本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑 * A X5 v& G+ |: {% V, g8 ]
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/ i" I( d$ w z9 `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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( C, F3 c! C" S! k+ M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。 7 E2 j: R& e9 K" V/ T7 I

, y. |1 F$ k5 A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* v( f; i. _$ p* h; ]
一、HTTP网页服务器$ u% S9 ]" M' {& b* F2 F- L) N) y
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;' F( o* z# D8 [4 D/ \$ y1 a
- socklen_t addrsize = sizeof(struct sockaddr);
8 @5 K6 B% _& l/ S. T - bzero(&servaddr , sizeof(servaddr));
|/ H. c: y5 b& b5 x - servaddr.sin_family = AF_INET;
& V* d5 J5 W7 `7 A; t5 E - servaddr.sin_addr.s_addr = inet_addr(ip); _) [- Y: D: l8 h' H2 L, S
- servaddr.sin_port = htons(port);
* l* q7 `# e9 X. f! e) O k - int ret;
9 Q: c" F2 ?3 s' _/ w - IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)* E! c0 b; `4 E T2 ]2 m
- {
& y8 l# I1 X. S4 d1 J3 d - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);. @' o- D* a$ v* i
- return -1;
4 R6 o- S* z) v" Z! W - }
4 `" k8 C& ]! ~' X) k% Q - int on = 1;
2 U' Z% f; d8 F: i1 u0 }; Q - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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- printf("setsockopt error\n");4 n8 p' r7 T! r9 [
- }
' L% k$ Z" U# `' \! q1 F) [/ W - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
$ p9 W7 y0 {" B7 [5 q0 G - if(ret == -1)
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- printf("Tcp bind faiLED!\n");0 A, k4 B: |- j$ f
- return -1;
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- if(listen(*socket_found , 5) == -1)" V1 _3 w) `( t, X
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- printf("Listen failed!\n");5 b* k6 J/ o" O6 ~( i
- return -1;
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- return 0;' t, L& j8 q3 S; \0 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);7 |) P. Z6 K6 R; Q' H
- void * Thread_TCP_Web_Recv(void *arg)
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- 。。。
. v! g4 U9 m! H - while(1); m5 ~; w5 u ?% [/ R$ ]
- {/ N7 g3 V2 w( V: ~& u
- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);- L; Y& a( l5 @5 Z6 S; u& G
- printf("fd_socket_conn = accept()\n");% J" v& A- A9 H2 I
- 。。。, u& R3 N+ @4 V, W
- recv(fd_socket_conn , recvbuf , 1000 , 0);8 m, o* K5 |- P _; K' Q8 @1 \6 _: D
- }
9 v5 j4 H" ^* K, ?0 J - 。。。
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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) H1 Y2 N/ }7 F3 c
- pic_tmpbuffer = pic.tmpbuffer;
- v' _0 J/ n, u" I9 c/ j8 B - pic.tmpbytesused = buff.bytesused;
7 I% V6 b5 k4 Y# t% A - pic_tmpbytesused = pic.tmpbytesused;
/ y/ |% l* G. F/ q7 b - pthread_cond_broadcast(&pct);7 i# ]. T, c- u) @) ^8 e& o
- 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; v8 e& p& s+ m- i
- pthread_cond_t pct;, v+ `7 ~3 S6 K' }, R/ V% p( H
- int main(int argc, char* argv[])
0 V% O3 X) Y3 J. I) h3 i - {
- \. ~% Q+ ^+ W ] - ...
2 N6 O. X3 Y' J# u& k% e - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);. |+ `! b9 |1 o0 R
- pthread_mutex_init(&pmt , NULL);: c6 a- L( e: ?" T$ d* E
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);9 r9 i5 j$ B( S& D: t* G/ ]3 x8 I
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);6 ~; Z4 L6 G5 ^6 W9 w
- ...
7 `+ `! q% Y) l7 u - while(1)
9 ~' l# m4 @/ P, b' {8 n - {
# n* D) p, O; p6 c3 Z/ w1 c' {$ ? - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);! k- W( z. t) v( q4 R' J3 e
- ...
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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;">) X% j2 r& p- M- N; N
- </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 Y9 C" O1 r! O3 } - "Server: MJPG-Streamer/0.2\r\n" \
0 v, o( s& M* f# K# W - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
M6 I) z6 X7 m$ L - "Pragma: no-cache\r\n" \. c0 ~0 m/ o( B
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
( ~4 `4 ]: b0 v* E8 U - #define BOUNDARY "boundarydonotcross"
. m7 U4 A2 g* B0 ?& P. g - printf("preparing header\n");
$ ]: W0 I# c! N7 Q+ \ - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \/ E" m( M/ A* k
- "Access-Control-Allow-Origin: *\r\n" \
) T# g$ a- d8 K: c - STD_HEADER \
9 ~+ O& r; A! z - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
7 r: ~- @7 {9 O5 D' X - "\r\n" \ b. l3 @ X( a# H7 \3 \ r+ `
- "--" BOUNDARY "\r\n");# l# i+ e4 r+ E# |$ F" }% y& b
- if(write(fd, buffer, strlen(buffer)) < 0): i) l$ ^# g( ~7 W" u
- {
5 I% D+ u- [& V0 v, _0 \/ T - free(frame);/ v0 _8 j6 z. r! X) e* K
- return;3 _( ^0 t, ~! r7 {( m7 J* f
- }
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" \
) f. R& @0 r! k# S M7 P0 N7 m - "Content-Length: %d\r\n" \
& Z7 t8 [5 W% q% u0 | - "X-Timestamp: %d.%06d\r\n" \2 z8 l X" T5 D% x3 e$ R" l/ n
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);+ q; O( z6 U1 I5 |3 C- \- a: h+ G
- printf("sending intemdiate header\n");: F& c) S- @3 h( O4 Y
- if(write(fd, buffer, strlen(buffer)) < 0)
! w2 u( }5 l! O - break;
, W1 K5 w+ h; p: _+ u: x - printf("sending frame\n");
7 L U7 _( Y- @) E - if(write(fd, frame, frame_size) < 0)+ L$ }% j) W" h; C6 o0 q
- break;) G4 |' u6 }) {7 d1 h% u, j
- printf("sending boundary\n");' {: x+ W; g4 @' u% h
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
& [ l4 I3 a4 L6 Y! M - if(write(fd, buffer, strlen(buffer)) < 0)& {2 S; o: X( u7 y+ B- i. {7 m
- 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:3 \+ \$ I0 ~& `$ X, t& y0 D
- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)
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- *socket_found = socket(AF_INET, SOCK_DGRAM, 0);5 G+ h, `2 r- M. v
- if(*socket_found == (~0))
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1 Z0 F8 W0 a! K4 k. p - printf("Create udp send socket failed!\n");
- g, }- e8 X0 B# c* L% q( _ - return -1;$ W# T5 J0 H4 Y* p# Z
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- addr->sin_family = AF_INET;
; v: ^% e6 d# f/ z+ j1 p - addr->sin_addr.s_addr = inet_addr(ip);
0 p6 ^& h5 n, C K) L - addr->sin_port = htons(port);. P$ G# q4 K9 U- D& x: ]
- memset(addr->sin_zero, 0, 8);
% S9 J7 e$ ?- i1 \ - return 0;$ F" c( u4 v$ o7 h; c- o9 r3 U
- }
复制代码 # n4 \7 D* |6 Q P
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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:( h6 J4 c- @' X1 |6 |: x
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- while(fend > 0)
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- memset(picture.data , 0 , sizeof(picture.data));6 N4 L! ~7 r4 I" m! j" g: H
- fread(picture.data , UDP_FRAME_LEN , 1, fp);0 X* c4 v& H' S |6 N- X6 E
- if(fend >= UDP_FRAME_LEN)4 Z8 {/ ~8 f1 o9 a* s, @
- {& n8 z6 M8 v' o7 ]" `$ g
- picture.length = UDP_FRAME_LEN;3 L. ]+ K7 {' S( W
- picture.fin = 0;
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' y" S1 l- H9 {- l - else
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3 {, B% g: z6 q0 O9 A" L - picture.length = fend;) O8 o7 S' p. _2 }
- picture.fin = 1;0 d& ^! h: K0 N: c6 r) O$ n
- }
( Z: C6 G6 D5 p+ P& x - //printf("sendbytes = %d \n",sendbytes);, w0 R2 g# B' `( z
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);6 d3 ^- ^6 ?2 R' L, I2 q
- if(sendbytes == -1)
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! R" b% I5 r& p5 J - printf("Send Picture Failed!d\n");; S- h" ?. D& I) ]! v" ?9 D! q
- return -1;# x9 ^) z4 ^4 `, }2 E z
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- else. `; Z" U1 T# i7 I, `, h8 K8 T
- {) q P! Y6 O+ W+ n/ _3 l; O7 u
- fend -= UDP_FRAME_LEN;8 l' M8 P2 X9 e: U, @$ \! z- H% b- Q
- }
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复制代码 G" n/ \3 ?6 p. P% e. v1 K6 D
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iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |