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
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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。 . x7 @. J. s7 L% P5 c! x
一、HTTP网页服务器
5 }) c6 Z- E( o4 p% W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)0 }% b4 |& \- Z8 ?
- {# q% G) p8 _0 B, V' I: _
- struct sockaddr_in servaddr; Q2 M8 N8 Q& P4 G+ n" n- u, E5 ^
- socklen_t addrsize = sizeof(struct sockaddr);
. q$ m. }/ G2 i9 C - bzero(&servaddr , sizeof(servaddr));, {% d) c- z1 @% \ K
- servaddr.sin_family = AF_INET;* Q ] e; O) r% x6 X/ M
- servaddr.sin_addr.s_addr = inet_addr(ip);
, D% Q6 Q0 s0 v' s# v - servaddr.sin_port = htons(port);
* t/ U, ?5 F* j2 }) G# \ - int ret;2 a4 Y& z* j, ]) T
- 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);& e8 I8 D, g1 y- k! s" u
- return -1;" Y( [. P* T6 |, ]
- }
6 i" K) S2 W4 i" C6 z$ d - int on = 1;9 y$ b( S, J2 g7 M# A
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
- C v1 n# d. }% M, [& }" q - {
3 V; ^4 ~0 `/ Z3 X - printf("setsockopt error\n");0 j3 P7 Y+ \3 g$ U' ~
- }
! J% S" O, ~3 t9 S2 B4 j4 t - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
8 [4 Q% A1 a: M) U; n- \ - if(ret == -1)
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- printf("Tcp bind faiLED!\n");4 D( r# ` M& e1 t% _
- return -1;
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- if(listen(*socket_found , 5) == -1)
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- printf("Listen failed!\n");# x, t. H2 }2 \4 U9 h
- return -1;# R8 y; c1 k* P' ^$ l/ g9 a( H
- }
8 x( o! F6 Z* o4 ? - return 0;. y6 n i6 ^. h- \% K
- }
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);) w' {( E6 p% v- {! ~6 M
- void * Thread_TCP_Web_Recv(void *arg)2 K$ J! p2 M- f! {6 V. ~
- {
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- while(1)5 [2 M8 t4 q) r
- {
" M8 o3 w) [8 O0 [" O. T) C4 P - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
4 x2 R: s5 x6 F* |, q. k" D - printf("fd_socket_conn = accept()\n");
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- recv(fd_socket_conn , recvbuf , 1000 , 0);) c% w/ m6 h' K0 k, j8 q
- }
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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);
S& B+ P) F5 d, b/ D5 I) g0 _ - pic_tmpbuffer = pic.tmpbuffer;- D2 g# T8 U6 K0 r: n$ l6 ?( C
- pic.tmpbytesused = buff.bytesused;
5 t/ Z7 g- |" G3 t' N2 s" X - pic_tmpbytesused = pic.tmpbytesused;5 Z) D; A4 S9 @3 m% h6 M7 X- i
- pthread_cond_broadcast(&pct);
7 D$ _. `! x9 V+ e0 d - 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;# t! M, |" T+ K5 O
- pthread_cond_t pct;' i. \ @8 [: B8 L# y
- int main(int argc, char* argv[])
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- ...3 _( s: E: b, }% Y
- TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
5 ?0 O# v) E& |; m& K& H - pthread_mutex_init(&pmt , NULL); T8 b7 l1 H% q2 [0 a+ h& I5 s! u) J* u
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);
2 n( `% e+ Q1 @) }% z& E3 J - pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
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- while(1)
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o Z0 S8 {# ?* x: M# M - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);9 a8 l$ c+ X' R+ ]2 e F$ e8 M% G, g) L
- ...
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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;">( U- N8 O! } n" F
- </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" \
' G2 H1 v" X- p; ?: Y% M - "Server: MJPG-Streamer/0.2\r\n" \
. Y5 d/ G. A d; s - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \" b& D4 v/ A( u9 B9 F$ ~
- "Pragma: no-cache\r\n" \
" n/ B$ b x% U+ r& G( H" X - "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
1 J9 i' ~5 v! R: D8 G, q - #define BOUNDARY "boundarydonotcross"' o* w3 u( s3 X5 _+ T) Q
- printf("preparing header\n");
* P& y/ ~1 M- q& `# P M7 y - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \* w1 _4 t' v) H
- "Access-Control-Allow-Origin: *\r\n" \
: ?' l3 T* w% V# ^% x4 i4 D - STD_HEADER \
0 e' o6 ] d$ w M* k8 E - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
q/ `7 D8 z8 y, D2 P - "\r\n" \
" P$ ]) o" O$ i7 y7 p, o - "--" BOUNDARY "\r\n");7 a9 o$ S: J5 D( H% Y! Q
- if(write(fd, buffer, strlen(buffer)) < 0): |: I- b/ M) w6 V/ _" R
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- free(frame); t4 N, N7 p$ ^
- return;3 |! a5 I( X6 r
- }
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" \ ~3 d6 u! A% U/ S* J
- "Content-Length: %d\r\n" \" r8 G4 Q$ b- m# l% u# C" k+ o
- "X-Timestamp: %d.%06d\r\n" \5 ^+ i% G, O$ ^% w
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);5 q* l- ]$ f6 Z
- printf("sending intemdiate header\n");& K1 \8 M- d* p1 g- O/ N
- if(write(fd, buffer, strlen(buffer)) < 0)( j! f1 s; \% | J9 C- m# b, z. q
- break;' k# _$ v; b5 ?3 ~: B$ h
- printf("sending frame\n");
0 _; a( @& ~' D! G; @- _+ ]. z8 ^% I - if(write(fd, frame, frame_size) < 0)
$ M/ |( p7 t- V9 k% v5 z. P6 w - break;
: m/ v. { e& z. v s9 x0 } - printf("sending boundary\n");* O+ F) M" h, V* j6 M
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
" \! h. g6 O; n+ P; F4 ~( c1 ~ - if(write(fd, buffer, strlen(buffer)) < 0)
# N7 |! P7 X+ O2 q - 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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$ ^2 s+ c* |7 S8 i/ `7 U) _: |二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:
& L7 ~5 I, |, m- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)0 o8 q* |4 L1 E
- {
& {: [# K2 A, ] R+ A6 ^ - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);. Z; l/ l1 J/ S0 H; T$ U# m
- if(*socket_found == (~0))
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- printf("Create udp send socket failed!\n");
8 B+ D# D: I, T8 `/ X - return -1;
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- addr->sin_family = AF_INET;- O* `$ m& _5 r* t$ H
- addr->sin_addr.s_addr = inet_addr(ip);
; f2 U6 o" A- _) Y/ \8 u - addr->sin_port = htons(port);
% N8 |7 V u9 V0 j1 C' H9 x - memset(addr->sin_zero, 0, 8);+ L! A- a" c! L& w% z# H. [
- return 0;% q) F, |) D u! z) m! u
- }
复制代码 % ], D/ L m6 _
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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:1 S) \/ e* X: G: D
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* V0 D, v, l. d( L+ s7 q& x5 T- while(fend > 0)6 i/ ? G9 S2 Y8 A7 r9 t& r+ A
- {1 Z) ?+ F, L* R0 i" w( |5 I
- memset(picture.data , 0 , sizeof(picture.data));
" K3 i# Z$ U# e* h& k5 P6 t - fread(picture.data , UDP_FRAME_LEN , 1, fp);
$ h5 n: `8 j/ j' t& N - if(fend >= UDP_FRAME_LEN)- ~3 }3 f* I/ X' R/ w$ D
- {: E6 L. E+ Z- N! Z/ u+ j& X8 k3 _
- picture.length = UDP_FRAME_LEN;
J; I6 v4 [. r - picture.fin = 0;# e0 U4 I0 i4 b0 t7 m0 G; A
- }
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- {
* F) b0 {7 v& O! h! O( X8 l) E - picture.length = fend;
% x: n; i* g d" e& k - picture.fin = 1;2 P+ |0 q- o2 E, q8 _& w, ^
- }
' k2 y/ w/ l- @+ d+ R* E - //printf("sendbytes = %d \n",sendbytes);
7 x; |- H# w- m' t3 w6 z! ^9 G6 |+ s - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
4 ?, ^. o6 M; c& o" ] - if(sendbytes == -1)6 L* l3 f+ H( x! R$ j
- {
0 u/ h5 g4 u6 t8 w$ C3 Y - printf("Send Picture Failed!d\n");# ?6 J& x( p. O5 S. g; ]: }3 c
- return -1;- A ^3 G) U# _
- }
7 j T8 {! q; A$ F' U - else
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/ }* u$ v. {* k - fend -= UDP_FRAME_LEN;4 s7 `) G; F2 D' a2 ^2 w
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- }
复制代码 4 v1 f- c% J; R" Y. w1 w
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9 j7 S a9 t# J2 ziMX8MPlus 核心板: https://www.forlinx.com/product/136.html |