本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑 9 m8 Q% ?- i9 i: ~6 E: l! s% X5 }& h
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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.html
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; V) L8 x. a+ N2 V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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$ f1 ?4 Y/ V, l7 a: y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。 ! \: u3 {& P9 N6 d0 W6 ~$ q6 e
一、HTTP网页服务器$ r5 X# ^# v* X+ a. B$ ^' J1 Z/ b
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)- F/ N2 ]$ r' L+ q/ o& u a
- {
/ l/ E/ i1 U+ j2 u5 I6 P2 L0 L - struct sockaddr_in servaddr;9 H% d# M: ], z( y. d) C. g, I# w
- socklen_t addrsize = sizeof(struct sockaddr);5 M! A2 m3 N; V f) Y
- bzero(&servaddr , sizeof(servaddr));
3 ]+ R9 a7 |/ ]9 _4 d3 R' n7 M - servaddr.sin_family = AF_INET;
* W) V1 L9 |! B, e; E" ]* n - servaddr.sin_addr.s_addr = inet_addr(ip);
& H* h" Q5 t! F) j' i5 f$ t - servaddr.sin_port = htons(port);! F2 A& Z+ O% `6 b/ b% ]
- int ret;
8 a# h2 s2 z0 d. t2 H1 Z - IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)
& S$ c9 h8 I F5 t - {
3 U( t7 S" e9 w- d( M3 D - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
4 u3 _+ q' H+ _/ V% P* w/ b - return -1;) p9 e8 b1 G, I$ W m. Y
- }# ~% h, s2 k/ K
- int on = 1;& K) q" N9 @- s* l8 J t) J
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0) e }8 T8 U n, |3 x1 s
- {
4 f* I& R9 B% V- z& s& M - printf("setsockopt error\n");
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- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);! h8 m) L# w( a! w* V
- if(ret == -1)
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- printf("Tcp bind faiLED!\n");
; s- \* Y. C p( I2 m" D5 W - return -1;- ~. r1 w; Z2 x* }8 x
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- if(listen(*socket_found , 5) == -1)
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3 j" B* I4 w% ^$ {# p2 l4 ]& I - printf("Listen failed!\n");% [. n/ P# O- I. g7 m8 k! ^" b
- return -1;9 H( f4 a/ }- M+ [* I* q' `, r+ O) ]
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- return 0;: F4 S* Z9 m1 J% @, h
- }
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 ?0 A! H, I - void * Thread_TCP_Web_Recv(void *arg)% s3 \" b' \ M) S6 M+ s% G
- {
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( U. m: R+ O) n) T; ^) }1 u - while(1)
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! y: A" V9 S/ U! c" t" D - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
9 f' }$ z8 H+ A: R) l& L! i6 { - printf("fd_socket_conn = accept()\n");
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- recv(fd_socket_conn , recvbuf , 1000 , 0);! P1 @# [2 }, i' P
- }
- O4 G" F/ j4 d0 B$ I - 。。。
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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);" u. [2 D' H5 A' t+ |- A' N( @
- pic_tmpbuffer = pic.tmpbuffer;, W: D; }/ }9 D5 g
- pic.tmpbytesused = buff.bytesused;0 j H7 I: ?- q+ @4 v$ D
- pic_tmpbytesused = pic.tmpbytesused;
0 E$ T" A. r4 ~! W; N9 { - pthread_cond_broadcast(&pct);$ \4 M2 U7 B0 ]" r: F% l! k, z
- 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;
( J3 k4 A8 N- `# T. l - pthread_cond_t pct; U- Q0 `* Y) @% }5 u6 l! g* t% k
- int main(int argc, char* argv[])
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- ...
, D1 e& i! T8 p+ n& t# P - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);5 X% U( l0 R3 e
- pthread_mutex_init(&pmt , NULL);2 ? L; Y: N5 s5 n& F0 @2 z$ m, P
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);
% f3 {/ ?+ H7 v! E% @6 I+ \ - pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);7 W6 t" W1 T7 }+ T8 [/ {
- ...1 @# W+ K! Q6 K- n* B1 u
- while(1)
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3 ]8 k) K# n, }4 u5 L - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);
: G3 Y& [( q0 Q- d) S0 a; V+ q - ...
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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;">5 O8 Y+ ?8 w9 E' L' m4 h
- </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" \! w; h& w9 O. ~2 a& Q6 _4 s/ s
- "Server: MJPG-Streamer/0.2\r\n" \
- J8 _/ N# E# G' X# q - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
/ ^ q7 r* i% [& A8 X - "Pragma: no-cache\r\n" \1 C1 M: b. z- a4 Y4 H ~: _
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
8 [( K& ~6 d1 a - #define BOUNDARY "boundarydonotcross") F4 C$ \4 l& y- c4 H
- printf("preparing header\n");
% Y" w$ y; V) A# |. X - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
, k3 @; O* @! s: x4 H. I, O - "Access-Control-Allow-Origin: *\r\n" \" ?# a; P6 Q6 f
- STD_HEADER \. g! b; ] M& g& Q" f
- "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \. _3 q" r& C* T( y( O
- "\r\n" \, a: {8 I, j9 p0 j2 o% K* g) m7 `
- "--" BOUNDARY "\r\n");6 n% G' p! K0 l2 c4 o
- if(write(fd, buffer, strlen(buffer)) < 0)
+ ]; U+ e* z: B; b6 ~. K: U/ L - {
& q( E# c4 `: x. A) m& u0 w - free(frame);
6 v: ]* ]. G2 @% F: G - return;
+ o( K3 N& U$ q1 x4 n. ?0 l7 z - }
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" \
0 t4 \. I- m& D% `! ?* B - "Content-Length: %d\r\n" \/ _3 W0 @" C/ ]; r- G& e1 G3 v
- "X-Timestamp: %d.%06d\r\n" \
5 F/ L( i. B1 d- i - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
6 F( Y! U/ E% @ - printf("sending intemdiate header\n");
5 V6 A: a# v8 e+ i9 u1 v. ` - if(write(fd, buffer, strlen(buffer)) < 0), d4 j( R" ?: e& J; M+ E
- break;
2 @. V5 a" Z( h( k8 e - printf("sending frame\n");. i& V5 C; E7 ~( Q
- if(write(fd, frame, frame_size) < 0)3 R# {& i* t$ T) L. E/ K
- break;3 J8 M5 s# _: ?+ y) O
- printf("sending boundary\n");) z3 X" f* z) T& R( e
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");2 j( \8 l+ F. p* k
- if(write(fd, buffer, strlen(buffer)) < 0)
# Z* I( T2 t( e# w$ 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。  2 u" F( g( M. v

" s( V# Y' {) [. a" p二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:
% k( }4 U0 k R% O5 P9 G- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)7 P: M, A' v# D% g5 W+ {
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- *socket_found = socket(AF_INET, SOCK_DGRAM, 0);
' B: Q) |( U) X% A; u, ]; X - if(*socket_found == (~0))
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- printf("Create udp send socket failed!\n");4 r( c/ P: j5 e. t# _
- return -1;
* ]. A* J4 t% g0 M! d - }
. P) D1 y3 w: M [* g/ H - addr->sin_family = AF_INET;$ c5 A2 z2 E0 }; M; k! y7 G: x
- addr->sin_addr.s_addr = inet_addr(ip);9 E2 B8 R7 e1 u; y' N2 l, C* ]
- addr->sin_port = htons(port);
3 h; L+ U, q& C - memset(addr->sin_zero, 0, 8);+ r7 u7 `; y' S0 I% B! C* t$ l1 y2 g
- return 0;& H! g& A/ {/ [7 I6 r, s; P
- }
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:8 {' Y5 n- a' G! `9 ]
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+ S. s0 c5 e5 k. W- while(fend > 0)
2 N! \7 |1 m4 F5 L - {
0 a& l( @5 f5 `* ] - memset(picture.data , 0 , sizeof(picture.data));
+ |- C [* k, l6 O: Q! z - fread(picture.data , UDP_FRAME_LEN , 1, fp);
) @8 C& m* D6 ~* S, V - if(fend >= UDP_FRAME_LEN)
# p$ J0 k6 L( |! Z* O - {6 _# z$ m( U6 [+ b
- picture.length = UDP_FRAME_LEN;
2 y; d/ Q6 [6 S - picture.fin = 0;1 q) A' h" P( m' R
- }
$ i% I( b6 C" L8 D- B8 u" n - else
- ?! v. L, b; G* j" d1 }. G. a - {
3 Z' Z0 _ ~6 l - picture.length = fend;
$ A! o0 ]3 z5 [/ v: [" k- [ - picture.fin = 1;
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% o7 m4 N' g. c6 b0 d$ z - //printf("sendbytes = %d \n",sendbytes);
" }* d9 G. x! W9 E. |0 w; m - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
! `6 b& m0 `: ]0 A8 W - if(sendbytes == -1)& K. J$ `! L% y) a& f+ n
- {
" G& M9 z. K* j, y" D' t$ c - printf("Send Picture Failed!d\n");; c) {) W2 b; r$ n# [* z. ]
- return -1;
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9 G7 w& `5 ], j$ e7 f0 l% w - else: |- D9 ] {' P& q/ `
- {
) N' C: i8 d0 Q# E3 Y. E - fend -= UDP_FRAME_LEN;1 Q" r' n: Z8 M+ I+ }
- }
- `( Y/ w1 _# V8 e- Y - }
复制代码 3 x5 \: L, _% c( K
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iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |