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0 k/ }; c: o6 R# j: \" i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。
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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。 . T+ x$ X. ~7 K) x5 ]4 q! ?
一、HTTP网页服务器
7 p3 u# z+ N; a/ u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) I* q8 j- x( g) L. \% l( D3 E
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- struct sockaddr_in servaddr;
/ V% Z) H7 ?0 k/ I' s; X4 K. l - socklen_t addrsize = sizeof(struct sockaddr);
7 q- l9 ?3 Q* m l - bzero(&servaddr , sizeof(servaddr));
0 d6 U4 T; u' g" F" w: p! I2 G% z - servaddr.sin_family = AF_INET;# ~5 g: v$ K5 b9 C; t% c% i3 \
- servaddr.sin_addr.s_addr = inet_addr(ip);
& R4 o6 g' S2 `5 v6 v4 Y1 B7 p4 m- ^ - servaddr.sin_port = htons(port);, S5 C1 f1 o0 \( Z {- @3 t
- int ret;+ g( [. I! C( X' B& ?/ @8 N1 z
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)
' H M6 k B" M - {
# q, m3 w$ ?5 N6 y - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
) Y0 k! P0 D# | - return -1;
! k" e/ V$ T' h" i - }
! S b1 U# N5 m# `1 D+ Y* C) q- z - int on = 1;
1 I; I/ _& `. ~5 \/ W/ i# w - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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- printf("setsockopt error\n");+ k& R! k) l- b! S
- }
* M- Y# K; a; \ q* Y& O' s- Y - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);+ \0 X, v$ N; o+ B; f
- if(ret == -1)) z) j1 O J( A; y! I' T* g2 b
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- printf("Tcp bind faiLED!\n");5 H/ F! ^" H% O( |4 E
- return -1;
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- if(listen(*socket_found , 5) == -1)
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- printf("Listen failed!\n");
) l! g" X" _/ A4 I G" R, t - return -1;( [9 g. Z, \8 o, O
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- return 0;0 B. s' c9 |5 q( O0 ?& _
- }
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);, ~: [/ e& d0 V& P9 r5 w
- void * Thread_TCP_Web_Recv(void *arg)! p- I( t. |3 m7 |2 y% m
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- 。。。$ |, p3 {* M' U
- while(1)& ]- G0 E/ L" f1 X3 M3 d$ T
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- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
2 p: p L* w. C- {# ^9 J0 s - printf("fd_socket_conn = accept()\n");* b2 K" Q) o$ }# }* D1 t
- 。。。( W9 V# {! w4 X" w+ g D+ K/ Y
- recv(fd_socket_conn , recvbuf , 1000 , 0);
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- 。。。
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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);* H7 ^. b3 [+ F! I8 }, E
- pic_tmpbuffer = pic.tmpbuffer;
0 B0 T% ]0 B9 D! b3 k - pic.tmpbytesused = buff.bytesused;
8 p" b& f5 j" T H) @9 E - pic_tmpbytesused = pic.tmpbytesused;
1 g# ^5 \" K7 c, N5 e6 o - pthread_cond_broadcast(&pct);% c5 u( K- o' N5 \& i" z3 x7 ^% 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;# V# H4 }* {2 v w7 t
- pthread_cond_t pct;0 \: j9 @0 c& f0 ]$ g6 ]
- int main(int argc, char* argv[])
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- ...
$ T. b# D5 ^$ t0 c2 r* `0 C6 { - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);8 E% A% ?+ t/ u
- pthread_mutex_init(&pmt , NULL);( y3 h9 H4 v) E" I' e. F. j
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);( l1 k$ L" H8 W- |2 \
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
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- while(1)+ a- O) L* l$ d7 P6 U' p* P
- {
/ i# v1 \: j# H) m - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);
8 Z6 \$ {9 g3 ^ - ...
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6 w- I- V4 |: t; \. 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;">
* O: V: [- j0 ]1 w9 c2 [1 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" \; _& v7 d k8 n& l: E$ m/ K4 U( a
- "Server: MJPG-Streamer/0.2\r\n" \5 d$ [- T7 M0 y @0 V9 S* y
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
2 L+ p* P- }. D# I1 [* V/ C - "Pragma: no-cache\r\n" \0 K k5 z# |: f% ]% N1 _
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"/ A& I p& m3 T0 T. q
- #define BOUNDARY "boundarydonotcross"
) x3 c! s6 z. H/ p P - printf("preparing header\n");1 L# X" Y0 T/ E* ]4 d- F4 n
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \" t, o- h, f" ~$ c# }
- "Access-Control-Allow-Origin: *\r\n" \
& d9 K+ e' |: N) x# w* a, H8 E7 p - STD_HEADER \
: M7 f# B8 e1 ^" A4 x" w - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \9 `8 ^) t, ^! }5 d
- "\r\n" \
( x7 N# Z h/ K& d: L, O - "--" BOUNDARY "\r\n");/ V. W$ p9 [6 r% a
- if(write(fd, buffer, strlen(buffer)) < 0)& L0 d0 p V T% E" u5 h
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- free(frame);- ^0 `3 a/ u. ?* T" _* |
- return;5 v+ K# B0 b% v9 _/ B
- }
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" \
, g8 o, T' G, L - "Content-Length: %d\r\n" \( l9 S2 n' Z) E1 J
- "X-Timestamp: %d.%06d\r\n" \; X$ Q* D$ j! S
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);' D [) |* y0 d3 m+ o
- printf("sending intemdiate header\n");
3 `7 h A0 S; _+ ?; ?1 y6 L - if(write(fd, buffer, strlen(buffer)) < 0)8 _. m' {/ ~( {5 S
- break;- N) g6 l' I" Q7 r6 P
- printf("sending frame\n");
0 }; V. s2 ?& W9 }! i) \: _9 d, R - if(write(fd, frame, frame_size) < 0)8 d9 f* y2 _- T5 E7 m5 f
- break;* N: [$ o+ {4 `; w
- printf("sending boundary\n");
# D5 E) J) q' S) Z - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
1 W4 M, N' B; i0 F - if(write(fd, buffer, strlen(buffer)) < 0)! L$ {( |0 C# h' w) i7 o; m
- 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。  5 t0 E4 o1 e- E8 @
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二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:) L1 R& _, c2 k& e8 _
- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)3 R0 W7 G( A$ c, ^* b
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- *socket_found = socket(AF_INET, SOCK_DGRAM, 0);
6 Z6 }$ Z; P! ] - if(*socket_found == (~0))
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, Q' x ^$ h% }4 D, J4 D - printf("Create udp send socket failed!\n");5 ^0 I/ y; n6 R
- return -1;% i8 {8 C- O G. R- W
- }
# J1 V$ ]& K- o1 D$ M0 G5 m - addr->sin_family = AF_INET;& b% N X9 Q# I( ~' Y E$ }3 J
- addr->sin_addr.s_addr = inet_addr(ip);
# V, w% c' n0 F. A( K - addr->sin_port = htons(port);
1 C9 ]4 j `: ?% c3 [4 U% O$ p - memset(addr->sin_zero, 0, 8);
3 b0 T+ g) k( p - return 0;$ ~, j# ?' j; Y+ N; _4 c
- }
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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)
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- memset(picture.data , 0 , sizeof(picture.data));& k# \, v- G8 ~4 W+ X& E3 S1 _
- fread(picture.data , UDP_FRAME_LEN , 1, fp);
9 m1 k3 c" N0 s" f- h1 L) ` - if(fend >= UDP_FRAME_LEN)
6 n; y$ \2 l& ]8 Q( ]7 o - {
' N& ^* Z! K5 W( ~; h! |& m" [ - picture.length = UDP_FRAME_LEN;
* W! c9 @" g1 t" O' D2 ?3 ], M$ i - picture.fin = 0;, z' _8 f9 X7 r, Z- ]5 u+ R' s
- }
3 U6 ]" G) J6 \' | - else
9 B# b# ?! c1 ` - {
( ]# R p$ e2 H1 F& O4 J - picture.length = fend; l' P6 J. i9 Q2 ^
- picture.fin = 1;) a0 ?5 \0 ?3 ?; I7 W% H6 Y6 l
- }# k& X# m" e- O S4 \: [7 K' G4 _
- //printf("sendbytes = %d \n",sendbytes);
7 T, G4 m2 ?" N+ H" J1 S- R" P - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
8 h" F2 G4 t" g! {4 l. E8 U - if(sendbytes == -1)
6 m7 n4 n& W& C' i# E - {
3 f \- o5 S' X6 A# Y" U$ z( N - printf("Send Picture Failed!d\n");
v8 V" _( C( y, O - return -1;* _& j, q! r c% r( }3 }7 O0 p
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- else% M3 o' w, Q. j8 }# U* @9 _8 @8 j
- {
6 Y' ]+ D, M, K, t% O6 c5 A - fend -= UDP_FRAME_LEN;
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- }
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) [/ T+ Y. r6 C# }4 uiMX8MPlus 核心板: https://www.forlinx.com/product/136.html |