fd, frame, frame_size) < 0)& x9 n7 P# M& ?( `7 P4 K" M
- break;$ J- ^1 Q5 k" `. r
- printf("sending boundary\n");/ q% w1 X9 u/ H) V# F: j! W. x/ G
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");6 s8 E/ ]- Z% t# B: o+ Y. ?7 {
- if(write(fd, buffer, strlen(buffer)) < 0)
3 q9 m5 X: w: o! F" h+ Z* u - 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:+ `4 a1 Z( P& X
- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)$ p, C% f! U3 b! Q4 r
- {
& R. a- b$ x0 V. Q; r3 v - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);* ^& i& i; X, k( D" N1 i
- if(*socket_found == (~0))
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- printf("Create udp send socket failed!\n");
) [" ^' ]- m( M* S' w - return -1;
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# A4 e- r( y. c6 g" q - addr->sin_family = AF_INET;
4 u- s; {5 s9 ^3 B - addr->sin_addr.s_addr = inet_addr(ip);3 X& ~$ M4 h; t( F6 v
- addr->sin_port = htons(port);
( m% ]2 `9 X8 g: z2 ]2 M+ b - memset(addr->sin_zero, 0, 8);
. y @: p- E1 n2 a+ u" u2 k1 X - return 0;: t* S6 O' K- _* a7 w
- }
复制代码 1 n. o7 C) v- _ _# B( l9 J5 f
: Z2 `: o# c- X4 |- C* @ o5 w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:; W9 X+ R1 i! l+ z
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- while(fend > 0)
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- memset(picture.data , 0 , sizeof(picture.data));
) ?1 Z8 r$ s0 O* T5 D. J - fread(picture.data , UDP_FRAME_LEN , 1, fp);
" {# l% C* W% B! ?! e; X - if(fend >= UDP_FRAME_LEN)* \& C6 B* n0 w2 @0 Z
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- picture.length = UDP_FRAME_LEN;
& l) i; c7 R; M2 f" N - picture.fin = 0;
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- else
1 s- d" O. B. V - {
4 ^% y$ h6 M& s7 y: u- s0 f/ T - picture.length = fend;
3 w% M- ~" i' j! O& [ - picture.fin = 1;' G! |3 A( r. H( Q x
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- //printf("sendbytes = %d \n",sendbytes);
9 Z* Q$ u: D- h* _. M- C% _% f - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
, Q- s( l; ]$ t3 y& [* { - if(sendbytes == -1)0 N7 C2 s) y5 O9 x$ g
- {
4 Y/ h6 J+ L" M/ R+ p - printf("Send Picture Failed!d\n");; f$ v) Z8 p& z
- return -1;
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& F9 S3 }0 D T* v; p- D" k - 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 |