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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" }/ c: O6 E! |7 W Y4 q
# @6 K! v3 l6 w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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0 I" `' `- l1 U4 P& g t" K$ I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。
4 \5 S1 a+ k. H2 b8 R$ I一、HTTP网页服务器
% T) h8 v' n( 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)8 f, T1 a0 W% a4 E
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- struct sockaddr_in servaddr;
9 K. s: J5 {3 E Y& h0 R1 R l - socklen_t addrsize = sizeof(struct sockaddr);
, P: A( X* u2 I3 ` - bzero(&servaddr , sizeof(servaddr));; ] V: h# R/ N( X' E' s
- servaddr.sin_family = AF_INET;
: V) D! s& s9 N6 ^: ^$ i/ [2 ^ - servaddr.sin_addr.s_addr = inet_addr(ip);
& {7 P; n$ Q' D2 h - servaddr.sin_port = htons(port);
: h1 @0 g8 M2 J$ I - int ret;
8 z; H' M2 A; f: _6 w& u - IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)
; y3 o% r6 G2 w) _% ] - {
& _9 B# h& k- W& Y - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);$ r' k* e5 g2 [5 a0 |! _+ n3 V+ k
- return -1;9 j( j) u& k/ l8 s
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- int on = 1;5 _5 c' ~. n- v: O" i0 a
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)% B4 H& P1 O; p2 z0 n0 c. l! o
- {
) l, s J# u0 K8 u: k - printf("setsockopt error\n");8 N7 K, r7 }0 w Z' P& `$ _) {
- }( Q8 d, \2 ]. |% Z# t; i
- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
! q0 m. d m) l+ v8 g' j: \2 b4 N - if(ret == -1)
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2 z6 [+ c4 Q& e# ^! p( \; e. f2 i - printf("Tcp bind faiLED!\n");: e' v( m- i8 T5 R
- return -1;
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- if(listen(*socket_found , 5) == -1), a# V. y! W; }% h! ?0 z
- {
% `4 [& l8 N8 v n* K - printf("Listen failed!\n");
- I+ e9 q1 Z; ]" P9 S& ]. p - return -1;
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- return 0;0 \" ]# b7 U7 s; m q. N
- }
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);% y6 N2 v' R+ O' O5 {
- void * Thread_TCP_Web_Recv(void *arg)
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- while(1), m3 x, d+ P6 K9 R% k
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- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);6 G9 z b( ?: E: x
- printf("fd_socket_conn = accept()\n");8 z1 y. S1 Z* D' D9 t8 |
- 。。。7 K% p% L$ A. S0 O. l
- 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);: T2 [# W0 u; E; N, u% ~* L
- pic_tmpbuffer = pic.tmpbuffer;
6 f9 K7 f* q) n3 I. X) g0 y - pic.tmpbytesused = buff.bytesused;
0 h) Z9 |1 ?1 W* l - pic_tmpbytesused = pic.tmpbytesused;$ [ V$ }# \4 ?1 y8 L6 k( _
- pthread_cond_broadcast(&pct);) k# d9 C+ F" o4 |5 r' o3 p3 {
- 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;& e5 i6 h5 m4 s S# c, t# d8 Q9 A
- pthread_cond_t pct;
" z) q8 d+ Q7 _ h2 e; u - int main(int argc, char* argv[])
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8 ?, d* x Z! h, v6 G' b8 p - ...
; Y* p$ v6 C; o7 j d - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);5 h: y# ]# s% _( h0 f
- pthread_mutex_init(&pmt , NULL);
7 D* m" {$ T- B) j8 { - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);
4 A. q3 ?7 M; M5 H9 G - pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);1 K) G; F+ I; ]0 l0 K; A
- ...
/ o+ @* S' O' Q f - while(1)
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- 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;">
1 I: T# U% a" r) H7 P3 U# l - </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" \
/ l$ ?5 L. ^& A+ J* n+ l - "Server: MJPG-Streamer/0.2\r\n" \
. S3 u. s) `' h1 B& N( N) _9 y% t - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \) w; @* |; D8 D5 H
- "Pragma: no-cache\r\n" \
+ G4 j, ~% F/ S* p5 R - "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
% b' r" `( I! C2 r3 [8 N - #define BOUNDARY "boundarydonotcross"7 z. s& l W# y( I
- printf("preparing header\n");' H9 m N; p. _3 \& V4 s) d
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \+ W/ t# V0 E+ U* x' s" n
- "Access-Control-Allow-Origin: *\r\n" \$ z3 ~, ]1 A. _) ?1 p. m2 B0 i) a3 w
- STD_HEADER \
* e4 ~6 O- ~; i o, l7 p, G% p% V* X3 y - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
3 Z$ E9 L# J B4 T - "\r\n" \
. P& u% O" S+ [ z1 e4 d2 ^3 v - "--" BOUNDARY "\r\n");4 y( ]8 {. E7 R3 n% b" Z7 J5 _+ i
- if(write(fd, buffer, strlen(buffer)) < 0)5 S( j! l$ E' R) @ g
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- free(frame);
( ^. M& `5 @! `9 W! g" R- p - return;
' ~$ A7 K9 ]4 U- O9 L9 |+ v - }
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" \
, S3 e* K% \ L1 w" V5 G5 q2 e5 } - "Content-Length: %d\r\n" \# w/ n' p. ?$ U% x9 H
- "X-Timestamp: %d.%06d\r\n" \
8 |2 V- s1 n: |! i3 F8 [+ G8 g - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
5 W8 t7 s# u, G5 K - printf("sending intemdiate header\n");
7 s* C4 z6 I' |7 ? - if(write(fd, buffer, strlen(buffer)) < 0)
* z. V8 |/ r% k) P$ P l - break;3 j- ?/ P8 v: S* d2 B) S' S6 p
- printf("sending frame\n");7 u8 q2 q% b9 [6 p: E4 l7 X
- if(write(fd, frame, frame_size) < 0)1 I- ]8 Q7 z1 _: c1 @
- break;
4 Y# P* o4 ^* |# Y - printf("sending boundary\n");
( C% E- o( t: H2 ~% u - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
1 r3 m6 s" T' O' [. x, @: v3 Y+ K - if(write(fd, buffer, strlen(buffer)) < 0), N% D8 v, j9 _. t
- 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:
+ T) S- E* Z& L+ [4 W. r" T- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)$ E4 b# q: ^8 O# B( k( ^
- {
& s7 i5 F( ?/ o - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);# Z3 C! @& a: \: z
- if(*socket_found == (~0))* a6 g. F$ q7 C# P1 j; V7 E# K
- {4 R8 T! ?7 q/ k+ c- i
- printf("Create udp send socket failed!\n");
7 l9 }) }$ l1 S4 q - return -1;
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8 d; d1 @: q# [8 V1 K0 C1 y - addr->sin_family = AF_INET;/ u; n6 x) N u1 r* U; e
- addr->sin_addr.s_addr = inet_addr(ip);
5 H% G3 [4 X& M - addr->sin_port = htons(port);( m& a1 Y, y, p! i2 j
- memset(addr->sin_zero, 0, 8);
+ f, O5 j6 l8 f4 ` - return 0;
* z1 u5 l, Z# g. n: n! F - }
复制代码
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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:
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5 ^6 | n+ {! d8 e9 `' R; i f! j- while(fend > 0)% C$ H8 |" ?4 E; d% R
- {+ F+ N* R2 N% h; f H& r- X
- memset(picture.data , 0 , sizeof(picture.data));
& M6 d; D. o% _, _( Q% s, d - fread(picture.data , UDP_FRAME_LEN , 1, fp);( s$ O- _; t0 k$ D* j7 ?0 e
- if(fend >= UDP_FRAME_LEN)
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- picture.length = UDP_FRAME_LEN;% \- C6 c& z" R* H* r' t) A
- picture.fin = 0;2 ~+ `5 t( e9 Y u2 @8 S
- }
" ]! y3 A% o3 V2 z) \ - else( |' z6 ]# g8 B, W$ v
- {
; k. ~$ e0 e. P3 H8 f/ \4 Z - picture.length = fend;# j% T- X U" A3 ~# v
- picture.fin = 1;
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/ e% B+ a( ~( b, N7 e& f( @ - //printf("sendbytes = %d \n",sendbytes);
- Y( M( T( G9 @ - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
' P; w: i- ]- a- R - if(sendbytes == -1)$ A& x' Y) Z& @- \
- {
& Y1 m W2 e+ a* X6 I a3 D1 ? - printf("Send Picture Failed!d\n");$ [6 \/ o9 @0 N+ E. j/ `( f
- return -1;( s" g5 `) L2 } d* O8 X
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- else- M1 T* j6 j/ K4 X
- {% x9 G- i9 a, e
- fend -= UDP_FRAME_LEN;
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复制代码 ; M* `0 ?& |0 g$ h
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5 V' Y# h) ^8 f/ riMX8MPlus 核心板: https://www.forlinx.com/product/136.html |