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- L0 l+ y7 M/ l* o( ^1 A8 S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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. T- K/ f8 v m3 V9 k7 }( T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。 8 z% L4 t! P# Q: h+ {8 z2 G6 G) K1 S% q

4 c" V! V9 M# R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。 X6 u; A7 t' c6 t$ R
一、HTTP网页服务器" P) @7 }! B5 F/ |: `& }! w0 F
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); d n/ M6 p$ e% x4 i
- {
( S1 G% L7 a' b$ ^- @5 p - struct sockaddr_in servaddr;
$ \: \" ]' }6 t$ \ - socklen_t addrsize = sizeof(struct sockaddr);5 t& p% \8 ^; b9 q# O: c' Z0 `
- bzero(&servaddr , sizeof(servaddr));, t0 B' S$ H L. N: C9 ?; x
- servaddr.sin_family = AF_INET;0 }1 l* }6 l1 B. O$ [
- servaddr.sin_addr.s_addr = inet_addr(ip);
" G/ a- i! T4 s& l3 W - servaddr.sin_port = htons(port);
+ L6 j* b* o' s" l9 y6 G - int ret;
5 z$ p' o: G$ Y- X* b; w" ^! o7 B - IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)
0 n+ B: b+ C; j" R d2 I - {
c+ {. u0 h- w/ X& k9 T - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);1 o( N- g' S+ L4 i8 O
- return -1;
% W: \" X& Q. v - }
8 x( q9 L. y* @( o+ w - int on = 1;
) D8 A" ]" b, g8 v6 L - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)+ S- |! R7 w$ D& ~8 ^; |% S
- {9 d4 X( |4 |: R$ l
- printf("setsockopt error\n");
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- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
/ ?% l7 t5 ^3 F, P6 F: T9 D - if(ret == -1): Y L# J+ x @' H' e
- {
G2 u* z3 O$ e; e- k5 ^7 T; M( w9 @ - printf("Tcp bind faiLED!\n");
% \7 x) A# f4 m9 @+ l( s$ | - return -1;
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- if(listen(*socket_found , 5) == -1)- J5 O$ |$ O/ x6 B
- {
% ^1 A" W T! y - printf("Listen failed!\n");" ^; [+ O; J( w- A
- return -1;% e- g" K; z: i
- }
! b+ x9 }( C: E* e - return 0;3 n4 `7 P7 W4 m- Y
- }
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);
Q& |; \! z5 ` - void * Thread_TCP_Web_Recv(void *arg)
e) P& ^2 Q7 s - {
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- while(1)
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- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
& v3 S8 d2 \* _ - printf("fd_socket_conn = accept()\n");4 M/ S- M" O( U9 ] M% o+ s
- 。。。
3 K, v0 K# r! a8 B" D - recv(fd_socket_conn , recvbuf , 1000 , 0);
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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);
7 R: K+ F4 V$ j- ~0 h, a7 h$ z - pic_tmpbuffer = pic.tmpbuffer;6 c9 D# \9 v7 k" I! \
- pic.tmpbytesused = buff.bytesused;
: b" i G$ ^# ~+ i+ Y1 v - pic_tmpbytesused = pic.tmpbytesused;
' j- W5 s: ]) Y- k4 Y' M& K - pthread_cond_broadcast(&pct);
d, P t9 E* ]+ A - 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;
2 ^3 C, I/ N1 K' I: I - pthread_cond_t pct;
6 X b+ H8 k3 b - int main(int argc, char* argv[])
/ L& k3 H, o. q5 J: w3 Z- y5 O - {
9 Q' T6 J' U' y6 D. y - ...
# `+ N' K: Z# h* y1 p6 z+ H2 i - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);; `" s2 ~' A& v, m" _6 Z8 ^% Z
- pthread_mutex_init(&pmt , NULL);
8 e) K# x" y3 l# J, Q0 n6 O& ` - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);* Q. q& G$ ]$ _$ {
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
! ~6 J# m, \- n" Q- U# a - ...
