本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑 4 \% u0 X. _$ ~9 p
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) I" k5 O+ S7 F9 T6 E( T2 o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.html3 Y# V- R; p7 U5 U+ z+ A( P
" L% c( J$ a/ Y/ c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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+ c. h4 O* l/ z1 V( y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。
( `+ h$ [+ [! U j) P一、HTTP网页服务器
& t' r6 {4 w2 q: G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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v. s. ^$ f% B& \ - struct sockaddr_in servaddr;4 w9 d/ F$ z9 G
- socklen_t addrsize = sizeof(struct sockaddr);- ]+ Y/ K$ {2 H$ k& p/ R
- bzero(&servaddr , sizeof(servaddr));
% ^# g; N# P. V8 R - servaddr.sin_family = AF_INET;8 f8 S' T; I+ K8 F; N" ^
- servaddr.sin_addr.s_addr = inet_addr(ip);6 [4 B1 H5 g6 l4 R$ P+ T
- servaddr.sin_port = htons(port);, E2 q, _5 a( e- m
- int ret;: t7 O5 S6 L. I' z5 S8 f6 d
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)
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3 N+ W4 \; {- L( y2 L @ - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);6 o% ~9 _6 x: Q9 c" e
- return -1;
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- int on = 1;" U: Z9 h5 n4 v& Y T1 K
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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- printf("setsockopt error\n");
[- O2 o9 U2 z) a Y3 o: \/ E - }
# Z8 U9 T* |) B4 Q- e4 R9 v$ J% {, }+ Z' X - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);8 ?8 }3 a4 {1 o
- if(ret == -1)8 u- O) ?0 N2 J9 b
- {' H4 U" {. |: B1 H8 L6 b( b
- printf("Tcp bind faiLED!\n");' g6 ~- f/ U% V# X, M7 a
- return -1;
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- if(listen(*socket_found , 5) == -1)' H% O, ^: m0 U- y" F
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- printf("Listen failed!\n");( \2 u4 y2 q& c, U+ `5 A
- return -1;7 k3 F* g( X3 k9 S: i" I: `
- }
& {2 w j8 ]7 M8 m7 A" E - 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);
# [; n+ y9 e- a* H4 h( k - void * Thread_TCP_Web_Recv(void *arg)
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- 。。。
6 p; Q( K! b8 C" h R - while(1)
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9 {0 i" f; O5 F - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);7 l; L a, C2 o. e
- printf("fd_socket_conn = accept()\n");4 v6 c1 r' R; I1 ?4 {
- 。。。
5 @% X Q( R* z7 d8 ]+ ~- R( v* b - recv(fd_socket_conn , recvbuf , 1000 , 0);
0 ^: S4 V7 g+ v0 A& @ - }
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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);
% m. R9 M% A; |7 q% }, H - pic_tmpbuffer = pic.tmpbuffer;/ S, B' B1 }& @ t! x/ A, b- j5 |' d
- pic.tmpbytesused = buff.bytesused;+ [1 {, ?% `0 X9 ?) P
- pic_tmpbytesused = pic.tmpbytesused;
% {# U3 T3 Z' h' Q7 o. c8 ]5 P C - pthread_cond_broadcast(&pct);
" A3 k! N9 s) }0 a! o1 z5 y3 b - 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;
* R! {" q) H7 U' b5 F6 Z - pthread_cond_t pct;
6 K5 S% \( X/ _* O; R3 b6 N - int main(int argc, char* argv[])0 e0 l: C$ e2 J4 I% O" n3 Y& p
- {
2 q8 K* s) Y! D2 k - ...
: c; y& o$ { U0 k4 `4 s0 m - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);% R5 F. h0 n+ Q2 `3 z
- pthread_mutex_init(&pmt , NULL);
, ^7 K" V6 W& E - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);
+ P2 u& ~3 g8 l( y. _/ |0 s. z - pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
; q" E) K$ _8 X* `5 w - ...
$ P3 ~- _7 _) E2 @/ @9 E - while(1); f( Y8 r9 z1 w! Y
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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;">
7 f( ]4 U1 D) f# a - </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" \' ]! h# S5 P+ H/ A- a9 X
- "Server: MJPG-Streamer/0.2\r\n" \
7 z% u9 J# G/ }6 j - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \8 }, i- f/ O! k
- "Pragma: no-cache\r\n" \
]* x A' o0 l2 E3 U$ |3 @5 g - "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"" F: D. Z% }7 ?, ^: B
- #define BOUNDARY "boundarydonotcross"1 ~& P' m% ^8 y+ h- x
- printf("preparing header\n");
2 h$ K/ C2 t: w- D# d - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
0 v8 R! \2 U" u - "Access-Control-Allow-Origin: *\r\n" \
G- }* D: O+ X( q, }& W4 y - STD_HEADER \
% K6 J" a0 v" H* V) U' O% p9 A - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
' }0 k* w# X* d - "\r\n" \
4 Q2 W6 U3 N3 b& k" _8 Y9 J - "--" BOUNDARY "\r\n");. L! _* j( U+ k6 s& U# E
- if(write(fd, buffer, strlen(buffer)) < 0)
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6 U( b: ` N, q - free(frame);
& x/ B- K4 {. W, Q2 D, I - return;" X0 p: ]! q; T( N1 f) Y
- }
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" \
* I4 a. g1 M7 D/ Q4 D; z n - "Content-Length: %d\r\n" \$ ?" Z1 j3 `9 o4 _( ~; R
- "X-Timestamp: %d.%06d\r\n" \1 I) n/ J& R& X
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);% d( D/ v! W! N. j5 U0 f! U8 g
- printf("sending intemdiate header\n");
4 z6 c5 l$ O. u2 D - if(write(fd, buffer, strlen(buffer)) < 0)- z8 r) k9 b! m6 [* n
- break;
& Z% R7 }5 M. J; e1 f - printf("sending frame\n");; p- h: ]' l4 q" c) w
- if(write(fd, frame, frame_size) < 0)
* F; E' _% Q* }9 i# M' q& ^# ~ - break;8 G# ^- N: ]5 K2 A6 o7 s
- printf("sending boundary\n");4 u: g; u. g r; z/ |0 o
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");- `$ H ^, F6 W
- if(write(fd, buffer, strlen(buffer)) < 0)
/ u' F( [; p8 b! [9 M' Y+ H" 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。  ^" Z/ l0 C3 X# ~+ S, W

0 Q1 \$ o9 Z/ d5 B1 ~. z3 x! K二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:
- K9 e# O- j& H! p- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)& ^+ V& I0 a: p, n5 r3 S; i% p
- {) A8 u, R$ w5 a- }0 K
- *socket_found = socket(AF_INET, SOCK_DGRAM, 0);
3 [, M0 d7 N3 {6 G$ D6 \ - if(*socket_found == (~0))3 L7 R( N4 i) ]
- {
/ Q/ `+ P) W% Z) j - printf("Create udp send socket failed!\n");6 H& p4 W$ \' i$ f1 f; \
- return -1;1 ]& \- h5 @$ o7 a
- }
# r6 }2 \& d+ q( M* N - addr->sin_family = AF_INET;+ t1 p- b& U3 u# o( b
- addr->sin_addr.s_addr = inet_addr(ip);# v' P3 e# p8 q6 a& h
- addr->sin_port = htons(port);
8 Q6 m1 a! V' z5 l - memset(addr->sin_zero, 0, 8);
* \0 z7 \+ h# f% f* H- N - return 0;6 ~* a2 L' R7 V( Y3 {+ v
- }
复制代码 7 E& X" ~# z; H% K
' n2 r3 A1 L6 d$ p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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! o- W+ s( s. x' `- while(fend > 0)
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- memset(picture.data , 0 , sizeof(picture.data));
( L1 {4 W1 b; p0 r _5 @ - fread(picture.data , UDP_FRAME_LEN , 1, fp);, E- M7 p* j% ] N
- if(fend >= UDP_FRAME_LEN)
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- picture.length = UDP_FRAME_LEN;
7 p) `+ @6 I" \# }, T - picture.fin = 0;
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- {) V9 u# Y6 _" F- O& J, N" u& k+ R: `
- picture.length = fend;
; H! M4 Z9 a! [ - picture.fin = 1;; a& a d5 ]0 ^% k9 x) ^
- }
- E( \4 `/ H2 x) P - //printf("sendbytes = %d \n",sendbytes);
: I G8 y2 L4 w0 M( R" s - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);' ^0 ~2 D& F/ Z) E7 Q* T
- if(sendbytes == -1)# k+ b- t. n* r# z# F6 B* ^6 X
- {
' y- B: a% t# d- ?$ A, I8 ~ - printf("Send Picture Failed!d\n");
' w2 S# e9 q5 d% I4 x3 C* { - return -1;
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- else/ ~2 m( p( L! q( i# e
- {; b9 R9 }& P# O2 S$ l3 z; E! [
- fend -= UDP_FRAME_LEN;
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- }
复制代码 , T3 L) ]: i) @# G/ N4 R: U. L9 M) I
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iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |