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! ? x) e% n* C) r/ H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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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。
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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。 0 m a+ F; ^1 J6 R$ v; B
一、HTTP网页服务器9 C+ U2 a4 D9 m, d4 }4 j
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;
2 B+ p6 C/ r$ P - socklen_t addrsize = sizeof(struct sockaddr);8 L+ D" x e+ H' M
- bzero(&servaddr , sizeof(servaddr));
, w" z6 O3 k' {" a0 k" |1 e) i - servaddr.sin_family = AF_INET;( m6 {4 [' j- K" i: o! K
- servaddr.sin_addr.s_addr = inet_addr(ip);
0 x3 b: Q0 n: | - servaddr.sin_port = htons(port);
% k% i# F( _; D. I$ I- p - int ret;
. S5 B# S. |! g ~/ g - IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)% j: _6 o5 n4 J. A& u; y
- {" b" z+ X/ A; V8 G
- printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno); |( O b( a$ a/ j$ Q0 Z
- return -1;
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- int on = 1;
, Y0 f6 J z* s# e - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
3 _7 W& Z! H' _0 ?3 {( k' e - {
9 Z; q9 t) W& m- c9 C1 N+ o9 t6 F - printf("setsockopt error\n");0 J) S$ ]5 [7 W7 j! C6 l8 \
- } |! l: l' T/ r: w1 j
- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);* J. m- S6 p# S5 _+ H
- if(ret == -1)
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- printf("Tcp bind faiLED!\n");2 I5 Y. e, ?9 q8 g# T/ m
- return -1;: f& ~ J( p7 |3 q- m) Q
- }
5 m( j5 U D5 ^# H* S: U- q - if(listen(*socket_found , 5) == -1)
: ~9 B% x% F3 S3 |% N/ q - {
S4 n& M- ~+ r# L* L j4 X1 E - printf("Listen failed!\n");
; o, k( H5 P% M6 s9 X4 D+ o6 a - return -1;
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- return 0;2 A2 `; t+ x' F
- }
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);; i7 K7 \; o, U, O: N, ~ h* k: J
- void * Thread_TCP_Web_Recv(void *arg): L+ m) d4 Z1 m
- {
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- while(1)
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- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);5 }: g; ]! A9 }: q% r$ w
- printf("fd_socket_conn = accept()\n");$ ~$ v! K3 D7 b
- 。。。
- V! `6 v, d/ J7 n7 | - recv(fd_socket_conn , recvbuf , 1000 , 0);0 O0 a+ N; J" Z( o, _
- }
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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);( q6 _2 G; i7 z' I4 `
- pic_tmpbuffer = pic.tmpbuffer;
( V4 M0 d/ Y" E5 U4 l - pic.tmpbytesused = buff.bytesused;
1 c) V' R. ~: f - pic_tmpbytesused = pic.tmpbytesused;. y' `1 [& d9 u0 I2 S; @9 |! F6 \
- pthread_cond_broadcast(&pct);8 k) t5 t& B G0 W- O y
- 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;" `$ R& y+ Y' N; R3 o- ?8 l
- pthread_cond_t pct;/ L+ ^4 T' d2 L1 R! A
- int main(int argc, char* argv[])$ Y# P {" `) B+ f5 {
- {
* h; M" B) ]# n9 ^! r - ...
! r4 [& O4 e. g& {2 ]1 q% y; D - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
4 E7 G/ u Y' X9 p" N - pthread_mutex_init(&pmt , NULL);
) h2 e7 h( V- F( T - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);
* s$ Q9 d7 e& i/ F9 t - pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL); t9 V5 P7 I, u8 s. r2 ^1 K
- ...
9 Z6 m6 b$ y% z! B5 E. b1 ]" R - while(1)0 u( ~3 E5 Z8 K
- {
1 W3 Y) g. u) {) c' k' E - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);. a3 z$ D1 H% F9 Q7 q- q9 ?
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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;">" c- i( k# u% a. N
- </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 u# T$ B; I2 W - "Server: MJPG-Streamer/0.2\r\n" \
1 H+ ~ H+ u3 U0 p) R; a8 Z4 ? - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \: w5 L" F% Q+ i; H# M( F( i$ L9 c! }
- "Pragma: no-cache\r\n" \7 e+ n! S1 R- l: [1 H
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
# ~ j9 X4 P: K. K2 p/ P; T - #define BOUNDARY "boundarydonotcross"1 Y# u& t. e# m2 D
- printf("preparing header\n");
" e6 E8 c0 \& N+ m7 w* K - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \4 o% e0 p" }3 T9 @& I; Z8 T5 ^
- "Access-Control-Allow-Origin: *\r\n" \
( W; ?4 V( }2 g" c" n; A. f) Y# E M - STD_HEADER \
1 z6 X- t; t2 U3 q4 D; m - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \. `0 ?+ K6 m/ g" l# B/ c2 k2 d. X* Q
- "\r\n" \0 w. Z6 X4 e( z: R) D. D; D
- "--" BOUNDARY "\r\n");. {' n; V4 Y5 q' z$ D. f5 z/ W7 i
- if(write(fd, buffer, strlen(buffer)) < 0)
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6 N1 w7 K% `1 q! c5 f6 W- e - free(frame);5 }- G) ]' u; d/ ]9 N3 d. i
- 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" \! |- B( q9 ?, x5 R5 d
- "Content-Length: %d\r\n" \
3 t' T/ Q0 D- r( u! r" Y - "X-Timestamp: %d.%06d\r\n" \3 V1 d; R/ v @4 Q! E: l
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
# o2 t" u) q4 o. X5 m, v - printf("sending intemdiate header\n");$ `- T8 C/ w8 p) d. J
- if(write(fd, buffer, strlen(buffer)) < 0)
( F4 @6 q6 Q4 l E - break;; d t1 ^! K, r+ X# Y
- printf("sending frame\n");( h( Z3 b. ]/ M& c& d
- if(write(fd, frame, frame_size) < 0)
% k5 J' q F' e2 n7 x - break;
; Z$ b! Q, ]$ E% m2 R; Q - printf("sending boundary\n");5 k- C# C" A/ t5 S5 s2 V( U
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
1 O, m) N2 M3 c( K6 d- G: a - if(write(fd, buffer, strlen(buffer)) < 0)
! {6 M8 Y1 f1 B3 ? - 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。  4 `: Q2 r& ~! t& o

8 t3 \- f3 P1 y8 ]6 J二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:
2 e- }/ X* \0 L- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)/ P- d3 g3 [3 P: @
- {
& a) X& H% i0 }, t( d s5 \ - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);
( a8 y$ H* U8 X: ?' I/ H - if(*socket_found == (~0))6 q5 R: ?% |' j
- {
& ]# F! ~0 { w: x. _0 v, Z7 B+ d - printf("Create udp send socket failed!\n");
?! D1 C7 Z4 V$ t- B$ F1 s# t - return -1;
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- addr->sin_family = AF_INET;
! `; @ A) _- J9 |4 Y" @" E - addr->sin_addr.s_addr = inet_addr(ip);
# d( o* a @* p ?0 r k& d8 e - addr->sin_port = htons(port);' Q9 c- G/ B' {2 W
- memset(addr->sin_zero, 0, 8);
' f) H7 ]; I+ {$ B* Q% O5 J - return 0;: I# S' ]! b s
- }
复制代码
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( d6 a* @2 S# c( L8 Y! `4 J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: j' u$ K5 E# ?9 k5 k1 p4 A
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- while(fend > 0), P% M. b7 N7 V! D' H2 [
- {
7 y/ @2 U1 T* L3 Y7 F - memset(picture.data , 0 , sizeof(picture.data));
y# Q0 f8 o! x1 p6 a+ L - fread(picture.data , UDP_FRAME_LEN , 1, fp);
0 E. f! @" o# @; U# {! f$ `# m- _" F5 T; g - if(fend >= UDP_FRAME_LEN)
+ @! K5 j- ?3 Y" ]" Y; I+ d& A4 C - {
; @1 Y. _/ F- j' ~9 k6 \ - picture.length = UDP_FRAME_LEN;
% d; S0 G8 Q( a; p/ w - picture.fin = 0;
/ }8 I2 A i& q8 P: R; D" [+ s - }1 \' ~) i, \; }6 B6 ^
- else
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4 [9 v4 Y' L7 H+ t( W - picture.length = fend;5 F3 W: s1 ^+ {! ^
- picture.fin = 1;0 X0 w v- ?0 |7 I8 A6 I8 G
- }* E+ S a6 f( c/ `+ w
- //printf("sendbytes = %d \n",sendbytes);
2 k& j" g1 S: u; T9 a+ W7 G - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);* ?" ]9 D' J! u; k# Y& f3 M
- if(sendbytes == -1) I% w" j4 G. F2 B: h, W2 m7 T
- {0 V1 Q9 K+ R! X- Q" G- I/ L
- printf("Send Picture Failed!d\n");
( z& @$ o" s. u8 M; o! T$ i) c9 a - return -1;$ i* z' T- l' a9 P+ h6 r3 J0 K# I
- }
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- {8 s" D L4 x* `! ]6 k- I
- fend -= UDP_FRAME_LEN;
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- }
复制代码 2 z0 t$ A* W/ B' M
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iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |