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- k% {2 @/ P; C, N
. M7 r( o' k$ O" ]2 L2 l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。 % T* u! B) ]2 e% N$ Q7 {# J, r3 x

: q0 F" H: _2 }0 O7 L- z( Z! A7 z& W+ p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。
; F, E! t- ~! |9 I6 S4 L! M一、HTTP网页服务器0 q4 L0 e0 o8 P
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;$ Y$ }, H# ]7 ] r& M& g5 [
- socklen_t addrsize = sizeof(struct sockaddr);
) h$ C" C: ?: k, U, J! ]/ } - bzero(&servaddr , sizeof(servaddr));7 x. V; H5 b- p0 z4 O
- servaddr.sin_family = AF_INET;7 r: t% T5 l2 O
- servaddr.sin_addr.s_addr = inet_addr(ip);
- V6 n7 p1 D2 g5 D( } - servaddr.sin_port = htons(port);
3 [1 L# \8 R* T; t. O - int ret;. ^2 z, [ A# `; K2 ?
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)4 E; W m0 A& P. ]9 D, q& F6 e
- {$ I" K9 V+ K2 ? }8 F" a( Y: [
- printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
( z6 L* |" }: Q3 G1 t G - return -1;( D( v' a( j6 \, }. e# t! n/ e
- }
6 Z( x. ^/ C" i/ O7 R - int on = 1;
; m G; _, v- G5 E' B% Y2 l - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)- I9 H' @) Q5 `( D8 I! N# Y0 y
- {- B9 w4 C* G U& [0 C
- printf("setsockopt error\n");" b$ k1 `: k5 F0 g! ~
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- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);* L; E4 C# J; J! {* @
- if(ret == -1)
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- printf("Tcp bind faiLED!\n");% ?- v7 e1 p' b+ X% c
- return -1;$ |+ Q$ M% K3 h
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- if(listen(*socket_found , 5) == -1)
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- printf("Listen failed!\n");
D9 A( o; V' F - return -1;' V; F+ r9 ?: [' P% e
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- return 0;2 i( ~' p: j! d) k. q/ Y& p% u |
- }
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);
k1 H1 A' X, _6 C - void * Thread_TCP_Web_Recv(void *arg)4 u k% l; V( v$ e: `0 E
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- 。。。0 z3 l) N' e! i0 M9 A
- while(1)
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- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
' n, l+ W6 ^) W( D$ j - printf("fd_socket_conn = accept()\n");
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0 p3 X+ M! a2 a- ?$ { - recv(fd_socket_conn , recvbuf , 1000 , 0);! F6 {! u4 D" Y2 h9 x& ~( e5 ^
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- 。。。* n6 F7 ?7 F6 h9 u% o4 }
- }
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);
% h; t. X: c9 n9 c7 F' J - pic_tmpbuffer = pic.tmpbuffer;/ }6 K( O7 P/ Z' X
- pic.tmpbytesused = buff.bytesused;4 x) i. w4 L( _& ?
- pic_tmpbytesused = pic.tmpbytesused;
1 j' p- C* z% Y1 j3 X - pthread_cond_broadcast(&pct);
; ~, q& e3 m) x - 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;( Y) `( I* A5 W, b; E+ \9 N, `* l
- pthread_cond_t pct;
, O( Z9 U( }5 r8 ?8 Z - int main(int argc, char* argv[])
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- TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);% d( p, B4 o" O C1 X
- pthread_mutex_init(&pmt , NULL);
5 ?5 y7 E' e5 v1 @% p - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);" m+ K0 b7 F3 y
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);; F/ T& n% `9 P% H
- ...
: \9 G8 ?' ]; {, w4 E. @ - while(1)
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- 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;">( M7 a1 l; U/ s$ m
- </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" \6 Z. A5 t1 ^ a+ n& T! a) q
- "Server: MJPG-Streamer/0.2\r\n" \
9 n2 X3 T3 u% s9 I- e: @+ G. R: s - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
9 a ?8 j: l V: J4 q" z1 U+ ] - "Pragma: no-cache\r\n" \- B& E' J" o0 }4 M# {$ M) s
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"2 z% p* ^% z% ^" w6 |- _0 [
- #define BOUNDARY "boundarydonotcross"
/ A8 f, ? K) Q6 _' m) y0 u- h4 F - printf("preparing header\n");
4 ` B+ Y6 c( |) M1 l - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
" k$ c" D. r! J5 v: `; M - "Access-Control-Allow-Origin: *\r\n" \
' ]5 \ p/ O( ~( d# z# z - STD_HEADER \/ c) i. l& `, X5 j" H( ~
- "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
/ o0 p1 ~5 g* m - "\r\n" \
' Z5 \5 k. U* e9 J" p$ ?7 P - "--" BOUNDARY "\r\n");
+ ?9 p) ~" s2 V* v9 Z6 O3 [ - if(write(fd, buffer, strlen(buffer)) < 0). X& B9 R( E7 t; |& i
- {
1 d! {3 R# _' N& }, N. F) y* A - free(frame);5 r! |( c" I" k" [2 E6 E* |% G
- return; `- G- c& W. |' u- K9 N( Y
- }
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 d P- h# O) `6 ?
- "Content-Length: %d\r\n" \0 Q% Z; Q8 [6 o) ~8 ^ \
- "X-Timestamp: %d.%06d\r\n" \
/ A% c6 Z, k4 x( T2 i6 W ~ - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);$ W* q& @' }, X6 K7 v* N
- printf("sending intemdiate header\n");! t1 f$ W: C4 E
- if(write(fd, buffer, strlen(buffer)) < 0)( F9 a5 N# G; h; N1 j( S7 V) S
- break;
3 P9 l" E8 B/ O; Y* Z& M - printf("sending frame\n");
; t. ~5 u0 h4 L7 @0 s - if(write(fd, frame, frame_size) < 0)4 D' E$ D# W- o& i3 D
- break;8 W2 L+ k2 R) S+ m) w/ s
- printf("sending boundary\n");6 @/ i5 l% o0 C
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");5 y. A8 k; ^/ g7 C* t3 b; e0 M6 ^
- if(write(fd, buffer, strlen(buffer)) < 0)
% \1 e$ f# k* ~ \( `+ V+ c0 h5 ^; H- 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。  + ^6 s3 ?+ S! t$ C. O3 e

$ {. v' @/ h3 H1 Y二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:
! j$ x0 F. ~1 _3 a) o* W- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)- h& J0 ?4 P a- e! N# C: ?
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- *socket_found = socket(AF_INET, SOCK_DGRAM, 0);; ]+ N+ T# _+ u; G* ?4 B
- if(*socket_found == (~0))
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- printf("Create udp send socket failed!\n");
5 t9 C; l7 t3 A: r, d - return -1;
5 @* [8 z! T/ y - }
. v4 z/ [8 x4 m; g6 g - addr->sin_family = AF_INET;8 l4 K0 o& J5 D# l, z
- addr->sin_addr.s_addr = inet_addr(ip);
( w' q& u& \* t( A* b) o - addr->sin_port = htons(port);
2 `' f- z* D0 `" ~. f2 h' x" X - memset(addr->sin_zero, 0, 8);! y/ e* y7 j2 w2 A5 C
- return 0;
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复制代码 T# ~% N/ t: ^" K; c0 _
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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)) b; b+ ]- M4 i0 a5 x& O
- {
0 \, P; J' N R7 u! ~/ M$ D! U2 u - memset(picture.data , 0 , sizeof(picture.data));2 q- D, I1 i8 B) l8 \
- fread(picture.data , UDP_FRAME_LEN , 1, fp); c u) S/ u; Y4 l5 J+ s' h
- if(fend >= UDP_FRAME_LEN)
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- picture.length = UDP_FRAME_LEN;8 g8 }, i# a4 |; x
- picture.fin = 0;
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0 s. x# K& p+ F* `& H - else
4 `$ `+ n* \5 K# m1 C. Y5 b - {
4 T$ \9 D$ [6 D( l9 |2 J( k! X - picture.length = fend;
: x* y4 W' M$ C+ b/ c1 G" J1 l7 } - picture.fin = 1;
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7 b- Z6 ]" m/ w3 G - //printf("sendbytes = %d \n",sendbytes);) P9 g' V, z A0 N) F4 Q7 b' K
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);* T" u' I, a1 m `( }" h4 y( y
- if(sendbytes == -1)
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/ a; b# v4 f6 }; @0 H3 Y) Z" L - printf("Send Picture Failed!d\n");
! t: T9 u4 m7 W - return -1;
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8 r0 ^5 |( L1 M" ? - else
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$ M& H9 _4 D! K$ k- N; } - fend -= UDP_FRAME_LEN;8 J- D9 A/ l2 _1 p- U/ k
- }0 u! A9 u% R) k& ?3 k
- }
复制代码 . r2 C4 n1 J4 L8 m7 Q* x
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# ?' [/ r- V+ w- J3 T7 m. KiMX8MPlus 核心板: https://www.forlinx.com/product/136.html |