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+ f7 ^( J" T, X" N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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- C( c$ T, C$ p i u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。
% Y) Y6 ]/ }/ }% X9 m" Z一、HTTP网页服务器) l" E4 L1 R+ z' s+ w0 `- Z& Q
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;7 P/ ]2 X* R! t; T* o5 J$ E
- socklen_t addrsize = sizeof(struct sockaddr);* Y. F+ S; I+ t8 r2 x
- bzero(&servaddr , sizeof(servaddr));
p/ X% B! X% D/ N6 S1 ]6 M& l6 u - servaddr.sin_family = AF_INET;
& ~, c5 j: v7 k6 k( P- r1 I - servaddr.sin_addr.s_addr = inet_addr(ip);# k6 {% i8 G' A
- servaddr.sin_port = htons(port);
6 \4 g1 w$ F7 V4 Z - int ret;) H. \+ Z' `2 O. \$ K r
- 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);
" J2 w3 K' q8 q$ g% R - return -1;2 i: f% Z6 c" u' J
- }
, N9 o- v; d+ _1 O( x3 v - int on = 1;+ K# _5 i( v# W
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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+ D/ h! R! ^6 i/ S. _) R4 f - printf("setsockopt error\n");
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! w! n- O" Y# s6 ^+ X) d - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);5 G5 r) a+ ~8 f
- if(ret == -1)0 V$ m- b8 z% D0 i0 O& s) M" M7 Z9 t
- {
( o9 h0 M: A7 a! n% I9 R - printf("Tcp bind faiLED!\n");" P5 m/ }! w' ^1 \8 u4 u* y
- return -1;
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+ Z4 L$ {- W2 k) U2 P - if(listen(*socket_found , 5) == -1)0 f `$ F( g# V! o5 P
- {+ J0 B) W) Z/ B* t. l
- printf("Listen failed!\n");+ p' O0 i# k% Y3 v6 {+ S/ N5 V/ Q
- return -1;
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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);9 m/ x# S) v$ r8 u7 ]# j# y
- void * Thread_TCP_Web_Recv(void *arg)
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/ W5 e$ W" p5 N- m* @3 p - 。。。
@4 B: E. q) \, v% u - while(1)
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) y) V7 O3 k8 [9 E H - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);* U0 F p+ r) Z5 n$ c9 r9 z
- printf("fd_socket_conn = accept()\n");& f/ d8 m+ @- E4 t" w) p
- 。。。
" B1 C6 s* @1 I* \ - 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);9 @( R+ M5 A: R
- pic_tmpbuffer = pic.tmpbuffer;
2 D4 z! Y( D! ^" S+ k/ |2 c" ^/ u- d! A - pic.tmpbytesused = buff.bytesused;
" I! Z& z/ l9 s0 x* Q$ d - pic_tmpbytesused = pic.tmpbytesused;! H! ~0 D: m$ `( X1 ?
- pthread_cond_broadcast(&pct);: w8 {9 M' f- i& l
- 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;
r: N. s2 N$ y; F9 V9 D2 Q - pthread_cond_t pct;
5 t- B* Z3 V2 K - int main(int argc, char* argv[])
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- ...
6 x& r, ?! V& `1 K' N7 a - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
& C9 Q# I! B' R! ?2 e - pthread_mutex_init(&pmt , NULL);) ]2 A6 h+ r1 A* i. i+ Y4 E
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);
9 m- R K' q5 S - pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);2 _' D- t6 B7 w/ g/ {# Q) B
- ...
' S: }5 m0 F( e - while(1)
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- V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);8 h! W" T% {+ G, \$ z
- ...
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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" F3 a* q+ s& W - </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" \8 g; E3 G+ A" `$ Q
- "Server: MJPG-Streamer/0.2\r\n" \
1 m$ \# F' h& ~4 V - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
+ c& q. b" n) e1 u. V/ G - "Pragma: no-cache\r\n" \
" M- P8 o! M1 J( n/ V, P) L - "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
; l! J$ v+ d& [, o: E5 v& _ - #define BOUNDARY "boundarydonotcross"
% s6 q8 S6 k5 j - printf("preparing header\n");
' F% k8 x% _/ w+ ^* U - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
* w, D. H. L/ B - "Access-Control-Allow-Origin: *\r\n" \
0 D7 }, e1 Y7 n% a8 T - STD_HEADER \
: R O! R2 W0 D" g, O- D5 z5 ~ - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
- i3 K, y0 t+ ~ - "\r\n" \
1 i: x6 k+ J1 k* e! O - "--" BOUNDARY "\r\n");8 K2 K7 B1 Y u1 ?" H6 _+ R4 p
- if(write(fd, buffer, strlen(buffer)) < 0)$ I/ [/ M7 @ _0 f2 O3 |8 j
- {( e$ A$ ]7 ^+ ^9 q$ u9 }, e: `
- free(frame);9 `, D2 _3 Y- k6 @# ^* 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" \
- j! i. \) ?9 P3 D! U) \# K - "Content-Length: %d\r\n" \* B4 [% A* |9 f2 C9 Q# A: a
- "X-Timestamp: %d.%06d\r\n" \
0 q' o1 y. N, W- Y - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
2 V; h8 u' V, i4 G* } - printf("sending intemdiate header\n");2 u* v# ?+ {7 N' u: |3 W
- if(write(fd, buffer, strlen(buffer)) < 0)
/ i3 N! h* {8 U: o" |( d* C - break;; F: |$ E* h, w9 D
- printf("sending frame\n");
) z$ c+ j. M8 ~, u9 a: g1 c - if(write(fd, frame, frame_size) < 0)6 Y9 F5 c5 L: I& _
- break;3 ~2 V9 z2 J2 s7 k% O9 V
- printf("sending boundary\n");
) k) O2 L) K/ L3 s; U - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
5 ^# G# g7 \4 | - if(write(fd, buffer, strlen(buffer)) < 0): n! D. H# E9 _5 `5 S& |. [1 X b' [: R
- 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:& P; V" J* h0 j6 W' k* O
- 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);; v8 |4 D f2 e' ]" x
- if(*socket_found == (~0))
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, f! c& ~* Q* L - printf("Create udp send socket failed!\n");, g' b1 S! q( X5 W7 |
- return -1;
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- addr->sin_family = AF_INET;
3 A7 R% D0 ?4 |& X3 B - addr->sin_addr.s_addr = inet_addr(ip);+ U$ c1 o4 r3 \* n+ K# G+ z1 V9 N
- addr->sin_port = htons(port);& c' d/ F. f/ z/ a3 Y) p! u4 }9 j
- memset(addr->sin_zero, 0, 8);! {6 y" Q! I* ]* R
- return 0;: G- `$ W8 }/ c: \
- }
复制代码 . `4 Z/ y# ]; `
9 q/ [& i* c* H! x- V/ d! r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:2 A4 Z/ M& B* M; m6 S) C
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8 O# D H) d9 Z/ g. m- while(fend > 0)2 A8 X* G/ P1 s
- {
" y% D8 H5 w9 a) Q2 @" E - memset(picture.data , 0 , sizeof(picture.data));
: }; ?- A$ [5 x+ M - fread(picture.data , UDP_FRAME_LEN , 1, fp);) w* `- l& s( N2 A3 v6 I
- if(fend >= UDP_FRAME_LEN)8 V# K5 O* \& @- k% J' H4 H
- {
* k& C/ r0 l) l" j: H) X9 I; x - picture.length = UDP_FRAME_LEN;) m; b% ]7 o% Z+ N3 z/ S3 \
- picture.fin = 0;
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+ Y y8 s1 U% m J. z3 b% [- x - else
! x8 G& R+ `. R( ^9 P E- |% q - {
( a* i8 P s$ ~, q( z' z- J" f* P - picture.length = fend;
' \+ ~1 j* _' z! p; D* w, e - picture.fin = 1;
: [- ~* ^$ e/ l% g* o2 t4 t - }
/ r( A3 W6 e+ ]/ f3 H8 P9 ? - //printf("sendbytes = %d \n",sendbytes);
& X- k( d# D) o& V - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);6 u4 J; k y) ~: z8 v: U
- if(sendbytes == -1)
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. I) ^7 H M5 p7 C8 q9 s - printf("Send Picture Failed!d\n");! u5 \4 R F, h0 G+ j, Z4 o/ B
- return -1;" N' |( L) R t
- }
* [) Z' m5 s6 N) o1 v) a - else' m5 h9 N; r, X- a
- {4 p6 O- M# L. f5 ^; p
- fend -= UDP_FRAME_LEN;7 H4 G, V. J9 b
- }# ^( w/ ]5 S4 I9 V
- }
复制代码 ! |4 Y4 ?; P) w3 m4 k, [
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) V$ D+ R! K# t7 N# z1 ~- iiMX8MPlus 核心板: https://www.forlinx.com/product/136.html |