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) Z2 |1 O; i/ U+ }9 L+ o
% y4 T$ n- ~9 C% c/ ~0 L( s( \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。 3 N% A: {$ y( s, D* ` d

+ }5 W+ C5 N8 G @( i9 m4 B2 @" R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。 . F% Q! J" ^3 A! T4 r5 M
一、HTTP网页服务器
3 V0 \! G; j/ P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)
3 f; i- g. h$ P0 S; C - {
, n4 F1 ?* o+ P, f0 N - struct sockaddr_in servaddr;0 y: o' M0 w6 L2 B
- socklen_t addrsize = sizeof(struct sockaddr);! P; _1 p6 O. `: v7 K/ l5 v
- bzero(&servaddr , sizeof(servaddr));; U: ~. N, p. s8 E# l
- servaddr.sin_family = AF_INET;& C. M- n7 p- f' g/ q% _6 P! l: G
- servaddr.sin_addr.s_addr = inet_addr(ip);
& W& I! |/ W0 [! y* G - servaddr.sin_port = htons(port);
) H* b. b9 X- w# e - int ret;
: c* Z2 d* R% I4 z0 k, e* r - IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)7 t8 p8 M6 A' p4 A% ?
- {
# r2 ]; |; `1 A8 o - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);: s6 K) q+ s4 Y. @5 j, }
- return -1;
6 K. k' @; R: y6 O; a g - }
9 |0 V$ I6 N- H$ [! C - int on = 1;$ ^* ]- }$ d9 s7 u" V1 r z( U# G% b0 t# A
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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- printf("setsockopt error\n");; A- d* h+ b& j5 [: j& `3 @, Q& c3 y
- }
& v6 R, |7 f/ U& O7 |; \ - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize); e. j( N( {" a
- if(ret == -1)
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- printf("Tcp bind faiLED!\n");
* n) D" B1 K: ]1 R3 i& o. n( A - return -1;( M' { J. M7 t, N8 _2 T4 L4 x
- }
2 o; b5 ?% _9 e% L7 [2 b% N/ X - if(listen(*socket_found , 5) == -1)% v5 g7 p/ u& \* h. D4 q3 m" u
- {
" B5 Z! g* A1 m1 O3 v# q - printf("Listen failed!\n");
. N" }1 e6 s7 y) _ - return -1;
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- return 0;* m4 D. _! t0 J5 {8 \) t4 s9 n
- }
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);0 N1 i0 }) `* W8 |* l3 F* c+ M% n
- void * Thread_TCP_Web_Recv(void *arg)
1 T- i5 V5 ^5 m! z# ]* y3 ] - {
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- while(1)1 x ?+ d; E% `# t! U0 Q Z. E* x8 |* A4 z
- {
1 C/ h% _3 F6 e [4 { - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
" \9 e9 E! G/ [# l8 K - printf("fd_socket_conn = accept()\n");: o) M* V- H! }6 F
- 。。。0 @! A, a) X( G" u8 H8 t! w' r. N3 m
- recv(fd_socket_conn , recvbuf , 1000 , 0);6 u, s- \" y2 J! V
- }
+ ~+ T1 I7 o8 \; E6 D( Q [+ } - 。。。
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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);
6 K$ k& Q. \, S% G! Y ]7 t - pic_tmpbuffer = pic.tmpbuffer;
7 k, a' ^+ z' Z' v- l - pic.tmpbytesused = buff.bytesused;
5 T+ e7 M( ~$ g! p2 t4 E. b) b- S - pic_tmpbytesused = pic.tmpbytesused;
' N6 i/ E. w# x" m" L - pthread_cond_broadcast(&pct);
5 i9 R) X4 a. _+ l 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;
" `( F- J5 Q- M$ C4 Q y+ }; O - pthread_cond_t pct;2 X* A7 a4 n9 X6 h- P, Q
- int main(int argc, char* argv[])$ A, m; S7 ]1 T1 `3 }. N
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- ...! H+ P5 W. B) D' F; N, Y) V& a
- TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
6 U1 [0 c$ ?& P5 b' L6 g4 J+ n - pthread_mutex_init(&pmt , NULL);6 y* j$ U6 x5 [" v
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);$ ?1 l% {8 |* R4 h# G: K0 ?( T! |* Q
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);, O6 d" L! `$ @
- ...
* x, { \! e5 S& u: x2 b" Y4 ]: q - while(1)$ V) X4 P% V/ V& [+ f6 y
- {2 S3 H2 x; E9 J- F
- V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);
& o3 Y; D' H. {7 h/ G0 `8 ^- Z' I - ...
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- ..., @1 C5 E, P: e& G4 b/ L9 v. f
- }
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;">
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复制代码- #define STD_HEADER "Connection: close\r\n" \4 b/ b- p3 W) h. G! o" F9 B
- "Server: MJPG-Streamer/0.2\r\n" \
- J2 J2 |7 a# M2 K; s - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
; n) x1 d. B g! ~7 S' a2 r - "Pragma: no-cache\r\n" \# y3 e. e" J( L% }: S
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n" e& ? Y! @$ B: Z7 q$ B
- #define BOUNDARY "boundarydonotcross"! v9 ?2 |/ L; k( T/ I2 t! }
- printf("preparing header\n");
, f7 }" C6 x6 D1 J( M0 R - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \9 x- \1 h" n3 b# S5 Q B* k& ~
- "Access-Control-Allow-Origin: *\r\n" \) @8 Y/ h; h0 @, H" T/ E
- STD_HEADER \5 p3 a2 Q; t7 Q1 X* ?2 Q
- "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \, j! x5 q! |2 x2 N: u, [, q
- "\r\n" \. c# W u, `! y, t+ a( m/ }4 y
- "--" BOUNDARY "\r\n");
7 a9 p% s+ |4 A$ e! x/ I - if(write(fd, buffer, strlen(buffer)) < 0)
) F; `' u: [. F+ I - {
8 h. T; N% V0 E9 u" G" h3 U - free(frame);
3 L7 E, u- j3 S9 ?- J - return;
+ h9 W3 D6 P1 W# G0 J0 b9 Z% [: n - }
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" \
5 k0 A- n' J5 r* T$ q, V6 E0 R8 c - "Content-Length: %d\r\n" \
l2 v/ J0 P3 z) a - "X-Timestamp: %d.%06d\r\n" \/ C; J9 F) L2 v
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);" t2 q* a' i* A1 l
- printf("sending intemdiate header\n");+ H, A1 b/ Q* g( h0 }4 R4 q0 v1 t
- if(write(fd, buffer, strlen(buffer)) < 0)0 j, \7 v. z% A4 {8 g k
- break;$ d3 O C, R% v7 Z' M1 ` U( A/ V
- printf("sending frame\n");
I; Z# @; X7 r a1 c - if(write(fd, frame, frame_size) < 0)( D5 E! @+ T& \ g, v
- break;5 W% v) W V2 T6 w5 ]# W
- printf("sending boundary\n");
) _: D$ @# f, q Y! j( v, m - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
5 v! Y, J% C% B" X0 I8 H - if(write(fd, buffer, strlen(buffer)) < 0)
: I, o4 I- N# @; y - 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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- K. I6 E) i6 }. s二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:8 Y# N+ ~0 A- w3 Q" C2 n* C# q
- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)3 ?: Q; H/ b$ z L `% l
- {
1 w, y# [3 O1 |5 ` - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);$ A8 o; B/ ]/ i) r
- if(*socket_found == (~0)). D) x$ R& R' H/ H) q* A H
- {
! y& N) n7 }. c: N) G - printf("Create udp send socket failed!\n");
7 g- w, B" x3 |" S: Z& O - return -1;4 a: t ?; Z" @( c8 i0 `
- }) c' Q; q. X: p ?- w: e
- addr->sin_family = AF_INET;
6 f2 g" r% Z- x% D2 {. V, X - addr->sin_addr.s_addr = inet_addr(ip);$ [. A- u% m; E& y$ W
- addr->sin_port = htons(port);( K2 }9 |% Z) ]" a' V, Y' j1 q& \
- memset(addr->sin_zero, 0, 8);
4 \+ Z1 |4 Q2 d! g9 ?4 _& | - return 0;
/ |* }1 x# F: d - }
复制代码 & m; t) s" z6 X0 |& s$ j
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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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- while(fend > 0)
+ y- R, ?5 r& h/ u4 J b8 t/ r - {
, ~/ x) S9 b; [3 h/ s3 H& R3 [ - memset(picture.data , 0 , sizeof(picture.data));" B0 d9 b. w, W. @/ n1 W2 }7 k8 g+ w: ~
- fread(picture.data , UDP_FRAME_LEN , 1, fp);2 R U+ y' H0 I5 \7 l j0 E
- if(fend >= UDP_FRAME_LEN)7 l4 [$ k& n. C( ~& g
- {
! [$ W* t9 T" l1 ~; n1 Y2 _ - picture.length = UDP_FRAME_LEN;& g% _9 B! L( u
- picture.fin = 0;/ k4 Y# c3 t. c
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- else
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- picture.length = fend;
. L# h3 ~* e$ v+ ?' o% ~ - picture.fin = 1;
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9 ^3 t( k% k/ M. N - //printf("sendbytes = %d \n",sendbytes);
9 y" i2 Q5 y1 p T - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
; E! D9 E' N$ O0 Z - if(sendbytes == -1)
7 e" e/ S) Y Z( Z* K' L - {
/ t# B/ {5 d& q# h - printf("Send Picture Failed!d\n");
8 {4 o" q9 ^6 v/ o - return -1;. j ]! \4 \" i& i4 c8 W3 u
- }6 V5 O- L3 H! j+ Z
- else
% N# _- T: }. ]7 x - {
: u& S+ r' x" U) V' g/ n4 ` - fend -= UDP_FRAME_LEN;& c) Y: ~! ?3 ~
- }" T' }) v# D: \. J$ }7 s; R E' `9 R, ?
- }
复制代码 2 H9 l& i* |( I7 v6 W" _" q# g4 G& T
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- ^: [8 V: E( k+ T/ f/ P# hiMX8MPlus 核心板: https://www.forlinx.com/product/136.html |