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, D. N# }' x5 E3 O0 A
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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。 & `8 k5 l, F- m5 f7 e! U

" c" B1 {! f& K) w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。
* _) Y) l: h- |6 V& @一、HTTP网页服务器/ w }7 i$ f5 C$ w4 ]5 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)
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- struct sockaddr_in servaddr;3 u, P) W. x4 r) {
- socklen_t addrsize = sizeof(struct sockaddr);
% d5 J: w- {5 G8 u$ n. L; U - bzero(&servaddr , sizeof(servaddr));
) ]) n* _1 y+ K5 V - servaddr.sin_family = AF_INET;
. J1 p5 p2 B3 G. L% m - servaddr.sin_addr.s_addr = inet_addr(ip);1 t7 l' ~) A" |0 P2 s
- servaddr.sin_port = htons(port);
3 n2 ~+ n' r- M - int ret;) A7 l# s% |9 B' ^/ s4 Q. s7 }
- 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);
6 p' t% }' z* w* A( R" w2 C% A - return -1;
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- int on = 1;
1 e% K. T% x ] - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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- printf("setsockopt error\n");$ g: B w9 h( ?* N5 i
- }! C1 a4 r/ @& G1 D4 i
- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);" y* I) h& F+ K. O, j
- if(ret == -1)2 `+ F1 b- p' g H u0 c
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- printf("Tcp bind faiLED!\n");
/ [! k% B! ^( M2 q7 u - return -1;3 G. v* [( |7 l6 J3 `
- }
; D, F5 [) _0 N8 } - if(listen(*socket_found , 5) == -1)
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5 {2 F Z) u+ F4 @# k% h; _ - printf("Listen failed!\n");
" V( L- \0 ?. U# ? - return -1;5 `2 s6 I" }2 m
- }
& t8 G+ s( o- d& u; j0 D - 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);
2 c$ _) V+ p8 ^ - void * Thread_TCP_Web_Recv(void *arg)
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- 。。。
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- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);. B% S' @* B% R! }9 b& s
- printf("fd_socket_conn = accept()\n");
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- recv(fd_socket_conn , recvbuf , 1000 , 0);" J9 t/ V7 ]* l' A& l# ]
- }
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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);, _1 I$ h# H, d) n; e, i% k) N
- pic_tmpbuffer = pic.tmpbuffer;
# a$ {3 n/ i) `6 F# t - pic.tmpbytesused = buff.bytesused;
3 d, Z" ~' F& @% g1 { - pic_tmpbytesused = pic.tmpbytesused;8 w, E0 c W, ~1 p) |( D5 T
- pthread_cond_broadcast(&pct);
* b% h2 H$ o4 G0 O1 P' |/ Z i - 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;9 Y H0 l0 E( X. a
- pthread_cond_t pct;, r! J9 C0 A5 }0 a
- int main(int argc, char* argv[])$ l! U- t" S3 K3 e1 v3 B
- {
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% F2 \0 e% G. w - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);3 R4 P6 [+ W+ g
- pthread_mutex_init(&pmt , NULL);
0 n1 l, G0 o3 Q5 N - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);* t& i! z x+ ~* X, U! T
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
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- while(1). h, P2 I+ T4 x, I5 y
- {
+ }3 x$ J. f( K( a2 Z% b. N - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);* s' C/ ^/ z& i& |2 {+ @5 O
- ...
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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;">' {" ~" L5 Y0 {0 c9 l
- </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" \: C* U5 z5 M' D6 F) A
- "Server: MJPG-Streamer/0.2\r\n" \1 N4 |* @) {- G$ s" Z: C
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \( G n1 `. E+ K4 v
- "Pragma: no-cache\r\n" \0 R4 [* P8 Z3 L! ? K/ Z
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n". l2 m, f# x* a% J- Z& }5 v) t0 B
- #define BOUNDARY "boundarydonotcross"
0 |4 o) j; r8 |& n! M" j - printf("preparing header\n");4 {- Y4 v' h2 K' Q! D
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \2 d. [9 o8 H5 o: B8 d
- "Access-Control-Allow-Origin: *\r\n" \! @' L; x( H, x
- STD_HEADER \& ^1 h& Z2 ~7 _2 H
- "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \9 d) f; G6 S' e, g2 v- [
- "\r\n" \
# G" A$ w( B1 ~2 c, i7 X - "--" BOUNDARY "\r\n");. a4 k0 ?$ b: O7 H2 t
- if(write(fd, buffer, strlen(buffer)) < 0)
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) u: n. {/ }9 o( B% h - free(frame);
7 c4 b" p( B$ ^( u - return;
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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" \
W& m+ h0 L. ^0 |1 s" ]0 @: ]6 s - "Content-Length: %d\r\n" \8 m' D0 Y' m: t# J) X" m
- "X-Timestamp: %d.%06d\r\n" \
: B* K0 C7 _- b2 w9 M - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);& b% _ r+ M, k3 h6 p0 G
- printf("sending intemdiate header\n");% N9 X l, I% u9 K2 D- S
- if(write(fd, buffer, strlen(buffer)) < 0)
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- printf("sending frame\n");
4 y- {, I( k% o/ X& ^ - if(write(fd, frame, frame_size) < 0)
9 y. B9 \0 f% ?4 _: f, d - break;
$ [1 ?4 ^- ?9 H y$ s; L/ F - printf("sending boundary\n");
8 O/ c* [, |" t- \ - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");6 _0 F7 N1 K0 b% z" h3 b6 f+ V
- if(write(fd, buffer, strlen(buffer)) < 0)9 n* ?* I+ }% K! G$ G
- 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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- s+ }( Q, K( y( m二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:
9 z% _0 x7 y5 n% a3 b+ }7 t/ n- 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);
) o0 d6 S6 a! P - if(*socket_found == (~0))) n/ [, l, z2 J4 ^* t! M7 C
- {
) J( Q( m; C; v' ~$ J* R - printf("Create udp send socket failed!\n");
; }+ Z3 p, E! @6 w. J1 {' g - return -1;; D* V$ W; V# J! M
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- addr->sin_family = AF_INET;
. u' f) w2 R' K' x9 c5 h+ s; e8 B' _ - addr->sin_addr.s_addr = inet_addr(ip);
) v; D& h. z) @% w+ P4 j - addr->sin_port = htons(port);# X* U6 C7 K: h; T* Y8 n
- memset(addr->sin_zero, 0, 8); c# F( _0 X! a' Q; c, C
- return 0;" N/ L0 o% J7 v R1 p0 z
- }
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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)8 x* x1 G- j$ K* q* e
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- memset(picture.data , 0 , sizeof(picture.data));4 H7 J* l8 E4 X8 ~
- fread(picture.data , UDP_FRAME_LEN , 1, fp);- l# N( M% S& H8 J5 Q" R- `0 q* S
- if(fend >= UDP_FRAME_LEN), y4 s1 E. k# K5 g
- {
0 _6 _8 E6 Q" ^, u! q G - picture.length = UDP_FRAME_LEN;1 {/ ?. C6 f6 i* v
- picture.fin = 0;
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- else
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- picture.length = fend;0 g% ~( n/ V: ^* i2 Y' j1 q
- picture.fin = 1;! L2 U8 I" h5 d( o& |
- }
( ~4 s9 _2 t' s. k, @+ n - //printf("sendbytes = %d \n",sendbytes);2 i: r* X6 L& Z: W+ u, t
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);3 [3 z! _# Z# ^. c3 M% c e
- if(sendbytes == -1)
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. L' [4 p( V, y$ ` - printf("Send Picture Failed!d\n");
3 ?" a2 h. J/ Z( z4 \- g7 ` - return -1;
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- else; z! g& k2 _: I4 A( v
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- fend -= UDP_FRAME_LEN;( ~! I- j; F! C
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- }
复制代码
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' r+ z) r$ l$ V# l1 [! u! OiMX8MPlus 核心板: https://www.forlinx.com/product/136.html |