. H+ f+ N$ O- Z L' } - while(1)
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- V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);6 D* N$ ~0 p# p& P1 a" 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;">
* b' W1 Q1 u% G# l! O( T F5 ?* w6 \ - </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 {. V3 @, {6 o8 i: u3 { - "Server: MJPG-Streamer/0.2\r\n" \
$ y6 J2 M+ N3 _$ D! ` - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
* `8 [/ Z8 T& @, m! T - "Pragma: no-cache\r\n" \: p; R# [9 O* B' m# o
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"0 k: {3 H- ] i! l
- #define BOUNDARY "boundarydonotcross"9 }! t! ]7 E1 F* [+ p- K
- printf("preparing header\n");, ^, h$ `6 ~' J# f
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \$ E, B* S5 Y9 B$ n
- "Access-Control-Allow-Origin: *\r\n" \
" @; @ o& S1 ~( X1 S6 c. \ - STD_HEADER \. D8 A# o" J- S4 N* r
- "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \# s% I% G4 Z, M$ R5 Z4 R6 L
- "\r\n" \- o" ]9 R5 P0 Y4 ~- ^6 S
- "--" BOUNDARY "\r\n");8 U3 c/ y" \3 o$ M
- if(write(fd, buffer, strlen(buffer)) < 0)" n! b# x- \! E- d9 _* X0 P" M0 W
- {6 N# V$ ~8 c% t" i) m# L
- free(frame);
* j' ]1 C/ E- r# F# {+ E! M - return;, A3 H3 w4 v6 _/ q! [7 m
- }
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" \
0 b% e( [) M% t6 x9 T' p3 B - "Content-Length: %d\r\n" \
$ U' ]( U2 n0 w7 F - "X-Timestamp: %d.%06d\r\n" \
, @5 N: h4 d2 T8 Q: W9 i - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
?2 J6 h; g2 |+ u5 A, K - printf("sending intemdiate header\n");
% J) g O$ U* C: Z8 h, v4 I - if(write(fd, buffer, strlen(buffer)) < 0)5 K* t, `' H5 m1 n3 L
- break;, S: H2 [- j# u" C3 K$ x
- printf("sending frame\n");) R; M1 b9 t Y1 P
- if(write(fd, frame, frame_size) < 0)& i/ E( M/ X; q# {3 @
- break;
# @! g1 D; I: n6 R, B6 o/ A T - printf("sending boundary\n");) b) y9 h6 |+ t i! y4 n
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
# _/ a$ E, D: O4 R - if(write(fd, buffer, strlen(buffer)) < 0). V6 R0 E8 R. F7 ~$ p: y
- 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。 
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9 ~! r! ?. U! L7 q/ U二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:
" b; n7 {+ y0 P. z% @; w1 k7 T5 V! G- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)2 `. y# [! s ?. Z, G _
- {! V7 a6 M. t) q" `0 C
- *socket_found = socket(AF_INET, SOCK_DGRAM, 0);
' m" f+ i2 x7 j' B# R+ | - if(*socket_found == (~0))7 `. N- o' V' m# ~5 I8 q0 e
- {" f4 E* l, u: Z7 P5 |
- printf("Create udp send socket failed!\n");* \( d* R9 K% N
- return -1;: `1 G4 t9 U6 C/ Y* G
- }: x7 p1 a, @# G+ _/ \8 _
- addr->sin_family = AF_INET;9 Y" X+ o9 Z9 H
- addr->sin_addr.s_addr = inet_addr(ip);+ o- K' R) D1 J8 r7 p, C# L8 ]) d
- addr->sin_port = htons(port);
/ h" Y' Z. Y( q& n5 m - memset(addr->sin_zero, 0, 8);
% k" W; H. Z) R$ }$ X( |+ h4 Z2 ]. ^ - return 0;
# m( Y* N2 X% A' ?& N, j - }
复制代码
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2 _" P, o( {+ g- u6 y N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:3 m% B7 F7 d; ]" V' O1 ?3 V
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- while(fend > 0); K4 w1 |& Y2 F3 m- \! N# O# Y
- {& W0 {0 x8 B0 z( }( z/ t% l
- memset(picture.data , 0 , sizeof(picture.data));" O# c6 U: {: m2 |. m! i
- fread(picture.data , UDP_FRAME_LEN , 1, fp);7 T6 h1 w h- M! l5 h
- if(fend >= UDP_FRAME_LEN)
8 T% y$ p( g+ ^$ \' H/ \2 Z% N( x& ~ - {
6 _: M2 }5 A7 U* }7 e - picture.length = UDP_FRAME_LEN;
% V4 |; |. j( f/ ~8 x1 q - picture.fin = 0;5 l3 P9 s7 O2 {4 G3 V9 V
- }6 k9 [- L1 s$ b5 \5 b
- else
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- picture.length = fend;
7 o* t5 I$ E8 L9 n. o2 c1 k% A: \# k - picture.fin = 1;
9 j W9 b! m& p7 O* `2 ` \ - }
7 _7 J7 N% }$ P4 H - //printf("sendbytes = %d \n",sendbytes);
& }" x6 w. C- R n - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
% X0 ]6 r4 `" R; c9 s - if(sendbytes == -1)
; l: _: Z' b; C& Y6 h8 j. r# Z - {
9 C# n6 E* M; R0 H - printf("Send Picture Failed!d\n");
$ t& g- w2 D: x5 Z - return -1;) S8 P" p9 N8 T, x
- }
4 x9 \; y: M- } - else- V, ~0 t2 _; G F Q- r7 i9 b
- {
6 G& z4 J' {% q. J) N* x# J7 R( [ a - fend -= UDP_FRAME_LEN;$ O; Z& p" A* e
- }; [# O/ u* f5 v
- }
复制代码
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% m6 [, U* A7 ]+ W3 a; T/ a$ u- _$ p' viMX8MPlus 核心板: https://www.forlinx.com/product/136.html |