本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑
$ Z) P/ Z, D o6 c% D7 H( L3 H
. _& E, P5 D9 V+ ^3 {; P1 a. @ d+ @% G' S8 T
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. Q3 t' s) a+ W0 I3 \, l; ]
0 v6 ]& g( H- u8 c6 K( z' Y1 L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。 , {+ S% @" F* Y; A9 ?' \# j
 ( I9 U- c: Q4 |* l
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 n" ?/ {1 e9 d- r" P9 V
一、HTTP网页服务器& K/ N$ c8 q& a& p0 ^! 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)& w& }! t0 M: p+ G. e) s% U( R
- {4 k( C+ B1 k! d& n) k9 T3 e
- struct sockaddr_in servaddr;' p+ C5 I4 E0 D- }! I3 l: J3 V1 L
- socklen_t addrsize = sizeof(struct sockaddr);6 ?0 J/ _1 X! N
- bzero(&servaddr , sizeof(servaddr)); v" D$ d: x I, o, h6 Y
- servaddr.sin_family = AF_INET;: t* i# q6 k6 p1 G0 Q" }: ^4 t3 `
- servaddr.sin_addr.s_addr = inet_addr(ip);
% y, U8 ~* l9 Q6 n& ]% m - servaddr.sin_port = htons(port);
# W+ N( ?! r$ n# L, g+ ~ - int ret;0 J. u1 c$ x6 a P
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)! _& y) {1 L8 P# N/ G
- {
* R& L# ^! g3 e& q& O: f0 b/ w - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);7 }' d% H2 q' w) f/ [
- return -1;
$ j6 o# X6 n n5 J, Z: O* @7 Z - }
5 R i7 l* l$ v+ r3 Z, i0 o - int on = 1;' K: b5 _1 Y `
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)) v' a! i) N! B. e: Y: u* x9 G
- {
3 n7 E4 p- M; l5 J0 }0 V - printf("setsockopt error\n");9 L1 l4 @5 w/ O2 K6 T, I3 a4 `" S
- }
& z) b& m0 A j" [& Y4 q - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
6 B. ?) L5 K, G4 I; O - if(ret == -1)& p6 ^: e) e1 l* @
- {
. i( K# {) {* e; P( v5 _* Q1 h2 i - printf("Tcp bind faiLED!\n");
2 K) y; |9 h3 ?" m - return -1;
: ^9 g; K4 K6 s Z - }
$ F% ^1 A) g& N: \8 j0 ? - if(listen(*socket_found , 5) == -1)
% Z3 V- F( ~2 x: |6 g- r; d - {: p2 n* ~+ {. u7 H9 g
- printf("Listen failed!\n");
- ?) A4 Z m2 [$ A - return -1;8 O; H t+ h' v5 \ h
- }
1 ` @, x0 E1 T \ - return 0;
5 t) k0 _6 ?" A2 H9 [ - }
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+ P, c' B3 w* {8 ~; h0 |2 |+ u - void * Thread_TCP_Web_Recv(void *arg)7 ], @: E9 M! T
- {
& [; e. N4 a% ^' B% ^" J7 R9 {* f+ C - 。。。2 U5 e, F8 G) c, C5 x
- while(1)4 |! w' m% }8 S" f% W
- {
6 G/ ~* {% e; ~% U: J& x. |& E - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
' s- p3 \& w( ?- B7 u. O ? - printf("fd_socket_conn = accept()\n");* B& h# b- I# q; B- W
- 。。。
3 b6 x, @- N& h! r$ W - recv(fd_socket_conn , recvbuf , 1000 , 0);) V' x: |' v# W% i u' M
- }
* c& i$ |- h5 Q9 a" ? - 。。。
# \% d' g* b/ w- Z - }
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);
( P: Z1 R# ^' I X$ Y1 d- Q - pic_tmpbuffer = pic.tmpbuffer;! K& q+ T8 Z( a1 |; i ?; d
- pic.tmpbytesused = buff.bytesused;
- x% y& f/ U5 _: A+ f$ d% b - pic_tmpbytesused = pic.tmpbytesused;
7 }4 ]- E+ {3 c, a3 w% D - pthread_cond_broadcast(&pct);$ ?9 E4 f5 ^" y: v3 l+ ?) I
- 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;
) l. Z( ?* [3 R* _. r* {/ V - pthread_cond_t pct;
3 U5 ?9 `0 t$ s - int main(int argc, char* argv[])
- \# ~3 Y; X. u8 o0 R& R - {
7 s4 b' F8 y( J( j0 ?; j/ Q. Z - ...
2 _6 N: e) G' p- V2 D - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);$ V$ }$ W G* |; N% I
- pthread_mutex_init(&pmt , NULL);
/ n5 G9 @% s w: m! D! W2 ]- I - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);. l7 ]3 a# W& K7 j
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);/ L X/ a# Y& \+ E7 f- m; G4 i- I
- ...
0 ~+ t5 ~: R- z' X8 M9 L. p& O - while(1)
) g. i q( X& b - {, `, \! m, b& Y6 X
- V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);2 d& _# ?8 K b3 s1 _+ y/ @
- ...
! N; o! ]: p' E' L Z2 p - }
+ Y! H$ h v8 R; \4 U - ...
* o5 r4 p/ Z4 V; L) \. C; j# `4 [ - }
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;">
- R( W9 J2 V/ \# i! W3 w! O - </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" \
% N& K4 d) c% a+ u5 H8 }: U. f - "Server: MJPG-Streamer/0.2\r\n" \& F/ A. R! F; M
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
: i! Q* I- d, g+ K! L \ - "Pragma: no-cache\r\n" \
9 r7 F4 ~3 ?& w& N) B9 X - "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
% b; R; I0 j3 e! y5 p( B - #define BOUNDARY "boundarydonotcross"
2 A2 M$ ?' K/ z/ F - printf("preparing header\n");4 z: [9 H% G# k
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
$ {+ H# [+ D' A" W, W7 I - "Access-Control-Allow-Origin: *\r\n" \
4 C% w$ D1 e/ }5 N: h3 G- r9 \' \ - STD_HEADER \
1 t) A& ?5 R h. F: d! X, B" r - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
7 Z. g5 H- ?0 h. L; V" X - "\r\n" \( ]2 |) s! z! ~. w
- "--" BOUNDARY "\r\n");4 T8 _& d/ ]2 M: m
- if(write(fd, buffer, strlen(buffer)) < 0)8 N% V! n9 {# S: O9 N2 T( `' u3 f, R
- {- n. x5 }1 `1 C; I5 A- Y' d
- free(frame);
) S5 c% @! Z+ J2 h6 t - return;
. @5 u/ A Y: x. Q7 \) K - }
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" \) k( O* t( x' I# ~
- "Content-Length: %d\r\n" \) g ^. V- }- C7 X6 t; F9 k
- "X-Timestamp: %d.%06d\r\n" \
) l3 x2 B: O" H: h, u/ J - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);; R4 G! i/ k8 M' Z8 J
- printf("sending intemdiate header\n");; K e* M; o- u! @ X: g
- if(write(fd, buffer, strlen(buffer)) < 0)2 n5 b% E7 X0 M0 n8 D5 Q; H
- break;
3 w9 h f/ ^6 X- P' V - printf("sending frame\n");
5 P1 u) o5 z2 c ?$ L: `- O! z - if(write(fd, frame, frame_size) < 0)) Z$ P) ~* c: R9 U$ G( w/ A- j! e
- break;
& P9 \8 F! X5 T, `& l) r - printf("sending boundary\n");
( T3 D3 ^9 ~, I& W' V - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");9 v4 u6 _ K: }& ?
- if(write(fd, buffer, strlen(buffer)) < 0)% |5 i4 p4 ^# o, K# i/ K0 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。 
, P) k, R9 T6 W6 u1 Q
6 l1 x8 O3 a/ l* P! m1 k6 Z二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:
; y/ {4 V( z/ c& P: l7 S- q+ a. y- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)
: g' b/ V$ C8 p8 u2 W/ v - {
5 W' p R3 Q8 ^' j; N - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);+ }) T8 P: ~) E$ i Y
- if(*socket_found == (~0))& f% g" `+ W8 g. X4 f
- {8 D4 v& R# J- Z$ B" v
- printf("Create udp send socket failed!\n");
; l. a1 _/ V( L/ u+ s/ r; } - return -1;) j) N" C! h& o e* f ~
- }" ]# ]+ g3 g1 F+ `/ \6 }# k
- addr->sin_family = AF_INET;
9 p1 m* ^2 H% Y8 y& i5 J - addr->sin_addr.s_addr = inet_addr(ip);8 ?8 m `1 b" F' N5 |0 N
- addr->sin_port = htons(port);
% z- G9 D: M. h( V8 O% r - memset(addr->sin_zero, 0, 8);- j) H/ t/ i5 B* M* C* Z
- return 0;
: |( _" u/ l% [* Y - }
复制代码
% y# q+ `. H# Z/ Y7 ]- O1 u9 y& h- U$ Y$ Z5 l; 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:
e0 ?0 O, ^) Q& m
% G4 X8 [5 e- q: F( l, I- c" ^* u7 d# [$ v- I
- while(fend > 0)3 k7 R$ l; C' D3 c# Y3 n
- {* [0 e, F8 n" J
- memset(picture.data , 0 , sizeof(picture.data)); x5 E' b& i% v8 z; k. Z
- fread(picture.data , UDP_FRAME_LEN , 1, fp);8 W. A1 ^, T9 w* I8 B7 M r0 s
- if(fend >= UDP_FRAME_LEN)2 ~+ k% j# Y! ~
- {: a! N2 i4 D$ J0 N( I' F
- picture.length = UDP_FRAME_LEN;
^* u8 Q+ b4 I* i- K, I - picture.fin = 0;1 i1 p5 G0 u, Q8 d9 B
- }
# C W- o$ v$ q- M - else5 y5 x! [" y$ _! C
- {
! |# C; Q/ }, Q' ~, o - picture.length = fend;
! Z& p; {; N' S" S1 F1 N& I/ v - picture.fin = 1;
+ f$ w( Y1 p7 j |. I% A - }
7 Q3 E* O3 }, C* Z& s - //printf("sendbytes = %d \n",sendbytes);
% H. B* f; R* U! v, w - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);$ o& S U- o, O2 p
- if(sendbytes == -1)
' L7 V( n) D1 ?; a$ f3 x - {8 m9 O4 ^( c. U- e/ A6 f/ M
- printf("Send Picture Failed!d\n");
) H; A c0 x/ N - return -1;
7 Q1 d `: L( D - }! k( P) t" S1 [7 x5 j% i1 w8 x) T
- else9 m) a- o( F3 w7 J& @ z
- {
9 q. V, Q- c% m& O6 ] - fend -= UDP_FRAME_LEN;
$ L9 d) m0 }5 F7 X- ^8 P0 a: K2 c+ p4 N - }4 a% j- {6 {: w% p
- }
复制代码 0 o! L1 K; ?. X( h Z- U
/ {' y. |- Q' {1 M

) x J0 P2 J+ f
9 K- I) [7 ^# F7 E3 wiMX8MPlus 核心板: https://www.forlinx.com/product/136.html |