本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑 " x) q7 Z2 }. U9 W' S9 k2 a
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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/ Z) v' _- ^% R$ y, I! F# [' S
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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。 % c Y. h1 X- ] c' ~: f9 z1 ~
一、HTTP网页服务器! v( f) m! k8 h* i6 C9 [
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)' w1 }% u8 [5 |+ H8 u. e$ y
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- struct sockaddr_in servaddr;! r. A" t7 E+ e; D+ L& l/ `2 y8 N# W
- socklen_t addrsize = sizeof(struct sockaddr);$ `8 o7 r2 z: \# N+ I
- bzero(&servaddr , sizeof(servaddr));* e$ P* P( F. V0 A- f8 p8 S
- servaddr.sin_family = AF_INET;" Z6 o6 O$ H2 c. n0 l) g8 t/ `& S0 I
- servaddr.sin_addr.s_addr = inet_addr(ip);" \% z! k' F, ^( C
- servaddr.sin_port = htons(port);9 f7 k# z% z1 D/ w. s d
- int ret;
! b: ~' R7 s% c) g6 P9 D* L - IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)0 [) s, h8 }6 \ _& t
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- printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
. t- t( \1 a/ v6 m4 i9 M2 Z - return -1; t8 }! V1 L$ }; C5 y/ e
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- int on = 1;* S( u9 U8 N& ~ D& W# Q
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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- printf("setsockopt error\n");
u0 P/ A! v/ E% O& I - }
t ~" {% S/ A+ E) b - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
1 K+ i6 }/ i" j g* | - if(ret == -1): i; r7 e; L; r) x* r& `' i
- {$ l" p f# c" O) q$ h0 Y& i
- printf("Tcp bind faiLED!\n");) x# s% _- M2 ^1 i0 C* u0 X) ?2 x5 U& M
- return -1;
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- if(listen(*socket_found , 5) == -1)
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! H: @* B( g* r. n6 n$ g - printf("Listen failed!\n");. a M1 H( E# d5 m' s. b$ f3 I. G8 |
- return -1;
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& U8 u) a( f8 }& Y - return 0;
O( g+ I6 [4 ~1 W9 e - }
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);
Y/ G5 |( U4 g% S) A$ | - void * Thread_TCP_Web_Recv(void *arg)
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- while(1)& S# f* \% e* o. D
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- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
8 y" U" G- h2 c8 O2 W, ]! ~! s5 j: o - printf("fd_socket_conn = accept()\n");5 q4 X: @; G+ D* P
- 。。。, {6 P& {1 ~; j8 w7 Z5 c% \
- recv(fd_socket_conn , recvbuf , 1000 , 0);2 S9 `) C0 }2 a& i* V
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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);
5 H1 h5 H; m. y4 Q7 G - pic_tmpbuffer = pic.tmpbuffer;
; t+ ^% o: ^( e: p z8 w0 s3 U) H - pic.tmpbytesused = buff.bytesused;
: ?9 a7 K b5 Z$ d5 u* M - pic_tmpbytesused = pic.tmpbytesused;$ ]" B# W5 C' l" {' d9 y% x# P
- pthread_cond_broadcast(&pct);
2 m o3 R9 r: v0 u' w4 } - 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;
# _! ], D& b2 B6 U, a! d2 A - pthread_cond_t pct;5 S) [* w/ b I( `' m9 K
- int main(int argc, char* argv[])
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- ...
c9 t6 C0 b6 ~' A - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);* \, h+ Y, k* i5 x8 h3 L/ s
- pthread_mutex_init(&pmt , NULL);+ E; ?$ s6 j$ q1 x6 `3 N6 }
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);$ j+ S8 z; c$ z
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
+ ^# s) x# @4 j! ? - ...
% B" ^6 n1 n0 E, U/ |/ ? - while(1)7 a) A6 g; G8 {0 Y
- {
0 a* f0 Y: B7 k9 Z8 K: N) f - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);; S5 q% _+ K4 e+ T l+ R q
- ...
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- ...1 n% P" m1 B, R8 x: Y: x/ x P0 E
- }
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 {' r3 f2 G& a8 `7 M% T6 Y Z
- </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" \) W+ W4 ]! @* e1 @* d9 ?
- "Server: MJPG-Streamer/0.2\r\n" \
, Y( o- [8 N* C - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
1 ^4 H) `8 Z; D8 U8 u, b9 T - "Pragma: no-cache\r\n" \
4 m2 j& p% U" H/ t9 m5 D - "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"3 Q" L' C" A% ~. e
- #define BOUNDARY "boundarydonotcross"
+ @" a5 J. U7 u9 a8 u8 d2 `5 B$ h - printf("preparing header\n");
4 P, t0 Z2 U" m7 E, y2 N$ o - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
' l# A: C$ k# q- X, w; H3 [ - "Access-Control-Allow-Origin: *\r\n" \
, {5 l+ X$ |8 d- G& J1 @2 `0 q - STD_HEADER \
1 e4 u0 W W, d" D - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \. L ]- d: ?/ J
- "\r\n" \
2 \. ?' { A O/ Q' M# ^9 j - "--" BOUNDARY "\r\n");
9 U) _+ P( n5 M' h, v9 q - if(write(fd, buffer, strlen(buffer)) < 0)
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- free(frame);
: U2 O d* b+ O S9 D! ]! F/ N9 t - 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" \
" R* N, m: [1 v3 X! A6 d5 ^% c; { - "Content-Length: %d\r\n" \; B% ]1 x& T0 ~
- "X-Timestamp: %d.%06d\r\n" \5 h4 k6 e4 f6 l' p% k' M4 h; t2 t
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);" |/ Z. q2 l8 T' s
- printf("sending intemdiate header\n");
& g# \' l) K; w - if(write(fd, buffer, strlen(buffer)) < 0)
4 ~1 Y& n% u8 b, e6 A! F: N% J - break;
. d; u9 L2 f! Y4 R, K& P - printf("sending frame\n");
# D R4 t% j: h' e4 Y - if(write(fd, frame, frame_size) < 0)
! [! T* o3 e7 J- z8 i1 \ - break;
3 e) `- n7 _% I: C" B3 }8 c - printf("sending boundary\n");- ]9 c" C5 Q' Y8 h1 e
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
3 o, a6 {4 D: K( V: a, t - if(write(fd, buffer, strlen(buffer)) < 0)2 }( `2 U V. z/ |2 r* {( ^: Y2 U
- 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:
/ w0 A$ x, E0 Q" [- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)
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- *socket_found = socket(AF_INET, SOCK_DGRAM, 0);: D" R* E- g+ Z: K
- if(*socket_found == (~0))
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- printf("Create udp send socket failed!\n");
4 l# {$ t( P- s5 ` - return -1;
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0 W7 y) ?1 S7 S0 s; Z8 K6 r - addr->sin_family = AF_INET;" ], u$ T2 \( E& L* r. n& O
- addr->sin_addr.s_addr = inet_addr(ip);
7 c0 P& |( b R* x+ I* a' ^5 { - addr->sin_port = htons(port);
6 V: P; i* o/ J* U: ^$ ^& ] - memset(addr->sin_zero, 0, 8);) ?+ X3 B6 {6 \+ G( D; q! b
- return 0;
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复制代码
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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:4 f6 N7 F6 Y: p+ u
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9 e$ x$ m+ W" m0 I+ R2 t5 t, \- while(fend > 0)7 L* c; G1 |# j
- {
3 m/ `9 U0 |* @2 |# K" a; b - memset(picture.data , 0 , sizeof(picture.data));
/ p* w" T; N5 e; a1 w/ Q - fread(picture.data , UDP_FRAME_LEN , 1, fp);/ J6 H6 Q7 n- i
- if(fend >= UDP_FRAME_LEN)
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- picture.length = UDP_FRAME_LEN;
% }8 A0 {8 }$ x0 s6 o: p `/ j - picture.fin = 0;
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- else
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( M T( B; f. v7 [. x# x - picture.length = fend;
4 `! ?; C( j; B - picture.fin = 1;' F$ D n# o/ ~) z( V, @/ ~
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- //printf("sendbytes = %d \n",sendbytes);9 X' t3 w: t+ p& z" Y6 q, q9 Y8 b
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
' l/ G9 k, k# A0 T* W - if(sendbytes == -1)
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- printf("Send Picture Failed!d\n");
: T- O) u: k$ S+ H - return -1;2 j" ~: G H+ {; r! e
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- else
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- fend -= UDP_FRAME_LEN;
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- }
复制代码 2 k) M- J4 o8 a( ~. T
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iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |