本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑
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: d4 l4 E0 |7 C3 Y& A$ M& T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
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/ t5 b; P9 {. O( ]! D2 W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。 7 N5 ^# z9 z. w

^& K4 n( V% n1 X: x* G, L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。 ' X, W' @3 P9 ~$ l4 q0 j+ w: j
一、HTTP网页服务器
" Y5 b- T& C' i" K& k8 d& 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)6 p# S- F9 V2 h z% L
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- struct sockaddr_in servaddr;5 }) o/ g, }6 G% L7 W1 P
- socklen_t addrsize = sizeof(struct sockaddr);- d2 J2 e0 [, i2 o9 w
- bzero(&servaddr , sizeof(servaddr));
2 g% A4 _. T- E0 x7 s! K - servaddr.sin_family = AF_INET;( T: l$ k% v9 T( o( `9 [
- servaddr.sin_addr.s_addr = inet_addr(ip);
8 j3 n% y. s, j8 Y7 s4 Z Z0 z# m3 g - servaddr.sin_port = htons(port);; i: A, W, {6 k w" M/ s# Y' |7 z
- int ret;) x& ]9 |9 O# m
- 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);' S% o0 A/ E- u) l5 f) S1 f% e! h) Z7 s
- return -1;3 j+ w) t6 R2 n. x1 ]" l% h3 d
- }
0 @5 Z" T0 i3 r5 e3 ]7 X - int on = 1;; |* z; Z3 y7 w F- P$ n. X
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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2 s' ]& J2 u' Z/ _9 q2 w5 N - printf("setsockopt error\n"); Y, x! P* y4 n! u
- }
# ]+ X* \% V& p& \' J: N8 @) f - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);5 L# ]9 @" L4 f9 `" @
- if(ret == -1)
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- printf("Tcp bind faiLED!\n");
2 U1 m% @, b/ ?# i4 B1 e3 G - return -1;: F+ s& o6 D% D# p3 X. P5 a
- }
- U5 P% D$ M# H1 ~" B" [8 G - if(listen(*socket_found , 5) == -1)
( h b( _4 w% s - {
5 @8 _* W* i! f7 h: g - printf("Listen failed!\n");2 P+ W, c) E* l! y% F h
- return -1;7 n: L& B$ z8 p: D {
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- return 0;/ G7 n& v! {5 w2 Z8 t1 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);+ }" c" F. O* N- T% p- X
- void * Thread_TCP_Web_Recv(void *arg)3 g; c/ Y ?& ~, R8 |. E" H9 h
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- 。。。# ^) ?8 r( F% I! V7 J
- while(1)
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, l) }: m/ `+ U* T, d - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
$ C+ Z* N5 b4 I& O - printf("fd_socket_conn = accept()\n");
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- recv(fd_socket_conn , recvbuf , 1000 , 0);
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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);: {8 I4 F- B6 \' M* W; n) x: F
- pic_tmpbuffer = pic.tmpbuffer;
* c T+ B, h7 H( |0 @9 w - pic.tmpbytesused = buff.bytesused;
- }, {0 d+ i6 c1 B& t( d - pic_tmpbytesused = pic.tmpbytesused;! C" n' i: q! Q3 G9 ^$ T& }/ U: D
- pthread_cond_broadcast(&pct);. a$ E7 q, [1 _
- 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;% e( k: `- p) s' g n6 q
- pthread_cond_t pct;
9 J/ P6 ?8 x4 R9 L1 S - int main(int argc, char* argv[])1 B4 y" r* J9 Y" S) N+ s9 g
- {$ d' C+ _7 l- j
- ...
0 F* x9 F" }& u2 @1 r - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
" f9 r- Q5 }$ f# x9 c) } - pthread_mutex_init(&pmt , NULL);
" |( F/ F/ E) P: d9 x- D* N - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);3 D# y X4 Y8 g* N S* F
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
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- 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;">
9 p! s# i9 g/ ] - </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" \8 G/ D- `2 e8 B. u$ e
- "Server: MJPG-Streamer/0.2\r\n" \
1 [$ k* `% C. { - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \" P8 \$ s- ^. D( v o
- "Pragma: no-cache\r\n" \
) y, D+ n1 s; l; D/ V$ F. { - "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
* n" V4 _# R( c/ Y4 k% [ - #define BOUNDARY "boundarydonotcross"
0 x/ o L, L. m9 ~; Y2 U7 Z2 Q1 { - printf("preparing header\n");
; o, H2 Z$ L' w" v$ d) i! u8 n - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
- b7 J' R( D- Y D( i- {( } - "Access-Control-Allow-Origin: *\r\n" \
( c8 A Y0 v6 U! k - STD_HEADER \
* g2 c9 ~5 D: h - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \! X* i0 M- d4 V
- "\r\n" \
7 _; X6 T& P& f% n0 y9 M - "--" BOUNDARY "\r\n");
4 i9 }6 v2 W" N# M- K - if(write(fd, buffer, strlen(buffer)) < 0)9 f/ R) W( Y( P. Z
- {
! m9 C( [, F n' n - free(frame);
1 y: w) K4 K. a1 z - return;
8 O2 [" A* V) _0 `& m - }
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" \
7 R, I f: ^: v; j. x& U; q! h/ c; I - "Content-Length: %d\r\n" \1 q, }+ _. H. a, S* `" `
- "X-Timestamp: %d.%06d\r\n" \; w; x! Q' L$ W/ u% {; k. c
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
4 z. ^/ Q- Q* Z. v* H) i - printf("sending intemdiate header\n");( m% R: k+ P3 F# ?
- if(write(fd, buffer, strlen(buffer)) < 0)
1 k( c0 k1 `: p0 A! j& M - break;" S5 G4 l0 K) v
- printf("sending frame\n");+ ~! _2 U/ g$ o
- if(write(fd, frame, frame_size) < 0)
* v& D2 H3 V5 z( d) J( Z5 c( f1 A - break;0 D& N# _4 e8 Q' w9 |) `0 t
- printf("sending boundary\n");
# u' m6 f% U# a. b( F - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
/ C1 D- y5 w( s, O. t' M* [ - if(write(fd, buffer, strlen(buffer)) < 0)) f( T4 ~# D! n6 ?' k! s0 ~
- 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。  0 I% }) Y" B" f) G) ^' y
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二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:
8 c0 V2 _" I0 i2 W; {/ Q$ [- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)
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- *socket_found = socket(AF_INET, SOCK_DGRAM, 0); e& D7 _2 k8 K
- if(*socket_found == (~0))
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+ l' ~. f. X1 C - printf("Create udp send socket failed!\n");
( v- R- N3 T7 I, I - return -1;
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- addr->sin_family = AF_INET;
/ I( d7 y6 S1 R( I* k' @+ S - addr->sin_addr.s_addr = inet_addr(ip);8 W, ?( A$ h* N3 X& i# V: w& W- F
- addr->sin_port = htons(port);1 M4 `% d. V7 U- a' w
- memset(addr->sin_zero, 0, 8);
, ?3 R) Y6 \% f: d% M( `" R, T5 q - return 0;
" p2 |8 X& D, y& k - }
复制代码
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$ W3 d, h Q; ?* ^( |- v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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1 t! P) Y, C0 F \+ k- while(fend > 0)
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- memset(picture.data , 0 , sizeof(picture.data));/ B7 ^3 \; x' ]/ r6 {" A/ p
- fread(picture.data , UDP_FRAME_LEN , 1, fp);
/ {" }( e7 z7 _0 ^1 m" u - if(fend >= UDP_FRAME_LEN)5 q: G/ f8 |% n- c* C4 Y; \" d
- {
+ i: s$ ?& T9 l; g8 ?% |( O - picture.length = UDP_FRAME_LEN;
- R t8 q4 ? o! H% x. W/ ] - picture.fin = 0;
" b1 l' K8 }6 {: ]' v. b - }1 F: d* D" f1 `# H' L4 z
- else
& D6 L4 E& Z! y" Q/ m5 \& J% D - {
" Z; @3 ^1 Q+ Q1 p' x9 [ - picture.length = fend;
! i. D! K( q3 V3 F' p# F, Q6 ^' j( N- c - picture.fin = 1;% F& q, }; a% n* ]' a' Z& O& G5 d
- }
% }- V v5 n, E1 \ j - //printf("sendbytes = %d \n",sendbytes);7 |- M/ y! l1 X* u
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
2 U6 X; J- M) P4 i2 Y% H& v - if(sendbytes == -1)# x; z6 ?5 S2 k6 n
- {
7 X& p9 `0 V7 v) ~) q - printf("Send Picture Failed!d\n");" r8 {) Y4 d' B. d# W0 C
- return -1;$ s/ e2 Q) s- y$ @; U6 `
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- else
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- fend -= UDP_FRAME_LEN;: k" `! a, _$ u6 b$ n: G5 m
- }$ w0 T, N+ E Y2 P
- }
复制代码
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) c7 D% ?! u! u0 ZiMX8MPlus 核心板: https://www.forlinx.com/product/136.html |