本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑
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& B' _. E6 h6 }9 y0 O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! }# Q7 C! `. T; b9 \
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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。 $ K: e* u$ P$ x2 e
一、HTTP网页服务器
" ?5 h* K9 @0 u5 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)& D, K) B5 v3 G; B" I& @1 L
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- struct sockaddr_in servaddr;
( m: w( _' J; l9 O& u6 R* g+ } - socklen_t addrsize = sizeof(struct sockaddr);
; L" H7 \& r1 H/ b+ r, j4 G - bzero(&servaddr , sizeof(servaddr));
- R& m( K* j `! {7 [4 [ - servaddr.sin_family = AF_INET;: B! \ d; C" W& ]
- servaddr.sin_addr.s_addr = inet_addr(ip);/ d7 _6 _/ @; e5 K; L# Y7 x
- servaddr.sin_port = htons(port);& A+ }6 d( n+ P% N; x& }, F( P
- int ret;
( \% Q0 o( ^ N! P - IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)
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2 D1 K' Q8 F6 G* ]3 L - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
1 _6 y/ \3 w: {) U0 {' M - return -1;
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8 K2 o# L) D0 q+ K u% Z - int on = 1;- h: X9 _. h- A. c* x
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)0 U* y% A' i; P
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- printf("setsockopt error\n");7 C6 e5 {+ a* j1 Y) P3 ^
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- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
( L8 [) n- b" R2 D5 Q - if(ret == -1)
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- printf("Tcp bind faiLED!\n");- _* k7 n2 w q" S9 Y/ w* Z
- return -1;
- u) C2 n& C; k/ [) p4 m/ U - }
3 T/ Q1 Q5 u' E/ p" z - if(listen(*socket_found , 5) == -1)( f+ V- T6 A$ l! P G, e
- {
/ U, n i! x7 o9 ^ - printf("Listen failed!\n");
1 p# s9 H1 U. k' Y) ^9 Q - return -1;8 H4 X" `- P$ V
- }
8 E! l& A- T/ w# a7 h6 z - return 0;
7 [* y0 {$ {9 }/ F3 z - }
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);
0 U" I. ?8 a5 S- ], Q! M1 g# y# W - void * Thread_TCP_Web_Recv(void *arg)
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5 N; S8 E) x i7 o, [4 l) B - 。。。
& E+ l3 i; O" c3 Z - while(1)
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. O/ h2 m& K, I' O1 e - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);. O& H2 s7 T6 y1 L
- printf("fd_socket_conn = accept()\n");
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: ~2 J2 y% L6 k - recv(fd_socket_conn , recvbuf , 1000 , 0);
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- 。。。. u v# t0 n$ w" S* |$ K5 `
- }
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);
! m% F3 J( ?* V" A( F% y" v - pic_tmpbuffer = pic.tmpbuffer;
5 u$ x) W3 U# Q2 Q - pic.tmpbytesused = buff.bytesused;
N5 i% k+ x4 L. i( S \1 H9 e) O- z - pic_tmpbytesused = pic.tmpbytesused;$ y9 m- [: B& k5 U" t$ K2 b& T
- pthread_cond_broadcast(&pct);* I# X0 D$ X- O' L- m/ G
- 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;7 q) C/ l, [5 ]2 M3 O% `3 y
- pthread_cond_t pct;6 E/ u1 p! O, q) h2 w
- int main(int argc, char* argv[])( f Y9 J+ d! r$ t) A
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- ...
- X+ r$ G/ E! o- ]0 J# ^5 E( ] - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
4 h* O! n2 q% ~* T& E: I! ~+ n5 I - pthread_mutex_init(&pmt , NULL);
$ B v+ i2 D1 A( ? - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);- z+ U+ j2 y9 {( J- W
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);) P- z5 \. v! e* L8 B6 O$ J7 ^1 A
- ... X7 M. h+ {1 F# s2 f- ~3 ?$ ]5 j
- while(1)2 v k9 [4 I( Z4 a7 ?8 W
- {
! ?/ R, j. a0 w# s! e) i: m1 a - 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;">7 N7 A$ F! `- f5 {' L% F1 F0 _) x
- </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" \5 f( E( d7 y3 r g5 p' \' D- {
- "Server: MJPG-Streamer/0.2\r\n" \
% }' G7 |+ r4 ` - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
* R* x/ o$ H1 ` - "Pragma: no-cache\r\n" \* s K1 l+ G: \
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
' k9 ~4 L7 m5 W, V1 ~& [ - #define BOUNDARY "boundarydonotcross"$ D+ J5 J8 j3 g4 g0 F
- printf("preparing header\n");
6 \+ x2 s V- N- e1 A* D - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
7 n- d | ?- g) R' m$ Z5 y - "Access-Control-Allow-Origin: *\r\n" \/ W/ W( N- W8 M# _, j9 X4 n! X
- STD_HEADER \
! \3 y& i& Y! p1 H7 f! ]* j - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
, x$ m# q [9 a8 r0 u - "\r\n" \5 N; x" }, W- ?+ s u7 c
- "--" BOUNDARY "\r\n");& Z4 O& {# t) S4 t
- if(write(fd, buffer, strlen(buffer)) < 0)
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- free(frame);
! {: ^$ T0 j/ j+ ^ - return;" i6 k' b& [) p8 j" n y, Q$ `
- }
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" \ k; p0 n s P1 V8 e3 r
- "Content-Length: %d\r\n" \4 v( j+ w2 E& X% l9 J# [" M
- "X-Timestamp: %d.%06d\r\n" \
1 L4 v6 H7 y& G' i - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
. }7 J$ B8 D# m. \/ W3 {, b - printf("sending intemdiate header\n");
# R7 y- |: _; g" e) B4 G# {# U: y - if(write(fd, buffer, strlen(buffer)) < 0)
* U |% p4 n! H: p* M - break;
: b3 z" q4 H+ E0 B - printf("sending frame\n");! ~- v) X5 ]( D# m" i: v+ @
- if(write(fd, frame, frame_size) < 0)+ o Q ]" ?( s& t' m% t# @
- break;4 I# E; O2 V2 X' g: K
- printf("sending boundary\n");6 ~% T9 P, R. W9 H1 q7 h" o3 @
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");1 W; u' m* q% {% C0 H( V
- if(write(fd, buffer, strlen(buffer)) < 0)) W e0 e( X c( r, F
- 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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/ T V* ]' T1 d4 _ f二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:. d' S; l8 s5 G- b; C9 o
- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)3 R8 |/ u" G1 I2 a' Z* r
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- *socket_found = socket(AF_INET, SOCK_DGRAM, 0);6 f! l$ K y" v& U: D
- if(*socket_found == (~0)) v }- k/ a+ u8 w h( L7 j) n
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- printf("Create udp send socket failed!\n");
, j! H% Z* I) C. ~6 r. b - return -1;
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+ p) ]( Y" Z- _+ [5 m. [6 T - addr->sin_family = AF_INET;; H3 Y) S% v: C9 Z+ R# O
- addr->sin_addr.s_addr = inet_addr(ip);3 ^3 \( y7 }9 w5 ?
- addr->sin_port = htons(port); i# e2 W$ {/ r. [9 d0 E! X
- memset(addr->sin_zero, 0, 8);
6 a5 ~; G: x: P7 g. ^3 o - return 0; N+ y* }" N, J) d
- }
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! `; s: k- g& \/ O: f. P$ t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)
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+ Q+ J3 U; U- G* T) L K' t8 r+ z3 N9 p2 u - memset(picture.data , 0 , sizeof(picture.data));2 x; t/ P9 E) `
- fread(picture.data , UDP_FRAME_LEN , 1, fp);6 B! x7 T" U" U5 w
- if(fend >= UDP_FRAME_LEN)
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- picture.length = UDP_FRAME_LEN;
( r2 T3 g1 w; S E$ G - picture.fin = 0;6 f3 o7 f6 c: v3 _9 u
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- else4 u5 V1 }, H+ v# v( O1 [% k7 c
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- picture.length = fend; G# ]8 Q' `3 o
- picture.fin = 1;3 I7 {7 D- K2 R6 k- W+ ~1 X$ |% Q
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- //printf("sendbytes = %d \n",sendbytes);$ c4 X- W3 G0 x5 [
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
6 R& c) }* l8 ?& I& N - if(sendbytes == -1), i4 ~! H. [ P/ M& V6 `9 @
- {
! Y8 z/ `0 U8 N" x - printf("Send Picture Failed!d\n");
1 q2 k4 Y0 Z' ~0 w% R& r - return -1;
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- else
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8 x2 {! ^& R6 B+ [8 G: r- t4 W - fend -= UDP_FRAME_LEN;6 e1 p" D: {4 V+ k( q- [& X
- }
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复制代码 ! R# B% ?/ ~% L0 i* {
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iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |