本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑 $ C* j4 L8 X6 H% k' F& S. y
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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$ j0 d5 Z, h! A
: N& f% R. S$ o a' b2 `( f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。 $ u- l0 k; W6 A- q4 l; E, `

5 H( ~+ f" v$ X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。 & n' r D5 a1 X/ f: @6 }
一、HTTP网页服务器
& \' d6 K, M8 p# p# S. @1 N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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# u' g- t: m2 S- K8 C" c d( a3 W1 N - struct sockaddr_in servaddr;6 \0 Q2 a1 Y/ r
- socklen_t addrsize = sizeof(struct sockaddr);
5 t2 Q- O( Q2 x5 v- ] - bzero(&servaddr , sizeof(servaddr));) u, V) S$ V. C$ p
- servaddr.sin_family = AF_INET;4 `8 z0 c F. A$ y* V* s# q( o
- servaddr.sin_addr.s_addr = inet_addr(ip);
, ?' J2 f5 F5 y) Y0 P2 u( q - servaddr.sin_port = htons(port);% h- g% h8 ]3 _$ n* y; O7 w- ?
- int ret; w3 p' x9 T$ Q5 ^% {4 T1 M, i) _! J
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)
. R& D' i2 X$ e0 h - {
$ Z& x1 E# y0 v. J6 W5 B$ U% k/ n - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno); ~8 j: k5 n( |$ F
- return -1;
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- int on = 1;! R5 O8 s8 Z" o0 e9 m/ Z9 f
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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- printf("setsockopt error\n");
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% u# [8 @3 ^; C# u5 P: L - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);* g5 a8 k0 }: |) P- J/ K
- if(ret == -1), [& V3 b, k# q7 M0 R! \8 S; V
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- printf("Tcp bind faiLED!\n");
3 i$ X7 ~ r! j, E% u - return -1;
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- if(listen(*socket_found , 5) == -1)/ x0 g. v2 Y$ e9 Q5 M$ F# \
- {
% _9 K, `" ]4 z3 N. y - printf("Listen failed!\n");+ {) b& l5 V$ ? h6 v( x
- return -1;
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- return 0;2 [! @. f) ]# a
- }
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);
: i% \4 q% N( a! N6 A - void * Thread_TCP_Web_Recv(void *arg)
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- 。。。. X& G6 r8 w3 [9 Q: m* O! c
- while(1)" a+ U. `8 }. j% I5 P
- {
. I$ B2 P! X, B. {( {- c7 O - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
: X7 z6 G( v1 _1 r1 b8 N* \ - printf("fd_socket_conn = accept()\n");" O- k j, t* T/ w) r
- 。。。
# y7 V0 x5 {9 l8 E0 e - recv(fd_socket_conn , recvbuf , 1000 , 0);
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: {2 s, p& o- b6 Q - 。。。
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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); Q: p, t+ d' Y
- pic_tmpbuffer = pic.tmpbuffer;
4 L# j% n- Y; t+ H. r; E - pic.tmpbytesused = buff.bytesused;
* G! c) Z+ @$ O4 A( B$ A" u - pic_tmpbytesused = pic.tmpbytesused;" l! [! U# V1 f; g; E' I4 K
- pthread_cond_broadcast(&pct);* A7 O5 ` ?8 C7 D. ]! @
- 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;& N7 E" F& D* X: R
- pthread_cond_t pct;: W% V0 y+ U6 q) _
- int main(int argc, char* argv[])6 _7 S2 _$ _% G: p0 ]5 V2 F4 W: W
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- TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
" {6 {3 s6 R/ P. N: U } - pthread_mutex_init(&pmt , NULL);
) j8 L' F `: g% q* a4 J - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);+ [- s5 O* `; L7 F) s$ ]
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
7 S/ g) `3 E2 ~2 T8 \! h" G. g - ...
/ a2 ^6 p u' [( ?% l3 d/ s& h - while(1)
4 V3 e+ m7 e( o8 h8 [ - {
- X5 K+ ?' l0 i) c - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);
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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;">" L. i7 D; t4 A' t$ A' v
- </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" \
* s3 D3 f5 ~; Y - "Server: MJPG-Streamer/0.2\r\n" \
* u+ \) j# Z9 x9 E f* N1 u - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
/ ]9 O' W) k V" V - "Pragma: no-cache\r\n" \
/ Z \9 Z% ]* K; b$ a6 B0 [ - "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
- `' ?( a& ] [ - #define BOUNDARY "boundarydonotcross"! q1 b0 _, X; K9 z8 B# L T% Y
- printf("preparing header\n");
& X( O2 [ G# z& F5 {7 U - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \, @+ {2 t' k) o5 X2 t* K
- "Access-Control-Allow-Origin: *\r\n" \6 U- J0 z9 `5 X
- STD_HEADER \
+ h! j. ]. `4 j9 k* e( v# c - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
6 t3 @4 l/ U. H- ^+ t - "\r\n" \- }1 k( m; c2 L2 A+ b* C8 f1 A
- "--" BOUNDARY "\r\n");# k: [& W* W5 R" _# K1 p
- if(write(fd, buffer, strlen(buffer)) < 0)
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- free(frame);3 a8 ?( z# e% s8 t& e% B }
- 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" \
5 Q3 g0 U9 B/ H0 ~0 i; V - "Content-Length: %d\r\n" \
$ ? B% S/ g* C; x1 e# z - "X-Timestamp: %d.%06d\r\n" \( T z+ u5 D2 e1 u" g. I6 S: r v
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
: b2 _2 F3 D- Q3 ]: M5 h3 P8 q - printf("sending intemdiate header\n");
* ?2 q* ~; Y3 \# A* a - if(write(fd, buffer, strlen(buffer)) < 0): Z' f. m, R& W& r! e. q6 A
- break;
- F% M/ X4 m& q+ P/ P) B( f - printf("sending frame\n");/ |, Q- @5 C! ^. W
- if(write(fd, frame, frame_size) < 0)9 X7 Z8 P; o0 T5 R# A4 B: ~' S" f' M# n
- break;% _7 H! _6 c. q# k4 D4 a* X
- printf("sending boundary\n");
% l2 ?/ ~7 M' I2 _, F) o8 J l - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");4 u; T7 f! N V6 M( c
- if(write(fd, buffer, strlen(buffer)) < 0)" J R+ y' s8 d, c1 D' ~7 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。  7 i$ e/ G: \7 K. Q2 j
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二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:
4 r5 ~* L/ ?- ]; R/ y( j5 j: a, G- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)! k# l# U% x# [# V" p# x
- {
; E4 ^; t. V, M, w- C3 x D4 \ - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);
9 \! F& w- a5 N - if(*socket_found == (~0))) W" m$ k- q4 d1 j
- {
+ o) m9 S" Z* f4 t! J0 G - printf("Create udp send socket failed!\n");
0 Y& e& |, {5 z3 C) z9 L - return -1;6 w) |* A, |$ }! @8 p6 g
- }- p4 p: z- H) W& q2 D
- addr->sin_family = AF_INET;
% c# P* a7 r, R* |) x2 R+ } - addr->sin_addr.s_addr = inet_addr(ip);" A+ @5 Y* m2 a% O# v5 x
- addr->sin_port = htons(port);
: ? g: `* W+ F% i - memset(addr->sin_zero, 0, 8);5 m+ |& E" ?# K' m1 L' {7 B! y
- return 0;0 f9 x1 a' G- Z# c' p. q2 [6 w
- }
复制代码 Q; G7 F* T! H H5 j0 ~1 @
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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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$ |5 D' `9 |: u& ^- while(fend > 0)6 c; R) s" g3 V( J Z
- {
: V3 R- I' B) W - memset(picture.data , 0 , sizeof(picture.data));& E' k0 O: g8 Z& i0 M5 ]
- fread(picture.data , UDP_FRAME_LEN , 1, fp);* x. \/ ~% l* U6 ?+ J: G; a
- if(fend >= UDP_FRAME_LEN)
, a7 P3 O3 O! @ - {
+ [9 _/ a+ j7 h2 G" E$ ^+ t# Z - picture.length = UDP_FRAME_LEN;$ f) `/ F7 z" G( s
- picture.fin = 0;
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- r( h6 ^% a O% C" b8 L" B% t - else" |( `6 O- n. {2 e% L( L: E8 I9 B0 Y
- {
6 c5 K% @1 a W4 b6 m _* g0 X$ W! U - picture.length = fend;
0 f+ X! x& W" C0 t7 |* D4 K - picture.fin = 1;
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- //printf("sendbytes = %d \n",sendbytes);
* n5 p, {& v" @; g v' Z' e - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
7 Q& g) | k8 Y8 S' D/ P, h - if(sendbytes == -1)
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- printf("Send Picture Failed!d\n");
! P) A) Y* s8 n- R7 ~! p - return -1;
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- else2 ^2 ]" P7 g/ R5 d# d
- {* }8 ]1 [) ]# u+ h* H
- fend -= UDP_FRAME_LEN;
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- }
复制代码
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5 t( g' W( @( yiMX8MPlus 核心板: https://www.forlinx.com/product/136.html |