本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑
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$ e% f; H @4 y% O8 c( 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.html2 Z$ F( V3 P6 `- Z& A& t* y3 p
3 [8 N: G/ |! \4 M5 u: g: 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。
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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。
# i% D, ] S2 [4 C" n# ]3 z一、HTTP网页服务器
0 H! R. i) K$ K$ ]1 @& l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 k/ i0 U( F! [) U
- socklen_t addrsize = sizeof(struct sockaddr);; C5 H( S& e6 W; T
- bzero(&servaddr , sizeof(servaddr));; z$ F1 F+ w+ L! [
- servaddr.sin_family = AF_INET;7 ]; T! ]# o9 g9 @
- servaddr.sin_addr.s_addr = inet_addr(ip);
% N3 s# r6 N4 z. h - servaddr.sin_port = htons(port);/ w. T! [- i/ K- k' n; b$ N( i
- int ret;* m5 \- U8 y9 t
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)' d% e/ c6 R: r7 n8 \
- {
. y2 ^; t& i: r" F - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
1 N. e" O, u6 W0 t0 b5 i/ t - return -1;# u5 t5 _7 `' k4 a) h9 r! W1 g
- }% |9 J. M$ c" W: y& e
- int on = 1;
. l5 L! x5 j0 I( }2 Y& Z - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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- printf("setsockopt error\n");* u! J9 I C7 d6 `5 x3 B5 g. @
- }
6 I$ |3 B% X2 Y- N - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);/ P7 o9 w' i, x% c* R
- if(ret == -1)
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- printf("Tcp bind faiLED!\n");
6 n- l" f8 K0 E5 L+ s4 O$ V2 \ - return -1;
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- if(listen(*socket_found , 5) == -1)
+ m5 @$ v4 E5 y: N - {
! D3 Q$ w0 J4 n" ^ Y6 c4 E - printf("Listen failed!\n");
8 Z5 ~7 f/ C7 ^( Z/ ?6 v/ p - return -1;
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/ m, d: [! V) e3 K; t N6 i - return 0;
& ]0 [' h! e: 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);
2 s, \6 A2 W6 b( B0 a1 I5 ] - void * Thread_TCP_Web_Recv(void *arg)
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7 F' k+ M2 K& \ - 。。。
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- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
$ `+ J; c/ I; o7 G. o0 s( K - printf("fd_socket_conn = accept()\n");, Q1 U9 Q$ n$ a) e" _: r; x7 Y
- 。。。3 o$ l. N( j& B0 H
- 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);4 O" M t/ X) d4 p. Z
- pic_tmpbuffer = pic.tmpbuffer;
5 \" J% |% w/ c v+ c" ~& q - pic.tmpbytesused = buff.bytesused;6 V2 y' {' p0 A
- pic_tmpbytesused = pic.tmpbytesused;( V6 h/ A* G ~4 m7 a3 \; c
- pthread_cond_broadcast(&pct);$ h4 Q" k, _7 Z. o0 g
- 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;
7 p5 P e B7 p- \! A- d - pthread_cond_t pct;
; B4 l6 ^ S1 f! j" K - int main(int argc, char* argv[])1 c2 e* c% H# N- f. u
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- ...( J' @1 C6 Z5 i0 [( T: D) X6 K7 C' { H- p( w
- TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
$ p+ ?% e" H3 }( ^) S - pthread_mutex_init(&pmt , NULL);$ ~3 z B& G3 }/ B0 P R; l& M! @
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);+ E: k* |2 z2 O$ v; a/ ?
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);3 d. N3 \3 g* F& M" H
- ...3 o |9 f2 K2 {2 _
- while(1)
9 S7 e9 \) t4 h6 t1 N3 u - {
2 D) i! O6 d! `- K+ N4 q - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);
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- ...1 X- w" O9 m& Y6 V+ G8 Z: r/ z+ k' u
- }
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;">& {( [0 N% h* _+ I( Y
- </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. \3 X( v- b% ], v a; Q
- "Server: MJPG-Streamer/0.2\r\n" \' @3 R5 I+ G6 s) @/ u% @* H7 b
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
. W7 B- g# W# J: ` - "Pragma: no-cache\r\n" \- y: H: r0 [) V; O0 f) ?9 k
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
3 W5 m/ M6 F& P# T# ~ - #define BOUNDARY "boundarydonotcross"+ \$ _& ~0 Y5 t" G5 a
- printf("preparing header\n");1 W$ J3 u L$ D( H5 I
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \9 s. H1 z1 ~& }& j
- "Access-Control-Allow-Origin: *\r\n" \
% j5 K" U+ S+ h1 T: P7 G6 v - STD_HEADER \2 V% [) L" q T" T; T) m
- "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \; N1 [4 N- i' v) ^* C, n
- "\r\n" \ t; r; r. k5 ?, i! M
- "--" BOUNDARY "\r\n");- ]& i1 {" u6 t5 @, b8 a
- if(write(fd, buffer, strlen(buffer)) < 0)! f- [5 {7 d6 |6 L: i/ B2 \
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- free(frame);+ @9 L+ G" K' L) k! Q
- 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" \ Y* m( F1 e5 u% V
- "Content-Length: %d\r\n" \
( u4 H. y! L% e& U7 I7 R/ n - "X-Timestamp: %d.%06d\r\n" \. P1 S6 G) G2 [
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
/ ]! b4 Q. W6 i$ _ - printf("sending intemdiate header\n");+ u& l3 a9 _$ y# G m
- if(write(fd, buffer, strlen(buffer)) < 0)
' I, X% z4 ~) R - break;* Z3 D. I, f2 H5 Z& `, z
- printf("sending frame\n");
0 G/ B/ t, n9 ]1 H5 x+ | - if(write(fd, frame, frame_size) < 0)
' b6 n1 e8 z. Z* d5 U* \2 X - break;) U" \1 @) e4 p2 v$ Z7 L7 v; Y
- printf("sending boundary\n"); L3 B! i5 ~% c7 F
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
0 t: C) P: F* w4 b2 N' {5 @ - if(write(fd, buffer, strlen(buffer)) < 0)
0 R! z4 W9 [; | - 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:- P8 ^/ j1 ]8 [/ i( p
- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)
9 ]+ G+ x/ i9 i$ D - {
n4 L$ D' J. o6 g8 q - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);# N5 c4 J0 }$ d8 A
- if(*socket_found == (~0))% I* L0 i& t; \+ W8 X
- {4 A2 i5 Q2 d$ V$ w8 z! r, |3 K$ Q
- printf("Create udp send socket failed!\n");
0 |4 A2 u. ~: ^# e. K( f0 B - return -1;
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- addr->sin_family = AF_INET;
. ^" K% ^, ?6 L8 g2 I5 S) ^8 N - addr->sin_addr.s_addr = inet_addr(ip);
( n7 J" i3 V8 [( \9 s2 R - addr->sin_port = htons(port);
. z; A9 L5 q0 g - memset(addr->sin_zero, 0, 8);; D2 ]" I' ~! d+ _( I* x+ M
- return 0;$ O8 f. {% {- N/ Z1 O
- }
复制代码 # ]4 d" `+ c6 g m2 Y
. _9 c& Z* F" _3 J2 R5 O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:0 Y$ U* M: e; I/ z
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7 k; {, I9 j& O% J, o- while(fend > 0)0 W% O" X3 h" m3 d3 S2 D& X7 s
- {" S! @ R6 l6 y- j
- memset(picture.data , 0 , sizeof(picture.data));
9 @2 a7 Q* c! J9 e( h6 ?1 x - fread(picture.data , UDP_FRAME_LEN , 1, fp);
! M7 |1 m" l/ v$ L - if(fend >= UDP_FRAME_LEN)- f1 A! n# P0 B- o _9 [# w4 f( J
- {6 T, H0 M- l5 R# H0 v/ e( h- f5 o
- picture.length = UDP_FRAME_LEN;* o. G- v( x( y# ?
- picture.fin = 0; C$ b/ n7 I6 E" u/ B/ L" B
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- else* O% w/ |/ i* d' m9 [8 I$ P! c
- {- l, I, u* Y, P7 u! B4 o# I- \
- picture.length = fend;. _. e! O% a; N _' l. j
- picture.fin = 1;
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- //printf("sendbytes = %d \n",sendbytes);2 s4 j8 R' h; E; N3 X
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);8 x4 M$ f: e/ t M! B. q3 [
- if(sendbytes == -1)
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' f) A$ Q$ [1 u6 o) f: i - printf("Send Picture Failed!d\n");: o0 j7 o5 i5 z, O" C$ B
- return -1;
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- else0 c: E! F8 ?2 J( [+ s
- {
% \, ~. o4 W* X$ _ - fend -= UDP_FRAME_LEN;
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- }
复制代码
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iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |