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- S. P/ C. {. S6 C; A/ q& w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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5 I1 ?8 x7 V5 o B/ [; M @: c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。 - g' {. Z: o8 u0 w

% J7 s- M0 V1 x+ x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。
/ A" e' ], |+ S! B: Y一、HTTP网页服务器3 N# a0 T/ m/ I, u( C6 W
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), g* c7 h! B' p5 _; b. `
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- struct sockaddr_in servaddr;- |3 H' C+ B9 _4 J
- socklen_t addrsize = sizeof(struct sockaddr);
. d4 e/ ?: u* X* `3 }& ?2 j - bzero(&servaddr , sizeof(servaddr));2 l: j# \- o8 i1 d: B
- servaddr.sin_family = AF_INET;
7 r% R) C: X( P% e: x - servaddr.sin_addr.s_addr = inet_addr(ip);' x& K! O# I8 @. _$ C" U( F+ j
- servaddr.sin_port = htons(port);; x5 Y& G6 ^9 t8 h% Q. Y
- int ret;# K! `/ e: z) [8 F, o: R: w/ O
- 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);3 k# Y6 o4 u: u3 E4 |& H" f: P
- return -1;* N/ C$ w e/ G' m* W, z
- }
7 G. u; B4 j+ }. j" M% }; o7 [ - int on = 1;
3 C1 B. |' N! r# n- d& ` - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
* c- p' q$ }- ^ - {
0 A2 t6 A% }# V& V# c - printf("setsockopt error\n");) ] [+ ?0 [4 U" ~& F
- }
7 `% w5 B* S a - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
) G p5 Z, {8 _9 K" F$ ? - if(ret == -1)" y: t/ `0 H; P8 U; Y
- {
( @1 ~: n% }2 L9 D: ]7 Y - printf("Tcp bind faiLED!\n");
& f& M8 A; s, g7 L, T' T, C - return -1;
! D& Z7 Z1 o7 C# \ - }
, |) k- Y N; X8 e b" S# H9 ^8 K6 Z% C- g - if(listen(*socket_found , 5) == -1). m- h& t" y% y! C2 e
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- printf("Listen failed!\n");
D" I1 V$ F! L+ E& w+ L - return -1;$ o$ Y) \0 g% g
- }
9 m4 R$ w5 I' K9 b - return 0;4 |2 F- Q$ i4 s% Z3 i4 y
- }
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);
& \, z' O, Z& k; {( t; u; K - void * Thread_TCP_Web_Recv(void *arg)+ h2 H) P' s }4 L' Z c7 V6 y
- {
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- while(1)+ ^9 c% M6 B; Y" D
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- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
, A# ^* U1 J" }! S) p- C: v' ] - printf("fd_socket_conn = accept()\n");
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- recv(fd_socket_conn , recvbuf , 1000 , 0);
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- 。。。# F* }9 X. ~7 n: o
- }
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);) ?3 L: y$ M. f C
- pic_tmpbuffer = pic.tmpbuffer;8 o: a. S ^6 M
- pic.tmpbytesused = buff.bytesused;
) Q5 X9 R1 T1 d0 _ - pic_tmpbytesused = pic.tmpbytesused;0 I; m$ r0 o: H2 {
- pthread_cond_broadcast(&pct);6 j. q1 Q& [9 \$ ~
- 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;
$ l: m( [0 o. M9 d; } - pthread_cond_t pct;: G) I6 ]- k1 O, e1 i0 x/ N' Y+ z
- int main(int argc, char* argv[])
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- .... M3 F% y7 }; [7 R7 [. B
- TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);, g- P6 k* ]) b1 ]+ B. t2 v2 [. d" a
- pthread_mutex_init(&pmt , NULL);7 z, b ?4 s6 J0 d% h3 g
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);+ X0 @2 y( j; @: K
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);" q/ c5 @2 R1 D0 F, V1 ^$ z
- ...9 B; D+ f+ B/ E) y# z4 s$ B9 J
- while(1)
" A3 D b. s/ r+ G: R - {
( k' U: y* W3 i" a! b2 }' S( L3 Q7 c - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);1 k0 M; {/ A. ^
- ...
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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;">; H) f% y h3 p2 g
- </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$ H6 G& v& w; J- r - "Server: MJPG-Streamer/0.2\r\n" \7 u7 l: {% x3 l! t% A
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \. n1 q) h ]2 Y Q& e
- "Pragma: no-cache\r\n" \7 |( j" u0 i! ~9 V; S: P
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
3 \. X$ P7 S& {* n+ @. e# ~ - #define BOUNDARY "boundarydonotcross"
T6 z# o7 e: q5 k( E K- L - printf("preparing header\n");
/ s7 B( @! j1 h3 |# e c \ - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
! j/ M4 x F7 Y( e: Y' H - "Access-Control-Allow-Origin: *\r\n" \
+ b) W0 V S% {, V+ D" a - STD_HEADER \
3 b1 s/ S$ L! @. I( o7 ?' V6 s' A - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
' @" M7 e+ l# A, y! o% U! W+ X8 S - "\r\n" \
0 ^. w9 S' E5 ~# M - "--" BOUNDARY "\r\n");" H9 |8 Y, `" k) K! c& d, x
- if(write(fd, buffer, strlen(buffer)) < 0)
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- free(frame);8 Y7 u. h3 R5 h# g- ~. w
- return;7 h( q+ |( ?: W. F
- }
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" \4 G5 W" @+ A% o+ B/ {) z
- "Content-Length: %d\r\n" \
$ y! } w5 c* \" }! a - "X-Timestamp: %d.%06d\r\n" \' ?/ C- D5 P f
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);, m* }$ L' Q/ H2 r/ s' H9 {! J% N
- printf("sending intemdiate header\n");. [$ G3 \! g- I' z
- if(write(fd, buffer, strlen(buffer)) < 0)
, F1 O/ o, `" B - break;. Z3 N' A, X- x
- printf("sending frame\n");9 m# L7 }: R- q- w, G3 v; {
- if(write(fd, frame, frame_size) < 0)
4 m' q' \# i1 R9 W. p5 j - break;; t5 K. d- p$ k: h# [9 H
- printf("sending boundary\n");
3 Z8 u: N( b/ e, O4 X2 ^' F; ` - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
k' t5 D1 C* D2 h - if(write(fd, buffer, strlen(buffer)) < 0)
. I* c( @7 _) i' A - 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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a) a- Z1 k" J! _; }二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:7 R; h' f* p- \# y
- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)4 \+ E( W& x; [, K
- {
' x) Y0 g/ A3 ^! t7 Y# A! D4 r - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);
7 _7 l% ^) i. @+ O; n - if(*socket_found == (~0))+ g( n5 O5 h- M; Y, Q# p1 {# M
- {
) ?5 R0 m9 k0 `1 u' `8 u* { - printf("Create udp send socket failed!\n");
& i1 R5 U# f) h+ C x - return -1;
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- addr->sin_family = AF_INET;1 M5 c, c/ ?9 V* I I
- addr->sin_addr.s_addr = inet_addr(ip);' z9 t8 @( X' V: L2 L) X
- addr->sin_port = htons(port);- q& H& J2 q1 |/ ~% K
- memset(addr->sin_zero, 0, 8);5 S7 P$ L; N( l4 k
- return 0;
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复制代码 * |: G1 Q2 a4 d$ l
; Y S/ E2 F8 w U; B& ]+ 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:" y. _0 W" O2 G! r$ G
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- while(fend > 0)
. ]7 s! \2 }" U3 ~- x! u5 @9 D9 ] - {
9 c( d7 }( d2 i) [ - memset(picture.data , 0 , sizeof(picture.data));- l* C: l( r, o6 c7 p0 C9 _5 U
- fread(picture.data , UDP_FRAME_LEN , 1, fp);
3 V( o$ t/ v; F) Z8 ^. D" x - if(fend >= UDP_FRAME_LEN)
6 R+ J1 _+ I/ }2 c# L - {
/ m, H: o% A$ l ]/ r - picture.length = UDP_FRAME_LEN;
+ q5 V/ Y( t: |: J& Y6 ~. ~& R - picture.fin = 0;
, M0 C/ m5 Y% P8 g( V - }7 w3 c8 l' u1 U+ E, M
- else" n! |; t7 ^+ k' c
- {
# m& L8 M8 L3 C+ s8 c5 N# M3 j. f# Z5 x - picture.length = fend;
! K$ w; n' R9 d$ P" f- W Y - picture.fin = 1;
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' `9 C# d8 F" r% E- q9 I- u9 p - //printf("sendbytes = %d \n",sendbytes);" M: X ]6 p# C! A
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);0 M. B2 t, y- \! p
- if(sendbytes == -1)5 X. N$ ` j1 n0 `# u/ R3 \' c$ p
- {
$ R; L. H, V/ q - printf("Send Picture Failed!d\n");% j- r7 O( r/ U
- return -1;2 ?# n, I T2 R% Q: G
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- else# F6 |( M; e( ~" A1 H e
- {
3 c/ g8 ]$ p7 a& N" @, { - fend -= UDP_FRAME_LEN;
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- }
复制代码 / p( d; O( S% q/ p$ r
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# y* i- j7 f5 e; h+ MiMX8MPlus 核心板: https://www.forlinx.com/product/136.html |