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: q) h' C1 M! }% t1 A$ f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! ~7 j% E; j6 h* U, g
( I+ b" L! q1 C7 {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* n' _* V; ^$ R/ b

* k( R: n0 S; u" t$ f# E& }) \9 \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。
! d# r- A1 C* k+ v6 q3 c% l, k一、HTTP网页服务器
, U) h! ` @( w) p( i& L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)) B* I3 R0 O& ]* i, T6 j p
- {
; q2 @+ ]1 X- i9 q& Y2 Q" Z - struct sockaddr_in servaddr;0 N$ ?! p' {& y c
- socklen_t addrsize = sizeof(struct sockaddr);- [, h# ]4 Y5 d; f, R% P# ~. C
- bzero(&servaddr , sizeof(servaddr));
) o6 o! E% r4 w# K. j) ? - servaddr.sin_family = AF_INET;6 i: B% E; r' i9 j' ^9 W! l3 n- C" k
- servaddr.sin_addr.s_addr = inet_addr(ip);, d0 g$ [0 ~5 [/ U1 d5 _9 H4 w
- servaddr.sin_port = htons(port);
9 A; O. h* m# f7 W- k9 V% C' ] - int ret;6 i0 I' ~+ [7 R
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)- `4 Y/ E% g. M# C
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- printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);, }+ Y4 J' V) ^
- return -1;
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8 z8 J. A/ G0 \5 W; p7 x - int on = 1;! @4 C$ N; t. Q9 ]9 \
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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- printf("setsockopt error\n");
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- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);5 X7 m+ L) D, B p
- if(ret == -1)
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6 \2 b" t d: ~; G - printf("Tcp bind faiLED!\n");
8 o; g6 G! f% O+ [5 Y - return -1;
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- if(listen(*socket_found , 5) == -1) |3 d2 r2 ?: W/ t! ~) j
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- printf("Listen failed!\n");. \; e" u9 @) G3 K
- 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);
- Z8 S% V' t" }7 P; |6 z - void * Thread_TCP_Web_Recv(void *arg)% s: p0 M: j9 v/ W B1 ^
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- 。。。
- u) U' V! j+ [' B) m - while(1)
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. o% m- N* l( r - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);+ }2 r8 V7 \' d P/ r }. D
- printf("fd_socket_conn = accept()\n");
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- recv(fd_socket_conn , recvbuf , 1000 , 0);
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- 。。。# K5 L s5 N* S: I
- }
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);
7 F6 `0 D+ w/ R) }3 \ - pic_tmpbuffer = pic.tmpbuffer;6 Q4 Z) q& p B% y0 N! ^: _: @
- pic.tmpbytesused = buff.bytesused;! R `; w* b6 L0 q0 M0 m# Z
- pic_tmpbytesused = pic.tmpbytesused;% L" U( N6 J4 E6 K1 E/ y2 j
- pthread_cond_broadcast(&pct);( k2 B: n3 c& 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; g1 w Y# ~2 g5 X# v
- pthread_cond_t pct;( W# V j6 a; F, D1 }, r' a( A
- int main(int argc, char* argv[])
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- TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
) ~# `5 C6 Z2 A - pthread_mutex_init(&pmt , NULL);
, U% P% F) F% C6 Z - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);2 ^7 ]0 k( o2 p* \
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);5 u& T! R- B; t) N( k4 u$ }9 D
- ... u. t5 \ U; l9 z5 R
- while(1)
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/ B- c" o) f$ l" G! d( t8 w" {3 } - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);2 W1 Q; ]' ~1 U
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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;">
$ g7 ^% N* M+ ~! D9 S0 l5 @ - </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" \6 x' W5 p/ H, `: B
- "Server: MJPG-Streamer/0.2\r\n" \
- |( j* u! {6 q) G- S; m$ n - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \: R( N5 Z8 o( a6 s# Y
- "Pragma: no-cache\r\n" \
- b6 ]% _, N" V- r* h - "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"; q+ b& a% Y4 N
- #define BOUNDARY "boundarydonotcross"
. n6 Z$ R. P3 j - printf("preparing header\n");; i# d: v6 `& X: Z4 A( o. s
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \# W7 A) `, a" ?
- "Access-Control-Allow-Origin: *\r\n" \
0 t! J! B1 T: U2 [$ ^1 P0 p) Q- u% Y5 V - STD_HEADER \
+ |, f, F+ `3 I6 h% x7 I8 M/ B - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \7 g: L$ f+ O& |, W
- "\r\n" \
- W: V- o/ u# Q; u6 l - "--" BOUNDARY "\r\n");1 h0 x4 B( v! h* Q5 Q4 J) A
- if(write(fd, buffer, strlen(buffer)) < 0)
4 H( E5 S! e5 h$ l3 Z" r7 ` - {
7 [: W/ w) A/ E* ?0 ]% \& i7 G* B - free(frame);/ e# e; ]# t: M3 L9 t1 K" @
- return;8 ?4 ]* X8 y4 J$ o; m: j
- }
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" \# g) u. K; e+ N0 Z
- "Content-Length: %d\r\n" \( \8 _0 n- P3 u% b3 [9 ^$ z
- "X-Timestamp: %d.%06d\r\n" \
3 Q5 A7 V" y/ @% T" i7 d/ g - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
4 g+ C) z' W! H2 E - printf("sending intemdiate header\n");& O" _+ B+ w% p+ T# E% T4 Y
- if(write(fd, buffer, strlen(buffer)) < 0)+ w. @5 Q" W8 W- n/ A! Y, J# u
- break;: M! j, [5 n# `4 x1 d8 E/ x
- printf("sending frame\n");
$ ~6 R% d9 W/ g/ @) h A3 H" M - if(write(fd, frame, frame_size) < 0)$ L$ J* p8 `; n; F7 l, c
- break;7 o3 v( I8 F, [' H0 a+ `% b" Z( t
- printf("sending boundary\n");
: e! |4 c, L: h' U6 U0 q; I J - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");8 g- Z) }1 F0 G
- if(write(fd, buffer, strlen(buffer)) < 0)2 z7 |8 r: @: G& S( H
- 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。  ! Q& \2 H/ P! _
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二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:
$ A7 A- P$ K: f- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)
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- *socket_found = socket(AF_INET, SOCK_DGRAM, 0);
. }' \# v2 M0 {% S$ { - if(*socket_found == (~0)). U6 N; y. ~4 a6 ?: V
- {
8 e' }7 d1 ~* I. L - printf("Create udp send socket failed!\n");4 \2 m9 P% R; U& A0 o
- return -1;
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- addr->sin_family = AF_INET;2 S% s e# D- R7 N7 X% P. p
- addr->sin_addr.s_addr = inet_addr(ip);
4 k/ I7 H" X5 r: c% D; J% Y - addr->sin_port = htons(port); D4 O! j: A' r0 ]: }$ l+ f3 y
- memset(addr->sin_zero, 0, 8);
! g: E) u2 d- @& y, D - return 0;
5 T( B- N- |3 U$ f* V - }
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:( e" q1 {) \/ O9 p
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- while(fend > 0)
: `+ d: y2 d. G8 E+ W/ d) ] - {
1 H0 J2 @" h3 R' b - memset(picture.data , 0 , sizeof(picture.data));" _0 Q; M' F- L: Q
- fread(picture.data , UDP_FRAME_LEN , 1, fp);# }! {0 ?. e; o7 l) I2 o8 i
- if(fend >= UDP_FRAME_LEN)) Y4 p& k" g3 S! h& _2 `. i/ |
- {
" C- R# J/ }5 s$ C! T2 k; c - picture.length = UDP_FRAME_LEN;$ D( b! a( K H# z0 d
- picture.fin = 0;
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- else
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- picture.length = fend;
5 v$ I0 k' W! p4 A - picture.fin = 1;
8 I' p3 f+ ^. A! i! f9 d2 i - }, t( t5 G; H$ y, z1 x" {
- //printf("sendbytes = %d \n",sendbytes);: X2 c7 v$ L# s5 E8 N2 r
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
+ u& |' k. W# ?! |; S: [ - if(sendbytes == -1), K" w. O1 e+ I+ n2 [6 ?
- {
1 b) }+ b9 |1 } o. K9 X/ Y - printf("Send Picture Failed!d\n");
2 v% s( u' p4 @1 W$ Q( A7 e, J - return -1;3 R- p1 X4 P% v" g4 O, Y
- }
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- {
, r. J$ K+ [* l - fend -= UDP_FRAME_LEN;, a. E V5 c: f9 ~; h. D0 v
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- }
复制代码
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iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |