本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑
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9 q' l+ i- s0 [, J# w) p2 F) j- _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。 ' x2 Q" X* p$ R2 d, W
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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。 ; \: u w1 U1 E% I
一、HTTP网页服务器
6 P7 w, O3 Q3 i% k6 t% y) z5 a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)2 |- M' z* B H: W: I* p& t8 E
- {
* @8 e4 L- n5 D. ? - struct sockaddr_in servaddr;; E+ e* N2 n; E8 l L1 u" x3 t0 o
- socklen_t addrsize = sizeof(struct sockaddr);9 K; M/ z- X* O$ y! ~6 Y4 }. ]
- bzero(&servaddr , sizeof(servaddr));
Z* v/ C: X% o; ^5 d' o - servaddr.sin_family = AF_INET;
" t% C: Y' k1 t0 j# Y4 }2 T - servaddr.sin_addr.s_addr = inet_addr(ip);5 s( U& V7 ]. F/ f4 }
- servaddr.sin_port = htons(port);' h6 f6 Q; w0 Z! f: G+ N" f
- int ret;
+ k5 Y2 N4 b3 q* `* O/ Y - IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)* b6 @9 N% B, Y& r; Y% o, X
- {
1 W: _# i4 M* N9 L1 J) o# @ - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);/ G! o6 s# J# d; `& x& I
- return -1;
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- int on = 1;3 d- {: H) N4 D9 W
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)# c: i1 i3 G, ~
- {
/ _% D b% u# P+ N. u, L( @ - printf("setsockopt error\n");2 | A, w) I$ J% o5 V) a- o' j
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- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);6 F" B, P8 R* G7 Y. D) D1 r5 j. j
- if(ret == -1) B! S+ U3 O2 E; m) |
- {
+ r( X# c. @/ ~) T - printf("Tcp bind faiLED!\n");
& G1 ? M w. Y; c6 D - return -1;
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- if(listen(*socket_found , 5) == -1)& H' e1 ^, K7 r1 \4 K, Y3 Q
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- printf("Listen failed!\n");7 s6 S+ J1 r# F" T A4 ^
- return -1;" o1 x; H9 r/ I) l# D
- }
& Y6 M, U- j8 a4 N; e0 b2 r - return 0;4 O+ D- q3 a$ |/ P
- }
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);, L H8 e/ ]2 x7 }/ N8 C
- void * Thread_TCP_Web_Recv(void *arg)/ A3 ^$ H z1 |* q0 t# }
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- 。。。" [! x1 ]5 V9 M3 Y9 P
- while(1)& ^/ d/ s: N: X2 |6 O3 ^
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- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);( \5 d7 G9 b% j, g; B& Y! V
- printf("fd_socket_conn = accept()\n");5 O* [; a/ ?5 A6 m4 H h
- 。。。$ g( j" v+ W- z6 n
- recv(fd_socket_conn , recvbuf , 1000 , 0);- B% c; `2 A' H. C, M7 s/ P# Y
- }
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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);
3 S6 J- }! [7 |. M' P/ ?+ o - pic_tmpbuffer = pic.tmpbuffer;
1 }* x b# Q7 p - pic.tmpbytesused = buff.bytesused;, a: A' M( e6 r8 O( d$ `+ |! B5 [
- pic_tmpbytesused = pic.tmpbytesused;) A9 l2 {2 ~# b, f4 D! O
- pthread_cond_broadcast(&pct);9 ^/ `6 h" U; A
- 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;4 |3 e; y2 ?, s; c. F
- pthread_cond_t pct;
- z4 m3 ^6 D( c9 r - int main(int argc, char* argv[])
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- ...5 S" u7 R$ q5 k$ |
- TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
1 O( z/ s5 H1 V0 Y& x - pthread_mutex_init(&pmt , NULL);+ f: c/ C; F% t1 F4 y2 S
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);: y& f0 P& F( z- H& }( N' p
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);0 t# i w* P5 y3 U! K
- ...; E$ z2 u/ |% G1 E& v$ O, ?6 {
- while(1): j3 e3 ^& C: B8 C9 l) C
- {
% d7 }% S1 F' C( g# r) G - 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;">" W; j" ]2 ~0 m9 q" d
- </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" \: |' b. @8 K; }( R
- "Server: MJPG-Streamer/0.2\r\n" \# g* `2 b7 A5 N) T8 Q* a+ p& q1 U
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \4 m6 t; s q- A$ N1 `% J- h
- "Pragma: no-cache\r\n" \- @# \( N: c% E8 E5 m Z( }
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"+ j; D9 z0 E I7 Q, K
- #define BOUNDARY "boundarydonotcross"
% h, M i4 d. O. w, v - printf("preparing header\n");/ d9 E* Y* y' z
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
' B6 ]) L) A6 X7 [ - "Access-Control-Allow-Origin: *\r\n" \* w: v) O# ]8 R4 L q! Q
- STD_HEADER \
6 e, H6 i5 m3 O& b9 d) e6 v1 w# K - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
& t/ s3 a6 n9 w1 C - "\r\n" \4 I5 {7 Z% U" D' W5 [6 b( n
- "--" BOUNDARY "\r\n");
+ i2 N! J2 N+ Q% z# s" I( m- R+ b - if(write(fd, buffer, strlen(buffer)) < 0)
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- free(frame);8 Q1 ~* l3 s8 g5 [
- return;
9 g i. x' S6 v& O1 e8 ? - }
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" \0 r5 P6 _2 g- r- Y- u
- "Content-Length: %d\r\n" \
: B0 v! O2 I. S- B - "X-Timestamp: %d.%06d\r\n" \& I# v$ z4 m, M5 r" x
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
! }; q$ k* r# H! N# ]- d - printf("sending intemdiate header\n");& a( |1 P3 i3 E
- if(write(fd, buffer, strlen(buffer)) < 0)
" \7 g" i+ C3 S! }6 \ - break;
$ U1 q8 w: L3 l: C0 L! u8 u5 g" l - printf("sending frame\n");
i, \6 }8 p0 Z" M1 X' r* { f - if(write(fd, frame, frame_size) < 0)
. J9 C$ b7 l- v# [. ?- @ - break;7 o- y3 _/ c; ]2 a
- printf("sending boundary\n");; y+ ?5 l' |& n
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");5 k1 U) c% C8 _4 H
- if(write(fd, buffer, strlen(buffer)) < 0)9 k7 _. I" f: Q2 M+ X
- 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:
* l0 L' ~( u" U8 b- ^3 \9 }- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)9 P( ?7 s+ ~, v2 O$ O e9 m
- {
6 _! x5 k$ @ _, H5 V2 V* A - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);
- K$ W/ K- T" h5 m3 n! I! ?8 p - if(*socket_found == (~0)): W: f. J r1 S1 j% v0 l
- {
6 L3 G. G5 |, d - printf("Create udp send socket failed!\n");( N/ S' ^; p! h# z8 e p7 i; O
- return -1;4 s* o0 P, h9 b4 T" {
- }
5 C# K- G% X# U1 ?8 m - addr->sin_family = AF_INET;
g; s1 j8 f% O9 |9 Q& S+ L - addr->sin_addr.s_addr = inet_addr(ip);) Z4 \2 I9 U C5 Q/ \. h
- addr->sin_port = htons(port);
" g' t. {3 o2 m4 v' a3 \8 |+ H6 }$ t" k - memset(addr->sin_zero, 0, 8);
" P. {" e: g6 R - return 0;
4 Z% J; L' ]0 G1 q - }
复制代码
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5 @9 N" q3 u$ l- o* p! y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:) }' k/ }$ S( S- R% f7 k
4 c t: @# Y5 d
4 s8 ?: c6 y: s- while(fend > 0)" K! u/ j- h7 K E
- {. m* @6 U% S: s3 [3 g7 m+ w
- memset(picture.data , 0 , sizeof(picture.data));/ W4 R2 z: D% d4 H) _' f
- fread(picture.data , UDP_FRAME_LEN , 1, fp);
" S: F3 }; n: x8 I - if(fend >= UDP_FRAME_LEN)
% r) M$ Q$ [+ _& F - {
) m# x$ E9 F$ M0 h; Y - picture.length = UDP_FRAME_LEN;
+ r1 E* N. L y% M# N - picture.fin = 0;5 B' H& Z m' G1 M9 Z7 @% o% a
- }: _, |7 W+ @; e) z% X. @
- else
* x- s+ E9 ^3 ^% y- J) g6 G) e - {
; d; @0 G/ {8 @2 i, l - picture.length = fend;
5 r5 D, a1 x3 I2 f" B! s, b - picture.fin = 1;' }( q7 c0 K" P/ M
- }
9 X I5 G$ S9 E0 E6 v& X - //printf("sendbytes = %d \n",sendbytes);
+ X) F* `0 d4 j! ^: { - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);% [2 B% u# Z6 Y$ v
- if(sendbytes == -1)% q6 @7 n9 a% g$ F! |1 ~% Y
- {
3 c' ~) {/ c5 @; ` Z - printf("Send Picture Failed!d\n");. q5 C I! H' S% ^# T+ b0 j
- return -1;
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- else% u5 c/ `1 D; ?+ p6 U
- {
7 t1 e! A# i, O0 z- g) e% ^ - fend -= UDP_FRAME_LEN;8 R3 s! Z6 P' J( N$ v( y5 H
- }: h0 r( {# U1 l5 i# R
- }
复制代码 ' l7 Y' P% S' e, h2 J* e
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1 z# I) P1 ~! z- d2 M$ KiMX8MPlus 核心板: https://www.forlinx.com/product/136.html |