本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑 4 ^9 x( [2 b) }- m. S# c8 x8 h
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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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& t# V' G3 K6 m3 i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。 ) c) c8 R2 B9 A9 A9 J3 g

# {' Y7 w6 }, L) Q0 N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。
5 y! G# X( m( n9 ^9 @2 H' m一、HTTP网页服务器$ a+ p: \" x& U. _
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)% N5 h% x& J0 t% b/ q" ]" {8 s
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- struct sockaddr_in servaddr;- s' }6 V! S: ?; Y, H* H
- socklen_t addrsize = sizeof(struct sockaddr);$ L* I9 R! | w" x+ x
- bzero(&servaddr , sizeof(servaddr));
5 R; q5 b4 y3 L# a - servaddr.sin_family = AF_INET;) L7 T% G4 Y$ \, L- g+ J: E/ b$ t
- servaddr.sin_addr.s_addr = inet_addr(ip);9 O4 b0 r2 Z0 ~0 y+ p
- servaddr.sin_port = htons(port);+ o0 p0 b6 f. v, @0 S. s4 F- }/ X
- int ret;! ?1 m( h( S2 Q5 l5 V' v# K: G
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1), _& w( e, p1 _5 p" Y9 ^4 W9 `
- {
) n. y6 a$ J+ X2 W, X - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
( K' n+ Q. G' ~2 O8 a& n: U - return -1;
2 O, K l" T0 J0 L7 H9 ^3 b8 M - }
! u2 R$ q3 w/ ?# I - int on = 1;
* z1 N K- }+ ]& E: @* E5 ] - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)# f0 O! T: K5 J; d/ N& O A; _5 q* s
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- printf("setsockopt error\n");
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' b* o) N. _. a% G8 O - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);4 {# w Z4 U" M' \* [' ]& D/ a& ^
- if(ret == -1)$ E- X: r( Y& e" P
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- printf("Tcp bind faiLED!\n");: g" P. d: U* M' f& p K
- return -1;
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p" t' y) M8 L1 d+ f: F - if(listen(*socket_found , 5) == -1)
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- printf("Listen failed!\n");, V9 U- e1 c$ \/ F9 N( R
- return -1;6 ]( |1 o$ E+ ]+ M5 c; { I6 s
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- return 0;' C' v. [1 j2 l$ P W6 P7 ?9 I+ h
- }
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);
+ V6 Z# y9 h( B( {! {2 h - void * Thread_TCP_Web_Recv(void *arg), C, _2 n/ i; z$ S& K9 m& n4 d2 G8 E
- {
2 F3 e/ ?" g6 V9 Q* h - 。。。$ I2 { S* }$ B$ Q" O) ^" h6 Y- S
- while(1)
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- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);. w+ ?, j: \* c! w( f4 ?
- printf("fd_socket_conn = accept()\n");7 A, V& p" M4 X% W6 g$ c
- 。。。
& D/ ]# _, k/ U2 G: _- Y - recv(fd_socket_conn , recvbuf , 1000 , 0);+ P' s+ @- E& c; l8 e
- }
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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);% w/ v8 P6 @! X1 p
- pic_tmpbuffer = pic.tmpbuffer;8 r1 ?: c- ?7 @! ]! `% O
- pic.tmpbytesused = buff.bytesused;
, h# K6 @8 j: s8 L5 B- _" u, E - pic_tmpbytesused = pic.tmpbytesused;7 r& H) c0 X' b% b4 ~" W
- pthread_cond_broadcast(&pct);; p. B' l1 l0 H1 o8 p6 @2 T) ]
- 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) j5 }/ ?; G+ o
- pthread_cond_t pct;
4 I/ `. X/ T& ~ O$ l }; J# x - int main(int argc, char* argv[])+ A5 I& m* Y7 T. r' S
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- ...
2 C. y' w# E6 u$ u9 X' z* c - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP); ?; ]% [2 j* u& I' f
- pthread_mutex_init(&pmt , NULL);2 j9 ~0 u0 n! T" D
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);
. x- N5 J" o' s3 I. |3 Y: d+ G$ {! A - pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);9 G2 {; O1 k' s
- ...
& b4 d# P. u. u% j - while(1)9 |0 Q% C j8 F3 E
- {
9 v" x' B: w$ q! L& b - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);9 Z) k4 d& e: m% J6 p% F3 {
- ...7 L- M* k2 h5 Q" f
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- ...2 R$ V6 Y8 C/ T3 L& C# T* L* m
- }
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;">; i, p* T, M% G: C/ \$ J2 ?
- </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" \
1 ?" @6 n; v% Q& f& p# ?, m - "Server: MJPG-Streamer/0.2\r\n" \
! ?) d$ V% ~) W% k - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
x% V, W( f9 b+ x( r$ N - "Pragma: no-cache\r\n" \: x( a8 c7 J0 I: g" O9 `: B
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"! ]/ I$ _* r0 f0 H$ ^, Y
- #define BOUNDARY "boundarydonotcross"7 w. x- y% l) y9 r! G4 c
- printf("preparing header\n");
1 d8 G3 n* u" f1 r/ @* d2 {7 b, E - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
" q& n. b$ S B6 j5 h* m- l1 O) _' V - "Access-Control-Allow-Origin: *\r\n" \: u9 u6 L4 k! J8 K5 ~0 b
- STD_HEADER \, W/ d1 v. p, W$ {
- "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \( ^+ d& p1 t' l/ H, F8 `
- "\r\n" \
% {; ]) h& A; @4 g - "--" BOUNDARY "\r\n");+ D2 l; ~0 n7 F' A* P! \
- if(write(fd, buffer, strlen(buffer)) < 0)( n9 u a; N% k" F) f: l+ r
- {
5 U& _* \+ O' K! m# Q/ _% V - free(frame);
/ O* c% u+ W: x1 H - return;( _. R1 r7 a+ E1 T% q) \
- }
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" \. p4 q+ H+ x" h! w$ h9 I
- "Content-Length: %d\r\n" \
5 k2 u2 A2 e3 S8 e! d" b$ M% T - "X-Timestamp: %d.%06d\r\n" \
6 |; f2 p+ s( d2 e - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
4 d. ?5 f6 Q% v9 I# O$ ? - printf("sending intemdiate header\n");
, `( h8 [7 H9 T( e- V( q - if(write(fd, buffer, strlen(buffer)) < 0); x7 M, x$ p) |8 I3 f
- break;" ]$ S( H e: O- i
- printf("sending frame\n");
& n v8 B, ~! l# Q9 _; R - if(write(fd, frame, frame_size) < 0)8 s7 t3 R& Z; u4 Z8 [7 o4 R
- break;
Q% h' H$ ?6 }- f5 a! F+ {9 Q4 K \ - printf("sending boundary\n");
4 C: t2 Z0 V) t0 M- V+ a - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");! {8 |' D: ~ S
- if(write(fd, buffer, strlen(buffer)) < 0)
% T p0 Q' Y. Z# A - 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:. y# v1 U6 V/ O0 J1 Q9 @* _' Q
- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port): r2 L: M* A) u& L
- {
* f9 s. G3 n' f: P% J3 l% Z - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);! H8 k. n- y- C1 m3 g7 c$ M
- if(*socket_found == (~0))
+ ~* R# ]8 }! C [1 b& P- s - {
/ |$ p0 Q# o# e" O1 a" e# Q - printf("Create udp send socket failed!\n");$ c# M% z- M6 ^% Y1 r
- return -1;9 o- T& w1 Y8 {+ A
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- addr->sin_family = AF_INET;
1 S1 R2 o& Y; o, p+ J0 @ - addr->sin_addr.s_addr = inet_addr(ip);
" i1 g0 s- G& _( l - addr->sin_port = htons(port);% `) T0 v! X: Y+ `) [5 Y5 s+ q. }
- memset(addr->sin_zero, 0, 8);
1 f/ q# X/ m: Y- A: g" b6 t - return 0;7 ?2 s* n* v6 }: V( l
- }
复制代码 9 S* |6 T+ f" i$ d, H9 ~% S
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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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; i7 H% f+ F$ Q! P$ a3 V! K1 k8 ?- while(fend > 0)
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- memset(picture.data , 0 , sizeof(picture.data));
5 J' [7 t& b/ P/ i, m - fread(picture.data , UDP_FRAME_LEN , 1, fp);4 i! a% i z9 g% t6 G4 f8 y
- if(fend >= UDP_FRAME_LEN)
+ K8 Q" F1 ]( T - {- r7 c, V" w9 g6 F8 E: r Y
- picture.length = UDP_FRAME_LEN;3 |& y$ I' b) d7 {; x' y1 \6 X3 K
- picture.fin = 0;
7 a l! m* F9 u* ] - }
4 ]( c- O6 S6 ^. D/ ]" K1 I - else
P6 z8 B! ?; Z1 H0 [" ? - {
9 s; X E( |, [) S/ c - picture.length = fend;
. O1 V! r) A4 K' M - picture.fin = 1;% v, t% n7 Z& E' o5 [# o4 w7 g+ Y1 J. t
- }) \ {1 L4 Y# v& x8 w. a9 k
- //printf("sendbytes = %d \n",sendbytes);
* h6 z, `# Z3 w# c - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
: \% c' g; z7 N( U- \ - if(sendbytes == -1)* C& y: K L9 c0 [( U
- {! E5 J$ J- G! w0 y6 P& x/ a+ D
- printf("Send Picture Failed!d\n");! j9 B, ~* O& E: K
- return -1;
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- else* G F8 f9 [) h) k) S& F2 I
- {' l# p7 A& ]+ g
- fend -= UDP_FRAME_LEN;
+ o" a! o3 x+ S$ w/ w( B4 }- ` - }
3 m% D T- t1 O7 D3 O' t! i - }
复制代码 1 M& H4 e( d, m2 e
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0 T6 p4 C- L& Y5 O- u7 n, N% \" |iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |