本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑
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2 e0 p! h; y5 H6 @% ]+ D" B q* u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.html0 N, a* O$ d. s
* z) D2 F2 u3 v- F5 S+ 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。 2 K5 V/ X5 d9 D1 n8 B

E1 n& r/ L9 ^4 o6 \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。
5 l5 m2 c1 U' j一、HTTP网页服务器
8 s6 O P% T! y! K0 T- q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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- struct sockaddr_in servaddr;
/ h F0 }4 Y2 N( @/ n - socklen_t addrsize = sizeof(struct sockaddr);
, J# Z2 j( e# O6 z! e7 G7 q- p - bzero(&servaddr , sizeof(servaddr));
: X& e4 p$ d: M" w# ~" Q - servaddr.sin_family = AF_INET;& B1 r6 a- b3 g% T. |5 I9 E
- servaddr.sin_addr.s_addr = inet_addr(ip);2 Q, z3 Q: ?$ E) L" Y) S
- servaddr.sin_port = htons(port);
! z+ B8 n; K& b3 A, L - int ret;2 y0 v5 m8 S0 F" ^" Y
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)
/ t" ]7 R4 E c) D - {
/ [; |3 Y( g- A7 f* r5 u. b2 z - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
. M( `. h1 v$ I7 i7 X2 c8 s - return -1;
5 S2 ~: U% h4 t" n# G - }
5 C' x3 u! }5 p - int on = 1;& k7 c$ D: q1 c
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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0 o- d4 n: h# \ - printf("setsockopt error\n");
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- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
, R/ a4 [3 V+ s9 C6 P" L - if(ret == -1)
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* V2 |: R, q( d0 G. N0 I0 @ - printf("Tcp bind faiLED!\n");
8 f& F/ M7 C/ U% s6 V - return -1;
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1 |& `& t) `3 F2 n - if(listen(*socket_found , 5) == -1)
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- printf("Listen failed!\n");
: X$ E% h9 c* A2 X - return -1;
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- G0 |! T1 s2 Q8 H9 b+ Q - return 0;/ W t4 X0 f* V4 K3 S# i
- }
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);
( Z9 X. D& g& R B1 d1 m1 _ - void * Thread_TCP_Web_Recv(void *arg)
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- 。。。
0 r/ b% [' Z$ Y. E* H5 r! @ - while(1)' B7 L9 f+ C* H9 [9 Y& X
- {
* A6 X, G; ^/ Z8 o( F$ ] - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
. Z& ^# z( U/ ?" C, s" n3 C - printf("fd_socket_conn = accept()\n");
- q- Z& Q: J* j, \( }9 G - 。。。
, P: y* S4 d# s - recv(fd_socket_conn , recvbuf , 1000 , 0);
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- 。。。2 b2 l& C( U1 Z) {# j( Z" j7 b
- }
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);
/ Q% }4 ~8 X: [4 h+ }: f$ E8 p - pic_tmpbuffer = pic.tmpbuffer;
, y* o d! m s$ C; g* j - pic.tmpbytesused = buff.bytesused;
2 @& M- K' i" b$ [( ]9 J - pic_tmpbytesused = pic.tmpbytesused;
3 j* P& B Y8 g8 \* `2 O - pthread_cond_broadcast(&pct);
+ M# ], R H4 A% J" x3 z, { - 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;' @- O6 G3 E. k: F. q) p% r5 m: B
- pthread_cond_t pct;+ M, l1 P; i5 W! k: z. a
- int main(int argc, char* argv[])- A: q* f6 T1 f+ G H! ^9 E
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- TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);5 R/ M+ x8 C5 _1 D, G3 V r
- pthread_mutex_init(&pmt , NULL);& h! O5 Y. M- L
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);6 K# A1 u0 G9 a, o1 Y
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);4 ]3 V" i& [+ [5 u5 w9 w
- ...% R9 m; I A0 x5 u4 A, G! K* A8 P
- while(1)- ~/ ^4 A, r, _; K0 A- ~" u" r
- {
0 D* l7 ?& c6 P9 H% _# `9 l - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);9 _6 O4 C( @# E& m* L) g9 W
- ...
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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;">
) [6 U8 @7 B# l3 v4 R. c - </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" \& x2 A1 z2 D3 w# {5 [" [! a$ g
- "Server: MJPG-Streamer/0.2\r\n" \+ Q6 ]& }+ \ Z8 n: w. F- n6 X" F
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
; ~1 B, Q5 H( _- q3 X& X - "Pragma: no-cache\r\n" \7 H# ~' T1 z$ T" w* B9 W% o
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"& ]; f# t6 g, K; m5 ~
- #define BOUNDARY "boundarydonotcross"" r1 n) ^1 u$ g
- printf("preparing header\n");
# j9 K5 D1 h2 ~# R - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \+ G& b; W/ _0 t: Q$ }9 ]7 T
- "Access-Control-Allow-Origin: *\r\n" \
- R/ ]6 l+ D9 Y0 \5 n" w* z - STD_HEADER \
1 D7 r: X7 V! m# |+ M. L - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
- A$ m5 `' ]# N# w - "\r\n" \
$ l9 @' P: C5 E+ \$ G, ?( Z4 Q' l - "--" BOUNDARY "\r\n");1 f, L- L2 s( o0 E) Q. D
- if(write(fd, buffer, strlen(buffer)) < 0)! `2 `# A3 l l2 y3 N( j
- {
" d0 O. x7 K7 g- ?5 o2 o+ t+ N W - free(frame);
n# u) q% i! C! ?5 z. @# c - return;
* {- J& R+ I9 W R - }
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" \
9 I9 E# z1 ?! W% L% e - "Content-Length: %d\r\n" \
; ?$ U' @% R1 x% R - "X-Timestamp: %d.%06d\r\n" \
% h* [9 `, X o3 [ - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);" r% N" {1 v0 p0 _7 X7 H \2 K
- printf("sending intemdiate header\n");' @' a9 T( n: O/ r
- if(write(fd, buffer, strlen(buffer)) < 0)+ p1 Q' W: t+ f `* O
- break;7 \ _. `3 P8 l( Z0 k! r8 A
- printf("sending frame\n");# c( a; W( Z/ N
- if(write(fd, frame, frame_size) < 0)
) |2 p: E" l/ _$ K% F$ C - break;
9 p( u6 o, M" J4 `, J - printf("sending boundary\n");) X# J0 |: [9 Q$ B
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");& T( z" e% M& [# f& c) v2 D7 v
- if(write(fd, buffer, strlen(buffer)) < 0)
8 L/ p Z4 s6 r* ] - 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。  2 e l& v1 `4 T& C! o+ }
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二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:
+ Z4 i- f; p$ r7 n& j- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)
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0 Y( ^& v% I) h& W+ Z/ V4 r - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);* _% Q: N# ?8 @3 j3 m' A4 E4 X9 N2 J3 {
- if(*socket_found == (~0))! l% C9 S l7 K% ]4 u
- {
; W) I- D3 J0 c$ A9 u2 Z0 J - printf("Create udp send socket failed!\n");
5 C( N# H/ ^( ~4 y7 M - return -1;
) q& ?* O5 Y' d$ E - }
5 f/ N- F8 }* i. u# }& a# i" b( g1 V - addr->sin_family = AF_INET;; v: N. M4 E0 a0 ^7 [# l/ Z1 u' M: Y
- addr->sin_addr.s_addr = inet_addr(ip);/ C b' U4 w0 f& L3 Q% `0 G0 x
- addr->sin_port = htons(port);3 T- {& t% o$ V) N& R! r- b& M' ]
- memset(addr->sin_zero, 0, 8);
. _/ o3 U+ A; \3 I& \' N - return 0;) L, ?' [5 V7 D
- }
复制代码
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, x, ^, B9 k5 N: v0 s5 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:/ z0 \3 B/ l$ l
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- while(fend > 0)
, U' b2 ^7 Z( l G3 X: Y8 v - {
f6 v8 i6 c, z Q$ o. i8 t) n - memset(picture.data , 0 , sizeof(picture.data));
) K$ S4 J" F z6 T4 u- [0 J - fread(picture.data , UDP_FRAME_LEN , 1, fp);
" C9 o) H8 o# p - if(fend >= UDP_FRAME_LEN)
3 s3 A2 x; c5 p( C: `: H, | - {
" q4 D7 N5 d' A$ L. v - picture.length = UDP_FRAME_LEN;
+ I9 Q! |* n% W- l! b+ f - picture.fin = 0;
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- else$ X- F) T7 Y6 Y/ A
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- picture.length = fend;$ e+ B+ n6 E. q
- picture.fin = 1;/ |2 J% G. J, K
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- //printf("sendbytes = %d \n",sendbytes);' A$ V8 a* ?4 Q+ j6 r& }9 l
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);2 b3 o0 H/ T' Q C) J. B- p
- if(sendbytes == -1)
; W# z B" Q2 H0 g- j- G - {
0 y+ U c/ b1 I" w( d% c - printf("Send Picture Failed!d\n");
" H o3 }8 u+ z0 E. K+ u - return -1;5 }+ d. D2 B. u$ Y
- }
5 u! ^. p& S. }+ v, i6 Q( ? k - else
( v& P& Z9 w, a. b" I - {
- b4 p8 p* D5 v$ t! a! X2 d% r1 ` - fend -= UDP_FRAME_LEN;5 \) I: E l+ y. C, U% ~
- }
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复制代码 % z/ \) j4 N: I/ R" q7 r0 |9 _1 Y
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: C: m* [( p: n% h8 e$ l4 TiMX8MPlus 核心板: https://www.forlinx.com/product/136.html |