本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑
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h: U9 `% z/ A" p9 A( a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- _' H# J4 g, Z$ K1 [: g4 g& L
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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。 " S7 y( T8 y3 k' e

% v& ?0 b2 h5 h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。
, x) p3 z9 I+ a一、HTTP网页服务器
9 I' T$ ^, E% z/ E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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. g6 p7 a( N/ x+ ^; d - struct sockaddr_in servaddr;4 {& R$ F) }* |8 K
- socklen_t addrsize = sizeof(struct sockaddr);
, d- N/ F$ ], c" W! ~- S! ] - bzero(&servaddr , sizeof(servaddr));7 m# q8 Z/ O8 M$ C/ W( T# w
- servaddr.sin_family = AF_INET;
6 B2 t! u& f4 J/ Y1 k- ^( Y - servaddr.sin_addr.s_addr = inet_addr(ip);
( D0 x# t" f+ \9 \+ g! C5 k - servaddr.sin_port = htons(port);( f! @# B/ _( \ l% y4 _. z
- int ret;& c) Z# ^$ N* ]1 |( K& E! J, C: ?! a
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)
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) f# k" L! o' ?7 t9 O- n0 J' Y- Y - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);% q x8 P C8 n; K
- return -1;
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5 M+ `9 p* `$ \" ] - int on = 1;7 y# N4 [* P% _7 F
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)- C* {8 W1 a" n" d {$ }: H7 A
- {
2 B1 m; p% i; V& ~ - printf("setsockopt error\n");6 x: W) `2 C" Z$ ~3 }* q+ k' l
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- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);2 k" A) T8 X0 c) y
- if(ret == -1)6 O* p. D& F# B% f( W6 z
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- printf("Tcp bind faiLED!\n");
, e1 B F: C7 Z2 g+ ~2 L - return -1;
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- if(listen(*socket_found , 5) == -1)4 N: T' J3 m2 S- V9 j' _; }; P
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- printf("Listen failed!\n");. J7 m: x+ |- t* \1 Q
- return -1;7 A2 ], B) x# a4 n( C3 W: |
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- return 0;! r/ i9 T( u! G1 S" \. c! ]; S
- }
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);
' c+ z1 g4 I) `5 Z4 ?$ r - void * Thread_TCP_Web_Recv(void *arg)% `0 \, D/ _2 G7 k! F9 s. q
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- 。。。
' h+ e# U. F2 \7 ]% f - while(1)
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- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
4 A& m; c# W: m$ {- u" Q5 Y+ Z* r - printf("fd_socket_conn = accept()\n");
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- recv(fd_socket_conn , recvbuf , 1000 , 0);; L4 x* r+ y/ b+ K8 Z! N
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- 。。。
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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);
+ C8 Z( f& j' \ - pic_tmpbuffer = pic.tmpbuffer;
3 u9 |( d; z ]& S - pic.tmpbytesused = buff.bytesused;2 z C5 l% o: w# f: w, h
- pic_tmpbytesused = pic.tmpbytesused;
( f8 I/ U( [9 p j& A% n - pthread_cond_broadcast(&pct);3 S* Z: m8 `6 {/ I R$ t
- 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;+ ^& [* V: R6 I& ~ R1 l
- pthread_cond_t pct;
) t+ `! Z5 v* e. }( i z3 W. I - int main(int argc, char* argv[])
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- TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
( J- m6 z( C, i: x- j4 Q( P - pthread_mutex_init(&pmt , NULL);
1 `( ?& D& A& b9 r. o; p - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);& s W) R8 {" k0 q
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);& F) y# `! h+ u7 d8 T" K9 _* P
- ...
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- V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);7 a' X C3 c! A
- ...
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% t \4 y3 B, ^$ _9 r; 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;">9 u+ y/ i5 t2 h) I% E# K/ Y: w
- </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" \
! ^9 L; B k, ~' k$ _9 B - "Server: MJPG-Streamer/0.2\r\n" \
- L" S5 N5 E0 X$ \5 T e, W - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \+ K8 o! ^, U# F/ X$ J3 W) t
- "Pragma: no-cache\r\n" \
7 b& L( h/ V7 W0 j/ F: A - "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"/ v' E- t& g z2 M- t. p* [
- #define BOUNDARY "boundarydonotcross"
4 c r7 {* w. i; Q5 A. r - printf("preparing header\n");" h! _7 n7 }& P3 h3 p! q
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \8 C* z$ M& k& u$ l
- "Access-Control-Allow-Origin: *\r\n" \
U6 z8 T+ r$ D& d - STD_HEADER \, i% }- E: x4 N- P9 J$ l) }# j: a
- "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
% n; u/ R# p4 f# d - "\r\n" \
; a8 ^/ J' U5 x8 F - "--" BOUNDARY "\r\n");6 Z$ k; |8 m v' U- y. O
- if(write(fd, buffer, strlen(buffer)) < 0)
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. d( R" \1 ]5 g/ [: `% \ - free(frame);
( X, _& r, O. }% W7 A! Q: r: Y' M - 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" \
1 W5 B! y" K9 F8 Q& o$ l - "Content-Length: %d\r\n" \( O; {4 G* o- v, B/ |
- "X-Timestamp: %d.%06d\r\n" \
- `) o# q5 r( u6 _4 f - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);% W- b/ D. V' G8 _/ U3 j# M
- printf("sending intemdiate header\n");
4 z: R' {3 w- ^$ L% b' k - if(write(fd, buffer, strlen(buffer)) < 0)2 g) y7 Q3 C4 P0 t/ a) W2 L
- break;$ |9 j) c: |" j7 J3 _
- printf("sending frame\n");
1 P. J, t" @# d6 l" u - if(write(fd, frame, frame_size) < 0)% N$ G1 ^* x$ |+ V
- break;
" e% C% U8 _! n - printf("sending boundary\n");4 K: f3 S- d& _# |( ^, G6 |
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
% i3 j- }# v8 E - if(write(fd, buffer, strlen(buffer)) < 0)8 a8 } L* X0 H0 r, V
- 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。  + S* m9 d- d% ^# W) n/ R
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二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:" }2 k2 C1 R/ {0 A+ v/ [. }* t5 B
- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)
+ i- ^6 ?, E* _1 K4 X - {
# [# |' l! a+ ` - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);0 J" m( s- l9 u, l k x
- if(*socket_found == (~0))
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- printf("Create udp send socket failed!\n");, A7 o+ W) v% k+ a2 |+ n
- return -1;
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& U. G" M7 ^% O - addr->sin_family = AF_INET;# c" Y3 p* ~/ Y, C
- addr->sin_addr.s_addr = inet_addr(ip);; Y; r" i+ K8 i) c2 v
- addr->sin_port = htons(port);) N5 a* x" |3 C$ B, c4 F+ |- u
- memset(addr->sin_zero, 0, 8);% S" {2 R6 j p8 h. u
- return 0;
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复制代码
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' V) Q! ?" z( w& p0 T% b* K8 _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:& Y* X3 \4 o, w) I0 o
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, d8 U9 ~% S8 }7 T8 s, p- while(fend > 0)* i* g7 U% ?, W. j2 C
- {
+ F5 y+ @* b2 ^9 b9 q* w% Y - memset(picture.data , 0 , sizeof(picture.data)); v; ~/ a2 ^$ ?
- fread(picture.data , UDP_FRAME_LEN , 1, fp);% Z; Z8 J( t G: r) Y9 _
- if(fend >= UDP_FRAME_LEN). y' `: S5 {; l; Q6 o! ?
- {* h4 i! k& U- k! l/ z$ C8 M2 u
- picture.length = UDP_FRAME_LEN;
1 z: I! {8 N# ] o+ S; D, K - picture.fin = 0;- j, b, u4 X$ W9 z9 e- O
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- picture.length = fend;3 E i4 k8 E0 Z- b5 d
- picture.fin = 1;
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- A0 L* }2 o* n M5 f# _, W - //printf("sendbytes = %d \n",sendbytes);
7 x. k+ n0 s6 @# O0 Q - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
4 j9 T( u) ?, ^$ { - if(sendbytes == -1)& i& y6 h- e& Z9 n' |1 |# c
- {
: o# P5 b/ }8 r( R - printf("Send Picture Failed!d\n");' d; [' ]- X2 N/ |+ B
- return -1;
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- else
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- fend -= UDP_FRAME_LEN;9 q: b8 p" x* E8 d$ X
- }
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复制代码
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O; L" h1 ?. ?9 I- `. FiMX8MPlus 核心板: https://www.forlinx.com/product/136.html |