本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑
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- V1 ^5 V9 Q1 m- 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.html+ }/ I9 H T! M. l" X, V8 B% Z) u
- S' N# Q% E4 Z# 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。 % Q9 C$ l, ]7 S) }
一、HTTP网页服务器
# d0 t* ]9 q6 Y: E3 _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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: t3 n; q( @" y j' ] H( D - struct sockaddr_in servaddr;
3 ^# j9 @$ W# L3 ? - socklen_t addrsize = sizeof(struct sockaddr);
: v, e; v B3 ~, f W0 P2 y+ d0 n - bzero(&servaddr , sizeof(servaddr));
5 O( r8 q% ~) u6 _. p$ I* S - servaddr.sin_family = AF_INET;$ \* D: [7 r" O1 W- C! q \; e
- servaddr.sin_addr.s_addr = inet_addr(ip);
) D0 X$ g6 {7 m3 M, W% ] - servaddr.sin_port = htons(port);
5 J0 X l+ V' ?, A - int ret;
& f$ D8 |- g3 ]) \8 b* x5 Y1 z) ] - IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)
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# q" G" t6 A" j - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
/ u9 X; N5 p' ^& ` - return -1;7 f) e, ~: U* ]$ l5 E
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- int on = 1;
/ T$ V3 ~. l% d* G* N$ b; h - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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- printf("setsockopt error\n");) `' ?" u) w( R* j
- }
5 @$ ?- M8 t$ c" |* s7 } - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);0 \. j: {8 |& a* }+ P2 e
- if(ret == -1)* @+ x' D0 q3 h. Z
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- printf("Tcp bind faiLED!\n");
) k0 U" N" o5 y$ W6 R0 O7 {9 C - return -1;
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- if(listen(*socket_found , 5) == -1)
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- printf("Listen failed!\n");. i, i0 O K# f# N* e+ X7 ?
- return -1;" n& w, z' D9 U ~8 a; T& u+ U
- }
6 N" q) J7 G4 l% L6 O6 O+ R2 g - 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);/ `* j- x$ q; Q3 P8 q& h. [* d$ T
- void * Thread_TCP_Web_Recv(void *arg)- t9 ^0 ]; S, z: S
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- while(1)
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$ Z; ^3 w: V7 f9 F - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
5 |$ }9 {2 {, u' K - printf("fd_socket_conn = accept()\n");
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/ j+ b$ `- E( Y; R% {. U5 d - recv(fd_socket_conn , recvbuf , 1000 , 0); Q: [+ @* J/ p2 ^! j8 k
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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);
. ^7 B8 l6 n' t, B2 W# v, t - pic_tmpbuffer = pic.tmpbuffer;
9 B2 _5 _1 k( T1 [ - pic.tmpbytesused = buff.bytesused;
7 i+ R+ ^" |2 [; r* i7 x& ^1 V+ Z - pic_tmpbytesused = pic.tmpbytesused;! |3 W, {( M2 S8 }7 x3 ~, F
- pthread_cond_broadcast(&pct);$ Z7 A+ p- _' }
- 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;
% D3 k# R# T7 T4 X, G$ a5 _5 {; K3 R - pthread_cond_t pct;
3 ^% r; K Z" c( \" K: u# q/ Y - int main(int argc, char* argv[])% a" e" o3 v* H4 [% b8 n6 e4 o5 W
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- TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
/ ?" [/ m9 n) B - pthread_mutex_init(&pmt , NULL);
# x/ C' u2 ~( G& |( T# V) S - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);; @9 I" k' L- U3 }; u0 k# _, y+ x0 h
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);# N* f/ {* V1 I, X4 @
- ...: }& r( S: h- K
- while(1)
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$ U: Z. G" N) d - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);1 L7 D B- }* Q2 j+ ^) r$ s' Z
- ...
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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;">
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复制代码- #define STD_HEADER "Connection: close\r\n" \
, J/ H3 w2 y' M1 ^, z, z - "Server: MJPG-Streamer/0.2\r\n" \2 f- e& h7 w% ]3 l/ f) v
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \; {3 u4 H% p1 W2 b' A, Z( S
- "Pragma: no-cache\r\n" \
, K }: N1 `1 Z& c) s) J# I7 j - "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"' F) v" X4 s8 Y" @+ L$ B5 F
- #define BOUNDARY "boundarydonotcross"1 |% c2 V; S0 P5 H
- printf("preparing header\n");- h5 \( e) ^) ^7 E, E# q" ~" N9 {
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
+ K4 a E0 t# T4 {& l% n - "Access-Control-Allow-Origin: *\r\n" \1 K; W7 ~6 n- p
- STD_HEADER \
. k( r$ R) m" c( B2 D0 w - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
0 ?. A% [* n7 B - "\r\n" \
1 v; \! o9 }9 A - "--" BOUNDARY "\r\n");8 n6 x9 _. V3 X+ J
- if(write(fd, buffer, strlen(buffer)) < 0)
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& _3 D% b+ F9 W) o/ O - free(frame);
! S: K2 l5 q, @5 ~/ x& Q - return;1 r* H$ T9 t7 \4 u+ _
- }
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" \
% n% Z2 G; X, o& k - "Content-Length: %d\r\n" \8 Q1 r; q0 ?" R3 t1 E
- "X-Timestamp: %d.%06d\r\n" \' S5 V+ Z3 `! M4 X; j+ U
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);1 B- I2 G3 ~% ~, J0 X+ a
- printf("sending intemdiate header\n");' @9 f: P( a- v( h( n
- if(write(fd, buffer, strlen(buffer)) < 0)# p- [, G$ g& ~
- break;& F* s/ f2 X' A1 k c+ u
- printf("sending frame\n");
\4 o* U W) Q; R) d+ B/ g8 y* q - if(write(fd, frame, frame_size) < 0)
7 P: T! g6 k; Q. j3 u; C- X - break;5 a9 \4 ?+ a2 L7 B P! @. A5 a
- printf("sending boundary\n");
; _1 _0 |8 p3 _: Y, F - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");% P" D3 o2 }# P& i) [
- if(write(fd, buffer, strlen(buffer)) < 0)
1 c9 N% V+ q# D! `/ l - 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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5 o l! j7 H' S( s, D二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:1 [) g8 H" @! n8 l- j/ K* Z
- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)
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* y5 @! Z* T5 f - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);9 e K- q% H$ l$ h3 ]
- if(*socket_found == (~0))
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/ L: g4 U$ R* w6 _2 Y2 t; p+ u8 Z - printf("Create udp send socket failed!\n");
2 n; o! v! ~0 o - return -1;
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" s/ C2 v S0 @/ z8 u+ Z - addr->sin_family = AF_INET;$ d \# ^- _) y8 _( H
- addr->sin_addr.s_addr = inet_addr(ip);% `; y* R: j2 C- U+ k
- addr->sin_port = htons(port);
: w; F6 a0 ?6 J+ b5 h - memset(addr->sin_zero, 0, 8);
, Y% o: w! a3 T# ]8 W% a9 I F) j - return 0;
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复制代码
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+ z! k9 I, a% d' w" }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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% @2 M& @$ d, z# w! `- while(fend > 0)
: O/ K7 e6 v) g" L8 L9 d - {
$ b- b/ m! T* Q - memset(picture.data , 0 , sizeof(picture.data));
5 n5 q G8 {$ l6 ?5 L! g: b. C3 ? - fread(picture.data , UDP_FRAME_LEN , 1, fp);
3 R% ^" e3 F6 }% A - if(fend >= UDP_FRAME_LEN)
- F, I, |, V, n* q0 W! a - {( [7 ? {3 { ^8 [# @# g
- picture.length = UDP_FRAME_LEN;
1 l7 S5 w9 B; Q/ J+ ` - picture.fin = 0;
# K# d0 {- m/ _/ B% ] - }
2 U$ O5 r# z9 p* t+ N - else
( O: E, h- |/ B/ N) J - {
7 \8 B$ d; |' @6 E - picture.length = fend;
i" L% Q5 E6 x6 f - picture.fin = 1;
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; G; S( {1 X0 p) S1 f" |' g - //printf("sendbytes = %d \n",sendbytes);
. W9 y7 V4 ?) {2 r - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);/ {7 n) O! @! Q
- if(sendbytes == -1). h+ ^$ ~1 K( o( w7 ~1 k
- {
% F' J* Z/ @ \/ x3 g - printf("Send Picture Failed!d\n");% x) [! D' b5 a
- return -1;
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8 j: \" p+ r0 | - else
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) X; O0 ]$ v4 I# A S7 i+ l6 W - fend -= UDP_FRAME_LEN;( U, o$ D8 u% Y+ A" S4 S
- }
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复制代码
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* k4 r/ h; z1 v' {% IiMX8MPlus 核心板: https://www.forlinx.com/product/136.html |