本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑
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4 ^! w# Q* c' {' A" S1 o5 j: Z' S( U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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6 r4 k4 K, p6 L) Q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。 - _7 n9 o8 i7 Y+ c

5 v5 m+ N( k: B2 L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。
/ I" `0 H8 t) j* Z3 Y一、HTTP网页服务器
) W, j" p) p' z7 U. [3 S1 z# p7 |1 l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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5 ?2 ?8 v# G3 _8 Q; J - struct sockaddr_in servaddr;
6 H; a: N, C; ~3 i - socklen_t addrsize = sizeof(struct sockaddr);& x0 @1 O/ x1 ], c: ^3 E
- bzero(&servaddr , sizeof(servaddr));
8 U" s/ j" U: B4 ^ - servaddr.sin_family = AF_INET;+ u/ V) W, l# m+ g- x
- servaddr.sin_addr.s_addr = inet_addr(ip);# \5 u# [% @: p8 L0 s
- servaddr.sin_port = htons(port);
) r. ]& X l1 R8 u( \ - int ret;4 `- R) R4 }) ~; F. e
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)
) M& y0 Q9 n7 N( x - {
% _, R, H) a& T8 G1 M! x/ Z - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
! d9 ` I9 X, i- q8 d4 _- A; c% C - return -1;1 m0 K! J( c: t
- }7 r% ]7 @9 w7 D" y
- int on = 1;
- r' _/ H) b7 f X; L U' S2 n* f - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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7 z3 S$ B% X0 H8 E# ` - printf("setsockopt error\n");) u; t' l9 B( r# G% W' _
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- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);# c* n. [/ S8 z# Z% u3 M
- if(ret == -1)
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6 n: w% U* _6 n8 M - printf("Tcp bind faiLED!\n");
: N: z0 q; o9 K% t" ]1 Y0 O - return -1;
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- if(listen(*socket_found , 5) == -1)
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- printf("Listen failed!\n");/ J; k- ~4 k3 ^3 n7 l
- return -1;* p( `7 e: `: z9 {8 X: T
- }
' b5 [: T: Y' E. z+ u8 a* ]+ J - return 0;; [0 R, H& w. r: o! x7 ~% ] x2 U, v( U9 I
- }
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);
' u3 J" K" m# h6 Z/ v8 ^ - void * Thread_TCP_Web_Recv(void *arg)4 `3 n2 V0 T8 t
- {
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9 C# M$ i2 x: k' h - while(1)' F: p. v: }. {$ O" I& b
- {
3 e$ ]' h- w, s! j2 t - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);8 V1 ]& T; S0 I! L
- printf("fd_socket_conn = accept()\n");
B) S$ |5 k+ ?* U - 。。。
" s% ~: S, ^8 _) W6 z3 F) b - recv(fd_socket_conn , recvbuf , 1000 , 0);4 L: m' e( T$ Y9 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);" u5 Z- w. X* D" H# Z
- pic_tmpbuffer = pic.tmpbuffer;4 H2 b2 P5 R( z( K8 x6 ~6 N
- pic.tmpbytesused = buff.bytesused;
. u% X- f2 Q# Z- m8 D - pic_tmpbytesused = pic.tmpbytesused;
6 t$ G: o! F3 h4 B# T - pthread_cond_broadcast(&pct);% [8 K* ], f0 _& b5 J' @2 T" }/ R
- 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;
+ K1 J! Y; ^6 d' v5 l - pthread_cond_t pct;
+ P4 U5 l7 e1 ~& x8 I+ r, j4 \ - int main(int argc, char* argv[])
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- ... U$ k$ Q+ L- Q2 Z
- TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);3 T5 h! a a j1 e
- pthread_mutex_init(&pmt , NULL);; N1 a) _5 X& [9 n8 C8 `/ Y
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);! i* o0 t. P9 ?' U$ L% p% Q4 t
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
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- while(1)6 N8 h: X/ d' B I$ f f7 k$ G
- {
- [8 U" [* |) l% O @' k - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);
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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;">6 P$ l' @# _% @) z! s/ x7 ]4 d
- </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" \
: N. F9 e0 G( l/ k - "Server: MJPG-Streamer/0.2\r\n" \9 a& S6 s% C( k; W* g
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \7 d! ]+ K5 r2 F) ?! N1 t$ M
- "Pragma: no-cache\r\n" \
+ f0 N+ {2 S. d' B, s% z - "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
. c; j! x' z4 ~3 b - #define BOUNDARY "boundarydonotcross") m. i( n3 o; Q1 r, e; @
- printf("preparing header\n");
( f& u! r4 D) ?4 j P - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \% t' p) P, H, C9 X1 ^9 p- U/ Y, }
- "Access-Control-Allow-Origin: *\r\n" \0 Y6 _2 e6 J5 B2 g( p
- STD_HEADER \, V9 w" @$ W! L1 e7 t4 g
- "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
$ x2 c' z l7 e1 S/ o/ ] - "\r\n" \
$ q% D2 i+ r- p' E - "--" BOUNDARY "\r\n");
( ~4 h" o. _; k ` - if(write(fd, buffer, strlen(buffer)) < 0)( c/ r7 a1 ?3 C% @
- {
0 N: `8 g& T! b/ V; l - free(frame);
7 K) S( R! T* F# g( m8 }, z( O - 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" \ f# z9 O" I' l$ d) H1 i5 D/ n
- "Content-Length: %d\r\n" \
3 {& v* {, }9 [( c' C' K, D3 s/ ] - "X-Timestamp: %d.%06d\r\n" \
1 l5 D6 |4 T% |# \4 C - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
9 K$ D) f/ D# E% m - printf("sending intemdiate header\n");4 k, v: J: _+ Y4 B
- if(write(fd, buffer, strlen(buffer)) < 0): t. b: U" p; C" |/ G, C3 z. a
- break;$ K1 n Q7 I' L% c
- printf("sending frame\n");
; _- d1 _+ I0 A6 H# G - if(write(fd, frame, frame_size) < 0)
6 k4 \' ~+ d! ]/ |3 p% G/ `* ]" H - break;, m8 x. Q r. b" M( y7 h
- printf("sending boundary\n");6 u6 x1 }2 ^( w& h _; B9 y
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
9 I8 ^# m9 ]% Z, F6 y" r$ b - if(write(fd, buffer, strlen(buffer)) < 0)6 \, T+ H' \/ ?$ s' D1 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。 
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9 a" E/ o6 H( Z F二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:, c' L' f* J+ @- Q# B/ z- I
- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)
% H: `$ T9 B- b | - {
: f; [8 x5 d; } - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);
! V2 M6 u- h5 T5 b; x; ~1 e - if(*socket_found == (~0))
6 d$ ^, v) w: C- V- Z - {
6 u+ w- _6 p9 l! R - printf("Create udp send socket failed!\n");
* ^+ c9 X" H ?2 G: K - return -1; y+ c9 d) d: N M u! T$ T
- }0 p" ?7 E+ O X4 C9 O3 L
- addr->sin_family = AF_INET;
* ]& y9 O9 Y' b- I$ `9 }- D. k8 h - addr->sin_addr.s_addr = inet_addr(ip);
0 v' ~* d2 X, B/ u6 I. y) i1 i - addr->sin_port = htons(port);( N! e3 H9 K- L: p
- memset(addr->sin_zero, 0, 8);
% ]0 Z) V* a: o4 G# r - return 0;
! ^2 Z1 d: q/ s; r. g3 \ - }
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)' ~1 l* ^- d" L! v9 G9 E
- {
' G( d& C6 R. Z4 a" k+ j - memset(picture.data , 0 , sizeof(picture.data));
, V4 O+ Y5 \6 ? - fread(picture.data , UDP_FRAME_LEN , 1, fp);2 Z6 ~) U# S$ ?2 G. Z
- if(fend >= UDP_FRAME_LEN)
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- picture.length = UDP_FRAME_LEN;' X3 U% B, C: z) X
- picture.fin = 0;
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4 c. j/ t+ T1 H" G8 y - else; C8 n* \0 \5 q/ J
- {
/ \3 @( ~' Q. h' m- m# c. u+ F - picture.length = fend;3 q: v6 o$ U! n
- picture.fin = 1;9 l& W* k: e# Z$ P5 p
- }0 w- }+ u* V4 Y( b# j* E
- //printf("sendbytes = %d \n",sendbytes);
) ]. T; N' Y2 p6 W, ~ - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
5 ^! m7 @# o, A6 z& x! U - if(sendbytes == -1)
# D( H2 Y- H9 u* n3 K - {
8 O1 G! Q& W8 } - printf("Send Picture Failed!d\n");
* @* _$ B+ p0 p1 D2 c - return -1;$ c; A/ r4 b% D- r" {
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- else! c6 y @- n& p6 z
- { p9 y+ h( R' H! O8 J9 T. S
- fend -= UDP_FRAME_LEN;
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- }
复制代码
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iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |