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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" `$ L$ ^' b" B# l6 D/ }
* O0 M7 V# R9 Z1 ~' q& v- `' X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。 9 Q, }% c& N1 d

% U/ |" O% m- h$ B9 @4 B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。 ( W, e! C) R% H1 e6 G
一、HTTP网页服务器
: x! r2 g1 i! J; t* ]* i+ F0 a, [& @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)# Y" f7 B& o G7 y v9 K
- {! Y1 t" h6 n5 X/ }
- struct sockaddr_in servaddr;5 D! T, z; b( K8 v C: T
- socklen_t addrsize = sizeof(struct sockaddr);' |2 w6 L6 i8 ?& C; E
- bzero(&servaddr , sizeof(servaddr));
3 K' K/ Y. {+ N# Z+ I$ Q - servaddr.sin_family = AF_INET;
7 K4 x! ~; C0 m* _& L& [ - servaddr.sin_addr.s_addr = inet_addr(ip);
0 y* ]. W6 V$ b! f! F, a3 B; n - servaddr.sin_port = htons(port);
; ^# E) L5 X: q. j# G: z' b4 ~ - int ret;. V7 b" X3 g2 [
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)& O6 m' ]+ s8 ?5 J0 |
- {
: F! q- Y) r* Q' U3 |! d - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
, V5 V1 H1 |& X0 |1 d, C& l$ X! i& } - return -1;
, I& w5 F- b1 T5 E) |' @% h0 a9 ` - }
3 J+ t6 a9 b6 c, }' P: m - int on = 1;; M U9 H! B. ? T7 } F% o/ N
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)+ E5 ^1 C; z, u* }
- {
) P. Y' `8 U/ K0 a* v - printf("setsockopt error\n");
: ^- d) G8 M9 ? - }
) |5 p8 r, l( Y" _* M - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
2 t& f- h* @" `7 M - if(ret == -1)7 C, _9 N! F; ]( V [
- {
+ f% x- u& _3 S; N - printf("Tcp bind faiLED!\n");
4 N" o, H, Q2 F. y$ y: ? - return -1;) L" ~* I" D) v' G0 ]9 K4 X* e5 ]
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- if(listen(*socket_found , 5) == -1)
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- printf("Listen failed!\n");. o8 [) c8 K, Z( j, x" Q9 t
- return -1;
( m; S9 o+ c5 }3 @ - }
4 \5 M5 D' A' v( b& {/ W( f - return 0;
* G0 G3 u7 `9 {. I& f* |# c - }
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);
1 I P' c" m1 J# ]4 N - void * Thread_TCP_Web_Recv(void *arg)
9 e7 E2 F% \% u& D - {# o7 U2 `9 Z% @$ U" P* F7 K
- 。。。( C& l! d* n- u& x3 s
- while(1)" q8 N* f, i* {5 Q
- {
: o/ f+ |/ Z% `. G - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);4 ^* Q* d* n' I% a
- printf("fd_socket_conn = accept()\n");& p8 S# F+ \% }$ v; O& V/ ]" A
- 。。。, V0 R+ A1 b4 N: v" c3 _ E
- recv(fd_socket_conn , recvbuf , 1000 , 0);1 X, e( g* ?9 _5 X4 {' K
- }7 s1 C* {+ S7 N" A* h. A- B7 p
- 。。。
7 }0 P- z$ j& | - }
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 t, p; d* X6 o. g* ?3 H
- pic_tmpbuffer = pic.tmpbuffer;4 Z& u$ ~5 Y' T" g6 E
- pic.tmpbytesused = buff.bytesused;3 ]- A3 w+ _( L8 J
- pic_tmpbytesused = pic.tmpbytesused;
6 ~! J! D9 q! V5 Z2 w - pthread_cond_broadcast(&pct);0 U7 ^, }% Z4 \) s7 X
- 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;
5 T! ]8 v6 k. ?" k4 T* L* ~ - pthread_cond_t pct;
! i4 j4 u+ \. l* X2 K+ U7 O/ b - int main(int argc, char* argv[])8 l/ F( I7 R( S& Q z' |
- {
; q: T) T0 p2 P5 ` - ...
/ b0 u+ D( q7 R# n& P- J - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
& @4 e6 X5 G3 F C - pthread_mutex_init(&pmt , NULL);
& Q+ W0 p2 o* d6 S - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);
" J G& e! v: d4 x0 q8 v P - pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL); V" E: f* s" E0 a$ b* W
- ...
: S5 F7 v+ m! [+ G& V9 j! P5 _ - while(1)
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- V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);
3 z+ x% R7 H3 h6 \$ t3 q& e8 ~ - ...
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- ...9 T# X: c/ V) e- L6 a( s; `: k
- }
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;">
3 P8 C+ {2 O( E2 ? r7 T( p% _ - </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" \1 E1 J9 {7 k y6 c9 A
- "Server: MJPG-Streamer/0.2\r\n" \7 ?1 b+ `7 v6 y# i* p
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
3 s; I3 C7 k$ g9 F+ `% }! G" P - "Pragma: no-cache\r\n" \5 Z1 @8 u* S) {: S3 V4 x& T5 p8 k( k
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
* {& {5 C2 v7 U - #define BOUNDARY "boundarydonotcross"
, C5 b& N; X5 g( p3 _) Y6 [- D - printf("preparing header\n");4 ^* i' s2 u7 s3 u* V4 w
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \# |0 V* ^7 e: _0 V! ^) ^
- "Access-Control-Allow-Origin: *\r\n" \
7 Z& ]+ `' t8 p% y. ?3 [6 z7 B - STD_HEADER \
% q( A- z, x0 S9 M. H - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
' u9 L9 `7 U7 r; n5 C* o1 b1 Y - "\r\n" \
, P% O3 v* t" ~; `2 o/ X - "--" BOUNDARY "\r\n");
& b* V% D# m, Q& p! d - if(write(fd, buffer, strlen(buffer)) < 0)
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- free(frame);" J. _; w& X6 l3 q8 e$ g( G
- return;+ ?+ H. w. i, M" q* \8 v3 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" \1 Y8 C. g( q3 K/ S2 |% l* o
- "Content-Length: %d\r\n" \; z+ b4 Y! }4 ^& h# {4 O1 I& ?
- "X-Timestamp: %d.%06d\r\n" \2 ~# p- C0 }, }$ k! s+ R
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
7 q v! m: q6 M0 |, U' N* Y: W1 o - printf("sending intemdiate header\n");
' m8 |' Z7 }, ?5 P: R. ` - if(write(fd, buffer, strlen(buffer)) < 0)
. U$ D! e( a$ A: A5 k1 e - break;
3 [# M: Y6 }" A4 K5 `& B3 F P - printf("sending frame\n");4 t _9 X4 h5 ]8 Y$ f, o
- if(write(fd, frame, frame_size) < 0)
1 Q5 J& ~) B; A/ E+ I% Y - break;4 P. R. b: |, p. G3 o/ d
- printf("sending boundary\n");, W; o( Q% v1 K8 B9 B% X, R
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");1 s6 I5 U: R4 S" v2 R
- if(write(fd, buffer, strlen(buffer)) < 0)% P% C. J- J# e( o6 `, F
- 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。  ; |6 v& h9 q" Z3 |

1 E- e3 d. s- z& G9 Q7 r% |' j二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:: b+ h- `) O+ M" f, k2 s0 t$ s4 \" }; H
- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)
& p; V- `' v+ }+ u! E: E - {( j9 P7 [5 u0 K* l
- *socket_found = socket(AF_INET, SOCK_DGRAM, 0);* U8 ~! G2 }1 u, f( ~. a
- if(*socket_found == (~0))& i5 t# ?* _" T! _* a! @6 ?
- {: J O0 Q! I2 J& ?$ h1 J( }
- printf("Create udp send socket failed!\n");
`6 A7 P: l$ T# n, B% b8 [! G \ - return -1;0 y/ S5 _+ r6 U$ T1 v6 E `
- }2 P4 x3 ~ P) I: J
- addr->sin_family = AF_INET;
1 {) k; f9 D' u' `$ A1 P - addr->sin_addr.s_addr = inet_addr(ip);6 m! w0 ?% d6 r3 d+ V$ J: c! L% I
- addr->sin_port = htons(port);
4 _0 [. T2 \, u) G - memset(addr->sin_zero, 0, 8);4 v5 s$ Q$ P- a3 \, k% r
- return 0;
' o3 P: a1 x) [ - }
复制代码
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2 f$ C- H/ s* r9 }; r" m2 W9 d2 s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:
; @2 q6 {7 V/ a) ]/ W0 P
0 F+ O# S1 y- g I9 h' i: U P
) I' t9 b% O, X& ]0 a- while(fend > 0)/ H* W( o8 H/ i, E: H/ T
- {* P c1 {. g/ @# i( z/ c& T
- memset(picture.data , 0 , sizeof(picture.data));# b" \( Z: x; Y% l- `" w& ^5 p
- fread(picture.data , UDP_FRAME_LEN , 1, fp);2 Z6 `- a" D/ t" b, x- `
- if(fend >= UDP_FRAME_LEN)
, Y+ V7 L ]. M' E2 f3 [+ x - {+ Z( M0 p! D4 K5 V1 b$ U! q
- picture.length = UDP_FRAME_LEN;6 I( @9 r2 E) M
- picture.fin = 0;/ f F& T0 F2 c0 d6 h
- }8 Z: T B& K4 \2 @5 g. R- o
- else
9 d3 [! B V: [* r$ ^6 h1 x - {
; ~( Q4 x x4 Z( \# J - picture.length = fend;
4 {1 l$ R% C% r5 j( M" E0 ~ - picture.fin = 1;
; b% q2 |7 s) v - }
* S6 @5 l# v" b2 z1 |% y) s7 v - //printf("sendbytes = %d \n",sendbytes);
& ^$ F8 a5 F# ^ - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);1 C8 d+ y8 Y7 Z2 K, [
- if(sendbytes == -1)
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- printf("Send Picture Failed!d\n");
0 b7 u# N2 V% m - return -1;, m q6 O1 M, P+ G: L& ?2 u
- }
9 \9 P! B, a# W: }& ? - else
6 B. M' D4 Y' _( J - {/ A5 j+ r) C& Z8 A* k
- fend -= UDP_FRAME_LEN;
+ f: }& s2 Y+ [& N: T3 x- [ - }
+ V. R* I0 O {6 z - }
复制代码 2 z) G& {* v1 M) l
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# r7 R6 w: v( s! N i }iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |