本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑
+ i: p" L% h7 q. i5 K1 ]# V ^( J2 t5 q' p$ D& m* n R+ m6 @) B

J! Q2 ^0 _, z9 |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# l, C: _9 J3 j% Q7 T6 g* w) Y6 @
1 z6 s, f' L0 w/ I
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。 * z G- C& q6 U4 {! O% U! z
 5 f/ a1 r& G- W' c5 b) G9 _ `! }" ~
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。 7 m7 `4 m6 C$ Z9 R
一、HTTP网页服务器4 J' S) H. v) y& G; 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)4 t/ s r4 @4 T0 _- {* s4 B
- {
5 B% T" s1 {8 @+ Y) B/ V2 T/ m+ } - struct sockaddr_in servaddr;
. S. N& z7 E! t5 D0 ?; ^ - socklen_t addrsize = sizeof(struct sockaddr);) }4 B1 n1 J# D/ K
- bzero(&servaddr , sizeof(servaddr));
6 C: M& Z. R7 I" p. X: ^+ G/ l - servaddr.sin_family = AF_INET;( i2 n5 q6 o( I7 @4 M1 b/ ~
- servaddr.sin_addr.s_addr = inet_addr(ip);
8 @! z& }# M1 B( D" v - servaddr.sin_port = htons(port);
: {$ i7 r* j1 t& o) y# R - int ret;
& C' D! g7 i# R7 ]' [) o. m - IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1); }- r+ g$ [7 x* @& D# R
- {
$ w* a# X5 c' j - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);; B3 e' a* v/ o
- return -1;
~$ Z# Z+ S6 S X - }2 p# |0 q6 H- c) m/ g
- int on = 1;
1 E1 s6 o; B$ I- K6 l5 W! q4 r - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)/ Y! x4 s: i5 |: n" ?, x5 k' ^
- {0 ~& [- W0 \3 g
- printf("setsockopt error\n");0 V; ?4 D- i+ B Y3 D
- }
7 Q# o- c# e7 \ - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
0 z4 D1 D6 b% l - if(ret == -1)8 `, L/ b0 c) ^: t ~ a2 E# \
- {
- ]1 P( I! _) g( k - printf("Tcp bind faiLED!\n");
?" V1 G4 Q0 B* D - return -1;
/ e. a% d. h* ] - }# q, V( ?: \9 L$ Q1 ?
- if(listen(*socket_found , 5) == -1)
4 u2 m5 U/ U/ f& A - {2 I8 I! J% }9 s3 Y1 b/ j! o
- printf("Listen failed!\n");
6 j5 [$ `7 E( M - return -1;( l" F1 [. T6 D( f& ~) H2 r
- }2 W V+ G0 r1 C1 O# {( ^" w( a) I
- return 0;
W4 e# G. b+ [8 Q9 m5 l - }
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);
0 r+ Y: O4 T! U( l- T# L - void * Thread_TCP_Web_Recv(void *arg)
3 |) ~# `" M( B6 T/ L) @ - {
" A5 m6 `# j2 o - 。。。
4 R8 F+ T( T P' {" @ - while(1)- j) z6 p. F- c- F3 O( j
- {: L9 i% A0 _) w
- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);" z5 h A% \' ?/ a# x [
- printf("fd_socket_conn = accept()\n");
2 O c7 ?7 E. h7 G# y, W8 X( R - 。。。3 o8 u5 h" k& j9 a- _
- recv(fd_socket_conn , recvbuf , 1000 , 0);
! U8 Z3 W- L! `1 F* {2 Q8 G - }
2 N1 I/ x, n u, y3 f - 。。。9 u+ J/ r" C% H+ j d& Z& \2 a
- }
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);
* h$ f/ `* {- C; }' p$ [! V, X2 P5 w - pic_tmpbuffer = pic.tmpbuffer;
$ Q& A( f: Z1 U; R4 V% o9 \! M - pic.tmpbytesused = buff.bytesused;) B. C3 D# Z/ S( t: Q1 n
- pic_tmpbytesused = pic.tmpbytesused;
3 j i3 i' P/ B# F+ Q - pthread_cond_broadcast(&pct);
8 v/ y2 o, q: f2 {$ W: 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;( f9 V1 A C o
- pthread_cond_t pct;
o$ o. ?, L3 D, F% U* V - int main(int argc, char* argv[]) {& J2 K) {. O2 r& J+ T
- {
5 @& O% r6 l6 B9 c - ...! e4 u+ Z7 u7 b$ p' U
- TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);% E, z& A) S6 t
- pthread_mutex_init(&pmt , NULL); k/ K4 y/ D3 S& S% B8 A
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);
+ Y; C) o: K# d, j0 ]6 ? - pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);6 ?5 n- h' F. @7 d) ?4 ~% {
- ...1 @( r) W3 U( T+ z6 ?4 p, O! j) B
- while(1)3 t; d' q( z& R# `* y. D
- {) O8 \# E, k! m( }/ y' ~8 ]
- V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME); U! o! s0 j( U) P9 i; B
- ...9 K9 _3 _" \9 _1 E) v6 o
- }, g; v& t: k5 P3 y7 S- `0 }6 i9 K
- ...( J7 R4 Z/ L' b. z8 N7 P
- }
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;">
: `( ^1 f' Y& E- 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 p, G* J$ H8 y+ j0 Q8 b: n
- "Server: MJPG-Streamer/0.2\r\n" \; i! H7 P2 m5 w# Q
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \2 i; _" f8 Z+ X6 H2 q
- "Pragma: no-cache\r\n" \ f$ s5 f- }+ j4 t4 u7 }
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
& O4 f* y2 \* K - #define BOUNDARY "boundarydonotcross"
?% F6 {3 ]. c. X$ \" s - printf("preparing header\n");
7 q# x' v' L1 e5 N x - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \. H L5 `) x: W+ S; y
- "Access-Control-Allow-Origin: *\r\n" \; l: I5 U" J- @( s1 n) F- a
- STD_HEADER \6 p& x: ?% r: t/ s8 @
- "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \# c6 `& z; W. n u/ J9 y
- "\r\n" \
5 `' ]+ D& Q# \# x8 W9 O - "--" BOUNDARY "\r\n");
& X! ]0 I2 y1 I9 T - if(write(fd, buffer, strlen(buffer)) < 0)( i1 M9 d1 N" V% ]* r+ d
- {
" q9 T3 C) L; w4 `' ^- y - free(frame);
# D. \/ @7 D) m - return;+ J0 \1 `4 S- }1 c2 K+ Z2 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" \9 h" m" Z2 M6 i" B% A! y, _
- "Content-Length: %d\r\n" \
" E: Y! o, @9 k Y$ A0 V - "X-Timestamp: %d.%06d\r\n" \
0 }- ~3 r/ m) c, k& K - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);/ r9 d [- M" |" n( t u* r
- printf("sending intemdiate header\n");0 @1 M% Y% a' d
- if(write(fd, buffer, strlen(buffer)) < 0)
3 j; r4 i+ s0 O9 R; m2 [) ] - break;& p# g# Z' f" u6 v( ?2 u+ ]/ o2 d' Z; w
- printf("sending frame\n");9 R% S/ o/ }$ x! e/ h3 m
- if(write(fd, frame, frame_size) < 0)& F' f0 H; ]- m) R) a1 H
- break;
, m4 b% p( \/ a3 R" t: F2 ] - printf("sending boundary\n");. r* n3 p3 T0 v) o' ~
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
5 T3 g- Y- |/ m5 X: ]% ~, o - if(write(fd, buffer, strlen(buffer)) < 0)5 j$ N9 v; ]' x9 H5 [
- 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。  : q! W, ?" [, Y) J1 K# f
 ) @) E& ~5 B3 {: {; S/ H) i
二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:
3 e c( {# S: e# z6 H$ N# y2 J& `- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)
+ C( X! `/ y/ l0 U3 v. v: r - {
# [( Z' o$ q g q8 v - *socket_found = socket(AF_INET, SOCK_DGRAM, 0); W% ~1 @+ O" e7 t# v0 p8 q8 I+ E
- if(*socket_found == (~0))/ {3 [, }% b7 M# @+ ~; r
- { N, d$ P( L, z t1 Y* B4 V
- printf("Create udp send socket failed!\n");
2 b& ?, V6 Y6 z8 v - return -1;/ c( s9 A! N% S# M( H
- }
# } }6 l$ c% }. ? - addr->sin_family = AF_INET;$ X. C! V5 b! R" W) F( I, T: [
- addr->sin_addr.s_addr = inet_addr(ip);
* U$ X3 Z3 m0 S; H7 X0 P - addr->sin_port = htons(port);
2 p" x( ^" R |& z2 H - memset(addr->sin_zero, 0, 8);
/ ?( ?* L) B1 v - return 0;
1 w$ `) `5 d- b8 W1 {8 l! q. q" I - }
复制代码
: A2 L$ `! r, Y+ n
" n2 ] r; R% S ]( g2 F2 i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 {# I# ~8 \& t
9 \0 F8 w b4 i% \1 ^
" \ a* u H" S$ {8 a
- while(fend > 0)
3 Z) g4 M- i" F; I: A6 B# a - {
# N7 d; J6 N, [3 | k( \ - memset(picture.data , 0 , sizeof(picture.data));
: H. F# o( H6 ?6 m6 v - fread(picture.data , UDP_FRAME_LEN , 1, fp);
3 i. U6 w9 s m; }4 A; F1 Z/ d - if(fend >= UDP_FRAME_LEN)1 z0 v7 N* u. k1 w
- {
9 d$ G( S* t- t% h# l2 x - picture.length = UDP_FRAME_LEN;5 W( ~& P$ l1 v! h$ Z2 v( e# c) {6 h* E
- picture.fin = 0;
* H: R; m5 Y7 ]0 r R - }
) r& m6 p. M$ V H* d2 Z - else
0 e. N: q/ i' v" s - {( \. s5 S+ r7 K+ f" T- e
- picture.length = fend;( P2 u2 E- }1 B, p- i/ ~( L$ W; e
- picture.fin = 1;
$ ]* h) l4 b3 q- B - }
# `4 b, p$ ?$ m2 W* F% G - //printf("sendbytes = %d \n",sendbytes);
2 L# `. }1 ^4 X0 x- O5 O - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
* @: y/ H$ y, G9 a5 j+ M+ W3 m - if(sendbytes == -1)' n9 Y" N. _. ?% N
- {
( m2 V$ O( Y; o. F8 a! g3 g! P - printf("Send Picture Failed!d\n");$ M- M6 z2 z/ ]
- return -1;* e% }3 j- a" c$ E3 k' Y- C
- }
& e4 x* A G; q2 N7 d - else2 L& h" D1 b# f! @) Q
- {
# B) Z* R o5 e& q7 v7 o - fend -= UDP_FRAME_LEN;3 ^( n0 a$ ~! E4 O) S
- }- R" g1 h- W# x9 e
- }
复制代码 Y- U8 Y1 ^" K7 n: B [
. X$ I1 F* Y8 \' A" H1 p
 4 \' m' Z: l) D, t. n% r8 h
4 J& W8 U; G1 h$ g! c- s9 a. |
iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |