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- F) }/ c) O6 p1 n$ N6 Y1 @3 P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.html9 u6 m* I( Z$ Y9 Y f. f
# S) z5 U" s: }- B8 i* 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。
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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。
_- o+ ?1 E1 J* o* u, q一、HTTP网页服务器
! Q* |' |1 ^( e3 b' {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)8 f! M0 J/ y- a8 E& ?
- {
! H2 `9 f: h z9 E5 f - struct sockaddr_in servaddr;
0 T9 v; H+ |1 w& l, p - socklen_t addrsize = sizeof(struct sockaddr);( y9 `" J- ~; A( f+ O0 h! J/ t
- bzero(&servaddr , sizeof(servaddr));
2 @' C$ \* ]9 g# x+ y, _9 x - servaddr.sin_family = AF_INET;- I9 l' Y' Q6 B, w" v* F; L4 y
- servaddr.sin_addr.s_addr = inet_addr(ip);
1 u5 x8 n9 x7 s* { - servaddr.sin_port = htons(port);
% w( @- a9 I" W( _3 X* q - int ret;" J# k" E3 M0 J3 }3 s3 q4 d, }
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)
, g2 V2 Q# J, c- }/ f - {
1 k0 V1 E0 a4 ?1 `6 d - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);& A1 w1 ]" ^. O8 t5 A8 w1 B7 o4 r
- return -1;
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- int on = 1;
( L+ n0 t- s7 e& H' z8 l - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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2 k) [1 N! o- \5 x! Z - printf("setsockopt error\n");5 ?9 G- u Q" j1 o( A- A
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- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
4 ^: J; ?" j& m1 L! j3 q9 F - if(ret == -1)
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- printf("Tcp bind faiLED!\n");0 c% V1 f2 q i, [+ h+ b
- return -1;
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- if(listen(*socket_found , 5) == -1)
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% L3 b `& J( ^0 ]. q2 f - printf("Listen failed!\n");
' M$ U. v; p$ P( R' g- T. w - return -1;
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- return 0;( U4 v+ C2 a" J4 m D
- }
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);; j0 v- Y: F' } q8 e2 v
- void * Thread_TCP_Web_Recv(void *arg)% J( S5 d V# w) M Q P8 K% i" F
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- 。。。
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- {
3 U/ J8 Y- i9 G' ^ - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
% A3 k( O/ O1 h2 G, S - printf("fd_socket_conn = accept()\n");
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- recv(fd_socket_conn , recvbuf , 1000 , 0);& z, a( v- K& K$ \* @9 b+ D V; r
- }
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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( C, K4 Y+ V3 d0 ~9 ~% W
- pic_tmpbuffer = pic.tmpbuffer;
]; z. G! D7 Q- g - pic.tmpbytesused = buff.bytesused;
2 b* B+ Y! z" b, {1 Y - pic_tmpbytesused = pic.tmpbytesused;" G, w$ k' N9 v& v- v
- pthread_cond_broadcast(&pct);
& q( U$ G6 E& B7 V7 E - 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;
2 ?* c% ]9 I! t" ? - pthread_cond_t pct;% u9 ~; U. O7 I F) V( d8 }4 E
- int main(int argc, char* argv[]). R2 B a6 k) s) K0 J1 Q" f
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- TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);0 w8 d L, P. `' F
- pthread_mutex_init(&pmt , NULL);
5 U! K5 f, H1 j$ {+ Z9 G5 U { - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);3 I3 z; t# E+ \' G: ^) Y# s$ p( Z
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);! N- [/ ?; d+ w' ?, u- `) ]
- ...- R0 A9 \6 N4 p& {
- while(1)) o; w6 |& V* @, M5 A
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- V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);
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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;"># D a1 ^+ Z. p, `
- </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" \
; ^0 T/ Z9 |. N! S( ?- D - "Server: MJPG-Streamer/0.2\r\n" \) ]) T7 H0 M9 Z, c
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \% T3 j9 F# _( K! P. E) [" k! ] H5 J
- "Pragma: no-cache\r\n" \
% ~- C. g c7 i- ~ - "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"% H; N7 }8 y9 y) ], C, n t( _
- #define BOUNDARY "boundarydonotcross"
( U/ X+ H; `0 u& z: j# M# P' b1 }3 w - printf("preparing header\n");" z8 S" S% f! b8 h' G6 E0 D
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
$ H6 R% ?( U L - "Access-Control-Allow-Origin: *\r\n" \
( n% [: q: G' v0 g1 I9 m - STD_HEADER \
! s3 m; ~0 \5 U1 O; Q - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
1 o( ^0 B; Q/ W; U: q1 b0 s - "\r\n" \. X) }' @. [. [
- "--" BOUNDARY "\r\n");
) k/ Q- ]; n/ h N - if(write(fd, buffer, strlen(buffer)) < 0)
" N' G2 p3 c0 |6 b7 ` - {
" N! S3 I* p3 |% s7 ~ - free(frame);
8 t( \/ _2 b( B" |7 l - return;
6 h9 S2 U* P! T' H - }
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" \
4 ^' p8 a5 \! O5 B - "Content-Length: %d\r\n" \" {1 y) T, J0 k9 T b
- "X-Timestamp: %d.%06d\r\n" \3 O' j' H- R4 d0 d
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);- C+ E) Q4 ~- O3 r6 ~) H/ l) {
- printf("sending intemdiate header\n");% l, w( `/ B0 q
- if(write(fd, buffer, strlen(buffer)) < 0)
) L1 u0 R) a/ N - break;
1 H6 I, T) F2 E0 { - printf("sending frame\n");
$ J) ~* i4 ~3 A, W% A4 ]( J - if(write(fd, frame, frame_size) < 0)
! u& K4 j% \7 o! C9 O4 n6 x' [ - break;
; S3 n% n J: |* r6 V; F - printf("sending boundary\n");
; @2 g2 N5 J% W2 z. ^) r \6 a; \ - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
2 Y" S: h" @0 |! w - if(write(fd, buffer, strlen(buffer)) < 0)' D$ l5 i2 e9 L [6 j* 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:
. C7 j3 i9 x# b( m- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)
4 I4 J$ M$ z8 N$ S$ o - {
' V3 S# m; w5 z0 }. n; p3 Q - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);$ ~6 q) F! E' }) A
- if(*socket_found == (~0))
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- printf("Create udp send socket failed!\n");' K! n' g, t3 n& Q6 n
- return -1;
! k% R7 n' u7 B E - }
. T# @8 C, A2 X/ v* ]' c - addr->sin_family = AF_INET;5 C; X( W; R" W: T
- addr->sin_addr.s_addr = inet_addr(ip);
' V) i5 O! Q O - addr->sin_port = htons(port);& w% C! r6 i7 _2 \ T6 y7 i/ U
- memset(addr->sin_zero, 0, 8);
- q" i4 ^# m' M* ?1 }" O - return 0;4 P" D; d3 z6 z* g+ M2 P! P
- }
复制代码
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! m$ _: Y4 I: q% m! @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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7 r6 x. y! ~4 I9 Q7 ~5 c0 t- while(fend > 0)( t# w0 \1 `2 i8 |7 F
- { m# a ]: y$ N6 u8 X. o: u4 x* O
- memset(picture.data , 0 , sizeof(picture.data));+ V5 I8 F' O: V7 ]
- fread(picture.data , UDP_FRAME_LEN , 1, fp);
0 A6 f, K: X, m - if(fend >= UDP_FRAME_LEN)& S" _/ o/ W% }
- {$ C6 ^3 w- c' Z0 _- t1 K- n+ M
- picture.length = UDP_FRAME_LEN;
) ?: g" P8 \5 q0 z1 x - picture.fin = 0;' o% x) n `' H' y8 e3 L0 F$ N* z) i
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- else
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- picture.length = fend;6 Q6 |2 Y- { p% V$ o& y
- picture.fin = 1;
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- //printf("sendbytes = %d \n",sendbytes);# E5 y0 X& R& E
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
1 Z! v( o( F' ~" U - if(sendbytes == -1)
7 a# M# ]2 s+ ]+ S, e \ ~ - {
' S O1 V: L, F - printf("Send Picture Failed!d\n");
* l, |- M2 M7 b! l - return -1;
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- else8 o5 z+ z: n! E3 D# g! c
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- 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 |