本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑
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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- ] F2 L, ]! C5 E6 a
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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。
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. ^& r, s- a1 @# T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。
* Y- f' J! [' _0 `; H1 w一、HTTP网页服务器
% z: G4 d& H& M, j/ k4 |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)7 ?2 i; H3 v3 g$ U3 F
- {
7 x' ~/ x2 @/ N2 G2 S - struct sockaddr_in servaddr;
! w) e, Q) w% I1 D - socklen_t addrsize = sizeof(struct sockaddr);
0 Q9 D" H% P# j7 h5 a, [2 ~% Y - bzero(&servaddr , sizeof(servaddr));1 B5 J3 g/ Y1 \5 ^" t" i* S
- servaddr.sin_family = AF_INET;; y& S B5 w# N* |- X4 J% L
- servaddr.sin_addr.s_addr = inet_addr(ip);
! u6 Z8 x; z$ I3 b1 Z4 e - servaddr.sin_port = htons(port);& P. E3 K5 L! V6 D; V2 E7 X0 F* |- A# y
- int ret;( H# @" V. M: o% i: P2 D* R
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)
/ a/ i: q" b8 C1 b9 o - {
' z$ B9 G. e8 e - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);% ]7 l( f+ C) t/ X
- return -1;
3 P) `- G: m0 ]% [3 ` - }
" I4 j0 D& |% V. n9 W - int on = 1;
2 u# \0 Z- F; x1 N; d$ H$ m - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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- printf("setsockopt error\n");. u9 N: N( ^5 n4 K9 ?
- }
/ z7 t! v# w1 w$ K - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
8 C; s4 _. l8 t1 Z/ E* A+ Y% F - if(ret == -1)
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- printf("Tcp bind faiLED!\n");' b2 [* E$ J" U8 N% P" M: |
- return -1;
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( t, ~" G+ G4 p! P& w% ^0 h - if(listen(*socket_found , 5) == -1)
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V7 R7 H3 n$ {; m - printf("Listen failed!\n");
' G; Q" U5 B3 S) Y' {" T - return -1;$ D- M! r. G8 _% q9 I# V" S# w
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- return 0;' v# c5 x3 N, L7 u+ i
- }
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);
r5 e7 W$ b6 p' ^* |, e - void * Thread_TCP_Web_Recv(void *arg)( ]9 @! O# K" D7 R) [" T0 ]
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- 。。。: w( i8 f6 Q; h! Y8 {5 ~
- while(1)
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- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
: u0 @* L4 r" r - printf("fd_socket_conn = accept()\n");
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, q+ r0 x9 G$ J# R, x) G( k: @3 f - recv(fd_socket_conn , recvbuf , 1000 , 0);
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- 。。。' V, Y ?# I% B4 q/ S
- }
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);
4 U- a$ k9 r5 W& [4 x/ `$ @ - pic_tmpbuffer = pic.tmpbuffer;
! L0 i9 }5 v- F. ` - pic.tmpbytesused = buff.bytesused;2 b; Z' B, S+ n2 P) l% ~
- pic_tmpbytesused = pic.tmpbytesused;' U* ?* m7 Z& P! Z1 w4 C& {3 l
- pthread_cond_broadcast(&pct);
9 }# B6 C$ F/ Q& V! w6 c# ` - 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;7 f/ i. u, P8 P
- pthread_cond_t pct;
$ d6 q! G' U1 e, _' Y _4 [ - int main(int argc, char* argv[])
. I3 r5 j" Y3 h) l( ? - {
; }% M& D, X- R" k - ...; W* G! n/ \) r T3 [; B
- TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
3 O( s) W; F- {( F; k - pthread_mutex_init(&pmt , NULL);
5 S) l# R6 @1 }0 B - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);
: C9 Z' b$ i; \3 g( ^ - pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
( R( Z* P6 x: o9 I0 f - ...
3 J. b& E1 I/ R8 ~" n1 P2 o - while(1)
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+ R& w2 M/ R6 G* n9 F! G$ f - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);; w5 A2 F( K8 `: |+ 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;">0 I- F7 q1 M% N. e3 k5 T; ]" {" 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" \
" X5 G, r% b/ o - "Server: MJPG-Streamer/0.2\r\n" \9 a9 i$ w0 h& x7 T
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \+ [) V1 T: X: _
- "Pragma: no-cache\r\n" \: d" ~3 n- F* }0 y
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"; R+ |! s1 f, m2 _
- #define BOUNDARY "boundarydonotcross"
! a- \$ |( E/ w- |. O" ` - printf("preparing header\n");
' r7 t$ r+ ~5 h - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \+ E7 i: v* i8 [& e4 h! D
- "Access-Control-Allow-Origin: *\r\n" \/ j/ t9 r; h3 W5 |; w1 z
- STD_HEADER \
5 T2 Y4 p+ f- b' H% H& I3 Y4 i4 i - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
/ r9 q: B0 l7 q [ - "\r\n" \
7 K& F; N5 J" A$ k$ T - "--" BOUNDARY "\r\n");) ]$ O$ Q7 r4 k7 f
- if(write(fd, buffer, strlen(buffer)) < 0)
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6 I6 H' a/ Z! {6 S2 P, I+ ^" C - free(frame);
) m& _, t# H& P& E7 o - return;- j5 v1 ]' p6 B. \, f9 q$ I+ v
- }
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" \
0 _! G/ D/ T, l L - "Content-Length: %d\r\n" \
; r! y# Q- X- a1 z2 U, b. P - "X-Timestamp: %d.%06d\r\n" \
' M! T* ^( ^9 w `! [( M - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
$ @7 F/ c$ S$ y9 |2 T* z- U( P - printf("sending intemdiate header\n");- ^5 \8 Q; T7 \: x$ e
- if(write(fd, buffer, strlen(buffer)) < 0)
9 r2 d) V2 C7 E" P9 v - break;
) e, `, O9 t# D8 _% x - printf("sending frame\n");3 o2 Y! i& h7 I+ w& ^/ y
- if(write(fd, frame, frame_size) < 0)
& }& `. n s+ v4 H - break;) f( e) t$ w, ^$ A
- printf("sending boundary\n"); u/ `/ D- n: h; G1 G
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
; @2 a* z6 j) ?; y% N% J - if(write(fd, buffer, strlen(buffer)) < 0)
2 e% [' {# X5 x% v" j. w - 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:
( J( ]: K9 K. M F- w4 y- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)* o/ w3 \( U& A- Z+ _. F
- {
/ q$ n# C. m- g3 | - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);9 ]7 c9 }( N& {) G/ T/ Q6 w
- if(*socket_found == (~0))7 h: i6 @& K4 l) S
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- printf("Create udp send socket failed!\n");
8 V8 G% N* f3 j8 q3 a% z( `" q - return -1;
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- addr->sin_family = AF_INET; ?& s/ [* D* R- G2 I) D
- addr->sin_addr.s_addr = inet_addr(ip);
9 {$ r5 O3 T3 T7 \ - addr->sin_port = htons(port);0 R0 Y9 J. A8 y7 A
- memset(addr->sin_zero, 0, 8); _1 {; L4 `) v4 k4 w' D0 c0 S/ l4 }
- return 0;
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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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- while(fend > 0)
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- memset(picture.data , 0 , sizeof(picture.data));7 `+ E9 R5 H( R [5 |9 l$ N
- fread(picture.data , UDP_FRAME_LEN , 1, fp);0 e" D5 n& L- j: b1 ~
- if(fend >= UDP_FRAME_LEN)2 X3 u* O* k/ }; ^7 _) a9 n
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- picture.length = UDP_FRAME_LEN;/ `$ [2 T; v5 L
- picture.fin = 0;! @! \6 F# _. A p
- }
5 {6 L5 ?/ a. m3 J - else
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1 F# [) y9 \. i - picture.length = fend;
( ?9 ~+ X. ^2 `& B3 V5 o - picture.fin = 1;
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, ~ v& R/ z, v, m" I& y3 S - //printf("sendbytes = %d \n",sendbytes);1 {; @' A8 r, ^% H
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
, Z( ]4 w* s. Q$ e3 x - if(sendbytes == -1)
# \0 p' n! B c! R - {
* G; ]& T+ `5 ^2 V. y - printf("Send Picture Failed!d\n");
7 e* U. K/ ?: ~- X) c - return -1;- D. ~' y' R& I( }: c c
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- else! Y! q& k) _ o: u8 T
- {
* H, T+ _" w6 g. ]8 x! ] - fend -= UDP_FRAME_LEN;
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复制代码
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+ Z4 a5 O, B5 h, iiMX8MPlus 核心板: https://www.forlinx.com/product/136.html |