本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑 E _, g. q1 {% W
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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, y, @9 i O# [
7 M9 ^) L }- ~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。 " Y: Y) }' D* `0 {" g5 f
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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。 : H6 S: I- X! o$ s/ ?# ?. r
一、HTTP网页服务器9 ?; q$ K$ P3 j2 L Y( e' ^, ?
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)
* V' d0 F3 I# \) l' @3 j. \ - {
7 H" y! h$ R, j1 A4 x - struct sockaddr_in servaddr;* t* K- u9 P- o) a; R4 W
- socklen_t addrsize = sizeof(struct sockaddr);
$ H: F) ~& G' ~8 ?9 V/ k* S; \ - bzero(&servaddr , sizeof(servaddr));
. B- h+ y) b8 U! G - servaddr.sin_family = AF_INET;) g& n, a% h; ]- S5 b* e, E, p: W
- servaddr.sin_addr.s_addr = inet_addr(ip);
! _* c- I$ \3 j - servaddr.sin_port = htons(port);& \0 R9 I( i9 E% p J( o
- int ret;
7 y) L* g* ~: i4 \ - IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1) z; P+ z- Z" p7 _6 R* |
- {- ~9 z; U) N* V
- printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);0 c0 B$ K# x) L* |; }
- return -1;5 m' i5 h% k4 Q: v' }( ], e
- }
) Q7 ?0 T J( ?- @: {- a" k - int on = 1;
# ]" K$ {- c6 q: B* h, H - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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- printf("setsockopt error\n");
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$ ^# ^. X- W' B* L* r6 J) a - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);: I# }2 W* F0 r+ o6 S" B
- if(ret == -1)7 F2 A7 V- k/ r3 k0 z! T, j/ H
- {; v' A2 v. B) c. h F
- printf("Tcp bind faiLED!\n");
* M8 q6 _6 ]' l; C1 G - return -1;
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- if(listen(*socket_found , 5) == -1)
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- printf("Listen failed!\n");
' F$ R+ \6 u5 }+ ?' {+ n9 A$ u - return -1;
3 F3 m4 a: x2 G& Z/ E2 P# \/ k - }
/ B- Z% ~: Z! S" y' Y+ _% s! B - return 0;
9 I( i. M& Q0 ^) T - }
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);
( t6 |) n- R1 E7 j0 c3 K5 a; q - void * Thread_TCP_Web_Recv(void *arg)
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* _/ _+ w y9 [% q" l - 。。。& Z5 `* g; j. ~: E$ n& B
- while(1)3 I! V8 m& A5 I( Q
- {
. H+ s; Z4 K: B: |2 n, `+ G - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);2 L4 ]8 ~3 a! k3 ]5 X0 R' x
- printf("fd_socket_conn = accept()\n");* P3 X, {, ` R( n x
- 。。。; k" O. n5 \3 r8 \
- recv(fd_socket_conn , recvbuf , 1000 , 0);& \* f% p. A8 @ K2 W2 H
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- 。。。
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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);
8 i. M/ j i& M9 p) f( t - pic_tmpbuffer = pic.tmpbuffer;; _7 M1 K6 A* R @
- pic.tmpbytesused = buff.bytesused;9 @9 k, ~, i0 h
- pic_tmpbytesused = pic.tmpbytesused;% G' U; y. x$ c- t+ p6 d
- pthread_cond_broadcast(&pct);
! {/ j/ C6 u7 @) |, O* a) w - 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;
; Q* U4 ^) S; K - pthread_cond_t pct;
/ B$ c+ d$ A/ A( j- J3 p \8 Y; ` - int main(int argc, char* argv[])
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- ...
% R* c& ~% r5 ?( f7 e) a4 Z - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
- `, |/ A( _& w, x4 n1 Y/ E% L - pthread_mutex_init(&pmt , NULL);
$ q( }; `' O; L- z0 G/ a - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);
0 m( I7 x; m3 j, x. t - pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
" _) K& c+ R- p; l0 a& t - ...
* }8 H+ s" |* Q) x, @ - while(1)
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3 i @- L* m- O; G. I - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);
- F6 G2 n7 e. Q - ...
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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 X( _. L; {- Z# e- E% 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" \
4 E: h% t- i& G+ @9 {' L; ] - "Server: MJPG-Streamer/0.2\r\n" \
o% u" u+ v( w" G, u( ^- r9 T - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
/ F" L! ^% `/ P1 O9 Z - "Pragma: no-cache\r\n" \. z/ j( E3 g( V: g1 J) ]
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"+ Q. t% C: W- O5 {/ Q
- #define BOUNDARY "boundarydonotcross"
^4 E Q. Z# |2 L - printf("preparing header\n");
q+ E; a9 l( k6 W( ? - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \. }# p* E9 [( n
- "Access-Control-Allow-Origin: *\r\n" \
6 H c4 X5 E/ C0 J - STD_HEADER \
: A7 t0 m, I+ s7 Z% A - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
! U; x8 k2 ]9 d. L$ K6 e - "\r\n" \
* ]: q1 [# S; b$ J2 h1 p - "--" BOUNDARY "\r\n");1 ]7 i+ K0 V0 o, M% M. Q% R
- if(write(fd, buffer, strlen(buffer)) < 0)$ O( {$ d! B* S3 }/ n
- {# H' P8 X' Z4 U4 `
- free(frame);
7 @: |' {3 l. G. @" j/ l. B+ D _+ h - return;
% _3 E5 k6 T) r# R - }
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" \/ h7 y+ Q7 [- L
- "Content-Length: %d\r\n" \
$ A2 X5 f9 U) t+ W1 c* M Z+ L2 \ - "X-Timestamp: %d.%06d\r\n" \1 A3 z0 U: ]5 {5 c3 P- }
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);7 Q+ n& n W* f# u9 j9 Z4 j
- printf("sending intemdiate header\n");
" K6 _8 u+ c6 a5 t! [5 ^ - if(write(fd, buffer, strlen(buffer)) < 0)
& N# t/ F* `- C, z9 S& A( D - break;
5 d% B$ l' o, K: \ - printf("sending frame\n");
/ ?& u+ p; L9 e' i& e - if(write(fd, frame, frame_size) < 0)
* e1 h) p, F: `! a' ^( ~5 \1 | - break;
7 g7 `' \2 y" i1 u* o3 L - printf("sending boundary\n");
$ [) ], F: Q" k# ^: k - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
- R5 x* K H4 h% T; R$ `2 b - if(write(fd, buffer, strlen(buffer)) < 0)
3 ~" Y" w4 J2 i, A3 P2 x - 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。  : h* H; |, t0 Y, ?3 c

0 s0 J9 R( U! W" ^, x# T( f二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:: ?% o9 ~" _3 m4 i' R
- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)
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- *socket_found = socket(AF_INET, SOCK_DGRAM, 0);, g) _+ B. c; C& V9 n) B' W: P
- if(*socket_found == (~0))
: H5 _/ M, e6 d3 u3 B - {
3 T# m; m* `/ N K! a: x - printf("Create udp send socket failed!\n");
6 q; R0 |8 ~) i; V) w" e - return -1;
5 q) e! T, G' h1 g: S+ o - }
" S0 T0 f" m2 D! N$ e% V8 W& X - addr->sin_family = AF_INET;
% j& N, W+ A1 F! |2 j7 O. D, L - addr->sin_addr.s_addr = inet_addr(ip);
! R8 Z# h. r3 P6 G - addr->sin_port = htons(port);
8 {$ d8 G/ C/ X1 z+ M - memset(addr->sin_zero, 0, 8);5 G# U4 Y4 J0 s. Q( z
- return 0;
g* `2 h$ l6 | - }
复制代码 * Y( q% v; @: L/ K* D
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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:8 s0 J/ {2 `' ?" s9 U
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- while(fend > 0)
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- memset(picture.data , 0 , sizeof(picture.data));
+ y2 Q) G" s Q/ Y( N- C - fread(picture.data , UDP_FRAME_LEN , 1, fp);
& ?# @9 @" z6 `: Y8 { - if(fend >= UDP_FRAME_LEN)
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- picture.length = UDP_FRAME_LEN;
2 o! w3 R7 W$ X- E& D; m5 T% Y - picture.fin = 0;9 w+ Z4 N$ U4 s+ |- y5 O6 J+ E9 P
- }$ l/ |- m8 p' [
- else/ _/ M% i/ n* C5 c0 S& C2 |2 g& Y
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- picture.length = fend;
& s8 g3 i% s/ A& T! ^/ D, N - picture.fin = 1;
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- //printf("sendbytes = %d \n",sendbytes);( x n2 `: k: A2 Q
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);/ `2 t' l2 {$ j# R: B, ^: \2 `- r
- if(sendbytes == -1): _/ I- k {8 }6 y5 ^
- {
1 x( B+ D5 U- X5 M+ ~0 e - printf("Send Picture Failed!d\n");
& }( j2 T: j H! S+ ~9 a, c - return -1;" t* K( {% l9 [
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- else0 z: |: Y. g& q' q
- {
- K _# Y W! \6 a/ @ - fend -= UDP_FRAME_LEN;
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复制代码 4 J. m5 j# S. d1 l; }' s
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3 S5 l9 K# H1 j) piMX8MPlus 核心板: https://www.forlinx.com/product/136.html |