本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑 / z, S. Q/ }. o
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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
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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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" ] h* M1 C5 u0 m* \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。 / x4 Z# x. s. o! o7 o
一、HTTP网页服务器. `2 }+ x/ q5 K, I+ H
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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6 B3 \5 F2 |9 o - struct sockaddr_in servaddr;
) O7 a3 n4 ?; o; z' D - socklen_t addrsize = sizeof(struct sockaddr);
' x1 c( S! S7 U3 W/ U1 g - bzero(&servaddr , sizeof(servaddr));, m* l+ I2 H5 m
- servaddr.sin_family = AF_INET;
* o4 {+ V! z% G8 Y$ p' g$ @' d - servaddr.sin_addr.s_addr = inet_addr(ip);
, H6 C& v- V0 j - servaddr.sin_port = htons(port);
* C) ?4 _4 ?" ~8 | - int ret;9 ]# g* v4 c8 w, h4 U
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1) G# h5 x* h4 j" Y
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- printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
+ u, h" G" u& q) m5 p" s - return -1;
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( i& `' u* J/ j/ Y - int on = 1;
4 o, t; ]3 \* l - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)9 c0 p) X# I# d/ O+ Q5 [
- {) p$ z: I B; u% Z9 e
- printf("setsockopt error\n");) T9 }+ N7 D. B: u3 c# ^, z0 }
- }
}0 J6 m) s8 V% A. b& j% J/ r - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize); o1 ] A5 a5 m/ T/ U/ S3 ^
- if(ret == -1)) J+ A, _/ ]# m
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- printf("Tcp bind faiLED!\n");
3 a" ?9 i. S* e' J- s - return -1;
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- if(listen(*socket_found , 5) == -1)
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- printf("Listen failed!\n");& @4 u6 N& z5 K% u
- return -1;
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- return 0;9 ~6 `: {* x2 u5 r$ 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);* |. @# v( D4 T5 h5 n
- void * Thread_TCP_Web_Recv(void *arg)
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- while(1)+ Y7 M' E, `+ `" l
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- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);" l" P& h9 P, @, D
- printf("fd_socket_conn = accept()\n");9 o8 a% G( l1 B+ E3 ]; @; {4 s: C
- 。。。) U8 n2 Z$ K o6 V+ S h
- recv(fd_socket_conn , recvbuf , 1000 , 0);$ i) t! I3 \; a" ]$ Q
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- 。。。" n4 h: a G9 k
- }
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);
N; b: x/ E5 T* ^# h - pic_tmpbuffer = pic.tmpbuffer;1 t" t F( A, ~
- pic.tmpbytesused = buff.bytesused;
+ z: z7 p6 b" m" B( E1 Y+ i - pic_tmpbytesused = pic.tmpbytesused;& \2 m1 E7 w! @ A" i3 \, z
- pthread_cond_broadcast(&pct);
( _1 Z8 p7 T# ]2 a7 h/ u - 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;0 r; F. k; L( m! r" h
- pthread_cond_t pct;
3 w5 V% w5 ]. {* G1 ]# Z x - int main(int argc, char* argv[])
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- ...
7 h* |7 p! R/ B - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
2 }4 d i& g; b& U7 c - pthread_mutex_init(&pmt , NULL);- A7 ~# Z3 j9 q; K9 }, Q- |2 b( K, i
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);" ~0 W% m V1 \9 L, t4 P' `
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
6 ]- j7 l& J& _& L' Q3 v - ...
6 g6 n% B, l5 v6 L2 ^ b - while(1)' r2 j5 m( C1 u3 W+ k. {
- {
5 y4 }" E+ v7 l# d0 S* n: a - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);! k) a) V" A( i+ ` D" Y8 x
- ...+ r4 Q" d0 ~5 W1 O! G1 h" H
- }
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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;">
1 g3 {, {1 _& W - </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" \. [6 w* x& j/ n9 T, L* M8 N2 R) Z
- "Server: MJPG-Streamer/0.2\r\n" \
5 Z9 C2 N: n* A+ q& I - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \* |1 G2 G1 S- I. W* E
- "Pragma: no-cache\r\n" \ l" k8 G" ~8 Z- o: w/ {4 G
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"3 r2 k \- X5 {$ J" F4 R7 Z3 {
- #define BOUNDARY "boundarydonotcross", i% z% @6 S, l! m5 d
- printf("preparing header\n");
5 Q8 ?) s( K# @ - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
' E+ m0 h \; V1 e S - "Access-Control-Allow-Origin: *\r\n" \" k, R: Z; m% }, T3 [3 j$ `
- STD_HEADER \
. U7 r8 e r. `6 l - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
1 x' f3 d, z, j - "\r\n" \
/ @0 g$ r& d- [* b" L% c( K2 J, T( L - "--" BOUNDARY "\r\n");: d; o8 ]2 }0 F; o3 M1 J Z
- if(write(fd, buffer, strlen(buffer)) < 0)! K+ A, [7 U2 N Z+ q# d4 B
- {# ^8 D' a, z# u2 x6 `$ {' Z1 {
- free(frame);8 _8 S2 ~) [- D5 D" `
- return; d) }8 K! H5 {8 n$ b
- }
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" \# p2 k& L/ H4 @4 ?! x
- "Content-Length: %d\r\n" \' ?: L. a( h! U: a
- "X-Timestamp: %d.%06d\r\n" \+ b6 L. ^% @( V+ Y. }: W
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);4 q/ n& D0 i. a7 p9 X& r6 d; A7 q
- printf("sending intemdiate header\n");: C9 ^" K( m/ o) R! w
- if(write(fd, buffer, strlen(buffer)) < 0)1 k8 ^2 k/ d! o' ^3 M- A4 @4 y5 D/ c
- break;
8 o( V, R5 ~' Z - printf("sending frame\n");
; N2 v4 w) ~: w0 a - if(write(fd, frame, frame_size) < 0)
0 R: ~: D: {* X3 Q" M; u - break;
9 ^( @1 S8 H. {9 U2 l4 w - printf("sending boundary\n");9 Z$ V `' [$ d' g. \) Q8 ]# p, F
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n"); m' P' u9 J1 A4 \3 y# ]
- if(write(fd, buffer, strlen(buffer)) < 0)7 U% a, [& y( Y
- 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:" B4 B8 {( Y8 f
- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port): J* L3 t! _2 D1 U5 J- ~( W* F2 n
- {
* T4 j) O. |; q8 k) e - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);
5 A5 v Z% b0 X1 W5 X+ Y/ \ - if(*socket_found == (~0))
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- printf("Create udp send socket failed!\n");
. \9 }4 x1 u8 C% P6 e2 S - return -1;1 f- {& n- t1 V6 q. Z' d3 j
- }
; Q9 x+ t. b' b& U( j - addr->sin_family = AF_INET;
: z M' j% Q% N% j4 g8 e - addr->sin_addr.s_addr = inet_addr(ip);
9 x, T% Q/ ~3 [9 c [3 q& f2 _, T& T - addr->sin_port = htons(port);2 d( ]5 {2 X9 [) Z1 ^5 K0 x
- memset(addr->sin_zero, 0, 8);
3 V9 P) V1 ]2 N$ c - return 0;5 D" q1 X5 ?. i5 W2 \
- }
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:
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- while(fend > 0)& P( [" s" ` [& E k
- {
' W, a; F+ Q9 o - memset(picture.data , 0 , sizeof(picture.data));
& ~! s0 H& p) I1 A& Z - fread(picture.data , UDP_FRAME_LEN , 1, fp);$ t' C1 k: l9 i$ b8 Y: i0 V$ e( O
- if(fend >= UDP_FRAME_LEN)
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- picture.length = UDP_FRAME_LEN;" I$ Z# i! E9 y% g; G2 q# x' V% D
- picture.fin = 0;8 \1 \$ H& n$ A! T
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- else
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- picture.length = fend;
! @7 `" D* N4 q: G+ s - picture.fin = 1;
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- //printf("sendbytes = %d \n",sendbytes);
: e1 q0 ?5 s9 T+ q5 n4 X - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
9 `: Y1 i% Q- E! D5 f - if(sendbytes == -1)
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) I2 `# L# T4 @ i& I - printf("Send Picture Failed!d\n");& u+ s2 d5 f$ U" ^0 k# ^2 p
- return -1;5 V# e9 L. Y6 C7 T6 E
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- else1 I$ X% A, W/ z2 n" U. Y
- {
6 u! ^3 u) Y! `5 w3 h. {0 H - fend -= UDP_FRAME_LEN;1 T K7 c* T; z& Y+ m9 N1 m8 O* v+ ?
- }6 t9 j; M' W+ ?$ ?
- }
复制代码
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* i& M1 `) O/ N. Z2 \+ p9 V& viMX8MPlus 核心板: https://www.forlinx.com/product/136.html |