本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑
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! u0 D. q9 @: c3 g4 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& D# W# j X6 j+ ^* |1 w
; [+ f+ b9 y1 {" @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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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。
. M5 V% S2 g- }( @6 G6 p( s) D一、HTTP网页服务器0 k9 O4 r) M3 H2 V' s" {- e4 q
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;! t6 e) J( T+ A" |. h$ o
- socklen_t addrsize = sizeof(struct sockaddr);% a D! ^+ B( u1 _2 W
- bzero(&servaddr , sizeof(servaddr));
4 V: \' q# w1 F0 _/ h - servaddr.sin_family = AF_INET; K: h7 X" ?+ a
- servaddr.sin_addr.s_addr = inet_addr(ip);
/ z6 l! j \1 ]' U - servaddr.sin_port = htons(port);1 z" F0 ~! p% q- O* w! C9 T4 `' u
- int ret;/ K+ a- O/ G- K4 n! A. K) A, Y
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)! ?- a- J( h7 Z8 t+ a
- {
" _( f5 B( s% z U - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
' L9 s7 z; \4 w. [ - return -1;
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- int on = 1;0 |1 b: [) [/ S$ g C% f& G, E Y* m
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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8 R% O9 k C# S; z5 c, U- \" q* G - printf("setsockopt error\n");
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! O' _4 J8 }' Y9 J% G2 B - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
) q1 N- s* L& [% S6 D9 C - if(ret == -1)
; _- }, Z' n l - {
G! z; F p; U4 J; y - printf("Tcp bind faiLED!\n");0 h n8 `& g( Q, c& W
- return -1;" l% f: A0 Y8 a2 j5 }* ~
- }: [; c& H: N" w$ W7 I; E
- if(listen(*socket_found , 5) == -1)
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8 }' M$ t* R; {% n6 w. A - printf("Listen failed!\n");
+ i- _4 ]' B4 E4 t! L! P) P - return -1;
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- return 0;
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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);$ q m; K- N( ~3 w7 L
- void * Thread_TCP_Web_Recv(void *arg)3 E( T' x8 L' c4 ?4 U
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- while(1)* v2 W* l. Q* X5 a. l* R
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- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
: [7 R" ?9 }9 |, ]* ~( I - printf("fd_socket_conn = accept()\n");/ m2 B9 ~! I& R1 e" |: D/ f
- 。。。
, m+ {9 s3 Q& C6 [ - recv(fd_socket_conn , recvbuf , 1000 , 0);5 c# Z) |. R& I
- }
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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);
; J7 A) r, Q2 p$ T; k/ e - pic_tmpbuffer = pic.tmpbuffer;
: z- N- F9 F0 G$ C2 ~- ~ - pic.tmpbytesused = buff.bytesused;7 x0 T8 r5 `' d, o4 L
- pic_tmpbytesused = pic.tmpbytesused;8 _. ~8 `2 U: F' U0 x9 w4 W
- pthread_cond_broadcast(&pct);* r9 b9 F9 R) A0 C6 b4 e
- 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;
& H& d% p5 v( R" X - pthread_cond_t pct;
* Y+ y I* T" ^% N - int main(int argc, char* argv[])
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- ...
* C/ z! _# o: b" |) p - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
, K% p* L( w) @) N - pthread_mutex_init(&pmt , NULL);
5 G- y$ o+ t2 c8 K% t" u* o# X3 d - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);7 a& O6 C4 N V& i4 I
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
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- while(1), n$ S1 A5 a) B4 H% D
- {
7 r, R. I( u/ f! r: y! Y2 V - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);1 N$ [; R0 v5 a1 B& {
- ...% t. w+ W2 v7 V) S, h
- }
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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;">% c' X. d! L7 J9 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" \ f* s$ e `7 G/ M
- "Server: MJPG-Streamer/0.2\r\n" \
l/ X5 C9 J' t - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
0 X; e/ g' T' K - "Pragma: no-cache\r\n" \2 m- `* a4 G. t9 Q
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"$ K0 M; R. Z, e
- #define BOUNDARY "boundarydonotcross"
" t1 w8 x+ ]; v% E - printf("preparing header\n");# J. t7 {; e5 n4 l. m/ u
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \: i7 a$ y1 A/ F8 h7 w' H U
- "Access-Control-Allow-Origin: *\r\n" \6 W! ?9 p9 c, D% c
- STD_HEADER \$ e( m3 e& M8 Z! L( Q
- "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
. {& Z2 J' t1 ?# W) p - "\r\n" \6 Z9 G. S1 Q. ?' Y! v1 V# V6 f
- "--" BOUNDARY "\r\n");
7 M. p& U9 N5 @) Y) F - if(write(fd, buffer, strlen(buffer)) < 0)! p9 R) h# ?# y8 e* d1 F
- {- v2 B) t; D1 O/ S
- free(frame);- A6 v" |% O+ m8 k
- return;
' J5 r% z$ ?# O0 C; n - }
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 y- x- s) `5 |2 ? - "Content-Length: %d\r\n" \
+ }& ^$ ^! T9 _0 X" m/ @/ ` - "X-Timestamp: %d.%06d\r\n" \
) L( U- a3 j; b8 q4 K - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
1 b3 |. x3 Z. J+ v$ v - printf("sending intemdiate header\n");
) ?: Z, y/ L2 Z2 l1 Y, I' a; I - if(write(fd, buffer, strlen(buffer)) < 0)0 C8 u w1 k' d: ]
- break;
8 u p" a# F, y# a" E - printf("sending frame\n");
8 z! g, ^ j. x( M6 X - if(write(fd, frame, frame_size) < 0)2 `+ I) v7 ~7 u* k" r4 u# D
- break;
8 y! a# l- Y4 Y3 i3 s& K+ S - printf("sending boundary\n");% w! v% {1 w! |3 m+ t! e
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");# X2 f* I( w. A* F9 {( G
- if(write(fd, buffer, strlen(buffer)) < 0)8 h# R1 H: W* V
- 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。  1 e" H" v A7 E1 E n$ k1 d" k/ m

4 e. n# n6 B0 y二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:
# Y4 [* F! l/ n: o* [3 C. c5 Z9 \- 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);4 a4 G/ x% }, n+ s
- if(*socket_found == (~0))
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- printf("Create udp send socket failed!\n");
5 w* M2 m; n1 Q4 }- c+ } - return -1;
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* E/ q/ Z: I. [+ R - addr->sin_family = AF_INET;
0 P' V: ~% L% z) @9 k9 N( H - addr->sin_addr.s_addr = inet_addr(ip);
1 m/ Y$ P) y6 G+ r - addr->sin_port = htons(port);3 \+ h' x$ y6 j% i! |) }
- memset(addr->sin_zero, 0, 8);
$ \8 }( r/ a4 g ? D) t - return 0;; ^4 _# m) m+ \( C9 C) h3 l$ r$ m/ U
- }
复制代码 Z: W% r: F" {$ S% `
9 |5 V, V/ x' l2 U而UDP文件发送则要比HTTP发送简单得多,只需要将文件切片,每一片为固定长度的UDP帧长度,逐帧发送即可:" U, I, y1 N* z
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# C9 T: \9 u$ k! g S; z& K- while(fend > 0)9 J) `( n5 j8 U# Y) m6 ^
- {
' d5 x' @6 l1 X5 ? - memset(picture.data , 0 , sizeof(picture.data));
6 e* ^6 p9 s+ a3 j9 q$ t8 ]' ` - fread(picture.data , UDP_FRAME_LEN , 1, fp);/ n q0 _& Z* U# S( _' p
- if(fend >= UDP_FRAME_LEN); g- \) ^4 w/ z- m& V. N( d
- {
v8 e9 C: w' S' [ - picture.length = UDP_FRAME_LEN;
K+ M. x" @/ |4 H# c4 i% ?# Y - picture.fin = 0;
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- else% @* l7 n% O2 I; L" E& X% q
- {) ~& N- h3 C& V9 s& D( m
- picture.length = fend;
, g8 g0 ^2 l) \# F0 o - picture.fin = 1;$ M" g; o2 U$ F, n8 H
- }
+ h0 e3 ^* Q6 V+ e3 b; S" h - //printf("sendbytes = %d \n",sendbytes);4 _, ]/ x- q% x! l2 J! ]1 x3 ]" c P" S
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
/ L' o8 f+ Y& [1 n( L - if(sendbytes == -1)
: ?* ~/ P. p2 v: s: n - {
0 c! i9 T7 a; a; M' \ - printf("Send Picture Failed!d\n");1 v. [2 c. T$ {1 x, Y
- return -1;
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7 F7 G5 |. P7 F$ J - else
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% {9 z7 x, h- j. K V - fend -= UDP_FRAME_LEN;3 F+ L( v: L5 d4 H' v
- }
& U, g! h5 k* m$ ?2 a$ f - }
复制代码
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( L$ T* ?: E# d4 f( f0 U) F# ~3 ZiMX8MPlus 核心板: https://www.forlinx.com/product/136.html |