本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑
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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' t0 R" u6 w% a+ X# S. L0 \/ o
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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。 1 J) U1 v1 ^2 s8 P4 l

( X5 }9 G8 X: K- F0 R) [3 ^. o9 S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 D ?% U0 ?6 q9 N" F% E5 }一、HTTP网页服务器
$ A+ x! K: X: H t' Q8 o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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3 w$ h/ E1 c! T9 z, t. r S - struct sockaddr_in servaddr;3 t2 l5 ]6 J" h- s
- socklen_t addrsize = sizeof(struct sockaddr);
' \1 p9 S( [; o: K - bzero(&servaddr , sizeof(servaddr));
6 p2 K5 ^! C7 { P3 O& Q- u - servaddr.sin_family = AF_INET;
, w( S7 Q0 [( _) g - servaddr.sin_addr.s_addr = inet_addr(ip);
2 M( Z& l- Y! {& ? - servaddr.sin_port = htons(port);
m# V3 E1 t# p w( F - int ret;$ ~5 K( J3 {+ i3 |/ \
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)! W' O I; E8 [+ e4 ~$ O- Q
- {
- X" L$ ^* v/ w& \4 ?5 S2 ? - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);5 a% k; N! w* m% x' g% x
- return -1;* w8 Z% ]% @5 n- A1 v
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- int on = 1;
9 f. Z Y% h- F; I4 n - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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6 x. W. v. _9 |: ]5 T8 b4 [ - printf("setsockopt error\n");
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0 p; t @& C6 ~0 }! x+ z2 i - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);2 e' y% L% E; H8 F+ T, T3 x. [
- if(ret == -1)/ m& }( L0 B0 }# f& A
- {
2 f; Q7 l: t9 q- I - printf("Tcp bind faiLED!\n"); |2 I' D, C" F3 o& A
- return -1;
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- if(listen(*socket_found , 5) == -1)
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- printf("Listen failed!\n");, B2 D$ w) L3 [ z4 }7 k
- return -1;7 t9 b+ z( w. d& E% a/ z) V) N
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- return 0;$ l5 \* L3 W, b6 t
- }
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);% d& ~# Q2 m% S- |! Y; _
- void * Thread_TCP_Web_Recv(void *arg)3 T5 B* R# Y2 K1 J3 X9 U. O
- {
- Q) T6 R- N' K3 L3 ]+ z# n% @% S5 _ - 。。。
3 i- B0 f0 \6 w - while(1)
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- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
" f( e+ H G ~% [: g; x8 S& J - printf("fd_socket_conn = accept()\n");' V# T( ~" ?& r/ ]4 m% {
- 。。。
Z1 T9 r( _) l8 r8 J: O7 G) t - recv(fd_socket_conn , recvbuf , 1000 , 0);
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7 n, t! H. u* G; z - 。。。
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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);0 v$ o: {8 ^# o" | p
- pic_tmpbuffer = pic.tmpbuffer;, t; c- ~. u: {; c8 j" m3 g- U) u8 L
- pic.tmpbytesused = buff.bytesused;3 H7 H% [9 a( k" X+ i3 O! M' [
- pic_tmpbytesused = pic.tmpbytesused;# ~: e' y4 J" D
- pthread_cond_broadcast(&pct);
/ p1 L l3 O& S4 V- J. j6 g5 D$ L& p - 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;
3 |8 R/ x% d( T - pthread_cond_t pct;
+ D2 W/ ?+ z3 m* W& z8 L - int main(int argc, char* argv[])+ `2 k. q% o! \/ q: O R7 h
- {
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- TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
" @$ g# b! R* B) `( U( b - pthread_mutex_init(&pmt , NULL);
' k; _+ G& _5 Y o9 W - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);- e5 b7 r& c i, g; s- F5 n J
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
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- while(1)
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, }1 i: o) x% D& d+ T, Z3 c - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);
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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;">9 m- V+ H# S* o5 j4 p1 ~1 t8 X
- </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" \' L. U7 X6 p$ c& _/ Q
- "Server: MJPG-Streamer/0.2\r\n" \
; n6 v' w' J- ~, F0 r' u- ^ - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \: k+ M- l1 g0 ~! Q( x. s
- "Pragma: no-cache\r\n" \: _5 t J2 L8 s; j' J" K
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
8 A& F6 z* q9 d3 N- t - #define BOUNDARY "boundarydonotcross"& b Z$ ~' ]3 g2 h
- printf("preparing header\n");8 ?: w8 p& `4 @, b6 P
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \9 |) X( N5 y4 ~2 |/ q
- "Access-Control-Allow-Origin: *\r\n" \
3 x- u1 N4 O7 F# }5 ?! v - STD_HEADER \
8 U* o3 b" x& W6 |) Y. @! v - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \# d) w$ r4 A* v! Z3 K" U, I; @
- "\r\n" \
3 a3 A) k" t0 C - "--" BOUNDARY "\r\n");% ]' m: `* v. e2 b
- if(write(fd, buffer, strlen(buffer)) < 0)
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- free(frame);. l- ~$ f' z h0 @# x
- 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" \$ H% a, J: g4 D# M1 F4 \+ b
- "Content-Length: %d\r\n" \
9 U; W: p5 c+ p$ U4 w! R/ v - "X-Timestamp: %d.%06d\r\n" \
! U: l5 V, @% j - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
" a; z. _2 E" p8 M - printf("sending intemdiate header\n");1 [) }, [, l% @8 y2 i; b
- if(write(fd, buffer, strlen(buffer)) < 0)
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, b5 X" h0 W5 G2 h6 ^ M - printf("sending frame\n");
! O5 @( B* T: h$ T# N9 H - if(write(fd, frame, frame_size) < 0)
9 R. f- C% }+ z3 i - break;
u) U0 j3 V3 h4 C3 z* U6 k - printf("sending boundary\n");
6 J9 K2 Y M: N" y) [ \( f5 [/ @ - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
0 a( }, D( @' `" B- \8 v9 U - if(write(fd, buffer, strlen(buffer)) < 0)
, @+ B7 W! O4 n/ b/ W" Q u3 y9 s. K - 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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二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:
2 @: R; c! k- U6 @ i- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)/ p! ^0 \/ @- u2 d' i7 G/ O$ {
- {
4 [6 Z1 s; Z8 H1 u1 w/ G - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);
7 ~: V/ T7 T( @ - if(*socket_found == (~0))
% ]6 ~0 N: y: r8 c - {
9 t% x; Y: X; w - printf("Create udp send socket failed!\n");
7 F2 A z7 U0 _1 Z - return -1;
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- addr->sin_family = AF_INET;. M! X2 |& _( E4 h9 V0 a/ v
- addr->sin_addr.s_addr = inet_addr(ip);$ H% G6 i. l0 ]# a4 R
- addr->sin_port = htons(port);
+ T) B' @( Y% c9 N2 n! O6 @ - memset(addr->sin_zero, 0, 8);
/ D Y2 W7 P& l4 g* G6 M4 q - return 0;
( [% q9 D; j# z! }! x0 Y - }
复制代码
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) v( Z7 c# V- g) R: @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:/ [+ v/ A3 E3 e/ z0 p( p" X
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/ j) q" V( e9 H2 b- while(fend > 0)9 a! M4 Z. W: F# S3 o; ]
- {
. S- Q+ K V6 P f8 ]. e! m - memset(picture.data , 0 , sizeof(picture.data));: h8 s! X" b* K. w- E: ~- p
- fread(picture.data , UDP_FRAME_LEN , 1, fp);( i) L; V& B2 T, t4 D+ r5 b
- if(fend >= UDP_FRAME_LEN)
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- picture.length = UDP_FRAME_LEN;
* B# w) l7 g7 n* J% T - picture.fin = 0;
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- else
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- picture.length = fend;
" L% V7 c D7 M, | - picture.fin = 1;: `+ y* f9 m b+ r" B
- }
0 S2 o2 h. L+ c, f - //printf("sendbytes = %d \n",sendbytes);6 W* n2 Q$ w* |- a k
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
( t. {! A/ k$ ?' Z/ | - if(sendbytes == -1)
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- U/ x: n3 U7 e$ e - printf("Send Picture Failed!d\n");
3 f: y+ ]" s% ?+ Q' i - return -1;
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8 c9 x, Y! }+ @" m" g - else
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2 X8 ^. u5 r6 m1 c - fend -= UDP_FRAME_LEN;0 S% S. W7 f7 q8 l
- }
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复制代码 , ]9 d3 H$ Y1 Q8 t Z# [
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% ?6 ?/ {, ]0 v9 g% fiMX8MPlus 核心板: https://www.forlinx.com/product/136.html |