本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑 / r4 u2 H+ B! _0 f) T
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% H) Q# r; l# v5 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
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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。 * Z- }8 r& ]0 J: x( @0 k8 N
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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。 % V5 |' b4 `( V7 u0 O, p
一、HTTP网页服务器
) [- ?' M) i# ^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)1 n1 ^5 |/ F& I) s6 D
- {
6 @% D) x5 w! m$ F; c - struct sockaddr_in servaddr;
6 i$ N3 m6 o" L: N - socklen_t addrsize = sizeof(struct sockaddr);; ]! o) Q- M9 X% z# t6 \# ]
- bzero(&servaddr , sizeof(servaddr));
* ?" a. \. A" I* y7 g. v - servaddr.sin_family = AF_INET;4 E" ?# ]9 i. T" J
- servaddr.sin_addr.s_addr = inet_addr(ip);2 y7 r" b" A4 y4 E
- servaddr.sin_port = htons(port);! K0 P c' h. U7 k% P# [0 s% ^$ S
- int ret;
9 i5 R8 i7 ]% o L% S* G1 p - IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)7 j( S! H* f+ b0 B
- {3 ~, T6 ?6 N+ W& _* \: K9 X, @
- printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);+ e4 ~2 c5 v- g& C
- return -1;4 b+ k" g: T! w0 n
- }
; g$ o# Q8 r/ ]8 c/ \ - int on = 1;
" D) I+ Q4 X6 e0 T) N+ M - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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/ r. V& o* E% h0 Q$ N! \; z1 d - printf("setsockopt error\n");
; F! _9 l/ D2 t' P% a2 L - }
. N# v% t& O8 G! x- w4 Y. [ - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);7 O7 `% p$ }( q; v7 i" ]6 S
- if(ret == -1)
1 W" g& y: K$ h+ C - {
5 H7 k# [' p, a! D/ ~ - printf("Tcp bind faiLED!\n");( j$ u3 ?) r' T# n3 g6 G# N
- return -1;
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- if(listen(*socket_found , 5) == -1)$ K& S0 |/ B2 j3 y
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- printf("Listen failed!\n");6 k* y) u6 h! Z2 r; q
- return -1;+ H0 s: P' t( @8 d. U
- }
5 X$ b( N, a- C9 g! q - return 0; D! D+ E; d, j6 c5 }7 S4 m w
- }
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);1 ]% t( _; n. @: b
- void * Thread_TCP_Web_Recv(void *arg)/ A1 ^! W% Y9 Z' C Q6 o: I( I
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- 。。。" e( Z9 B! ^( k5 e
- while(1)
$ M/ G1 U P8 x2 m0 ?2 X - {
4 `" u3 v, O: h1 J s - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
- A1 Y. _. b* N1 k" s, D - printf("fd_socket_conn = accept()\n");2 O. B& [: _/ g. Z1 u2 k w3 a1 y
- 。。。7 G- J3 h* X2 |. M
- recv(fd_socket_conn , recvbuf , 1000 , 0);1 q3 w/ l. n8 R0 R( E, h
- }. P, `! y2 g4 }2 a' C
- 。。。
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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);
. y F. N; N `4 o - pic_tmpbuffer = pic.tmpbuffer;2 @8 o' [- b3 q7 `
- pic.tmpbytesused = buff.bytesused;! W0 Z* f) U! F
- pic_tmpbytesused = pic.tmpbytesused;, L$ a; b! l( L+ }5 D, |6 b/ m
- pthread_cond_broadcast(&pct);5 m0 X6 }; _3 c/ w0 e w) F
- 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;- H* L" u7 D/ I @+ l- ~
- pthread_cond_t pct;
* d0 P4 ^% p6 Y" V1 |9 [ G/ u - int main(int argc, char* argv[])
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- ...
& h% o% B+ B2 O7 c - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);+ O' Q+ e3 W k
- pthread_mutex_init(&pmt , NULL);
4 \5 T/ U9 }5 l% Q - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);7 _% r' a& G( ^, O! L7 J, s& L
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
8 b) E( M" @6 P% l7 j - ...
0 t: Q5 ]! l y; M; `5 } - while(1)
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- V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);5 ]5 i, h9 L9 I H' ` ]8 k+ k
- ...
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, v3 P# k' a# o) G2 w. n - ...
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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;">
) F$ l& V9 ]/ ]+ g" x$ |. E - </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" \' P6 X# }2 j: i8 I% Q+ s2 T
- "Server: MJPG-Streamer/0.2\r\n" \
" P6 ^" a+ |7 ?1 W3 ` - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
/ r# f' Z% }4 D - "Pragma: no-cache\r\n" \
/ r! _/ E4 S8 g: Q; A1 x: s$ K - "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
6 N' m* ?& U' Z% j. C - #define BOUNDARY "boundarydonotcross"
7 B2 H# Q; f1 ~8 F! C7 o* ]% f - printf("preparing header\n");' l8 j# K ^2 A) E* e' c
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \- J' \3 H, O, }1 S
- "Access-Control-Allow-Origin: *\r\n" \8 A& }" z4 d7 Q. n. F5 i: P
- STD_HEADER \
4 ]2 N/ ~# ?0 Y# t9 k - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \9 t0 G, h1 X7 e( Q7 ~9 p7 |$ [, X
- "\r\n" \
' i. G; m0 K/ y3 M - "--" BOUNDARY "\r\n");
' \ F: Y: ?; t8 X: l" |8 D - if(write(fd, buffer, strlen(buffer)) < 0) U: ]% n3 t/ r) ?% o5 {+ Z: ?
- {3 Y0 t5 T1 W8 E" A5 p
- free(frame);
% q( c0 w# M; I1 X- P4 g$ l - 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" \2 n' Q- f# {2 p: \4 ]) x
- "Content-Length: %d\r\n" \1 W( a: j9 z7 O7 X6 @8 x3 l
- "X-Timestamp: %d.%06d\r\n" \9 F4 r7 ]2 ?* I7 l) m1 W: R
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);4 X) N$ H, P2 W4 C0 P' C! O2 ]
- printf("sending intemdiate header\n");8 Y/ i# I. y/ H! D3 a* F5 _/ @
- if(write(fd, buffer, strlen(buffer)) < 0)
; B" }5 i# ~! |' m( c/ c* n - break;, @# P/ k" E+ }" Y& @
- printf("sending frame\n");0 ~, S+ _* T4 U4 U) e
- if(write(fd, frame, frame_size) < 0)
6 J, o# ?* P$ i - break;
) V* g0 t: n: v) q0 B - printf("sending boundary\n");
& Y0 W5 ~, |6 I# [" r3 G+ x2 r - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
" F+ g# G9 B6 L4 D - if(write(fd, buffer, strlen(buffer)) < 0)
% O/ @6 `3 r$ I# O7 t9 R - 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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, P3 i& m5 k: T; z9 b二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:+ o A% F" h% b6 q( d% o
- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)% Q/ B% R0 m( G3 L- L
- {
" L; K9 d2 b: ~3 i. q - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);
- t( C) U" m4 M- X - if(*socket_found == (~0))
. k _1 d# g6 Y1 N! N: G6 E - {8 z0 f$ p+ i3 A. y
- printf("Create udp send socket failed!\n");
: R8 m1 L1 c! `1 O( h. C - return -1; F! b K3 n: K4 _# I% G
- }
- z2 K3 q4 P* `; L - addr->sin_family = AF_INET;
* Q: z6 k; F ~4 z# V0 H - addr->sin_addr.s_addr = inet_addr(ip);' x, p# I4 t; S; P. r
- addr->sin_port = htons(port);3 {5 A& G" S9 U# r. p: S8 G2 s; n
- memset(addr->sin_zero, 0, 8);& c, z& I/ |6 p( a" P
- return 0;; q( a. G; V" D0 C0 ]3 i
- }
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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. c' l$ Q6 v" u3 g+ v L8 _- while(fend > 0) b, I% B Y. V# o0 _# a
- {& j& l E, h6 W3 H9 A8 J5 I6 }
- memset(picture.data , 0 , sizeof(picture.data));
* J1 L- C4 P7 @1 K - fread(picture.data , UDP_FRAME_LEN , 1, fp);
& p& L- V! O- J8 ^' P- P - if(fend >= UDP_FRAME_LEN)* F, U) j# f& u4 A. ]
- {
) \/ ?+ S; N: s2 f2 c - picture.length = UDP_FRAME_LEN;
# z0 a. u$ a0 u7 v3 ] - picture.fin = 0;
! R, h1 H" \! i" w - }
8 n/ z6 I( E/ Y0 [" b w - else! z7 o' Y4 ~$ Y+ [+ v$ T" k
- {
- B$ y: J# p F2 S - picture.length = fend;4 g" a6 e/ s# C8 t6 S
- picture.fin = 1;5 E+ d1 T4 y9 o; w: `
- }
d0 ^0 N' q. t - //printf("sendbytes = %d \n",sendbytes);
, @" c7 U. J& e( X - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);% H3 X$ z0 |( ]
- if(sendbytes == -1)7 I! V' {! q& q' J
- {
9 Q& @; t& n3 q; f3 V& f& u' {, c" F - printf("Send Picture Failed!d\n");
& v q! b: k4 Q4 Y+ j/ l; L* h$ J - return -1;
r* r9 z1 [9 j% b( _. C - }
3 Y! V! [& U; k* e5 k8 x3 G - else
, m4 i% ^$ o4 H; q# g - {
* N$ B7 A0 A/ K. s% ^; L# B - fend -= UDP_FRAME_LEN;; d! J; O1 k5 X) G+ r, Q( G
- }
0 s$ i8 {. @! ]7 W" ? - }
复制代码
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iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |