本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑
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" i, ?! d4 y# ~* c- ?! \. D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+ R1 @: W5 P! ~/ X0 {
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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。 - K! Y3 Y7 O( l

5 }$ C9 | `7 G! h$ d5 O/ b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& H7 f. q( _. G, E一、HTTP网页服务器2 j: m# | g' m# i
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 J; Q8 p0 \4 O( D6 y6 \0 i4 O3 L. k* V* d - socklen_t addrsize = sizeof(struct sockaddr);
' t7 p% M# U/ M' k - bzero(&servaddr , sizeof(servaddr));" y- p, B/ w* s& n
- servaddr.sin_family = AF_INET;1 f) i6 ]' w3 r1 e
- servaddr.sin_addr.s_addr = inet_addr(ip);2 ]6 z9 m( e6 I- d1 F( s$ B1 n
- servaddr.sin_port = htons(port);3 R0 ?( P6 u9 Y$ Z$ C9 w* C: z% K0 |
- int ret;% b! a, r G! o: } L
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)# M0 V- N* \- A* |9 E
- {
1 R4 P" n5 a/ E- A' X& V - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
5 |4 r% T2 `# h - return -1;: c; C! u1 V4 M; R3 T
- }4 T% b R7 `- `. a/ h
- int on = 1;) x# O r$ w X+ _$ r
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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- printf("setsockopt error\n");6 h, k9 g E: [4 j" A1 P
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- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);7 t. I2 C' y/ v( q: v+ m
- if(ret == -1)3 l+ t/ d# { l9 e4 K
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- printf("Tcp bind faiLED!\n");
. a* F2 t; K* F! \ - return -1;; D# D$ b8 g5 m
- }
# O. b9 x( c! _5 m0 J& } - if(listen(*socket_found , 5) == -1)1 B6 u' s- y) D7 m0 j/ M2 F
- {# R3 J/ R4 |& T- n6 u
- printf("Listen failed!\n");
6 \3 H0 m: s8 O - return -1;0 H* J5 E, U* ]; [3 R& y7 a3 ~
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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);
% Z; T4 V2 T! \* j$ f - void * Thread_TCP_Web_Recv(void *arg)% S: ?# x3 @* W* ?) Y
- {
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- while(1)( F8 X0 }" T+ ^" }+ C8 b
- {
9 }8 f: W+ o3 i+ v - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);0 b$ I* ^% C* b+ Q' f4 c, [
- printf("fd_socket_conn = accept()\n");' ?" v$ ]/ }4 O# M% U/ h2 F+ X! ^6 F
- 。。。; g* v+ V2 r2 w7 K: G9 `$ o
- recv(fd_socket_conn , recvbuf , 1000 , 0);1 y6 [- A/ B0 \
- }
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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);) V# `6 _5 \- h* u1 L
- pic_tmpbuffer = pic.tmpbuffer;+ O U' }4 `3 m$ \$ @. Z4 d5 A
- pic.tmpbytesused = buff.bytesused;$ Y6 I$ k( J1 S. o. n6 ^
- pic_tmpbytesused = pic.tmpbytesused;
, x- @3 Z% J1 K6 q- Y - pthread_cond_broadcast(&pct);
* B: T" ^. M2 m8 g. T - 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;
7 _. R. w5 g3 \2 p6 _/ [7 h4 d/ Q9 r - pthread_cond_t pct;( @# ~' { y8 p2 F3 I/ _+ M
- int main(int argc, char* argv[])
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- ...
/ R3 @9 ]* o: _8 u/ ? - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);& N. w; f6 h, N$ Y6 s+ a
- pthread_mutex_init(&pmt , NULL);- F" r6 d3 b( m+ U: w4 ~, Q
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);. h7 V( q8 a. W7 x# y5 s* u
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
4 C' D8 L# z; e' y+ N - ...
3 n }' |8 n/ b q5 ^, h4 A - while(1). s6 o. g9 `+ E& c
- {
: e/ }" O c$ B - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);3 X; J5 w5 u9 h& }( M
- ...
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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;">
% c7 I& m' }- ?# ]! _+ z - </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" \
+ u! b' `2 v# k - "Server: MJPG-Streamer/0.2\r\n" \
+ s& ^7 S6 C+ l# h8 Y - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
/ _9 Z6 b1 @. l5 Z( _" i1 f - "Pragma: no-cache\r\n" \
* J& g9 `# o, B3 a - "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"0 p! f1 M% c: h) y" a+ P, S: f, S5 s
- #define BOUNDARY "boundarydonotcross"
) h/ {# K7 v+ g2 D* v. h k+ M - printf("preparing header\n");7 X! b# Y. ]: W3 {" H
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \" T3 G# _; j$ i; [' h$ M0 d" L/ w
- "Access-Control-Allow-Origin: *\r\n" \# L/ K: A1 u* o' ?& q' d0 @' M
- STD_HEADER \7 b0 M' J$ r7 n
- "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \: l5 T& l; c) j
- "\r\n" \& f5 d3 B; f# T% N8 X5 s
- "--" BOUNDARY "\r\n");
4 l" B0 }: t+ ~: F6 j2 @ - if(write(fd, buffer, strlen(buffer)) < 0)
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1 e2 ?) C( w9 q9 S5 I - free(frame);) k* B% k# _1 X. n" Z5 N2 N
- return;/ {1 d( z* ]- h2 v4 P3 q8 L
- }
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" \4 q( l& T0 |, S! H$ D5 y# d& c. _" p/ m
- "Content-Length: %d\r\n" \
8 w! G1 x4 `+ P - "X-Timestamp: %d.%06d\r\n" \
) V! M0 H, ~: o6 o/ C5 v/ ?) r - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
1 O2 p9 V" H2 y) T8 @ - printf("sending intemdiate header\n");) v8 z, y6 [7 H. u% Q! S' k
- if(write(fd, buffer, strlen(buffer)) < 0)
8 G9 h) t# y2 Z0 Y( D3 k( N - break;) P: m' C, a5 w6 Y% k; q2 E1 m! g
- printf("sending frame\n");
# e( f6 p; n- w; s3 Q6 \ - if(write(fd, frame, frame_size) < 0) H$ j% ~/ h6 J4 K1 P+ |$ g) \
- break;. b4 e( Q6 r5 G) N
- printf("sending boundary\n");9 R2 X" H1 h- q! O( L: m4 H- \9 ^) I
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
1 @( Z/ m* h" \7 l% \) o - if(write(fd, buffer, strlen(buffer)) < 0)' c6 c8 x" V7 O) W% B' @! b
- 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。  % j$ O# G! D) u, v' ^

9 [6 B9 H. U k+ d2 e$ h9 r' i二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:/ U; z' _: \- ~/ g, F
- 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);
3 v: W& Y1 a) a4 t - if(*socket_found == (~0))2 q( I" ?9 o5 M7 K. ~7 r9 v2 m
- {
" k6 Y6 w4 t2 ^% H - printf("Create udp send socket failed!\n");
+ E+ J6 U( |2 i2 R3 O s- z) Q" l - return -1;
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- addr->sin_family = AF_INET;
2 W* P( H) o" h) o: V - addr->sin_addr.s_addr = inet_addr(ip);
* ~, w) v+ G8 [" F( p! S- z* H - addr->sin_port = htons(port);
0 i7 l+ X8 o9 Z% r - memset(addr->sin_zero, 0, 8);
$ K8 l P' D0 D- ]( c( } - return 0;
4 A0 E0 J$ ~) W6 ]8 f. l" x; V: e6 F - }
复制代码
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J* d4 M% K: d/ m3 O$ y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:: d3 z5 c I& t$ l' n( p
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- while(fend > 0)( C' P7 O7 k! o1 U; }
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- memset(picture.data , 0 , sizeof(picture.data));( e7 ^7 h3 @( P7 f3 h, h
- fread(picture.data , UDP_FRAME_LEN , 1, fp);
. H# Y/ L! B; ?: L, ~9 F) A - if(fend >= UDP_FRAME_LEN)
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- picture.length = UDP_FRAME_LEN;2 B' \5 s( E7 l6 R
- picture.fin = 0;
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- {
: v' S8 h8 V2 L - picture.length = fend;5 y$ K+ }6 Y4 [! j1 v
- picture.fin = 1;
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- ]9 ?7 Q4 y; Z8 }" s - //printf("sendbytes = %d \n",sendbytes);6 a& p" Q' g0 z% t3 l
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);' I/ }! `1 r; } J7 s& Y. {9 ^
- if(sendbytes == -1)
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; N2 n: H+ g+ t5 m+ E8 | - printf("Send Picture Failed!d\n");- i4 O; d; t; u: x0 R* R
- return -1;. G& E, C) C- O8 I( K/ v8 t2 A+ R; W
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- else
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3 r& `" P& e. A! { - fend -= UDP_FRAME_LEN;0 R" C9 D# c$ F
- }
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复制代码
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4 Z, C! Q0 Q& N5 _5 f: H& niMX8MPlus 核心板: https://www.forlinx.com/product/136.html |