本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑 . j- ^$ X2 e: O1 N+ z# }# Y( ^& P
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$ l* d6 K. ~ @, y; M' ^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. I5 E" z. m0 s) s( ]% T% v
6 K2 d- Y2 T+ o) H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。 5 ?* A$ N: _4 A9 `3 z3 v; ^

8 v. `" I4 H4 G( r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。 * C% L2 s0 k1 ]7 l. r
一、HTTP网页服务器
/ T( o/ _, D8 b! r Y! q" X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)! ~; |. f( s8 \* n1 t' C4 T
- {
2 o6 j3 r! p( X - struct sockaddr_in servaddr;
3 Y4 M- Z% x, M) d9 [# ~ - socklen_t addrsize = sizeof(struct sockaddr);* ?: b j1 z y. Z9 M6 b/ q7 @% M/ X
- bzero(&servaddr , sizeof(servaddr));$ k: d$ w& g8 [0 K/ z$ `4 N
- servaddr.sin_family = AF_INET;* k( q6 ?" z2 i2 B v
- servaddr.sin_addr.s_addr = inet_addr(ip);
2 O: j+ [5 e, @& W% _6 z! N/ W( F* F - servaddr.sin_port = htons(port);
/ P6 U+ ]' S2 W; Y- \ - int ret;+ o8 g- g% S# I6 s- L" i7 [5 T
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)
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- printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
/ H9 V# W: N2 ^& r - return -1;
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- int on = 1;
- r) X' [( x, c0 X* K - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
S- @* ~( m \" @ - {
' F( V q" J5 y0 w; `8 c - printf("setsockopt error\n");* C/ S9 C4 L: {. e c- h( L D0 D
- }
2 D F. K! A9 i - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
3 ~9 g& e& m- d- `6 ~ - if(ret == -1)
' u# [1 A) t; I- x- Z. J$ V) j; _7 \ - {
/ k2 e! m* O/ z& k( T& O) ^2 b - printf("Tcp bind faiLED!\n");
! j1 F7 U4 w" N - return -1;
- S2 v" f, y+ t9 L$ W1 R - }
5 w6 e0 A/ W [% f) L - if(listen(*socket_found , 5) == -1)
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! h; C6 M2 @ v& U - printf("Listen failed!\n");1 X3 }! ^, F5 ]1 z" J
- return -1;) d$ ^9 C3 ]- _2 q4 P
- }
" G/ s& u+ v5 b/ @& P$ b4 r# ~9 P0 R; ^ - return 0;; R) c# K4 Y0 ~, ~+ {% K o
- }
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);0 u- R: c" e2 u: x7 W; T
- void * Thread_TCP_Web_Recv(void *arg)' h6 s$ l# R$ H0 \. L
- {
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- while(1)/ o% w6 k5 e0 Q! n1 p* u# s" Z
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- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);) T8 ^9 p0 B( h: L- ]
- printf("fd_socket_conn = accept()\n");1 Z, x5 C/ s T1 e
- 。。。
' K w" P5 i' x4 A# \ - recv(fd_socket_conn , recvbuf , 1000 , 0);7 G: r6 \9 O6 L9 Z# ` ~
- }
3 T1 a! ^5 c. A# x - 。。。
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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);- A# D3 }8 G# I+ K6 V2 h: x+ _! H
- pic_tmpbuffer = pic.tmpbuffer;* `. a* t5 T; S
- pic.tmpbytesused = buff.bytesused;
9 f) ?% f1 ]" ]5 l- ]8 E3 O# I - pic_tmpbytesused = pic.tmpbytesused;0 j" ~, u) L4 G
- pthread_cond_broadcast(&pct);1 V1 b7 ]& j8 D. X. i: b
- 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;; r7 o8 D' \9 Q9 E
- pthread_cond_t pct;
3 u2 h) V" `: q8 W - int main(int argc, char* argv[])- o8 G( I/ K" `+ r; C
- {
( k5 p' e ] Y3 } - ...
2 p( V2 M2 ?- u& m3 C3 R - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);1 ~' `! y, ]3 J/ r2 Z, H+ O* r/ c/ v
- pthread_mutex_init(&pmt , NULL);
4 J8 q& Q; q' U9 z. [+ C' l9 Y6 V - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);
! l1 Q! C Y8 w9 A" F0 X - pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
1 r5 W& w5 _1 I1 | - ...+ Q( x1 V, x% Z2 E
- while(1)
8 {# E& \* L+ p* A# O) x4 S9 D - {4 u* _! z* ~) h, G7 z1 A9 c% \
- V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);( D1 t0 ~& g, ]2 {3 g( d* }& n6 y6 q
- ...2 @% F5 ?; h* f' Z
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- ...0 Q+ e! J5 c( W5 ~$ v- ^
- }
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 I7 {' ^! h# 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" \
/ z3 c) J' h) o3 f - "Server: MJPG-Streamer/0.2\r\n" \) T- O) X. p1 X D/ h7 \' @
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
! `9 g# r' D. F. b2 J3 \% C% n - "Pragma: no-cache\r\n" \9 U' F5 X. B/ Q1 c. i7 g7 n. N
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"' n, H+ z7 J" {3 s
- #define BOUNDARY "boundarydonotcross"- Y, X$ b1 i6 C3 S( h
- printf("preparing header\n");* `" U s" n$ O- d1 ]$ c
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \+ M3 D, V$ L/ p+ [& F+ ]
- "Access-Control-Allow-Origin: *\r\n" \0 V T |0 O5 G1 i
- STD_HEADER \
; _3 M, N' W! e+ k( i% f X5 ~ - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
# J+ ^. h# O6 C - "\r\n" \# u5 M* R# [8 u% s' W
- "--" BOUNDARY "\r\n");
0 O+ s- d% U# b# p: C2 R7 p - if(write(fd, buffer, strlen(buffer)) < 0)/ {% ]$ b3 A% Z" g, X' T& G
- {' |# G4 s) }! j# z$ Q
- free(frame);7 B5 u: u1 W" `- C
- return;" T! l: S) G1 o
- }
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" \
' S4 ^- _- l! y - "Content-Length: %d\r\n" \
3 k! w7 S9 r3 C. n6 L& x2 d$ L6 b; q( k' ` - "X-Timestamp: %d.%06d\r\n" \3 L3 I4 @, c$ M3 i9 U' S/ m# ~+ V
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);: Z+ |* G* w& _. w( c: w
- printf("sending intemdiate header\n");
4 k* K9 k# N) A' p# ^3 m7 D3 j1 c0 ` - if(write(fd, buffer, strlen(buffer)) < 0)
& t2 d. o3 x- p6 ] - break;9 P% j4 i( j, P; A; u4 \
- printf("sending frame\n");& x* f( u% D( z3 ^7 j3 c% c
- if(write(fd, frame, frame_size) < 0)7 `* F7 o; [2 s; P5 U. I5 S
- break; b% m- r1 ~1 t' D( }
- printf("sending boundary\n");/ E7 f, q# u9 P: b! b$ a2 N8 \
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
; B2 F% q9 X0 n; ]$ I2 n - if(write(fd, buffer, strlen(buffer)) < 0): g- Z" ` \. }+ Z+ N
- 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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$ I7 D" p1 Z/ x2 L _1 f3 i( G" t二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:
8 i0 G: P% C2 Q: r3 r) _! l- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)
, V. G1 D6 ?% z/ T+ x9 [ - {2 `( I* U( [7 E, y. M! f
- *socket_found = socket(AF_INET, SOCK_DGRAM, 0);
; B' N" H+ V' K! g9 k% I - if(*socket_found == (~0))
0 i/ S& P2 p& ?; f( O: Q% c - {
4 W z! Z# V" e$ b - printf("Create udp send socket failed!\n");
' U& j1 R7 f6 V6 b - return -1;
2 `" V2 j6 \% N& Q/ j5 Q1 ~ - }
) c: ]1 p0 F: G Z( j4 ?8 h% b - addr->sin_family = AF_INET;
v$ `+ T( m5 F+ k - addr->sin_addr.s_addr = inet_addr(ip);, ^! A* D- s+ k
- addr->sin_port = htons(port);) s0 F! r6 z9 M& y4 |, a3 Y* h
- memset(addr->sin_zero, 0, 8);
' U) ~- }3 A S+ ?6 T$ _, J d H2 e - return 0;
! s, T& P' S6 v1 V5 X! W - }
复制代码 v" A" w5 l2 ~4 I$ m
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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:
' O2 t; v; a" M1 p' S0 o% z! [7 I* E6 E
; W$ j5 U- _, H- while(fend > 0)3 m; q% S$ i3 r* o# O
- {! w: b4 F; z( r8 c! l, A
- memset(picture.data , 0 , sizeof(picture.data));7 I6 {; n6 d8 f9 B8 ~# w9 n( ]- m5 x
- fread(picture.data , UDP_FRAME_LEN , 1, fp);
J& J& o3 D7 M' v4 S) ^" k$ m2 @, Y - if(fend >= UDP_FRAME_LEN)
! u! R' g, U3 ^3 ]2 V - {! {' G2 r& q" a; ?8 p8 n. R
- picture.length = UDP_FRAME_LEN;
+ ]& A" G: @6 d5 i - picture.fin = 0;
7 b) h: V' J$ P/ A* R# R; A - }
$ D" T1 T- }7 f# _+ Y5 S" J+ J - else; e$ \% r5 t$ h7 |$ e
- {
2 |" |$ \5 K) o6 ~ - picture.length = fend;1 C1 X# m& ~2 \
- picture.fin = 1;
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- //printf("sendbytes = %d \n",sendbytes);) P; }, \4 T9 T1 g9 l+ I
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
3 l9 `& s( G/ q3 K' l - if(sendbytes == -1)
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- printf("Send Picture Failed!d\n");
4 W5 a) e0 x2 ?' F - return -1;$ ?0 U+ c& y" }( F7 u
- }
" H. ~. q" s. n9 L2 a( z' p/ R# } - else0 w2 \$ Z4 E! B/ B+ T
- {. c1 L" S7 A( U" ?8 G2 x
- fend -= UDP_FRAME_LEN;
% @7 l' ]# x1 V$ e. A - } e! f5 d3 U& J, s
- }
复制代码
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iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |