本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑 - x4 f: h* K4 ~
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/ F5 f; O; U+ H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" |" }; A5 i4 ]) G# i# I$ s
; h: E& g! l( G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。 , Y) g; K! }* o/ y4 D9 @

$ ]" N2 N) I. R1 O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。 - @+ m7 {; H6 }! N
一、HTTP网页服务器
9 P3 o! a. }# I0 T2 V( 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;$ `' _' S0 z& |3 ]' ~
- socklen_t addrsize = sizeof(struct sockaddr);; ^, s' n2 n- }/ d
- bzero(&servaddr , sizeof(servaddr));" Q+ _# k% q: F" s
- servaddr.sin_family = AF_INET;9 q& P* T# s) f0 d2 U/ w# O
- servaddr.sin_addr.s_addr = inet_addr(ip);7 L& W6 N8 N6 @$ V8 a
- servaddr.sin_port = htons(port);
( L+ n# d9 I9 P! K - int ret;3 Y1 V9 Z& v8 z
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1): |* V Z) E* Z/ h. A
- {
9 L& O5 C* J4 B' J1 X - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
" H( r$ R: e9 p8 k - return -1;6 ]2 M; }( n' _+ {6 q7 N9 z
- }
@1 j- c4 ]0 C2 T) P( U- s - int on = 1;; J+ G+ F1 X5 ]; s1 x' _; i
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)% ~! E. i n' i" c# r) a4 D2 z
- {/ r5 c: T) \, ]* b; W
- printf("setsockopt error\n");
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6 v) X2 M5 `) B' t+ O i5 e, k2 \ - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
1 r' d$ C' v; M- |* C - if(ret == -1)
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$ J2 M8 p9 h( ]1 K1 K% { - printf("Tcp bind faiLED!\n");7 ^+ p; |8 g9 h" B) B
- return -1;
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- if(listen(*socket_found , 5) == -1)# R3 H5 x" \& Q4 @& e- h' H/ {
- {3 z+ e! \! p& c1 f. ^
- printf("Listen failed!\n");. ~6 ^: H' A5 `- i$ B
- return -1;, M, j# P) e3 [1 d# l, @3 J, G
- }
* X- } Q( F: l$ N ]; M# D$ H: M - return 0;
8 _" ~( E- }0 i9 O* E8 b$ s& P - }
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);( T# a* B" C" \5 B, i, A
- void * Thread_TCP_Web_Recv(void *arg)
1 g: X; l& A6 W - {
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- while(1)4 j, I1 s7 u f: W& ]+ z7 f3 m( }
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- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);1 K# ?$ o: j6 K6 g# u. Q
- printf("fd_socket_conn = accept()\n");0 _% G8 ?- F/ ~/ Q" \: p& U# W
- 。。。. V8 ?8 }% E5 r% _
- recv(fd_socket_conn , recvbuf , 1000 , 0);6 y7 U7 F$ d" i* ^
- }
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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);- J8 L7 g7 m3 [: Y' F/ u$ ^
- pic_tmpbuffer = pic.tmpbuffer;3 | }) j+ ^8 k. C
- pic.tmpbytesused = buff.bytesused;
! e. ^' K) c+ u4 C- f - pic_tmpbytesused = pic.tmpbytesused;( a6 c# P9 f, c# ]5 h' F
- pthread_cond_broadcast(&pct);
- Q+ e. \+ b2 p0 Z" ^) n - 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 Q5 s* R8 x1 v, _3 [ - pthread_cond_t pct;
' C3 I% f* T8 I% ]+ g3 h - int main(int argc, char* argv[])
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- ... B4 e8 _. N+ @0 \3 t1 R& P
- TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
$ l8 Q* P" J1 q1 ^- @% c* t - pthread_mutex_init(&pmt , NULL);) [3 c' m4 k- \% z }. S; D( n
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);2 _; g$ ~9 y$ H/ A; A8 J. U r
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
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- while(1)0 I' Y4 i- L' o! d$ V: `1 I. C
- {
5 }4 R% I, k* ^% s% K' P5 e3 W3 j$ I K - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);
4 x6 h; u" n+ p - ...
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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;">0 E* u3 E. p" }" h9 Q/ U
- </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" \7 s; {- `) a; l3 p
- "Server: MJPG-Streamer/0.2\r\n" \
$ }/ k* G# o# x& ~ n0 N8 C - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \9 s2 p# }0 o, f1 Y1 x
- "Pragma: no-cache\r\n" \ U8 J) @6 y5 h4 S' D
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
" \7 ~: i. {2 G: [6 I" i# |# J - #define BOUNDARY "boundarydonotcross"+ A8 ~9 s7 u* i U2 p
- printf("preparing header\n");5 R: y( p3 C3 O' }, A; |
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \# A% R. o* t* u
- "Access-Control-Allow-Origin: *\r\n" \( D; T& w7 C4 K2 t+ ~
- STD_HEADER \
, X1 `- o& i" I+ v$ U0 p; E: M7 v0 z! e$ ` - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \+ Q" r8 M; a D, l( f
- "\r\n" \
' A5 O+ I3 y' z/ E - "--" BOUNDARY "\r\n");- ^4 A ^( n9 v& ]
- if(write(fd, buffer, strlen(buffer)) < 0)" ^: p% U* {/ `9 j' T" U) }9 z
- {
% W; ~6 ]- h" c$ U0 u8 X: f - free(frame);
7 O: y3 [5 a0 F2 Z: \% u/ 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" \
+ {% i9 R- `- E - "Content-Length: %d\r\n" \
8 ?& O; f( T0 \5 Y9 ? - "X-Timestamp: %d.%06d\r\n" \% d$ Y0 O8 F1 b% j" u
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);9 h8 [/ F' o! k! d! U
- printf("sending intemdiate header\n");
& u& y' M( {4 k1 S4 o' R; U. G - if(write(fd, buffer, strlen(buffer)) < 0) M/ u8 D, \& z4 y
- break;
5 g8 l: ]2 f n+ O# ]6 Y - printf("sending frame\n");7 S; j6 W2 Y, b- o; q
- if(write(fd, frame, frame_size) < 0)
: F7 Z! M7 c$ h7 u! a/ ]( o - break;
0 F$ y, G, T ^* E0 | - printf("sending boundary\n");
z, c% s- W/ G) T. J - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
2 h- _, w& X4 S( }2 h - if(write(fd, buffer, strlen(buffer)) < 0). l! M" Y- q8 \0 d, s2 D" z
- 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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: q- N. j7 @0 | x% `( A! M二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:
0 U$ ^* w% ?9 Y- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)
8 P4 C( P7 ]: w' b" ^; m5 o- W/ Y - {
7 M3 b) w( f( @; V; u - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);
, }+ [* `6 g6 K* f - if(*socket_found == (~0))6 y( a, T2 x k7 d
- {
" s" U8 X3 j4 h$ s! p - printf("Create udp send socket failed!\n");
# v8 r3 O2 K4 e' t- | - return -1;
) l8 N( [9 T- U, C - }
o8 \& u% h4 N - addr->sin_family = AF_INET;. R7 m4 F( M' L9 q( {
- addr->sin_addr.s_addr = inet_addr(ip);, I( [) g& s7 @2 e) Q
- addr->sin_port = htons(port);2 _# C0 M e/ e% f7 ~& }' U( L
- memset(addr->sin_zero, 0, 8);
}3 Y* h$ Q* L8 ^$ S, O5 R - return 0;
5 |6 X* p' [$ X - }
复制代码
5 h X4 d+ x+ l! {. Q! C
7 L$ D$ R7 Z2 V# N- x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:1 x1 { p* W& y b9 ?
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' @' O- |6 d: q' H, h* c- while(fend > 0)
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- memset(picture.data , 0 , sizeof(picture.data));1 |4 V) }% t/ E& z& b0 k
- fread(picture.data , UDP_FRAME_LEN , 1, fp);' S. x: k. p$ {' g6 s
- if(fend >= UDP_FRAME_LEN)
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- picture.length = UDP_FRAME_LEN;1 b2 B7 \7 X) B' H% t6 a- U$ R
- picture.fin = 0;# Q: T& k' j) T6 V& `6 L7 I
- }3 j7 P a/ P0 r( m4 s# V4 O
- else. |; t% W3 K+ H* z
- {
7 j9 @% }7 X) }& l' a - picture.length = fend;4 h8 ?* T3 D Q) Q- E; t
- picture.fin = 1;
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- //printf("sendbytes = %d \n",sendbytes);
' C: r# ~$ {5 g' ? - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
8 o: T0 V' F$ c: u. Y: K - if(sendbytes == -1)2 f4 T' s, l1 Z' P! ^1 J) [
- {
4 T& z) v; \- F* F - printf("Send Picture Failed!d\n");
( p! _+ b" z6 `7 T/ J4 B+ ^; f. Y - return -1;
9 f w6 t6 B" }3 O1 H: o! Z - }
: B7 X( ~7 t3 l1 ] - else
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' m( D2 e% t7 b) N* A: |* Y+ [2 s - fend -= UDP_FRAME_LEN;; F" @- v. t6 F( t1 U# g
- }
; L$ m1 F/ a8 E - }
复制代码
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$ l- F3 n" q1 _iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |