本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑 & S1 g) F* G; |) p+ v* k* X' N
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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.html2 C) I/ X' Y7 Z' z. J7 T$ _
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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。 " [3 C; p; w" t: s
一、HTTP网页服务器
$ C( O; v( \3 N7 G U( K k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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/ C. s3 |* ?$ E% A g - struct sockaddr_in servaddr;
6 U8 b6 k4 V( M - socklen_t addrsize = sizeof(struct sockaddr);) Q5 N! J5 n: z- g
- bzero(&servaddr , sizeof(servaddr));
9 p: A/ G, f6 z1 w - servaddr.sin_family = AF_INET;9 I- C. c% C# D
- servaddr.sin_addr.s_addr = inet_addr(ip);5 H, {, [) F4 t0 k8 N( U2 [
- servaddr.sin_port = htons(port);& ^& N0 u3 Q. j* O1 p. }/ {# V
- int ret;0 E. R& l' M X% e$ p, Z2 i- G
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)7 H: _1 @3 Z2 a# u& l
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- printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);& n5 T( \7 P* i. Z) _' I
- return -1;
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: @% I/ Q, _) n2 D( E. `! w. n - int on = 1;
# h& Y; N$ H' C; d - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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- printf("setsockopt error\n");9 t# o* P4 u! a5 ~4 L; N
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- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
; W' c( ^9 u# m3 w/ w/ q1 U' b - if(ret == -1)1 l$ P) m7 Q1 w
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- printf("Tcp bind faiLED!\n");
( s" E: B" n9 D. ]! F0 Z9 N - return -1;
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- if(listen(*socket_found , 5) == -1)) z9 D4 K: f+ ?. m
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- printf("Listen failed!\n");
, p) V: P* f d7 I# D - return -1;
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7 @2 R) I" X3 F8 m: W - return 0;
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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);+ E/ K' g7 e# z- W) y+ \; e
- void * Thread_TCP_Web_Recv(void *arg)
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- while(1)# d! e9 _& `& ?4 T) ^5 Q1 W
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- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);3 C& L7 r3 Z& }, c: n
- printf("fd_socket_conn = accept()\n");
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- V+ A H8 m( O9 d0 A* \ - recv(fd_socket_conn , recvbuf , 1000 , 0);4 O% j$ v. n4 t# K) I4 _
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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);
) o3 F& o4 g( D4 ]" h6 v0 T5 S - pic_tmpbuffer = pic.tmpbuffer;
7 M, e( i4 }2 k8 E - pic.tmpbytesused = buff.bytesused;& ~7 D. a, V Z" X/ Q3 Z S Q2 A
- pic_tmpbytesused = pic.tmpbytesused;* n. G- a% e9 X' d
- pthread_cond_broadcast(&pct);# M# u% \5 h" q* f) 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;' Y( T2 ?1 d; r- Q F, J- Q$ O
- pthread_cond_t pct;$ w6 j( e4 H' u* E! C+ f& n
- int main(int argc, char* argv[])
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- TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP); @- Y8 q3 q0 g: R8 m: u5 }
- pthread_mutex_init(&pmt , NULL);( h+ C5 u |/ Y" K; d7 q" l2 n, M
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);% [, j0 ]0 l, Z( y4 ~9 A1 F
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);0 b! E" ~) m( d! \# o/ ]/ _% i4 s
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- while(1)+ b% v" f+ ?- }& o* m5 n. j, W# p
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- V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);* d- ]0 k9 h- h9 X; I2 v. O
- ...
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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;">
$ g6 E1 O$ y7 [7 q5 j - </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" \
& R( S2 ~7 C& z# A7 r' F' F - "Server: MJPG-Streamer/0.2\r\n" \
8 h# t/ t# a$ `3 }- L8 g - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
2 w+ W) H9 O3 q3 } - "Pragma: no-cache\r\n" \+ F% i+ I/ h/ O' _# m4 B! Z! K
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"+ U" I; D/ n5 W/ |0 k* L7 r
- #define BOUNDARY "boundarydonotcross"3 R8 r- \0 ^6 m/ `, g7 y( {
- printf("preparing header\n");
& F8 ]# Y) h1 ^* V - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \& U0 g8 {7 o. I) ]$ P4 {
- "Access-Control-Allow-Origin: *\r\n" \! ~* t/ s) S9 Z o+ G
- STD_HEADER \
7 K2 R" C: @+ Q& w2 U- X1 t - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \9 b w, F% ^; V7 p3 J; N( o B8 T
- "\r\n" \
& d: X3 `) Q- ~: \+ }- a - "--" BOUNDARY "\r\n");
m, \; m/ m- Y$ P) C - if(write(fd, buffer, strlen(buffer)) < 0)8 P0 z4 E, D" G2 i
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- free(frame);
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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" \
, P9 t+ W7 A9 y" W - "Content-Length: %d\r\n" \1 C! D* l8 L$ V
- "X-Timestamp: %d.%06d\r\n" \
- p9 N2 g3 }* r) z8 u% v - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
# A0 D' s) o- t7 K; p. h - printf("sending intemdiate header\n");
3 _# X5 w* n8 Y - if(write(fd, buffer, strlen(buffer)) < 0)
L& E, v1 x \8 R - break;) T! w' y- r+ F
- printf("sending frame\n");) V& j' @9 v; \7 ~% a
- if(write(fd, frame, frame_size) < 0)
7 f4 B/ K- [9 e" y! c Q% M, s - break;6 ]* i" M% [9 M$ ^) g; b& C
- printf("sending boundary\n");( W D* Z1 ]7 `7 F& I/ L8 r# }. {
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
; f. S! K4 U$ d2 V3 m9 _. f - if(write(fd, buffer, strlen(buffer)) < 0)
6 W% Q- M3 |9 c# X5 n. u+ S - 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:
/ G% w0 y3 w( [1 g& [$ g% q4 G6 p- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)7 U c) z0 `7 l
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- *socket_found = socket(AF_INET, SOCK_DGRAM, 0);2 G" s1 D( m. o, s9 C/ D
- if(*socket_found == (~0))* V( Z% D# D8 o( O) s+ l" }
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- printf("Create udp send socket failed!\n");3 E2 i+ T! C) n2 D
- return -1;
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- addr->sin_family = AF_INET;
: G- z1 [1 j3 L [4 h" m* D - addr->sin_addr.s_addr = inet_addr(ip);
4 f1 V8 c4 J" k - addr->sin_port = htons(port);
" F2 w! L* X1 ~; F$ H' E/ e - memset(addr->sin_zero, 0, 8);
5 o* [9 x- e, w( I. C - return 0;
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复制代码
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~; a# i$ p; k9 U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:1 l1 w! K& E( J: T% j1 e
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* R2 D5 g* s2 x6 T* v/ X0 n- while(fend > 0)" E. F! w9 g6 V+ R. p( {
- {
4 n+ w5 S' G8 o' M0 ?- G+ l - memset(picture.data , 0 , sizeof(picture.data));
j3 [, L b9 ?; I/ t - fread(picture.data , UDP_FRAME_LEN , 1, fp);% `* G) Y6 m2 X5 r5 T
- if(fend >= UDP_FRAME_LEN)
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) c& {& v$ Q' q- D% s r2 g* J7 M - picture.length = UDP_FRAME_LEN;
/ p: j8 C" K5 m& n% N - picture.fin = 0;
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$ a+ \! H/ O" H9 m8 E4 f - else
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- picture.length = fend;
( E1 N6 o0 {. y2 G T2 L: y: \ - picture.fin = 1; T0 a' T9 X1 ^" M5 B* ~7 L/ ?
- }
8 y4 ~: l, D+ C' Y0 n" m - //printf("sendbytes = %d \n",sendbytes);
) E! R7 i6 \( b* i. x, \ - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);3 c& Z. _5 Y6 g- N) L$ d/ q/ d! J
- if(sendbytes == -1)$ F# A( D& F7 v1 o
- {
! o$ g+ A7 J: `/ M f- L! z7 T - printf("Send Picture Failed!d\n");
9 a0 M! I) K6 c - return -1;* ~" I0 Y1 D) C! A
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- else
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( _9 h" u" t' d; x7 P, x6 Z1 t - fend -= UDP_FRAME_LEN;
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- }
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iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |