本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑
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" c t* q; }( F- 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 w+ v% \. g& n$ t* V u
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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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T6 c; T) z: E9 D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。
" e& y# I7 f# d- Z一、HTTP网页服务器" N/ u4 T9 B- Q; j& Q- \. k# O
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)) o6 N- z4 i/ i% T5 N0 t9 v3 P
- {
2 b7 ]# ?- q1 r9 S - struct sockaddr_in servaddr;
4 u7 b" `% b8 ^' V- H - socklen_t addrsize = sizeof(struct sockaddr);; @& `, B: c9 {- t# X* w. v
- bzero(&servaddr , sizeof(servaddr));; N0 }2 g+ s" \% Z, {/ R3 H
- servaddr.sin_family = AF_INET;
. U: A0 ?) H. j - servaddr.sin_addr.s_addr = inet_addr(ip);
. `5 F+ G9 O5 t6 K1 U( r; N - servaddr.sin_port = htons(port);0 j) s1 @' n9 h! k. K# l, s
- int ret;0 f, A1 y) \1 q; o6 k7 u
- 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);# O$ G1 d% E/ H
- return -1;- M- e8 D( ]/ g) ~: r* J
- }
- z( j8 p- h, u. k8 S5 `; _/ d. A - int on = 1;
, s! N. S# d. g% ~, t) `' s - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0): m+ d# @9 [ n1 U) ]0 m# F8 f
- {8 D+ l( l; _/ C, r
- printf("setsockopt error\n");
/ p2 S* O3 Y/ ` - }
7 H/ w" Z! M! t( o! e - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
- _ W9 K4 }8 D0 V - if(ret == -1)
\$ V" N4 _/ v% M: d } - {
/ D o: X9 w8 k" A: a/ x* M1 _ - printf("Tcp bind faiLED!\n");$ v$ j0 E+ l" Y. ~! d& y- ^
- return -1;
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9 v. { `- M" L& ` - if(listen(*socket_found , 5) == -1)
$ t" J3 u. _# `' B - {
0 C9 n! `# T7 J/ {3 c+ c# E( {' X2 X - printf("Listen failed!\n");* h( [& x4 s, z5 B# e0 }
- return -1;6 |3 ]6 L R) Z" D& L: d/ h; _+ m
- }
! m# p m( e8 k3 F& J0 W7 J - return 0;
3 q b/ q6 Z# v, y. w% ]8 A( C - }
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);2 {+ w; p' |7 w7 N* q
- void * Thread_TCP_Web_Recv(void *arg)" z N4 ^! a( U R4 ^6 ~. L. C
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- 。。。5 J ~% a: q# T8 o2 p" R) `
- while(1)2 H! A2 j2 g$ |% o
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- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);% X8 B, V7 S z* X
- printf("fd_socket_conn = accept()\n");' N6 B5 N& }; z% M# i
- 。。。
z6 g' I" ~* k: m S - recv(fd_socket_conn , recvbuf , 1000 , 0);
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- 。。。
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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); D( H9 g% u3 h! P( J
- pic_tmpbuffer = pic.tmpbuffer;
9 | C; ^6 g; Q B+ ?2 E1 g, W - pic.tmpbytesused = buff.bytesused;
7 m5 z8 b' ^) |3 { Z: y/ j" G5 e - pic_tmpbytesused = pic.tmpbytesused;
% g! d& Y9 @& z8 z% R* R5 J - pthread_cond_broadcast(&pct);
' ?& m! o# \8 L, |* u - 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;
" B" K) F$ q7 G- S# w: ` - pthread_cond_t pct;
/ @! z3 u% a: i, P - int main(int argc, char* argv[])/ D' \, ]* y6 ?
- {
" B$ J& f: H f# b/ ]$ h - ...
& C3 \5 m5 y- o5 ]" f! M% u0 a0 n - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);; A3 w, h* d; I8 Y
- pthread_mutex_init(&pmt , NULL);6 X# z/ `3 W( f5 D: X; _. p
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);) J# ^2 V T+ X" x; y, B' M
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
& n7 G0 e& G& | - ...
+ r+ g* T4 b w$ ?$ T5 }# O* _ - while(1)- c* ]1 |0 a* ?8 p+ d; ~% S
- {/ F+ C" I3 Y( Q* ` x+ e# i: `3 C
- V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);
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- }
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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;">2 A1 ?: V) Z" X5 E; o @- o# S0 I6 B; W
- </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" \
' q5 C, S% M9 g. V - "Server: MJPG-Streamer/0.2\r\n" \
7 R0 U" h \3 y( c1 A# n* K( T - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \. X$ E; |: R' ^9 D( ]
- "Pragma: no-cache\r\n" \
" P Y. @( J Q; k' r1 w, T - "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
# P' U6 A2 `3 d+ S7 ^( _' b, i - #define BOUNDARY "boundarydonotcross"" _5 A2 q6 v, k! v. H
- printf("preparing header\n");" D7 H' \* Z: r; d$ u# C
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
' v% y; v4 c/ H; X - "Access-Control-Allow-Origin: *\r\n" \7 f' ? F( ] ?
- STD_HEADER \
( m: L0 R7 i" |# |% a# n i - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \8 N* {% k, x% G3 Y- f+ E% G
- "\r\n" \% P. z) j, K$ b! A ^& h' w1 O& ]* x
- "--" BOUNDARY "\r\n");
3 D, m! u( c% [" T - if(write(fd, buffer, strlen(buffer)) < 0)
2 P' h5 @3 Z# I4 c/ O - {
4 \" n1 _. p# R) Y - free(frame);; u0 ~9 c: N9 |
- return;, ~& I! @, A/ N; _4 |. O+ q4 J6 [' [
- }
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" \1 r% y5 T* [$ n7 d1 l
- "Content-Length: %d\r\n" \& E/ ?, ^) }# Q a" X l& v0 z
- "X-Timestamp: %d.%06d\r\n" \7 H" P- i$ v$ N z
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
9 v# i7 q/ h1 ^/ j; W! b2 v9 q! B - printf("sending intemdiate header\n");
9 ?* @/ m J- g2 G - if(write(fd, buffer, strlen(buffer)) < 0), [8 \" A7 ^8 L8 V# g' N
- break;
- A" r( X$ h$ Q9 T; m9 w: Y* y - printf("sending frame\n");" V1 M0 U2 n7 S
- if(write(fd, frame, frame_size) < 0); o* U7 R2 H1 t
- break;8 O& c: i2 F- l6 w6 `+ c+ S( u
- printf("sending boundary\n");; N' I1 L; y" d+ M9 l! F! P
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
" Z% ]6 j2 R }2 N - if(write(fd, buffer, strlen(buffer)) < 0)
0 d3 x }8 j$ v& e: v0 k! S - 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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0 l6 J& h! J3 q# F1 `2 C w9 u8 r# v7 d3 e二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:
# F# j+ S. Q8 \0 b# w" x( R( ]! t" X4 W- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port), p, ^. P) c/ o# ?: @. l
- {
0 A& ]# s7 |0 ]6 Q3 Z6 g - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);! v% i9 @) O) [- Q8 T9 h2 i
- if(*socket_found == (~0))' F( c9 `2 M' F/ } L% n8 F
- {
& [2 x5 @/ N/ k/ [ I4 O - printf("Create udp send socket failed!\n"); l2 A6 H, N0 d, D3 I8 O. G
- return -1;% s" y: O- W: {
- }
& ~. J# o! b. Q6 G - addr->sin_family = AF_INET;8 l* U- A" T4 _( K% d
- addr->sin_addr.s_addr = inet_addr(ip);
0 {' T* l: V! C9 p! L* g% H - addr->sin_port = htons(port);
2 J+ k8 d) e/ A3 |) ] O - memset(addr->sin_zero, 0, 8);5 @3 V6 Y- S) {# e/ B/ O
- return 0;
, I" Y# W$ q; \7 k - }
复制代码 4 J, ]8 K( j1 E& \9 o/ K! J
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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)" a! s+ R& u. ~7 Z
- {
" `* w$ C# f# K6 P9 N2 h" \6 k - memset(picture.data , 0 , sizeof(picture.data));1 H. L! V4 T* _6 c- M" L' P! `
- fread(picture.data , UDP_FRAME_LEN , 1, fp);
3 r. ~. N3 q2 Q - if(fend >= UDP_FRAME_LEN)
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- picture.length = UDP_FRAME_LEN;
6 P, A' W# Z4 M( l* p3 n - picture.fin = 0;
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N# O& o* X, k4 D& x5 I. _! q$ a+ N - else4 K7 h) [6 ?* `# T8 e7 \ ?
- {
4 @+ f6 ~0 F z( a - picture.length = fend;
! f+ Z6 _6 @0 {- v( ]% f - picture.fin = 1;8 q# i9 j6 J9 \! Z
- }0 V" y4 w& S- [' x# i. G+ {
- //printf("sendbytes = %d \n",sendbytes);
) `- w* \, U+ W% `+ V6 B - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
( h' W# h( W0 M( y* I - if(sendbytes == -1)
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- printf("Send Picture Failed!d\n");
6 }- y) y1 H) X# q( `5 q5 o9 [ - return -1;
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# z2 `, b4 C4 k6 k5 j- ] - else1 x/ B( o: Y0 c8 ?: M6 l
- {
: Z1 R1 Y9 R% U% e. Q+ g - fend -= UDP_FRAME_LEN;; B# P) w0 T) Y: r7 Y" \( H. J3 W2 t8 }- s
- }/ ?6 N0 Y7 v5 a" S0 B1 \
- }
复制代码
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, W; f6 w' R. ^3 a8 ~$ [8 EiMX8MPlus 核心板: https://www.forlinx.com/product/136.html |