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.html9 ]) `6 c' x" m) t5 E. Z
3 B) a0 N- i. x8 d" D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。 . A( p" X! w' j" o

& M/ f2 S. _" U& X7 D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 N1 C$ F% {9 }- n8 G
一、HTTP网页服务器) }+ c7 @* y) B8 d; f: m
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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4 c+ ]/ h9 \& w" M: i - struct sockaddr_in servaddr;
+ j4 |% d# Y. C# t9 }4 @( W6 W - socklen_t addrsize = sizeof(struct sockaddr);
6 d& z3 v( u/ c9 i( W8 i - bzero(&servaddr , sizeof(servaddr)); b* I$ Y% }9 l
- servaddr.sin_family = AF_INET;! I i. k! u- N) _7 E, u
- servaddr.sin_addr.s_addr = inet_addr(ip);
, B# X5 h7 L. c( @, P- v - servaddr.sin_port = htons(port);
2 u2 a; x9 a. r; V - int ret;
* @7 z7 D, S! T% ~- v. L$ m. U - 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);
; Z) N2 `% [0 n( x - return -1;' C" z/ d5 x+ C8 S) S
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- int on = 1;; N8 G8 d1 y* ^
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)+ d0 t2 X8 y3 ^5 F' Y
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- printf("setsockopt error\n");3 P& H9 ?8 _9 a0 r' a& y6 E- M6 _
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- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
4 h; T) i6 U7 [. x' ] - if(ret == -1)9 n8 t( C9 @; r+ q0 S- I2 y8 ^+ W
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- printf("Tcp bind faiLED!\n");
! _2 c! z/ |- z {9 ] - return -1;
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; K* z: R# X& v) y0 K3 a - if(listen(*socket_found , 5) == -1)
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- printf("Listen failed!\n");
; H9 c* m/ M! B3 H" R" b0 ] - return -1; w; H9 Y7 \1 h% ]/ t3 v `
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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);
`: d( v1 s. t, w - void * Thread_TCP_Web_Recv(void *arg)
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- while(1)
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- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
! c0 r/ Y' \/ _! X' { - printf("fd_socket_conn = accept()\n");
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2 ^ G+ \' a& C9 r - 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);
2 B( I% c3 {/ ?3 Q. n - pic_tmpbuffer = pic.tmpbuffer;2 i. f( h1 J8 Q( Y2 P* ^
- pic.tmpbytesused = buff.bytesused;
' T8 }: C( }3 b- {2 l" ?+ K - pic_tmpbytesused = pic.tmpbytesused;
7 J: w7 @4 y, ]! M4 O$ p - pthread_cond_broadcast(&pct);: d' Q% M* m4 ~5 f! w3 u8 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;' @* R2 B; Y- Y: e, l
- pthread_cond_t pct;/ Q8 t: R) _1 J. W3 x2 J
- int main(int argc, char* argv[])
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- TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);' Q' F4 H& e) @
- pthread_mutex_init(&pmt , NULL);. ^, i+ s' E; [: }
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);& d' t& U' J* ?+ V
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
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- while(1)/ Q$ N* z/ e' l5 [3 r4 s+ k' r! T
- {
# ]3 X2 {/ J& i g - 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;">
3 J! c+ F e2 Y0 ^. C) | - </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" \9 h |6 Q. E% J0 z: \
- "Server: MJPG-Streamer/0.2\r\n" \/ B, I' j; \5 ?3 b* `
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \2 ^1 m! `, t9 m7 G8 G* l" i+ }
- "Pragma: no-cache\r\n" \$ [; }; J0 Y6 X+ L) x
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
! R7 r+ @) k1 `2 ^! S - #define BOUNDARY "boundarydonotcross"
; P! C+ {$ \5 @4 U1 [ `- G! M - printf("preparing header\n");
V) p# E5 o n$ A- ]3 Q' R: a - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
) v' N) x% M" g0 A$ R1 ~ - "Access-Control-Allow-Origin: *\r\n" \
3 L7 u' G8 x( x% U) B' d: H - STD_HEADER \
3 V2 o+ k" T1 M) ?" h - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
' r2 h5 C) _3 F, O; E5 p - "\r\n" \
4 i" f8 J9 m9 Z+ E( ] - "--" BOUNDARY "\r\n");" [# W. Y. h6 O+ b( z
- if(write(fd, buffer, strlen(buffer)) < 0)
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+ z Y3 | j" ~! x - free(frame);
- I2 c0 v B+ b+ z& ^$ ? - return;7 j& \, p q: q% w
- }
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" \
7 E" {! A2 x; {, q F" I* @ - "Content-Length: %d\r\n" \% Y7 G9 h& ]) A w0 w1 d
- "X-Timestamp: %d.%06d\r\n" \
; y2 n5 a2 n2 o4 x" D. ^' W0 d - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec); H- ~% W. J2 D
- printf("sending intemdiate header\n");
2 m8 A9 X7 n. I& z3 z+ r) Z. G - if(write(fd, buffer, strlen(buffer)) < 0)
7 v% {* \, _9 H2 L# O" H; c - break;
( E1 L* a& n' C1 X3 J2 Q; N - printf("sending frame\n");: q1 K' ?; _. R, H1 I( C
- if(write(fd, frame, frame_size) < 0)
5 i- l! e. L8 V4 r8 }6 o! L: J - break;4 x' a& m% m/ A1 K/ l- {* _
- printf("sending boundary\n");8 q) t2 J4 K `( ^0 C$ R6 o
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
6 D7 C& X1 I) L) \0 q4 Q% g1 I - if(write(fd, buffer, strlen(buffer)) < 0)0 c5 g( ^) }4 M' s% c7 Y; D& X
- 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:
9 h1 a( ? U2 J8 p! B- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)
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2 R; J8 @0 {3 j, \& d) L - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);( v1 n! m+ e1 s
- if(*socket_found == (~0))
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- printf("Create udp send socket failed!\n");2 c5 _ R: ]6 k
- return -1;" F7 c6 e; q3 Q1 c: i
- }
9 G+ w {$ c1 R0 _9 M - addr->sin_family = AF_INET;
% E$ j( A8 L9 \9 J8 l" l+ [% j5 A - addr->sin_addr.s_addr = inet_addr(ip);6 n/ Q7 ]2 o) \6 D4 f- ^( d
- addr->sin_port = htons(port);
. b! ^" J) k6 U# l- y# C" R - memset(addr->sin_zero, 0, 8);( {% c* M9 U2 J5 Q/ ^0 A
- return 0;- o: Z& k; |! l. ~# b
- }
复制代码
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$ a& e) m# Q! ?! k& |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:& @, ~& d, V7 C' z8 z" [; [' }
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- while(fend > 0)4 d# J) \4 b1 v% B3 l
- {
* h8 j, C4 s Z: h, C3 j) i+ L - memset(picture.data , 0 , sizeof(picture.data));: W* `! Y$ r t5 d/ |
- fread(picture.data , UDP_FRAME_LEN , 1, fp);
$ t# i, O; U. H/ W# P7 D' S% J - if(fend >= UDP_FRAME_LEN) [8 ?* ~2 B1 T( g
- {
* c: l$ [; {' r9 |1 s6 z - picture.length = UDP_FRAME_LEN;
$ D1 F, c$ D) ~/ k/ [ - picture.fin = 0;0 c3 T, Z) M) \
- }
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- picture.length = fend;: A- I! [# C$ O. j8 ]; u
- picture.fin = 1;# F) o9 i# @1 p+ s0 b3 ]/ X
- }
0 _, G8 Q4 g% G' l' f0 L V - //printf("sendbytes = %d \n",sendbytes);2 x6 E2 \* ]" T- w
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
0 e$ r% i9 l* H+ v - if(sendbytes == -1)
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; x% }2 d0 g4 e% K - printf("Send Picture Failed!d\n");
+ B: D9 j9 V2 p; i" {% _" i/ p- a - return -1;
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- fend -= UDP_FRAME_LEN;
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复制代码 4 @) u+ d0 W: Z+ V( L# f, {
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" O/ b- H$ [8 `) R& E" UiMX8MPlus 核心板: https://www.forlinx.com/product/136.html |