本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑
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' r& v% R( y; X1 S+ H; c; q$ i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.html9 E/ ^. c: D$ v4 ^
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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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) N! W+ U. |# a. w$ X3 F( h$ A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。
! H$ _1 _' {: K一、HTTP网页服务器
+ l. }: y' c3 r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;
, l9 f4 }7 g [; Y) i" G# R - socklen_t addrsize = sizeof(struct sockaddr);
' ^. C z) z' S- x/ C+ \; e - bzero(&servaddr , sizeof(servaddr));
; q+ a7 D7 Q0 q: t3 M1 x; R9 a7 G - servaddr.sin_family = AF_INET;. m7 ?/ v$ p: q0 \$ o8 L' l) X/ q) d
- servaddr.sin_addr.s_addr = inet_addr(ip);, o; P B, g3 E( _
- servaddr.sin_port = htons(port);
2 \ x3 O! U/ X$ g$ W - int ret;4 X0 z, Y" }* ?* c9 d( _# n
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)
: G2 X5 x3 B2 A+ h( e% V - {
3 e9 e; ~! A: n; S1 t! | - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
: v1 |- @& i& D5 w$ r; T7 K - return -1;- H% H7 e# Z1 r) N1 D6 S8 m9 U
- }
% c9 R9 q2 D- F6 T: \ - int on = 1;
1 g3 h/ i$ H* S* }4 \, N0 `% ` - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)' `$ x$ J& S: Z( F# ?& b
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- printf("setsockopt error\n");& r& H% V: D# W: e& x6 j1 Z
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- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);7 H# H# ~8 m: @$ Z5 [2 L1 ?/ _, Z) V% |
- if(ret == -1)+ o: r: Z& \: g
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- printf("Tcp bind faiLED!\n");
: ~9 h0 r$ S. q3 A- b - return -1;* U* y. c2 p" L! Z& m) V- ~3 c
- }
" c6 l' p1 i) d4 g' _3 q: b - if(listen(*socket_found , 5) == -1)0 ]2 Q7 G. g [% J) l5 C
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- printf("Listen failed!\n");
; z* f. k& |& y; u& k' i( S" M - return -1;
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- return 0;4 ~' p9 k8 d* j. J
- }
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);
: w2 ]' j6 ~6 f& i - void * Thread_TCP_Web_Recv(void *arg)
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- 。。。
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- {
' w8 v- e7 z' Z - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
3 j' {& Z' X$ r( F9 k ~' b7 Q - printf("fd_socket_conn = accept()\n");
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- recv(fd_socket_conn , recvbuf , 1000 , 0);) j6 d# S$ b' Q8 C. w
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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);
: n, n1 T M: W# P- o( X3 P - pic_tmpbuffer = pic.tmpbuffer;; V" k! l+ D5 u$ H7 m+ v, T# I
- pic.tmpbytesused = buff.bytesused;" `& I+ d" A8 M3 y; t
- pic_tmpbytesused = pic.tmpbytesused;: V/ `9 f8 b# _# {
- pthread_cond_broadcast(&pct);5 n/ Z# N: p+ K, M1 M" F( U3 o. ^
- 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;
% `4 A0 F1 B7 a5 R+ Y2 C1 Z0 {0 Z+ K - pthread_cond_t pct;
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- TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);# d) y: o3 i' p" x: a
- pthread_mutex_init(&pmt , NULL);
% e, K0 |7 Y) x: |( T - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);5 p: q5 f. A* _& i! q2 i
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
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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;">
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复制代码- #define STD_HEADER "Connection: close\r\n" \
3 w" S1 X* R$ I# O8 n# F" k& J. i5 O - "Server: MJPG-Streamer/0.2\r\n" \% _1 v" M& e( @4 a; x
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
/ _& a, _0 C' h1 Y6 H" G4 h - "Pragma: no-cache\r\n" \6 G- G9 [9 b3 D" Y# l3 l8 w
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
6 \0 b% u% s( b/ r3 M: |6 e - #define BOUNDARY "boundarydonotcross"
; E* Z3 k* v. Z$ ~ - printf("preparing header\n");5 `: z% _$ Q4 e7 Z( ^: V
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \$ f2 A# |5 f$ @* `) T
- "Access-Control-Allow-Origin: *\r\n" \; m$ f, J Q6 H! ~1 v$ `
- STD_HEADER \
4 \1 r, I- i' t - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
- F( @$ f8 Q. V0 N) G: t - "\r\n" \
3 E7 K5 {$ `: l. d- \5 T, i1 r5 l; d - "--" BOUNDARY "\r\n");
: U1 X7 w& L) }9 X) s3 i - if(write(fd, buffer, strlen(buffer)) < 0)
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- free(frame);
6 }3 y0 H. i5 G4 C' ?3 J, G% D - return;& ~9 I7 k5 K% {+ ~% `5 T: H
- }
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" \
, `# E! u4 G$ f3 r; i! m# T - "Content-Length: %d\r\n" \
. v+ K3 A4 p. f# M: `( N9 Z - "X-Timestamp: %d.%06d\r\n" \: Z$ |7 z; w- W
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
$ H& V2 e! v1 p - printf("sending intemdiate header\n");% h! P# D8 Y( v: p q- z
- if(write(fd, buffer, strlen(buffer)) < 0): H& Q& ]! I' J9 F
- break;. s* u( f; ^; L. w) o- w
- printf("sending frame\n");2 }. q6 R5 |* Y* Y7 X- W
- if(write(fd, frame, frame_size) < 0)
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- printf("sending boundary\n");6 X* `. c% F* G f0 O8 y4 L
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");; I$ E' F) o: n Q, m$ M- j- e" V
- if(write(fd, buffer, strlen(buffer)) < 0)% _( s0 z7 I+ w' 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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# [8 r- e6 E; u2 f$ H) C二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:' R$ g4 K% [( V f0 j4 y$ E' U5 @
- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)" h) ^# f$ { S1 T/ J) ]
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- *socket_found = socket(AF_INET, SOCK_DGRAM, 0);) A! W! _8 |* F, E, N8 C9 R3 e
- if(*socket_found == (~0))
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6 T' s- @- }; ?5 o* B( E2 t - printf("Create udp send socket failed!\n");& I, I8 e4 _" `) d
- return -1;
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- addr->sin_family = AF_INET;& v9 C. M4 A" ?# a3 r6 ~
- addr->sin_addr.s_addr = inet_addr(ip);
8 I7 h3 B) Y- T1 z6 q - addr->sin_port = htons(port);5 M9 L7 j5 v6 b1 J1 H
- memset(addr->sin_zero, 0, 8);
+ j- O' G3 j! _& J5 | - return 0;
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复制代码
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0 U6 z x2 S9 \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:: O( v2 W+ ^' [2 c% V
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- while(fend > 0)
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0 l* L/ R% Y& {; M5 s- ` - memset(picture.data , 0 , sizeof(picture.data));) S" {/ D* w9 G
- fread(picture.data , UDP_FRAME_LEN , 1, fp);& f/ R3 N' p- p$ k; |
- if(fend >= UDP_FRAME_LEN)2 V5 F4 \ t) `# R
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- picture.length = UDP_FRAME_LEN;
, O2 ]' z K& ]3 X8 e3 D: ^& W7 M, v+ q - picture.fin = 0;
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% v/ S" O5 N; o5 \9 L - else
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2 _+ x2 H/ ~' A - picture.length = fend;3 t u- d6 |3 L- F
- picture.fin = 1;' Y% e8 _, H0 H0 F. m: p, [8 P
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- //printf("sendbytes = %d \n",sendbytes);
5 e) F8 J" w3 [ - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len); p7 I2 P/ i' a( e. |, f4 J8 K
- if(sendbytes == -1)
% q S8 ^3 O6 e- N2 r2 \/ x+ M+ I - {
9 g/ l$ A0 Y4 h7 @$ c& ~; J; O( h - printf("Send Picture Failed!d\n");; i/ a+ T6 q# g1 v3 ]5 S
- return -1;$ K$ o% q& N: t7 b1 F" G! k
- }
9 k$ H. v! V- ` - else; e- r! U* Q2 m) O& l, S- _' O
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- fend -= UDP_FRAME_LEN;
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- }
复制代码
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iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |