本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑
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0 z# D5 y$ H( d3 R6 ^5 |; o1 J. W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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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。 3 s0 S! q& n4 a, r& m
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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。 3 c9 H2 b0 V4 M' G
一、HTTP网页服务器' e. x' i1 W( Y0 E! ]- L/ P$ 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), H/ M% N9 F& E* Y1 _6 `
- {
3 A d; Q0 D4 F2 R: W - struct sockaddr_in servaddr;
) X O/ G1 ^/ g' g - socklen_t addrsize = sizeof(struct sockaddr);
: l# B% z3 \! B$ l - bzero(&servaddr , sizeof(servaddr));
1 i8 B7 h- v: x5 y3 m - servaddr.sin_family = AF_INET;
+ D \$ G$ J6 x9 y4 \ - servaddr.sin_addr.s_addr = inet_addr(ip);
! b- n0 }" a! ^4 b+ \" A2 W - servaddr.sin_port = htons(port);" o# k$ c [9 n( D# o
- int ret;
3 g- r9 V5 n0 x% Q - IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)4 p$ X. ^! A" q3 M5 {. }" d) D$ q" Z
- {
# j0 e, p- }1 T# q( l - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);7 N8 P1 h2 I$ k3 m( _: r, z" k0 K
- return -1;
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0 K3 q0 c; P0 Y' T9 G8 ~. D) f - int on = 1;# X( T( Z( ]( i6 [4 Q& F) S/ W
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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- printf("setsockopt error\n");! O5 d l: B) N& S
- }
7 {" h6 q6 E( G - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
' V3 V% o3 s$ `; O - if(ret == -1)
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- printf("Tcp bind faiLED!\n");' H& k- A' s0 n
- return -1;! m/ H# z* F+ ~( j
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- if(listen(*socket_found , 5) == -1)6 h& }8 b8 T. m, M) e1 |6 u& R
- {, F% g; o6 P! P0 O& K' ]1 y
- printf("Listen failed!\n");
% ]* r+ b' P8 ]0 \9 ]& p - return -1;
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- return 0;
* F$ m l0 [4 b, B6 i% i4 g; ] - }
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);
, \: _' ?3 e% M' Y+ p$ z - void * Thread_TCP_Web_Recv(void *arg): O( D; S; k4 n( R8 W9 B
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- 。。。
' \2 e1 X. s. Y$ W t! y" B f' C# U - while(1). X. _1 F, c# x$ d* t( a
- {
0 m9 O% B8 h9 h% x+ ] - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
9 M5 j/ r5 e5 l/ W - printf("fd_socket_conn = accept()\n");, M" ^8 ]- Q K6 Y0 o' n
- 。。。
( H- S- c/ F. N - recv(fd_socket_conn , recvbuf , 1000 , 0);
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! H" I7 A: J! m* a" a - 。。。
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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);
. p5 D# d9 u4 Z - pic_tmpbuffer = pic.tmpbuffer;! I. _4 h, l- b; B0 ~7 j C. z2 H
- pic.tmpbytesused = buff.bytesused;
' R$ c9 O; c2 Z- E# N* I - pic_tmpbytesused = pic.tmpbytesused;: w4 M( }6 R ^+ ~6 a
- pthread_cond_broadcast(&pct);, m7 V; L! W8 y) U; u3 G; b. Z
- 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 z4 l% a" b+ q. h' ]
- pthread_cond_t pct;+ a) m% ~5 f% F/ M5 c4 x* g$ C
- int main(int argc, char* argv[])3 L4 E7 A3 C0 z4 j3 r# D
- {# b& B- y: v/ Y% h. M) s
- ...
/ F* N. O4 N8 r; E3 Q9 m3 l$ G1 p/ w - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);# v( _7 g; j: q6 A1 ]$ x% v
- pthread_mutex_init(&pmt , NULL);
+ q6 l& L2 ?4 d5 T/ S6 ^ - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);4 c0 B$ u) ]1 [( B% Q/ G1 A# m
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
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- while(1)5 t" a1 E5 `5 Z( j" W3 }
- {
; _: y0 ~" U% M, A; }, ~ - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);
# R$ I2 m# z& y# g3 d# X - ...
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$ H; O4 R6 Q0 g - ...
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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;">
1 W/ i B7 [8 v- W. l+ x - </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" \! r+ D/ Y8 V4 c d7 l
- "Server: MJPG-Streamer/0.2\r\n" \
) q6 y' G# O" } - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
, N/ `+ U7 Z: u, M5 { - "Pragma: no-cache\r\n" \
6 Z9 F* r0 B# [8 t& s - "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
0 P7 {% @) n3 |$ }6 s- v/ Z+ B - #define BOUNDARY "boundarydonotcross"" e% a( o1 L$ Q
- printf("preparing header\n");2 [0 ?7 S ^5 y) B8 w
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
2 _) X* E; W k/ ~' ] - "Access-Control-Allow-Origin: *\r\n" \# T! g! m* O, Z+ T# E
- STD_HEADER \
( T( h6 ]8 ]# a8 }7 M9 g - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
- t# x1 E' M) R9 l - "\r\n" \: E1 o0 t0 k# k. [. A
- "--" BOUNDARY "\r\n");
7 a9 Q# Q: ]1 d( T# } - if(write(fd, buffer, strlen(buffer)) < 0)
2 u+ I- y) z; Q! _; D$ O - {
2 v2 D6 N% Q8 P8 ^ ?' J - free(frame);; D- z: r9 X8 B& E8 B- N
- return;' q) v$ |. H0 P* [7 d
- }
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, R B) C( f! L% ^+ v4 c - "Content-Length: %d\r\n" \4 O# f9 _) [9 W9 z- h1 }
- "X-Timestamp: %d.%06d\r\n" \. }. u) C- z. P" K8 f" Y
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
1 j( J9 b3 j8 o3 f - printf("sending intemdiate header\n");) u. F8 J" {# k- a
- if(write(fd, buffer, strlen(buffer)) < 0)
9 `% m& P5 `6 l: X A2 }" B - break;. w. y) O1 ^# ^
- printf("sending frame\n");" }# |& l- E; A2 J$ C
- if(write(fd, frame, frame_size) < 0)
* h5 n' N Z H& z - break;9 D r) v! P1 U! `$ w5 v' Y
- printf("sending boundary\n");
, M; T$ ^( Z. m$ Z K2 a - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");. R1 M; l/ A' b3 V5 U9 G
- if(write(fd, buffer, strlen(buffer)) < 0)
7 ]* |8 s7 U+ f' V' e - 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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二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:
# x4 e% P5 @4 }; Z9 i6 q: y- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port). P3 {. ^: y8 a# ]9 e+ e, r
- {) M i$ G( ~# R: f: h( H
- *socket_found = socket(AF_INET, SOCK_DGRAM, 0);
K) P H$ ]& C" F - if(*socket_found == (~0))
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- printf("Create udp send socket failed!\n");
( ^% i( r% E. W0 j- M1 [1 B L - return -1;
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- addr->sin_family = AF_INET;$ o6 H, p L+ k" m& g2 ?8 a& s* u* z
- addr->sin_addr.s_addr = inet_addr(ip);# m& ]6 |+ J8 g" v. I
- addr->sin_port = htons(port);
9 j' m( h/ x0 S0 g2 r" d* ^ - memset(addr->sin_zero, 0, 8);1 u4 U3 A3 a2 ?+ }5 ]" _: ~; g
- return 0;
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复制代码
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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:7 n/ |: ^9 d' N! x& z2 K7 C3 c
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+ N5 A3 c, \, c. E+ l$ q( B- while(fend > 0)
# D+ x+ @3 B0 c* x* q) @ - {. P8 d z8 f0 h$ v: J; {
- memset(picture.data , 0 , sizeof(picture.data));
7 }& U3 ?, z) Z/ P; k8 V - fread(picture.data , UDP_FRAME_LEN , 1, fp);
& ^. ^& H4 I \, b [- e6 y - if(fend >= UDP_FRAME_LEN)
7 a* f6 q. y5 w2 j0 L) x" Q/ s3 v - {
) V& M2 K- w1 F3 R! W# s, o - picture.length = UDP_FRAME_LEN;4 X9 f- T W5 t0 Z0 X
- picture.fin = 0;
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- else
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- picture.length = fend;
6 [9 T( ]; t( {; ]5 n - picture.fin = 1;
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- //printf("sendbytes = %d \n",sendbytes);* j! w$ X# N& R+ U
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);" o2 w1 Z! N1 j
- if(sendbytes == -1)8 P0 n, ]8 Z8 W2 X; E' V$ C9 A
- {
. t A3 B1 x% m$ j - printf("Send Picture Failed!d\n");9 N8 s' g. m' D! K, o' |. U
- return -1;1 a2 F& Z4 e* X% r
- }
6 K1 c) `# e4 z8 |3 L - else
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- fend -= UDP_FRAME_LEN;
) d# n6 @# L9 e+ m - }; ]% N, y0 B3 _
- }
复制代码 ; ^! V+ r1 Z1 a( U' k
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0 e3 `5 _: t9 S5 f3 DiMX8MPlus 核心板: https://www.forlinx.com/product/136.html |