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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9 P9 j( L: G" E8 @7 U9 ^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。
1 U4 J9 m& a1 a. s/ V一、HTTP网页服务器" `# J& o% p# g
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;; g" }5 }9 e, `4 t& P2 S) W
- socklen_t addrsize = sizeof(struct sockaddr);
# i! t5 X( g' G u& z2 `: @ - bzero(&servaddr , sizeof(servaddr));
8 h: G: t" A" x# Q - servaddr.sin_family = AF_INET;
$ b. d6 w4 s! q: B- i' l0 l - servaddr.sin_addr.s_addr = inet_addr(ip);
" p3 b' {! q, I$ r# L- G! d9 B - servaddr.sin_port = htons(port);
0 \2 e1 I. L1 i- x - int ret;
' x; A9 R; j: Y+ 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);
9 q, B* q0 V$ i% {* N6 U/ |+ j5 I - return -1;
7 s# p6 h8 I- |& b Y - }
: J7 {! ]9 Z4 g. F6 \- x - int on = 1;5 M, K5 D6 f& r( A3 x: h* j
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0), C$ T8 `' b* S) h# b, f# {& b
- {
% Z P: z4 U. r* B - printf("setsockopt error\n");
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- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);9 J( ^7 V5 v9 o5 y3 d I# H$ C; ]
- if(ret == -1). H3 T7 o2 e0 R
- {" Q$ l: w9 F3 [
- printf("Tcp bind faiLED!\n");! g! S$ O) X/ J! A, Y
- return -1;& u+ l& ~ X i5 y
- }
2 T4 y" i6 N) h2 m7 C4 m9 X - if(listen(*socket_found , 5) == -1)' A a& A8 K! I
- {
- H. F: J. [1 x* U - printf("Listen failed!\n");
: H$ t" z2 Q- X9 [: x - return -1;' Q/ Z% }9 A0 u, y* T; J
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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);% `$ T! J0 G* e6 X
- void * Thread_TCP_Web_Recv(void *arg)
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7 D) v9 b8 O: [, {$ b - 。。。
& T% W. x, U7 t4 c D* l, _& l# T# [ - while(1)
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- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
/ k% u/ V- Y/ y( V - printf("fd_socket_conn = accept()\n");' q3 L2 t& U) P' ]
- 。。。' [! m3 L. s1 R$ O8 o3 ?
- recv(fd_socket_conn , recvbuf , 1000 , 0);
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- 。。。' `1 z, {" h8 a; A
- }
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);
' A* ]7 a+ o5 ?# P; O+ B4 U - pic_tmpbuffer = pic.tmpbuffer;5 \# N! o% Z0 A, T7 a
- pic.tmpbytesused = buff.bytesused;2 Q# l' }2 |( ?% \" K1 ?
- pic_tmpbytesused = pic.tmpbytesused;" A" S! F! O, i' {8 f3 T
- pthread_cond_broadcast(&pct);: N( R: l" k/ X6 h
- 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;
+ O2 P) I4 u! Y2 W& I4 s& W. ?# j - pthread_cond_t pct;
- Y3 d$ \# i2 a: s8 z: ]' R, ?" M - int main(int argc, char* argv[])9 h+ p, E6 x8 b( N, |2 v
- {
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- TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
6 W5 Z; F- b) R9 c - pthread_mutex_init(&pmt , NULL);4 Z9 p: ]/ u8 I. W# B% R
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);. i* B5 S8 J% M* W4 H8 b3 e" K
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
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- while(1)
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( o' r( p2 ?) X, [ - 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" \. k. J. B: r, t
- "Server: MJPG-Streamer/0.2\r\n" \
& K9 b0 D% A( m. ~3 |# J( E - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \4 |0 @, Z/ N1 |* t/ F
- "Pragma: no-cache\r\n" \8 q N% \ ~6 q. m$ }- Y5 Y" V
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"- i, C, f4 x$ G( E `
- #define BOUNDARY "boundarydonotcross"
$ M3 T* ~# h1 k( {0 L8 G - printf("preparing header\n");
3 O: |4 I, t, F) l# p0 P \. s - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
! z+ z, ~4 q, N/ `7 h4 D - "Access-Control-Allow-Origin: *\r\n" \9 A s( F7 |" j# }6 Y }: x) K
- STD_HEADER \
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. O4 _- z/ E1 T2 M* P- n - "\r\n" \" [3 S% g+ w9 C
- "--" BOUNDARY "\r\n");
4 z3 ?$ x# w Q& v o) T$ U2 v - if(write(fd, buffer, strlen(buffer)) < 0)( g6 L. D+ s1 m2 h' Z
- {
# W' w; A |* b' y - free(frame);. I- S/ W3 F/ Q9 ]% h
- 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" \; ]$ z! g2 P1 `8 Z/ Q7 B9 X+ u" ]
- "Content-Length: %d\r\n" \2 @/ b. C. {5 V4 Y* D w9 v. K, p
- "X-Timestamp: %d.%06d\r\n" \
+ g1 g' f$ j+ o4 Q# i - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
% z `& H$ A% @, L - printf("sending intemdiate header\n");& N( I. b# c( j: E; R3 @' A5 i# I k
- if(write(fd, buffer, strlen(buffer)) < 0)- }* Y8 Z9 H$ l5 f' U) I. g# W [
- break;( i; |. ]# T/ ~. ^7 O( B' |1 B1 ^5 F
- printf("sending frame\n");
, v- C' h# Z* E; A# s - if(write(fd, frame, frame_size) < 0)7 M/ @8 Z) n+ M
- break;
" x6 {; ?3 I: ^# K2 Z/ Q3 v - printf("sending boundary\n");7 B# `& X5 P) s$ @' |
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
6 \+ y7 O# u# b$ `, I6 H - if(write(fd, buffer, strlen(buffer)) < 0)
3 d$ ]. V% m; ^5 Y - 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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# z* W/ b: K. _3 p* u二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:% O/ v( U0 T- d
- 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);. T' } X: m8 |+ s1 T
- if(*socket_found == (~0))/ I" D: _2 |' `+ E
- {
6 o$ U0 f$ b$ u; Y - printf("Create udp send socket failed!\n");
: r. }) s9 P+ @( y7 f$ ^ - return -1;
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- Y4 K7 ^) c! }" {0 X - addr->sin_family = AF_INET;8 l7 t) R0 K" j8 z9 x
- addr->sin_addr.s_addr = inet_addr(ip);
4 {+ Q3 t$ a s - addr->sin_port = htons(port);
1 ` y3 C8 ?: P; ~! Z - memset(addr->sin_zero, 0, 8);
( A+ B! {, W' u4 p0 s - 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:
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- while(fend > 0)
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- memset(picture.data , 0 , sizeof(picture.data));( @6 K" j3 ?" V; f! f
- fread(picture.data , UDP_FRAME_LEN , 1, fp);8 \ ?) ]- a4 T& t
- if(fend >= UDP_FRAME_LEN)
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, }4 b: U" k7 q4 C, B - picture.length = UDP_FRAME_LEN;9 M/ W3 y( O( ~4 Q" r' V& M
- picture.fin = 0;2 s2 d: c1 x. e2 X7 j* Z, B- l
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- else5 h2 [1 [0 U; F9 H
- {
5 E7 x2 n$ W$ { O, {6 | - picture.length = fend;
j2 a2 V3 f) G2 X. t, v6 U4 G - picture.fin = 1;% S8 c! M, [. @$ j6 j
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- //printf("sendbytes = %d \n",sendbytes);* W' s3 ^$ i1 e( B/ j" L5 Q; r
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
5 l4 S3 N* z8 q2 n9 A- ?8 P - if(sendbytes == -1)/ |# N& _; n" ~) p0 u0 o) K* y
- {/ ?5 O5 R" o# P6 A/ r4 t! H% u
- printf("Send Picture Failed!d\n");
- t" M% k2 G5 |8 N - return -1;, O6 Z# f# Y* [7 X" K' U. z v6 i
- }
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- {
1 Q9 |3 D8 i8 x: H3 S5 B% ]$ q - fend -= UDP_FRAME_LEN;
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复制代码 + X9 L" c8 d1 n; J9 U( u
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5 N: D% u% P0 v( R3 viMX8MPlus 核心板: https://www.forlinx.com/product/136.html |