本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑
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; W$ @0 B2 k* B0 J; h( J2 t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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/ b P" c& |' j$ G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。 3 N2 n: I+ T ?3 o2 k& K* D+ [$ p4 W' [

2 F1 w- n8 s3 r: K7 Q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。 ]3 {' n& ?9 X; h+ ^" S
一、HTTP网页服务器- e& X) {" _; d7 ?/ k+ D2 }- T/ v! L
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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- struct sockaddr_in servaddr;
1 O7 W; X% [$ H; J2 j- S - socklen_t addrsize = sizeof(struct sockaddr);
, C; r2 q& D* v5 w - bzero(&servaddr , sizeof(servaddr));' c! o7 Z# \' v* G6 o
- servaddr.sin_family = AF_INET;
4 x- W$ Y4 y3 G0 P) w3 n% ]! j - servaddr.sin_addr.s_addr = inet_addr(ip);
+ v3 D. q1 @9 F I" } - servaddr.sin_port = htons(port);; T+ W- t* G9 r, F5 h
- int ret;! q' q, I7 G. H l% M1 W
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)
0 G- ?, b+ U5 [ - {
( u/ D. R9 S2 O$ `8 _' V$ ]& b: } - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
. K+ W( ]/ X- E& u5 I+ ~ - return -1;
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8 a3 z, p5 `/ E* e) c p8 s - int on = 1;5 _/ I# q# U# k, V
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)1 S" T. C0 l4 X* J9 O, j
- {
1 G, P2 U& u: N8 f o - printf("setsockopt error\n");" ]5 o3 s2 u% w
- }; J ]; |$ V/ h$ o0 P$ z+ ]
- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);) I+ K1 P; y5 S. N9 i
- if(ret == -1)
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) d6 `1 L) r; M) \" Q! ^+ n" d - printf("Tcp bind faiLED!\n");4 w+ q7 X) ~' V4 S/ F, w
- return -1;
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5 i- n2 A& r) v; ] - if(listen(*socket_found , 5) == -1)
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, B% Z8 F$ C, D! I, e - printf("Listen failed!\n");
& ]! R9 B# p0 @* Y2 q - return -1;* m5 L2 i" h3 L: q7 D( }9 s
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- return 0;
1 S% L# A" O; t5 } - }
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);
" Y. Q8 a- Y, ]' A2 K$ o' Z - void * Thread_TCP_Web_Recv(void *arg). S# D+ X& |" ]% m, u
- {
0 ?7 Z5 W. ]4 t% E2 b2 r - 。。。" c. I, T6 m3 ~
- while(1)
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$ w& y6 N6 p4 w" a - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
/ a7 o- Q' \6 E1 m' y - printf("fd_socket_conn = accept()\n");/ N9 I. Y0 ?$ r0 ?: K7 X: Q
- 。。。' \. b2 w, r: ^7 J5 A. O( y
- recv(fd_socket_conn , recvbuf , 1000 , 0);! e) A- ^7 d& q
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- 。。。$ a2 @3 \6 z0 `, N! m. v5 m$ t) w
- }
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);" n8 V# [9 J4 O, _9 R3 b" o# D
- pic_tmpbuffer = pic.tmpbuffer;
9 K- H4 h) R/ q+ S - pic.tmpbytesused = buff.bytesused; b6 q/ K R6 S2 v: w9 p
- pic_tmpbytesused = pic.tmpbytesused;
1 b4 a! m( I0 O( e - pthread_cond_broadcast(&pct);# M1 C p0 a& E6 B) Z
- 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;, K) e) i% U* f( Z! K% A
- pthread_cond_t pct;
) Z. w+ M5 X2 V) Y - int main(int argc, char* argv[])
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- ...
0 R! n( W6 p0 c2 M8 P# T - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);" a, G2 f: m3 \0 }+ w/ h/ d
- pthread_mutex_init(&pmt , NULL);# y6 S# ^1 a4 x, v Z i- K
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);
% P( [% x3 |1 s) N+ t; R, r5 y; h - pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);- C% t6 J8 g0 z% H1 ~
- ...) s- M @6 F1 E
- while(1)$ q3 P; A8 H* I. u
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- V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);
0 F, q' T# V6 `7 e2 L - ...
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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;">" s6 g2 ?1 W m" t* O: T
- </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" \
% u" c1 x7 [; Y+ b8 G* _ - "Server: MJPG-Streamer/0.2\r\n" \% _+ D3 |6 @6 ^7 |
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \/ t+ X& i* B0 j3 P) I
- "Pragma: no-cache\r\n" \! x4 t! N5 O Q: h$ u9 M. y3 X% |
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
: D3 [$ ]+ \; m: j% n& G0 [: D* E0 } - #define BOUNDARY "boundarydonotcross"
7 Y3 y- b7 z% `* z* P5 `) R- P - printf("preparing header\n");
& w( o: |$ f. v* y; j7 {# K - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \+ T! H) Q: s$ y
- "Access-Control-Allow-Origin: *\r\n" \) R$ F) }% Z- O4 H3 v s
- STD_HEADER \
, @/ [$ g/ F, y" b6 q0 a - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \ W; s+ p3 \$ ]4 p) n
- "\r\n" \" ^! G, Y" Y* d7 t4 T
- "--" BOUNDARY "\r\n");
9 l% o8 D) n3 X" \) l6 Q - if(write(fd, buffer, strlen(buffer)) < 0)
4 D; h7 L8 g- D& M+ p - {
: ?0 C/ R5 i C( u5 S) R* N - free(frame);
$ R# J9 w& Q4 B. l4 g% C1 Q1 Q+ W/ \ - return;
, _! @& s3 T, ]/ y - }
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" \
3 o+ c E2 I( a- `3 U# Y8 r5 j - "Content-Length: %d\r\n" \5 B% Y4 h+ K4 Q
- "X-Timestamp: %d.%06d\r\n" \1 b( ^6 m3 g3 _) x! T1 q) T# V/ }9 K
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
5 b; N( g3 x/ `& { - printf("sending intemdiate header\n");8 Y: N7 F4 v L
- if(write(fd, buffer, strlen(buffer)) < 0)
: Q5 r5 k1 d. s e1 j) l9 ?- C% L - break;
$ B1 n2 a: a# W- N R* @ - printf("sending frame\n");
- F6 b) I8 ^6 m- f7 M - if(write(fd, frame, frame_size) < 0)0 m- T2 k- A1 y; b
- break;
- n1 S6 @2 S# \% q - printf("sending boundary\n");
! S: M- ^7 o% x! r' D - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
/ I/ M/ b6 w0 Y$ R8 g6 K" k8 [ - if(write(fd, buffer, strlen(buffer)) < 0)
; T; B! T. G' j" S( C4 `- v& a - 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。  * }2 l8 \% k9 G# i! ~4 s
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二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:
1 F3 b; K/ O$ |7 l- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)
# { X+ f0 c, N6 O: W! U6 m - {2 n6 P9 b6 f# y) D' m
- *socket_found = socket(AF_INET, SOCK_DGRAM, 0);1 {9 @" ]* ]+ E* g& q
- if(*socket_found == (~0))6 V; R5 ^1 i) T, L. l
- {+ ]7 n! N9 s/ P' i
- printf("Create udp send socket failed!\n");, v. [% i3 w) O. u/ l
- return -1;
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- addr->sin_family = AF_INET;( x2 A) J, X9 c: {4 ~: O; C
- addr->sin_addr.s_addr = inet_addr(ip);
& q" W+ b1 O3 g* x6 k& e - addr->sin_port = htons(port);0 f8 b& g5 o" n1 A! P6 \( s7 }
- memset(addr->sin_zero, 0, 8);
9 _) h7 C& k5 A, p, K9 W - return 0;
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复制代码 8 H1 J9 u) S7 n
L9 R0 V8 H4 K# e6 ?7 W! f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)% T2 B! H1 D. S1 ?% o% q
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- memset(picture.data , 0 , sizeof(picture.data));
" @7 n1 Z2 l, E* ~5 G; l, ~ - fread(picture.data , UDP_FRAME_LEN , 1, fp);
4 H9 j. m: y9 J. B$ G& Q - if(fend >= UDP_FRAME_LEN)
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f8 Q8 n4 w2 U- y2 J' \7 A& o - picture.length = UDP_FRAME_LEN;; M" G3 p/ `, @ H2 U
- picture.fin = 0;
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e2 E( b3 ^9 w b - else
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- picture.length = fend;
# h* X& }4 D F, A! _& l9 w7 } - picture.fin = 1;" Z |( x1 z- q* N! a
- }
^$ P* W, r% `$ W0 A& c: h - //printf("sendbytes = %d \n",sendbytes);
# M( \' M. S! f1 j, I+ g5 B - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
2 c& n4 H6 V. E8 f' F2 _4 w$ B* Q - if(sendbytes == -1), Z4 ]' E) T* B! Z( I2 p5 S* f5 H1 ~
- {: ]+ o; y9 n1 Q/ P9 R
- printf("Send Picture Failed!d\n");- @. k4 q& Z& d
- return -1;
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- {
+ U$ v0 ^/ Y' V- P - fend -= UDP_FRAME_LEN;3 e; x3 h/ p$ k% {, y
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- }
复制代码 / @; d& N' t- G: K
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2 @* c/ H3 Y% }6 Y! TiMX8MPlus 核心板: https://www.forlinx.com/product/136.html |