本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑
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' V7 i* d1 E0 A2 c( 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.html6 a# ?! W& l3 F( u0 \
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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。
5 t, f' g& W& E一、HTTP网页服务器, t @9 y" H! ?$ u% y
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); O0 ~( U& g3 j( X+ M
- {
/ ]) b& K- Y3 V" X - struct sockaddr_in servaddr;
( V( H, }) U# ^3 \ - socklen_t addrsize = sizeof(struct sockaddr);
6 _7 M. }/ w5 c- ]+ X# z9 ? - bzero(&servaddr , sizeof(servaddr));
! w( C% r, s% ?9 J# R. M - servaddr.sin_family = AF_INET; t8 G9 w" q% o
- servaddr.sin_addr.s_addr = inet_addr(ip);) p+ x! z+ Y, N, O# H
- servaddr.sin_port = htons(port);
! ~" N, V3 H- K: g( a) D, F9 S6 v - int ret;. U/ q! |4 N: U
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)# f- f) ^3 ~- N1 N
- {
2 `! U6 B& I0 w - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
8 c+ Y. R. K# K - return -1;! I6 T3 _7 l2 P/ a m: i; N ^2 a! G
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- int on = 1;: x+ n0 P( Y8 @% w
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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/ V* q/ I1 L( B7 ]6 W9 z7 J. R0 D - printf("setsockopt error\n");
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- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);, k( N# K- _% L
- if(ret == -1)
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- printf("Tcp bind faiLED!\n");4 D) X( f2 k4 \- y5 O- b
- return -1;+ q; z3 G! A+ X3 [1 j1 V- Z4 V; O
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- if(listen(*socket_found , 5) == -1)
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- printf("Listen failed!\n");
' C& y% M/ H0 p, X - return -1;6 Z1 q; M8 @$ l$ Q( L
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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);! f5 v2 p! y% R1 G( I5 T8 j* w
- void * Thread_TCP_Web_Recv(void *arg)+ G& P# q/ i1 X5 \5 k$ c
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- 。。。& r2 Q; H8 C$ x) x- f( E* ]& X- k, c
- while(1): X' H# o* q- Q, _7 y6 p
- {
; Q% f& E$ a. z8 f. J9 s8 u2 {% E# e - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);/ }( T* P; g8 H
- printf("fd_socket_conn = accept()\n");
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: [, Q4 G$ y( Q$ ?" Y8 h - recv(fd_socket_conn , recvbuf , 1000 , 0);
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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);$ y% p0 L: ^/ X E& ~* y3 u9 Q
- pic_tmpbuffer = pic.tmpbuffer;
" {4 k/ p- f% z - pic.tmpbytesused = buff.bytesused;
2 C( ?, u3 ?: N7 r/ c3 F - pic_tmpbytesused = pic.tmpbytesused;
/ s6 Q8 W5 K1 E$ ^% b3 Q - pthread_cond_broadcast(&pct);3 J1 [; W6 J( Z6 H8 A" g
- 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;
4 T* _/ o" e' a9 r; s - pthread_cond_t pct;
. Y$ A$ m" P& ~8 ^! c9 ?7 z6 S - int main(int argc, char* argv[])
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- TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);* b d. e" K& _
- pthread_mutex_init(&pmt , NULL);' Z4 M4 ^/ d. L7 X& P
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);$ _" B `+ Y4 m+ x5 F
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);2 {" H9 k3 w3 e3 \
- ...
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- {
9 Z' N' q7 T, s4 F - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);
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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;">
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复制代码- #define STD_HEADER "Connection: close\r\n" \% @: D! K% ^: K) b- g$ U
- "Server: MJPG-Streamer/0.2\r\n" \& G- `, f% q3 A& N! h/ H6 ?
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
' Q3 |0 v5 w8 j; F4 M9 M - "Pragma: no-cache\r\n" \
+ ]2 A6 ]" `& H$ k. a. h7 H - "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
8 e1 E% o* F' c, [2 U* a! S - #define BOUNDARY "boundarydonotcross"
1 r( f' w0 l% x: q( R; M - printf("preparing header\n");
$ F2 g) z0 m( E: _1 i - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
4 L4 j/ X+ c9 A, N- ] - "Access-Control-Allow-Origin: *\r\n" \! }' g$ f5 A2 K& B
- STD_HEADER \. M' y% z8 @+ U2 S
- "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
) ^" O; L& o4 `4 D - "\r\n" \; X1 d% o- i& x0 ~+ {0 E8 g
- "--" BOUNDARY "\r\n");
5 A% B; Q4 e. f" S3 H$ v - if(write(fd, buffer, strlen(buffer)) < 0)
6 _6 Q4 p/ E8 E - {
* |; O+ e0 g1 s C M& R8 Z$ L - free(frame);! W0 O- D8 G# q7 x
- 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" \
& v( f% u4 z7 a: n* e, V. ] - "Content-Length: %d\r\n" \( Y5 X' c9 x; s
- "X-Timestamp: %d.%06d\r\n" \* Z! R) a N8 X, I: [$ W* Y
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);7 \/ x4 a( g0 `# `& z
- printf("sending intemdiate header\n");3 ]* U9 `+ Q+ I4 H3 I, L' T2 C
- if(write(fd, buffer, strlen(buffer)) < 0)
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- printf("sending frame\n");# o( ` a C) ^# s; K* N
- if(write(fd, frame, frame_size) < 0)
9 H( }" P. ~$ v. p1 A: J0 T - break;4 H5 c3 ?( v2 \. n
- printf("sending boundary\n");
. ^! i7 }( Y/ T4 V' n. e - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");: S0 @/ Z8 L/ m- C+ x$ P8 |9 N! c
- if(write(fd, buffer, strlen(buffer)) < 0)
8 a2 s$ v( R' W7 W. D- y2 j - 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:
+ a: h1 U% \9 o) U# V/ p2 W2 v- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)- {# _! u8 B" U, q8 B
- {
- h! ?$ ^; @6 W3 U! ^ - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);' j. i) \2 F. D d8 U1 Q6 K: l
- if(*socket_found == (~0)), e' S4 ?) i+ O# T; r4 x' t. \
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- printf("Create udp send socket failed!\n");
, r; C: ^0 K7 A0 G% E' ? - return -1;1 A- X# G- J5 c/ l( A) S
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- addr->sin_family = AF_INET;
+ X2 _: V$ s9 E3 W - addr->sin_addr.s_addr = inet_addr(ip);2 v8 y/ \5 U+ b2 g5 m4 D' L* s, B& T
- addr->sin_port = htons(port);
- I7 g% q, a: B: i - memset(addr->sin_zero, 0, 8);2 b& }# @2 v* S8 U9 x" z8 @0 N
- return 0;: M( y3 H9 x! b0 {
- }
复制代码
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9 }8 N, V4 p) 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:
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' {8 R1 j0 ?6 X7 ?* o( X, R7 H- while(fend > 0)2 n' U1 u1 P/ S O* @& R
- {
* T. \+ p$ N) D; K- c b - memset(picture.data , 0 , sizeof(picture.data));
0 C# ^; I6 V$ Q9 K - fread(picture.data , UDP_FRAME_LEN , 1, fp);/ \: z' ~# H/ r" v" r& h" @# ?( \% K
- if(fend >= UDP_FRAME_LEN)6 r/ |# C- Z# N( v: M7 \
- {
( O x: n4 u; z* @ c( ` f+ ~ - picture.length = UDP_FRAME_LEN;
& U- }/ Q5 z- X - picture.fin = 0;! W$ A6 R4 V& b/ o# G
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- else
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- picture.length = fend;* k, _' ?1 v- [& b) ?
- picture.fin = 1;
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$ O# G; V3 U" U0 } - //printf("sendbytes = %d \n",sendbytes);
K8 G9 ?- [* R% e! b - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
6 A- u3 L+ Q& b! F( |: G1 l5 y+ @1 ~ - if(sendbytes == -1)
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- printf("Send Picture Failed!d\n");! }) q4 p; M) n, Z7 Q( B! Z- B
- return -1;
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- else
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8 p9 D* t7 y: S+ u T( V1 B - fend -= UDP_FRAME_LEN;
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8 z: G7 _$ c3 F" T# I - }
复制代码 3 v8 }1 n U: [% b
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7 b2 g. }8 T9 i" piMX8MPlus 核心板: https://www.forlinx.com/product/136.html |