本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑 : z. `+ c, p) w" i" D1 b7 B. k
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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+ m1 Q; _: n. ?; l/ {: Q) B% L
" k) E2 x/ u+ |5 m- Q* P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。 & I( ]& y( b& l- o
一、HTTP网页服务器
2 `% S& @# o- b" s. {/ A# j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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; y- J7 h2 i( A1 D7 F: y - struct sockaddr_in servaddr;, k; r2 ]6 ` ?; Z6 N' b7 S3 Y B
- socklen_t addrsize = sizeof(struct sockaddr);
5 p% B5 s" |2 r: U) c, z - bzero(&servaddr , sizeof(servaddr));# |, Y; O% S& C
- servaddr.sin_family = AF_INET;, f8 j( O, D2 N* @2 q
- servaddr.sin_addr.s_addr = inet_addr(ip);7 C2 F! D( X0 ~5 [: W& W/ `3 C1 a
- servaddr.sin_port = htons(port);2 o9 ^9 f7 D5 J/ a1 g& P4 H! b5 m% f
- int ret;, f. b3 I3 |3 u
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)
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- printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
8 A& q0 n7 Z B# y6 |% V% r1 ^$ s - return -1;
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$ P- b3 W4 V: c# b& ~ - int on = 1;1 h3 O' w1 r5 ]; K
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)4 T q( @: T) n; m8 _
- {
& `& S5 a' _* |+ Z; L - printf("setsockopt error\n");9 m( }+ r0 W' @- u
- }4 k$ R9 p' M6 N* Y2 K9 B
- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);1 |& L ]8 v7 n, p! [: \
- if(ret == -1)
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- printf("Tcp bind faiLED!\n");( b+ D) Y8 ~5 \ e
- return -1;+ z5 `+ O( s' j
- }
! @ _/ m+ ]% c- y6 @8 s3 K9 j, R - if(listen(*socket_found , 5) == -1); p2 Q: ~, j$ N% H: \! C A! O
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- printf("Listen failed!\n");, D5 S0 T2 M. Y2 k) M! P
- return -1;! r1 K0 C0 q" t6 _ H1 F
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- return 0;
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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);' `' L! I7 y0 A% j; C, p2 f
- void * Thread_TCP_Web_Recv(void *arg)
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- while(1)
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- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);/ ~2 |, R% M( I: @( M1 S
- printf("fd_socket_conn = accept()\n");
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- recv(fd_socket_conn , recvbuf , 1000 , 0);: e5 E9 b0 m" d$ G f
- }
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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# ]( @1 L) D5 Q- H0 B: \5 Q
- pic_tmpbuffer = pic.tmpbuffer;& i9 m9 {: Q, A
- pic.tmpbytesused = buff.bytesused;4 l* M3 e& Q& B8 _
- pic_tmpbytesused = pic.tmpbytesused;: n: |4 ]7 U2 c
- pthread_cond_broadcast(&pct);
7 b4 S2 n: p% K, y; n$ b - 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;
, m- ]- y+ a* H. T - pthread_cond_t pct;
: @# H% \! ^; A$ A1 w! R1 L. f - int main(int argc, char* argv[])
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3 e i$ z5 w: S6 B2 x* R; w) G& `/ b; m( g - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);/ L8 E0 |3 M, {$ \1 M( \* I
- pthread_mutex_init(&pmt , NULL);
, ]) F2 @" h9 P/ C# c( e8 F - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);
# U! J: g4 \% M% q - pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);- S3 W+ o) M( O6 Q( q- q( P
- ...
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- V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);. s M( H& u% L- ?1 _: G. e; `
- ...
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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;">
1 U1 s* x5 X& ]! y7 R - </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" \
( ~8 C/ w j3 W - "Server: MJPG-Streamer/0.2\r\n" \
4 s% s B6 Y% C8 j h2 ]6 n- D% R - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \9 L+ l9 S7 g+ G9 ?9 D6 E2 F
- "Pragma: no-cache\r\n" \
5 y& e4 J2 F& G/ G - "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"$ I. x7 ]+ e* n- T5 S9 q
- #define BOUNDARY "boundarydonotcross"
3 E; c' J: h; h- j. Y - printf("preparing header\n");
. N3 q6 H, J4 p/ y2 |8 M - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \, J- [ c/ {) u$ Z5 L
- "Access-Control-Allow-Origin: *\r\n" \
! p1 _, b/ Q, R* ~0 m - STD_HEADER \
& j0 g3 B- _; f9 k8 k - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
2 ~# i5 B; i0 f& { - "\r\n" \0 n0 d+ {( X; [$ c: y
- "--" BOUNDARY "\r\n");: P" f! L8 ]0 l8 D$ C
- if(write(fd, buffer, strlen(buffer)) < 0); @% W Q) I! L6 y
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- free(frame);" G$ ?: Q4 H/ g' Y* P
- return;% j: r# D, ^) Y2 b* f
- }
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" \- J( w7 V4 {! v4 Y9 A
- "Content-Length: %d\r\n" \% c' x5 F, N- l# b9 u6 M W! I8 n
- "X-Timestamp: %d.%06d\r\n" \) r% l% Z/ x' \8 M0 y: j5 O4 K
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);: h) i9 h* f5 W" q9 o
- printf("sending intemdiate header\n");
% E5 t1 n- G: H' E& Y7 ` - if(write(fd, buffer, strlen(buffer)) < 0)% j6 q. V( V1 f
- break;' M! a% l+ x9 n
- printf("sending frame\n");0 ~* @( a8 c% w. H, k' Q1 h
- if(write(fd, frame, frame_size) < 0)% \- U1 M/ R7 y5 A9 W% F: C
- break;% ?' I. o. D: u3 W `7 Y( F% u
- printf("sending boundary\n");# Z/ U4 S% G: G% l! ~
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n"); V* C3 c; |: M! H5 m9 n
- if(write(fd, buffer, strlen(buffer)) < 0)
& S4 S+ P7 }6 I0 @ - 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。  3 \% y' Y. g+ W1 g
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二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:* ?1 F, v3 m1 C5 R! ]. j
- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)4 D; h! [$ J, W0 O& u T" S4 k
- {
# r* Q0 ~2 ^$ j# ?: \( P) Q- \; O - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);, n) e9 b5 s( L8 N
- if(*socket_found == (~0))
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, c5 R* n$ K e8 h; d* W - printf("Create udp send socket failed!\n");+ ]3 T* }5 O7 f& I
- return -1;, V) Y! P- P% {" q* L. `
- }
e6 C! M6 T+ A; F - addr->sin_family = AF_INET;0 L7 ?' `$ A/ \8 s
- addr->sin_addr.s_addr = inet_addr(ip);' R9 [; w# I4 w6 Y1 V
- addr->sin_port = htons(port);
2 @+ [/ E* |( Z( I; P5 u - memset(addr->sin_zero, 0, 8);
6 v9 c7 l& o# v, | - return 0;
# y& H6 p3 L# ^7 |9 q - }
复制代码
1 n( `" W$ @8 k9 H5 X! _
; e! w7 J5 A& S. o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:4 m# p0 Q6 {0 U* y
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4 D. d1 Y5 K" P' m$ w+ G& {- while(fend > 0)+ ?9 R" i |- |
- {7 d: K& G' U8 H7 f5 Q* w% {
- memset(picture.data , 0 , sizeof(picture.data));" f' h8 R# O/ Q
- fread(picture.data , UDP_FRAME_LEN , 1, fp);3 N/ ~0 r8 k( W4 W F4 F7 a
- if(fend >= UDP_FRAME_LEN)
! Q' J4 e5 o) m - {
+ l3 M3 F4 T! b* j ^0 Q - picture.length = UDP_FRAME_LEN;
0 X% g7 ?9 h( _2 s! d$ X1 k- p - picture.fin = 0; Q" J/ u4 d5 ^+ Y4 N
- }
# K: |/ o5 H( M - else
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- picture.length = fend;
0 a ^/ X5 h2 D( G) v1 A! x - picture.fin = 1;
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- //printf("sendbytes = %d \n",sendbytes);
# f' c2 H$ e& k5 r# v - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
4 J8 i/ D/ |3 @6 _+ S2 r9 C - if(sendbytes == -1)
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- printf("Send Picture Failed!d\n");
! ?5 J$ t, w1 K: v- i/ b - return -1; M' s2 o3 Z/ D, e
- }
, Q1 y' ~* P; P - else/ ^1 t" h8 I/ @7 h0 C8 `$ [) Z o
- {
7 M( F' w, ^! H6 k6 ?- \# Z - fend -= UDP_FRAME_LEN;
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复制代码 . \' Z0 q: S# F! A
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iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |