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/ S, l' U5 _7 l* }2 W$ }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
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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。 + i& l+ I' ^" z
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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。 * I p: r0 K6 J8 i! ^
一、HTTP网页服务器' N- n: o0 M4 t% ~
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)/ w5 j2 X3 P' p4 {8 L. G
- {
6 N g3 W2 r' y - struct sockaddr_in servaddr;7 ]3 _. S9 w4 B6 s
- socklen_t addrsize = sizeof(struct sockaddr);
. v) e* _9 w) q+ R& D8 u: V - bzero(&servaddr , sizeof(servaddr));5 f$ N- W) W' ~. Y1 _. v/ \
- servaddr.sin_family = AF_INET;6 F9 C7 T( c, |' C- ?5 m# [
- servaddr.sin_addr.s_addr = inet_addr(ip);
}- D' \4 T# N" ~ - servaddr.sin_port = htons(port);& j9 ]' E( v: t1 v& s# H
- int ret;
3 x& B+ H8 c+ n' R* n' P* \' r0 ] - IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)7 o2 F ]1 u0 {# f5 c
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- printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
8 j% A0 ?# B$ H1 Z - return -1;
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- int on = 1;2 D! C9 R# O, W% U1 R! q9 n1 x T
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)6 B) g) V% T4 X# q8 \
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- printf("setsockopt error\n");3 \9 l% ?4 t; ~; w9 c/ \
- }
2 C# c# L0 ~6 ?* W) P - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
% p! f% a5 P# F - if(ret == -1)1 A4 u! M( A1 p+ O# p
- {8 {3 c6 z1 ~$ Q' D( `* p
- printf("Tcp bind faiLED!\n");
$ |" A* C" ~/ ~& [, b( T - return -1;
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- if(listen(*socket_found , 5) == -1). ^' R6 b6 j1 L9 w- Z8 b# D
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- printf("Listen failed!\n");: `! Q, t* A( i1 A+ s- n
- return -1;
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- ?5 V% K8 J% e2 e - return 0;8 l8 }# F1 T% {5 h3 P H: ^5 H
- }
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);
, ~9 a* t' ~1 \$ j( y3 N& m9 V N - void * Thread_TCP_Web_Recv(void *arg)8 f( j0 I9 T" L% i9 l
- {
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- while(1)
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% \/ n! K0 [8 }4 |: g( l z2 V - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);9 e4 x7 i* y$ _$ \- |" N+ m" S
- printf("fd_socket_conn = accept()\n");
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- recv(fd_socket_conn , recvbuf , 1000 , 0);
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/ ~0 y7 {2 ^% e5 c4 n - 。。。
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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);1 [6 U c# r& e2 ]' A
- pic_tmpbuffer = pic.tmpbuffer;
, K5 k4 _' H% Q: s% \+ C: N* ^ - pic.tmpbytesused = buff.bytesused;
7 B1 q: K/ ]8 N' m' V - pic_tmpbytesused = pic.tmpbytesused;
Q$ V2 G# W, j; i- w3 x0 h - pthread_cond_broadcast(&pct);" M X/ i9 D4 l! }4 ], v' g9 r
- 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;) |9 b0 B& ?1 X
- pthread_cond_t pct;
: F* V; i' T- }3 h9 f& q# X - int main(int argc, char* argv[])$ ~6 ]# Y+ x2 q
- {- T! {; L( Z2 |9 @8 r0 l
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- TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
1 _8 H& T6 i1 D - pthread_mutex_init(&pmt , NULL);% x9 H: u P4 E; M8 K1 D
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);/ k, _% X( @" x5 {3 _
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);9 l/ i8 w( h# {$ b* S
- .../ d0 J; s8 ^/ N2 I. ~6 r
- while(1)
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- V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);- l# h) z, A% _" \# m, v
- ...
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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 Q0 x: ^$ x; t; T a" J - </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" \& S. z, u# N* `* P
- "Server: MJPG-Streamer/0.2\r\n" \7 x0 V8 w0 e L/ u2 Y
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \7 e) c+ Z$ I( k
- "Pragma: no-cache\r\n" \/ Y& u, n' k) v! Z& l' ?7 q) V
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
6 _- s# V# V; h# z8 b2 ` - #define BOUNDARY "boundarydonotcross"
3 b* k* _( n7 x6 t - printf("preparing header\n");* H. ~- i: R6 s9 e8 |' n) H
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
, x# V( a( j6 J ~) f2 k% J4 B - "Access-Control-Allow-Origin: *\r\n" \" W2 j2 |3 @+ n3 F) e. @2 Y, [
- STD_HEADER \5 u, J% E8 W* c! F2 p' b8 F$ ^
- "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \0 x" u# r: |0 K
- "\r\n" \
0 N6 J, g. D6 f( W+ ` - "--" BOUNDARY "\r\n");: n- X9 f9 d7 z5 n
- if(write(fd, buffer, strlen(buffer)) < 0)! Z8 }& s& W4 ?+ R/ u2 u
- {7 _: e; O. V% C& k+ Y
- free(frame);2 v* p; t: y% H. |$ @- D
- return;
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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 V) M1 i- z, q. m" q
- "Content-Length: %d\r\n" \
0 F! Z7 ]0 v& J3 O% Y" P) W, K - "X-Timestamp: %d.%06d\r\n" \! S8 a" q8 U# s/ |: \
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
% m: d3 ` U) k0 B# e1 u; {- J* P - printf("sending intemdiate header\n");
6 y- D0 k' O, [5 a3 E" X, @4 ` - if(write(fd, buffer, strlen(buffer)) < 0)4 b4 \( e6 N1 V7 q
- break;0 v6 V2 D- y. ~8 W+ o
- printf("sending frame\n");
3 C+ K0 h, H1 F( i9 g - if(write(fd, frame, frame_size) < 0)
' T% Q* M8 o% ~. o5 t% I - break;
8 j& l j7 ?! M1 H7 @" k" S+ e - printf("sending boundary\n");
) D. i9 P& S. [8 t+ i - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");2 z: R9 ]5 F/ X$ y- D- `2 @
- if(write(fd, buffer, strlen(buffer)) < 0)
2 Q0 L& k: D. @' B% e - 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。  5 K1 h* ?2 g* r9 G; m. Z

0 [8 s& E n/ v8 r( f& q二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:1 i" O: O" e5 s4 H
- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)
+ M; {& M* z; u* E y. i* C - {
- Z4 H9 `$ E8 v. ~+ E - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);
; T2 O! k/ v+ J% x; K - if(*socket_found == (~0)) ^3 d/ d. {# W0 W% q/ }
- {
$ ?9 ?4 Q% h' L# i0 I" z - printf("Create udp send socket failed!\n");
$ J h) Q4 u3 V( O9 w6 ? - return -1;
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- addr->sin_family = AF_INET;
' ~6 S2 n: I: v! q$ e* B+ D6 u - addr->sin_addr.s_addr = inet_addr(ip);) g& ^7 n' b8 w, z0 t
- addr->sin_port = htons(port);
" N/ _) f/ y+ K# y3 X% ]# x - memset(addr->sin_zero, 0, 8);8 ~; b# n3 j7 S# ]
- return 0;
* w+ t2 T, I+ e - }
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:. p2 Z) c# V3 H/ Q g# }- Y$ x" K
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( G+ a& H2 K/ K) Q4 o7 e! o- while(fend > 0) P$ p- x# ^0 Q8 Y( M
- {7 M) M& x f* x* k
- memset(picture.data , 0 , sizeof(picture.data));+ [0 i2 a) n- Z4 x W. g
- fread(picture.data , UDP_FRAME_LEN , 1, fp);/ H6 o& x: h! E# ^7 o5 d+ w+ t b, {
- if(fend >= UDP_FRAME_LEN)
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- picture.length = UDP_FRAME_LEN;9 t9 q0 ^2 Q! Y1 Q. s
- picture.fin = 0;
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6 o% K) z( ]: m+ Q( `. C - else
1 }# y& v+ t( n% ]8 R6 h4 m - {
0 T* S( @' ]4 L* [1 Z - picture.length = fend; ~/ i- ~# x$ y9 L% Y2 Z- U
- picture.fin = 1;
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! n6 j' f7 l7 r7 d! j - //printf("sendbytes = %d \n",sendbytes);
9 Z9 O) d: ?) c3 [/ s* i3 q0 M0 O - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
8 E; A. p% k5 O- [ - if(sendbytes == -1)4 I: N& Y& E8 y3 I" P
- {( q& `2 N$ V( m: j! u k
- printf("Send Picture Failed!d\n");/ ] m6 \' x' d+ p5 _
- return -1;
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- else' l2 M8 m/ K# }$ \
- {
. L1 v$ ?3 z8 S5 X( S) c - fend -= UDP_FRAME_LEN;
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- }
复制代码 2 c, `3 A- k/ d1 I @, @. ^& [
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iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |