本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑
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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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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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9 e x( h" C. S( x2 a+ u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。 2 D. w0 u* D/ C w) _
一、HTTP网页服务器5 Q1 j( s7 @6 p6 p$ x9 O
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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# M) A) a( Q! Y, j, y" a: L' T9 ]) ] - struct sockaddr_in servaddr;
4 b! j, |. u/ o8 y - socklen_t addrsize = sizeof(struct sockaddr);
! m2 q& w1 x6 e" m0 [ - bzero(&servaddr , sizeof(servaddr));& f2 f; h4 g# W# ]/ s" v
- servaddr.sin_family = AF_INET;
4 N0 x' ^! X% p3 q; Q! A - servaddr.sin_addr.s_addr = inet_addr(ip);
, t7 O- ? D' Y; ^ - servaddr.sin_port = htons(port);; R" B. ]3 b/ Z. N$ A1 M. u+ n
- int ret;/ u/ S8 e+ A% e2 T& v3 W
- 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);. s' c' q5 A+ z( R! \, I
- return -1;
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1 s0 } F$ t/ G, K - int on = 1;
1 a( K& H0 t9 y5 H; |; I" T - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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- printf("setsockopt error\n");
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6 ^* u9 W* M' _3 A - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
. ?: |+ a Y- J+ A. U - if(ret == -1), b8 ?$ T0 Z1 l: h4 e( G
- {
6 F3 x2 w3 L- L) f, ?# y3 F - printf("Tcp bind faiLED!\n");
; q4 Y& p. h P6 B/ H0 E - return -1;$ E& Z2 g9 [% T' U; _
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- if(listen(*socket_found , 5) == -1)0 f3 v) r6 t0 J( }8 T! t& r# p
- {9 b" e7 w2 m% W: j4 {
- printf("Listen failed!\n");/ A# m( D, B9 O! p! Z L
- return -1; U2 Z) K- p+ J" w" C& @
- }
5 ~4 t+ d& a8 l2 f* N - return 0;% R8 C" _: Q6 B! l& 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);
: i; w4 J, y1 d) K) f - void * Thread_TCP_Web_Recv(void *arg)# s% } r" S: A% S8 E* C+ i
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- 。。。
, y6 N+ H/ d2 e# V. } - while(1)" c. t, S0 h) S. R) ^
- {
2 V' t$ f7 K: j$ t( F# C% ` - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);4 c- X/ t5 Q) E
- printf("fd_socket_conn = accept()\n");9 Y( V" D8 [( i! d" V
- 。。。& [3 c& j D1 q V" U/ l: y7 C
- recv(fd_socket_conn , recvbuf , 1000 , 0);
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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);" t$ I |/ }2 ~* A" D$ `
- pic_tmpbuffer = pic.tmpbuffer;/ n$ r+ ~# P: B$ j* i+ ~% }! _: b
- pic.tmpbytesused = buff.bytesused;
* u: s$ B- d2 @2 h& s) F - pic_tmpbytesused = pic.tmpbytesused;
4 l6 F3 Z; T% |4 ~' a' C - pthread_cond_broadcast(&pct);9 c9 j* x, v& F4 y. 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;
* ?% C1 F/ y8 t - pthread_cond_t pct;- g7 c$ P2 V& ^" \! P
- int main(int argc, char* argv[])
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- TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
2 A/ h' Y, z* V - pthread_mutex_init(&pmt , NULL);- y2 u1 u3 n/ V
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);
. }. G' M/ \% b7 _/ g - pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
9 s: k1 n' H% ~ - ...
3 D8 k. h4 D' \7 y* F - while(1)
7 W% `1 R Y3 k; L - {
6 M7 f3 T) U9 a9 h3 j6 C2 b - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);, {" | w3 s- L2 m9 r
- ...
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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;">) J$ K' R- H4 {0 c- ^7 ^# f
- </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" \) b! |5 d. Y* e- [
- "Server: MJPG-Streamer/0.2\r\n" \
; `2 y5 x- Y6 F/ m. b - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \6 [: g" u3 U Y( J
- "Pragma: no-cache\r\n" \: D9 E0 k: ]0 E6 x5 | a1 B+ D
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
7 {' e# b) E* G% r8 [, S# U - #define BOUNDARY "boundarydonotcross"8 w# P4 V {8 f
- printf("preparing header\n");
# B+ a+ M. F8 g6 [$ o9 V - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \* p$ U. j! t. c' R' d
- "Access-Control-Allow-Origin: *\r\n" \
& Y2 O8 F) F8 V( V% \, D _ - STD_HEADER \
# R" a) M. X2 Y' o6 n - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \* d3 N1 r, D/ r7 b% ?+ W5 V1 x
- "\r\n" \. l0 M4 F5 F- V1 J V9 |$ G
- "--" BOUNDARY "\r\n");+ e2 t5 h( w, S' C
- if(write(fd, buffer, strlen(buffer)) < 0)- T) @ W s7 S% G5 J, W: c
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- free(frame);; u( Q- a5 X6 ~' s6 B6 p
- 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" \
+ Q0 U+ |6 A; B& m! j- ` - "Content-Length: %d\r\n" \, E( U& }/ f3 x7 I1 C6 Z
- "X-Timestamp: %d.%06d\r\n" \
" a1 e( r& B8 g0 z& ]7 S - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
5 l. I, h7 B8 q$ u" W2 p h - printf("sending intemdiate header\n");3 K7 K& `% x# M n5 U3 X: r/ U/ a
- if(write(fd, buffer, strlen(buffer)) < 0); E3 k4 g# N% ^9 J+ R) j
- break;
. r) Z0 |$ J) V. I3 w - printf("sending frame\n");
# [* P% @- Y/ X$ q) d* O; D - if(write(fd, frame, frame_size) < 0)
, c! |7 r" L4 o1 u5 g3 o( U8 c( U - break;
, w1 H R" c; l1 i- d8 `1 _% o1 D - printf("sending boundary\n");
4 D6 _" v4 n& n, }& ^& Y - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
, F7 u2 ]8 k3 R5 Z - if(write(fd, buffer, strlen(buffer)) < 0)
. r2 e- o: l. m Q; T& B* V2 Z/ b - 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. n( d5 P# e# |6 X5 a二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:- b; Q4 j l# G. Q5 I
- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port) m2 Q" ^( F2 D2 \5 T* t) r
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- *socket_found = socket(AF_INET, SOCK_DGRAM, 0);
2 r4 ]+ ?2 @) {: A) g) u! |9 z# w% ] - if(*socket_found == (~0))
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+ K& l- _/ |: |. b3 }! i+ c- g - printf("Create udp send socket failed!\n");; O% s% h/ p {2 e L* Q; F
- return -1;1 M2 b l2 T3 m3 C9 n, Z: i
- }5 K* g' Z7 A8 c& ]2 g6 {
- addr->sin_family = AF_INET;2 Z1 E Z$ d" z* L
- addr->sin_addr.s_addr = inet_addr(ip);
7 {; N6 I7 ?$ O - addr->sin_port = htons(port);
0 l+ K- Q: m7 _6 `1 j: q* e - memset(addr->sin_zero, 0, 8);9 J& j; e9 I, S" O
- return 0;2 w; N) {4 q0 l
- }
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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: i) A: L, r4 C# F8 f
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7 D9 w" k5 }4 _2 k# l5 K5 |! h; {- while(fend > 0)
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- memset(picture.data , 0 , sizeof(picture.data));
' \5 f. \# L2 `; j) t - fread(picture.data , UDP_FRAME_LEN , 1, fp);
* G; U) l3 H. e( g - if(fend >= UDP_FRAME_LEN)) B B8 \+ s H0 x5 a B% K l
- {5 K% e0 ?; N p! ?+ m! J o9 v
- picture.length = UDP_FRAME_LEN;8 z x" `" a) J* `# N7 Y8 f& O. E
- picture.fin = 0; i- b* i) t! g6 Q& o, W
- }
8 r1 Y6 e- s X1 k - else
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- picture.length = fend;
( i8 B. z1 K$ \5 S3 } K) M. U# b - picture.fin = 1;
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5 i4 R: {2 y, G) A# V5 E& ? - //printf("sendbytes = %d \n",sendbytes);
% Y1 F& K6 R0 K1 k. e - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);- x' @' T" \; o% B( S
- if(sendbytes == -1)0 D' D+ [7 c' ]
- {2 U! Q1 {( _& t
- printf("Send Picture Failed!d\n");& w9 c$ d i+ Z: r$ _- l m8 n
- return -1;
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- else+ J) c6 `8 [) b7 s: s
- {+ M% v/ t, B# n9 W6 \
- fend -= UDP_FRAME_LEN;) Q% ^- ~' P9 _) R% G
- }
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复制代码
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2 W" c9 a# [: N0 t2 R$ n" XiMX8MPlus 核心板: https://www.forlinx.com/product/136.html |