本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑
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9 S; `$ R! V2 }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! D* Y9 S& F! p3 Q
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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。 % A. D/ I2 [4 C+ _# Y
一、HTTP网页服务器
& i! O8 |. u" r; }& t# }. I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)# |% H& ^% x8 I# w, B7 i7 J6 x/ K
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- struct sockaddr_in servaddr;
, k# h3 N6 ^% x/ y' ` - socklen_t addrsize = sizeof(struct sockaddr);
* H( b( ^9 W7 r3 W8 \" P - bzero(&servaddr , sizeof(servaddr));
& @" A# c W) U5 T - servaddr.sin_family = AF_INET;: h1 u" |! Y1 [( A
- servaddr.sin_addr.s_addr = inet_addr(ip);
- I2 e- l: S! i' I/ [3 A - servaddr.sin_port = htons(port);
. O. k, u/ @( c* T' }/ @/ ^$ ^ - int ret;
/ G" \) w( p* Y# s - IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)
5 [: Y t. A8 ^3 C - {
9 l5 {# M( | L, Y1 ], g, h- h+ v - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);3 L, U3 h3 R. I4 |" k% n% k
- return -1;' v' l) [1 ~3 X; z# I( |
- }
, ~2 ^' W; ?6 J& F1 }+ U - int on = 1;- k% y4 {2 {1 N; F
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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- printf("setsockopt error\n");' f! T7 D. T3 p1 j \
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- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);# m+ S0 y! o4 y) o: y! @/ X$ _4 ]
- if(ret == -1)! s, p) g$ y& K% P8 b3 b0 P
- {
* s1 r- j$ A0 E( o8 R7 K5 W. g - printf("Tcp bind faiLED!\n");3 k! [7 U% m6 G5 t+ T
- return -1;) Z( y# V$ U3 L1 a3 I
- }
# Z& w2 l4 v5 f3 f% q6 Q8 y* ] - if(listen(*socket_found , 5) == -1)
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- printf("Listen failed!\n");
- R9 z9 A) C" Z - return -1;- a9 t7 T) J# P; T
- }
$ x4 _' F% ~; S/ @( U - return 0;( q9 z* R+ @% R& N
- }
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# g; n; h2 K9 Q/ g# ]8 F' t' `$ W - void * Thread_TCP_Web_Recv(void *arg)" n8 @" r; `$ ^6 v% N# P
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- while(1)( Y1 V) U0 G# A* H& y
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- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);+ `- |3 x. Z; M, m; y5 f( J1 G
- printf("fd_socket_conn = accept()\n");, }9 k% U9 a' b" }5 e8 b Q
- 。。。
5 G5 q9 M# P7 p - recv(fd_socket_conn , recvbuf , 1000 , 0);8 F7 i' h+ A5 { `$ |
- }
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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);* N4 S4 E0 O' p
- pic_tmpbuffer = pic.tmpbuffer;
9 G- j* B& s* R: m* m1 ?+ Y# J - pic.tmpbytesused = buff.bytesused;6 Z: M2 M: D) \: |7 o9 V
- pic_tmpbytesused = pic.tmpbytesused;
# n- z& E7 O, p3 M% C7 ?. j - pthread_cond_broadcast(&pct);. p9 l3 k7 G; V
- 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;
3 |" p% k4 {/ @8 P - pthread_cond_t pct;
: I" Q! Y, n7 J% k - int main(int argc, char* argv[])# w) i. j6 n& ]9 ^
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- ...$ Z" S2 E0 a7 Z2 j+ D
- TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);/ }. r7 T7 F, h/ W
- pthread_mutex_init(&pmt , NULL);5 o- x$ v6 U8 O& |
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);7 H& m1 r/ k8 A/ n9 w; t
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
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- while(1)( Y( G1 o' A1 L4 p& M2 j- K
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- V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);: E; _2 m* ~& X e- @* _
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- ...$ u% ^( d2 K: F( Y
- }
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" \0 `/ ~) [0 E/ @
- "Server: MJPG-Streamer/0.2\r\n" \7 \7 j# w; ?- @# o
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \3 V( I5 W+ F4 ~+ b5 J% Z c
- "Pragma: no-cache\r\n" \5 q1 Q7 f7 ?! P- _ m3 J
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"1 D* |# Q$ ^, {% [0 {$ @
- #define BOUNDARY "boundarydonotcross"
4 X) @6 q. B8 j6 ? - printf("preparing header\n");# x$ }# h* l! s( n! T! u
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \' q! z9 W, X, S1 u
- "Access-Control-Allow-Origin: *\r\n" \0 B6 }4 k/ s* a" g3 X
- STD_HEADER \
* {# c; w1 J9 P: u, k. [+ z U4 v - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \# d' @0 u- P0 l' j
- "\r\n" \6 Y- Q8 t9 A2 M+ `0 g% @7 x7 u
- "--" BOUNDARY "\r\n");$ X( @ j1 F/ \8 W; B8 d) g$ T7 B# u
- if(write(fd, buffer, strlen(buffer)) < 0)
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- free(frame);
_5 Y6 p. I# t7 c( G - return;0 h+ a6 ?- z2 T9 d, |4 N" [
- }
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" \7 u. Q Q: g, r! ]& W; f& k
- "Content-Length: %d\r\n" \
: r' e/ |& n: Q! u* L7 u& D0 c7 h - "X-Timestamp: %d.%06d\r\n" \/ m) p1 b1 q* H
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);7 u, h, \! ?4 z P5 g* N* U
- printf("sending intemdiate header\n");) V6 L: H4 v& t0 s r Q
- if(write(fd, buffer, strlen(buffer)) < 0)
+ g7 a% d) _/ z3 b3 q - break;
L" P: t7 z8 w0 s* `$ v& F - printf("sending frame\n");, p' {6 L2 s' A! X8 o5 @& e( r
- if(write(fd, frame, frame_size) < 0)
4 Z* Y# q0 C, \1 _' U% K. p - break;
1 Z& _* \7 h2 g" N$ n: l - printf("sending boundary\n");
, j% _0 M/ N4 I1 Z! }, A% C2 p - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");# ^1 F7 c7 k& ]
- if(write(fd, buffer, strlen(buffer)) < 0)' r w& O* Q9 r
- 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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; ] e5 ~) H, J5 R6 Q9 x( S二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:
. j* o. i. k# W/ g- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)* t2 |; b! _ h$ o- P& ?) n H( _) o
- {
1 K- [ X+ I( N - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);' Q+ w- s k+ b6 }! J/ ^1 r: v/ w8 e
- if(*socket_found == (~0))
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- printf("Create udp send socket failed!\n");1 Y! ?# V' O8 [3 p
- return -1;
3 \- X6 w6 p% j1 P+ f- y c& m; Y - }
: a D/ y* E6 ]( b - addr->sin_family = AF_INET;
- B; M1 U3 n0 R4 |& _ - addr->sin_addr.s_addr = inet_addr(ip);/ e4 P. A3 B3 G& \( C f
- addr->sin_port = htons(port);5 h- j+ |0 K4 C
- memset(addr->sin_zero, 0, 8);6 w: g- J: e$ h; Z# A' p
- return 0;, ^! f0 R% Y/ t2 P
- }
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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( a7 k/ _* G1 a/ m- while(fend > 0)0 b; w$ A, k% ?0 c7 `
- {0 k0 H$ d( [, g [: M3 V; K0 i1 [' h H
- memset(picture.data , 0 , sizeof(picture.data));
1 A8 }- g# @* l6 f8 R$ c- O - fread(picture.data , UDP_FRAME_LEN , 1, fp);
' m& B& g' k- E - if(fend >= UDP_FRAME_LEN)2 S- g: r+ l& X8 O% ]5 Z: x
- {2 P) `- [5 `6 \; _) [
- picture.length = UDP_FRAME_LEN;3 S t4 d+ U: G0 N: _
- picture.fin = 0;$ f3 Z' V+ ~2 P
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- else, x! Z$ @" H# E q# M$ r$ f6 v/ c
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- picture.length = fend;
) b! k, S: U' w: o7 w. ~ - picture.fin = 1;
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- //printf("sendbytes = %d \n",sendbytes);- m0 B# C: I5 ~' ^% `
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);9 D9 x8 n2 q, }6 p- X( a: i
- if(sendbytes == -1)
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$ C. F+ E( _. i! c# V" E3 J - printf("Send Picture Failed!d\n");) y+ I% x0 m. c5 A( P% r
- return -1;
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& S {3 n' W: n4 I) S3 d - else) G3 K, |- s& T: i. I
- {' T) J$ f, |* j. ?/ s8 \7 k7 U
- fend -= UDP_FRAME_LEN;
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- }
复制代码
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iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |