本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑 " q; \" n5 C Q" B7 y
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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
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9 C, V, K# c" N4 A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。 8 B6 [; X6 w% V; [: ^/ _
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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。
, v: A& {- ^! H7 b) ]7 Y* T6 p一、HTTP网页服务器
0 _" v4 Y/ Q7 v6 f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;6 y3 B( |& |# h8 R X$ s$ o4 p
- socklen_t addrsize = sizeof(struct sockaddr);
? a( ~6 `) I% @' W$ o( i! V - bzero(&servaddr , sizeof(servaddr));
$ u: e- F; s: \ - servaddr.sin_family = AF_INET;% u. ?4 B7 }1 q0 y9 Q& c
- servaddr.sin_addr.s_addr = inet_addr(ip);
* C1 R& k5 U# P. E, t - servaddr.sin_port = htons(port);7 m, Y$ a* u2 n. @9 f
- int ret;, s, O4 S0 z4 r0 v3 U; u
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)- H% s9 C# u7 V2 [7 y; r# Q; \: z
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- printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);9 K6 @0 b2 X* d% @, P7 j
- return -1;
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" k$ z7 }" G; q$ L2 x( J. [ q - int on = 1;8 V1 s" i% C: S
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)& \* v6 T$ S" p2 {0 z- V2 Y
- {
0 G! k0 ~ [* d - printf("setsockopt error\n");
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2 V+ T/ Q' X# f$ O3 `* g2 B - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
- e4 c: k3 q3 b/ E0 J) ? - if(ret == -1)
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- printf("Tcp bind faiLED!\n");
4 a7 E( a0 Y! |5 B" ~ - return -1;
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0 `* p% r% }% v9 U% ] - if(listen(*socket_found , 5) == -1)0 t: L! t4 m6 U! X" B
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- printf("Listen failed!\n");6 U' A# H) b4 @6 W
- return -1;3 `/ @) U5 U% Y2 D* p
- }
_( a# y& P" ?, a0 h. T - 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+ E } { - void * Thread_TCP_Web_Recv(void *arg)
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- 。。。9 g% x: c# S* A9 I: i# z
- while(1)
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1 o% c" m+ x+ t( E9 T' l* r( z - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
: d) o6 r% E+ ]* Y" g" k2 W( ]; X - printf("fd_socket_conn = accept()\n");# m' c. s2 y1 y) d% I/ ?
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- recv(fd_socket_conn , recvbuf , 1000 , 0);. v3 j6 R0 e& {8 u- ~ p" p
- }
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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);* y" e; \% {+ ^0 [: \0 X
- pic_tmpbuffer = pic.tmpbuffer;, L# z+ Y7 E' v# U6 V
- pic.tmpbytesused = buff.bytesused;
8 Z% L# B9 g: A/ D: V - pic_tmpbytesused = pic.tmpbytesused;
: w- |* t3 B/ a; F. I K" e* g& V/ X - pthread_cond_broadcast(&pct);, Z+ N+ [% u/ X
- 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;
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! W3 F+ ^* z& C( m7 | T* u/ m& C - int main(int argc, char* argv[])7 C. }" S2 ^( |0 e
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- ...
& D: ~4 h' N2 s - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);3 d- e! Q _. q# k) c% ^
- pthread_mutex_init(&pmt , NULL);. i- _& M$ K* j) }2 x8 K3 K% `
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);# x! P5 f$ p3 i, M
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
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- while(1)
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" J4 i4 C$ g: L$ o2 V4 o6 e - 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;">) B: |6 m+ P$ R D
- </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" \
. ^3 w1 l8 Q0 T+ S$ P" P- }6 T, j - "Server: MJPG-Streamer/0.2\r\n" \
" r4 S/ G$ ^5 T; j9 V - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
; D- p: ?9 R/ O" h* v7 a' E& E/ U - "Pragma: no-cache\r\n" \4 D( s2 s2 ?: }- V: }; y8 a
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
* b: G% n% R) D5 y, z _: a. O7 x - #define BOUNDARY "boundarydonotcross"
) s( K4 v" Q1 U E5 T - printf("preparing header\n");1 i5 M7 y3 R. ^3 w' D! u
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
4 m$ p4 C, c4 p0 T$ ?! m; h* L' y3 t - "Access-Control-Allow-Origin: *\r\n" \
" V8 S% e" s3 n# D. S - STD_HEADER \
4 Q# k! ^( R6 l5 E2 N; i* i - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
/ b4 n7 i6 v2 |7 ?$ o+ [ - "\r\n" \9 B0 j1 r) A6 F
- "--" BOUNDARY "\r\n");- k+ h! R$ I; t
- if(write(fd, buffer, strlen(buffer)) < 0)0 p# N9 h1 m4 ^3 L" ?
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- free(frame);
5 j# X9 X1 E3 B4 r& C, V. q - return;
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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" \, @! f$ l" |# s6 {& S
- "Content-Length: %d\r\n" \5 H3 i1 k4 M0 s. @
- "X-Timestamp: %d.%06d\r\n" \7 ?8 e) O2 {+ v3 V$ Y) x
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);; c; R9 r5 |# ^+ K
- printf("sending intemdiate header\n");7 S/ Q7 z( K- n& r' A
- if(write(fd, buffer, strlen(buffer)) < 0)
9 i1 i5 p$ n* W6 v' [5 ^ A - break;
4 x; \; a( J% r0 P6 h/ I8 }5 n - printf("sending frame\n");
% R7 v4 c* {5 m$ ?. U - if(write(fd, frame, frame_size) < 0)
, N2 a p6 f, O" Z1 w% O - break;
6 Y5 c) R" G1 r' F6 Y5 P - printf("sending boundary\n");+ G/ H" [7 o# F' p/ g
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
1 P/ S4 `7 A% V. d# _: ` - if(write(fd, buffer, strlen(buffer)) < 0)' O3 P2 f1 ?1 J# i% s# y
- 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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二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:# B! P+ n5 b ~- A2 `0 [
- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)
% F& W% a; S. F - {
7 p# \* l0 j4 I5 v - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);
6 Q; ~) g- _' P B- x. h; D - if(*socket_found == (~0))
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6 x3 y, o0 B" u- X9 a& O - printf("Create udp send socket failed!\n");+ Z2 l3 Q3 T. o5 l( M' x" U
- return -1;
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- addr->sin_family = AF_INET;9 ?. F% W2 `6 o5 i3 M
- addr->sin_addr.s_addr = inet_addr(ip);
1 X+ j6 v a, j' t7 c$ ` - addr->sin_port = htons(port);: t$ P8 B; @) { a6 z9 B6 D
- memset(addr->sin_zero, 0, 8);( I T3 r* v) _- p/ W0 q4 A$ F- N
- return 0;. [$ }# C g% c9 q
- }
复制代码 ' x0 n/ D; n0 j; ?" D* U- I: q% Q
9 B3 Q1 s/ w: j. P0 c! |7 H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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' _, Q2 Z5 |* u9 t# ^5 R) E- while(fend > 0)9 c g: `. X5 R' `) \
- {
+ t# Z0 \' _& P* U4 G - memset(picture.data , 0 , sizeof(picture.data));. ~6 c) L. _ ?% I" k4 v/ ]
- fread(picture.data , UDP_FRAME_LEN , 1, fp);
# L4 T/ \' H7 ?5 _2 q6 L - if(fend >= UDP_FRAME_LEN)
0 }1 w2 e! T! b" U7 r { - {
6 m0 T& R( \: P, y - picture.length = UDP_FRAME_LEN;
. R' ]8 H! A t- [ - picture.fin = 0;/ A# Z0 g7 z7 v4 V, J& l
- }
7 W4 j$ d9 R( u3 K/ R6 T* A - else
1 w6 n0 t" X# W+ ]. l - {
9 Y7 e6 q. o( B4 f3 R* M8 Y* O) F& N8 [ - picture.length = fend;+ I! Q- E# g: |2 S
- picture.fin = 1;% \1 E% U# q8 Z; `
- }
m0 P% Q2 u1 u - //printf("sendbytes = %d \n",sendbytes);. E( N4 k# ^# T5 d( j
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);) _% `" j# ~+ w8 M1 y
- if(sendbytes == -1)
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- printf("Send Picture Failed!d\n");- s* g9 T4 E1 e$ X/ Z. y
- return -1;6 p$ T x$ b: w# g' ` c- p1 ~
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- else
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# ]1 G4 o! x$ l9 Y' \4 g - 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 |