本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑
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% R* l! T3 S! F7 t% Y& H/ g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% ^' G1 N2 d3 a# }0 v
! F: k u5 m S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 v# O/ ^7 W$ M2 u- d M

/ s# A9 B1 ^ N7 ?% V- S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。
) d/ M; f* |3 M- f; K一、HTTP网页服务器2 X& N, @0 C+ v
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)% l. ]3 K9 o. p; o. @3 {
- {
. R$ y+ r) u& h$ A& \$ d" l; Q - struct sockaddr_in servaddr;( A& u3 `# e4 N O- U0 M% u
- socklen_t addrsize = sizeof(struct sockaddr);( _9 q" [0 N% w. z0 g
- bzero(&servaddr , sizeof(servaddr));2 X; g) _( u5 L3 {# V4 e$ ^
- servaddr.sin_family = AF_INET;7 b& F7 Q7 ^8 M$ R
- servaddr.sin_addr.s_addr = inet_addr(ip);
; Y9 n2 s* @1 P$ j - servaddr.sin_port = htons(port);
* o2 F# U! G: m' E6 K4 \, u* I - int ret;
% l1 A' e1 a) O7 p8 P. } - IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)
# A( g, m' ?2 S. T - {1 D, F) ^% g0 u4 b
- printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
# F$ q9 C/ Q0 y0 T' v0 C/ K2 ?4 y! | - return -1;
2 a" `: m+ ~: b3 a7 T - }
1 {( P- ^/ T7 L* R; z0 m - int on = 1;: A8 D7 k# O/ S" J# a+ ]: {
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
9 o) a8 l. i" k$ H: w, H' \ - {
2 C8 ^" n! q L" T/ G; R m0 D - printf("setsockopt error\n");# A/ { i( i5 U) x3 c
- }) C9 Q+ Q! ]5 ` G6 E
- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
- V' I) e0 ~0 U# ]) c) ]" Q7 n o - if(ret == -1)& s1 h- U0 [- V7 r, c
- {" m# b" N+ ]0 o" M7 j8 ?7 I
- printf("Tcp bind faiLED!\n");
$ ?5 k$ o, p0 Y4 _5 W - return -1;
0 u9 K: n4 g$ e - }
# x) |) O. k% A4 k6 y - if(listen(*socket_found , 5) == -1)
6 w# }, q8 O, h: D% P/ [ - {
" ?# x1 E5 G3 W, }, Z" x- y - printf("Listen failed!\n");
8 G2 d% {7 ^ \/ `' ] Z T - return -1;
# } I7 a2 _& T& z' Y2 G$ J - }
" C; Y* I$ B- ~5 ]6 E9 @+ S - return 0;
+ v2 R9 {5 u- e) Z - }
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);; P, s* C v) L$ J' V# [+ T- n
- void * Thread_TCP_Web_Recv(void *arg) M% g6 d( d) f2 v: u' l; U
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- 。。。
( V# X) q1 V, L! J7 k/ r/ R - while(1)/ m) I4 B! p9 Q; }- d3 B
- {
# ^" w5 r+ [. O: t; A3 m6 L' D' P - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
) x/ w3 _' }+ A - printf("fd_socket_conn = accept()\n");
7 F. z! p$ T5 W1 m - 。。。- e" k$ h8 Q9 `+ @2 Y. O
- recv(fd_socket_conn , recvbuf , 1000 , 0);- t$ l( |! k4 h. R6 k# J/ I8 T0 g
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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);
9 ^8 D" b& [# x B( n, J - pic_tmpbuffer = pic.tmpbuffer;+ U; e5 E1 d W' W
- pic.tmpbytesused = buff.bytesused;) c6 T, Z1 r2 _
- pic_tmpbytesused = pic.tmpbytesused;
' Y2 B9 `1 O, j2 a" C - pthread_cond_broadcast(&pct);7 Q- r) O) b% S
- 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;
; m. ~& M& K& k6 U2 Y" U3 B0 h( p - pthread_cond_t pct;
' b; z' E K- Y* d+ h - int main(int argc, char* argv[])' U/ Z# |. m7 T1 V; N- ]3 v) x! Y L
- {
; S& }) O" p# H9 {* ?. \( C - ...
. }7 v3 R8 b$ j - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
9 j: E6 R# Z/ N+ p( n! m1 T. h - pthread_mutex_init(&pmt , NULL);4 e* r) m7 `! a+ G1 s' Z% a: j1 N
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);
, r! i$ R' T4 F5 {4 L - pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);/ E5 U: S7 j) \3 V
- ...
. |0 @& \7 e }' d* }& d- S0 L - while(1)( }% b; s" l5 n& f; ~! s; i6 L
- {
2 W6 _; i; K6 ~* G8 ^+ G - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);8 n; W8 u: D+ F9 T( ^
- ...9 V2 s! X9 j# v3 N* E; y* L
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- ...8 |0 W1 j% M: l, C, r: f/ X. g
- }
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;">* l8 j% g; D8 y: J1 l. c* O# }; A2 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" \
- T: ^0 e) L0 B' k) k4 p - "Server: MJPG-Streamer/0.2\r\n" \
: C; w `" z. n- n) a4 F8 F - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
/ d- h/ \/ i& ]7 c; A. E - "Pragma: no-cache\r\n" \
2 `0 j4 |" B5 H8 z5 Y9 O - "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
* p/ M% A6 \' S- j4 p0 U$ ~0 _8 J - #define BOUNDARY "boundarydonotcross") k3 K( R5 f M( t# v
- printf("preparing header\n");, J. H) p6 s5 A" t6 S! T3 F
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \+ U! d- h) f3 j4 K# j& _+ k
- "Access-Control-Allow-Origin: *\r\n" \
& O# ]. ?. x/ r8 N$ |/ _; @ - STD_HEADER \
0 } B, L# _8 r' d7 m - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \# R; ]. f5 N! T2 p% [: w( \
- "\r\n" \+ q4 F2 F! u( I& S) ]
- "--" BOUNDARY "\r\n");' S- f$ i) S3 I% U+ }
- if(write(fd, buffer, strlen(buffer)) < 0)
" P9 V2 L( F/ ^0 a- X - {
; R+ W! R6 c3 R1 W: A0 l9 ?5 U - free(frame);
! T* @; [7 v: G& e/ c - return;
, E/ F/ Y5 b0 k% `) ?3 j+ s! T - }
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" \5 h& y+ O( T6 j. m
- "Content-Length: %d\r\n" \
1 m: N( \6 s- e- G7 l) E* i+ h - "X-Timestamp: %d.%06d\r\n" \
& C6 e+ c0 Q% N! b- P( L - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
. C) q+ i+ q/ k) E- v( A/ q - printf("sending intemdiate header\n");
& d0 S6 a2 @( g- @. e3 ~5 P - if(write(fd, buffer, strlen(buffer)) < 0): j; z6 `6 G4 R& ^5 W" N
- break;! F E: ?2 ~9 A8 Z( I3 m# |$ i
- printf("sending frame\n");
% Q' Z6 P9 ^2 D# L( a& w - if(write(fd, frame, frame_size) < 0)
6 p# ?% e( j: f4 K. H) K$ F$ l - break;, {, X) ]/ X0 r% B
- printf("sending boundary\n");
/ @% c' w8 N n8 U+ r - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
0 _3 y& K- u( @: @/ M h: e - if(write(fd, buffer, strlen(buffer)) < 0)$ n* D6 A* A7 ~- c% Y8 ~
- 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。  7 S3 ~3 N. b, O) i0 j( _; R, b

& b8 L' @ x, b! f二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:9 G/ i+ |' s* W/ S
- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)
& f$ g. V7 S* g# P% P - {
+ ]7 u! Q2 D! |9 t# _7 g( i' S - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);
" R* R( K1 j% P) t% ] - if(*socket_found == (~0))% q7 k. y# u# _2 i9 o% A0 H( F9 s
- {
( V2 k- }# U6 s. U8 I* C - printf("Create udp send socket failed!\n");. w! b; K( [* ^1 b; L! b
- return -1;0 `; O/ S" i% L/ c. V
- }; Z2 ], K8 r! t8 R2 K9 r% O; V- @
- addr->sin_family = AF_INET;+ s/ ^ X1 l) Q' x" u" m: F& N# c: `
- addr->sin_addr.s_addr = inet_addr(ip);; w1 Y" x& x# x) o ~
- addr->sin_port = htons(port);
- X) c6 x& O6 x - memset(addr->sin_zero, 0, 8);/ c3 j2 V. ^/ O, t( B* _6 g
- return 0;
8 x2 P! D; R2 t7 ?5 ]+ a% u; ?: f - }
复制代码 $ `' A* y7 l i
4 H& y6 e# m& u, |! ]$ @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:7 g9 ^" q7 }) _5 w: e
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- while(fend > 0)5 F* {- X c5 J( s2 i
- {+ F9 j, h+ |1 T0 Y; m `3 k4 C! \
- memset(picture.data , 0 , sizeof(picture.data));
9 O, F* i! T6 n5 L% R; T - fread(picture.data , UDP_FRAME_LEN , 1, fp);
/ U8 h* I6 T% s" G. |6 _ - if(fend >= UDP_FRAME_LEN)
+ ?) p. Y: G; q/ Z$ R' ~8 q - {
: d9 r3 s* N8 m* E - picture.length = UDP_FRAME_LEN;. `/ g# |* o9 h8 z1 c( E9 Z) T
- picture.fin = 0;3 ]! K( b# |5 }! }
- }1 u3 m. Y( r5 {3 |4 k4 v" F, G
- else
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- picture.length = fend;
2 t" w, M+ @+ @- {6 V - picture.fin = 1;
/ T) b% ?& ]* B E) w - }
1 u8 X" L# `4 s) |6 L - //printf("sendbytes = %d \n",sendbytes);
+ q/ S! J( o3 W; g1 c: U - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
# V! ?; Y0 h$ N - if(sendbytes == -1)
$ u; m0 A+ C5 J# i# c/ w A. j - {- H* N" S |5 t3 e9 {/ S' | a6 p) ~
- printf("Send Picture Failed!d\n");
0 @& ~3 b8 |! X4 a - return -1;% l5 R; @2 r6 }7 a0 }2 m% G- [
- }
: d; M8 w) R. H - else& W2 D' _/ b. _* D
- {6 ]+ |6 G9 \: g
- fend -= UDP_FRAME_LEN;3 s/ T& @. p* C0 v! d5 S, d" o
- }
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复制代码
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iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |