本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑 . R2 ~9 a! [5 Q3 R, ^
! u$ c# p7 k+ ?

) C1 q1 ?& C; ^/ 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 w6 ?4 V7 H3 ~( g/ S
( B1 u! B% ?' |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。
6 K% W# H Y3 y% n 1 f! `; Y9 q, v7 E" @- H
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。 5 B6 B3 l- f" M6 p
一、HTTP网页服务器
0 X$ n/ \& M2 G( 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)" b* s6 N8 |7 o& V: Y2 R
- {
! p& I+ V0 i3 L. ]- J2 ?' F. X - struct sockaddr_in servaddr;& e8 ^, S+ | X+ z
- socklen_t addrsize = sizeof(struct sockaddr);
7 X( o4 Y6 Z# k2 C! v0 X: s - bzero(&servaddr , sizeof(servaddr));; M$ s6 |; ?$ u- z7 O; g0 z1 A) k
- servaddr.sin_family = AF_INET;2 k( ?0 X0 B/ R1 S1 |' W
- servaddr.sin_addr.s_addr = inet_addr(ip);0 t% A0 O4 {" V. t* c- A9 A
- servaddr.sin_port = htons(port);
* i* Z% |# D- D - int ret;- W1 i9 }& O* l5 @7 z0 s ?
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)
" \6 I8 A/ Q* J3 R - {
" e2 z- ^5 ]! e6 v" f% Y8 j - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno); S' K+ { q& i4 N! R& p$ S
- return -1;
- {& E! q0 h1 u: } t - }
2 `' ~1 A* D( R6 m' m' z5 o - int on = 1;9 c$ h! G$ y [- g
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)" d; Z* l: t9 `+ G- L% h
- {( }5 m& D8 Z0 [! Y& r+ r: `
- printf("setsockopt error\n");
2 o2 H+ ?: _$ T4 m5 V2 V- k* L* w - }6 m$ h/ E# u' t2 L
- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
( X3 }4 W* I: q/ n/ H7 m - if(ret == -1)' P: P2 [% {! n: I# |. @% g1 b' U
- {
! \/ I5 r* L$ I; B - printf("Tcp bind faiLED!\n");5 ^5 q7 I! v6 b7 _. X
- return -1;
; H" f4 k s* P: O - }2 P) B3 n* y6 z7 z% A6 j5 Z
- if(listen(*socket_found , 5) == -1)
8 A6 r4 T/ @7 A) |- P - {9 C* G/ F2 O4 \* N, T7 w. y+ \
- printf("Listen failed!\n");
: l) M9 J+ b7 j. W6 D+ R - return -1;
. b1 C- J: G, n I; g2 f% | - }3 L5 k# O, f/ \! |. |& [; t
- return 0;
5 ]: }4 d! i5 n H+ q, N - }
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);
! L. T: W3 d& e( I/ u, y - void * Thread_TCP_Web_Recv(void *arg)
# w+ ^! ?: \5 M) }; Q - {* y D" e/ _. z
- 。。。
0 p& M5 y6 k8 A+ }/ [ - while(1)
7 W2 h; ~2 q, z! I - {/ ?* s0 s7 ~) C! i8 v9 V
- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);. ]( T6 X- X, \+ b* A
- printf("fd_socket_conn = accept()\n");
% E% A+ p! V) ^0 ~9 T! R - 。。。$ H- ?6 z- x, v3 [/ Y9 [5 R
- recv(fd_socket_conn , recvbuf , 1000 , 0);
; q7 k; [; d! m& Z# ^ - }
6 d1 L& W" J$ q) c( { - 。。。5 D+ n- t3 v0 O5 M }
- }
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);
4 }7 D* ?: x% j - pic_tmpbuffer = pic.tmpbuffer;
$ S2 d* g; y; t - pic.tmpbytesused = buff.bytesused;! \2 q1 `8 T, Y2 I6 w
- pic_tmpbytesused = pic.tmpbytesused;& R+ A" h j* s4 v
- pthread_cond_broadcast(&pct);
. r7 c2 V8 `& w+ c2 P4 K: h w. ^ - 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;0 ]$ J* ~6 i2 h1 S
- pthread_cond_t pct;
4 j2 Z- z, e Z. X - int main(int argc, char* argv[])
0 u) T( [; G8 c( S, A- [- s - {
0 a. v# P. Z: Y - ...
) ^8 y) u. I6 B# }2 H - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);0 e8 ~- Y8 c8 W8 q& p# b
- pthread_mutex_init(&pmt , NULL);) c! j% x0 @6 u* Z9 P
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);
: H' y* w7 V& Y - pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);( |# w4 V% g; @/ O
- .../ Y- h* i7 m/ J( d# ? I6 c7 z
- while(1)# N4 M z' I5 h5 ?3 P: G
- {
' D: r: E- E4 g+ V ?* ~ - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);3 ^7 r9 a" p3 {
- ...
6 A, W+ N ?, J - }+ L `4 |; x& u9 R9 H6 {8 [1 m
- ...
* B' ^! l/ ~' I$ w - }
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;">( `' T4 e( N z2 Z5 w& j
- </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" \
) \+ j2 ^7 \ v3 k/ r% q0 } - "Server: MJPG-Streamer/0.2\r\n" \# E$ a7 A2 c2 q! ?5 w; }
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
9 U7 H' S+ I7 \/ e4 k8 I2 I+ d - "Pragma: no-cache\r\n" \
# f% g# V9 R8 a1 G7 U/ w. e - "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"7 ]0 C# r) D4 S$ h; B% ^# ^5 J# g$ ^
- #define BOUNDARY "boundarydonotcross"$ W# I/ D+ ?2 J8 x. V5 r+ ~( C; _3 ~* v
- printf("preparing header\n");
8 H: S; y: O, K4 P8 H$ @$ q7 y - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
& |8 f) g: Z* z - "Access-Control-Allow-Origin: *\r\n" \. u6 L2 Y. W, g9 q# [) `
- STD_HEADER \8 A& w5 u& ~$ ^7 E2 f
- "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
; |3 X/ @ |6 b' S: H# i: S - "\r\n" \
" N$ {, D0 a* D - "--" BOUNDARY "\r\n");( n& Q( u2 D) ~ x
- if(write(fd, buffer, strlen(buffer)) < 0)1 S8 w% {' P3 ^1 z, {
- {
" O) R% O* v0 k0 q2 T; D9 c: G3 m9 } - free(frame);+ ?- |" L j- H
- return;
% t3 _5 z F; Z% Y. B" @ - }
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" \
- y K8 h9 J7 w8 t1 |+ O, x - "Content-Length: %d\r\n" \! k* T% n2 D# k1 X& Y) S& Z# Y
- "X-Timestamp: %d.%06d\r\n" \$ D; t( C- r' ~5 @: K+ i: j' u
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);: [+ C1 k- Z, K% S3 c0 q" B! y$ `+ A
- printf("sending intemdiate header\n");: |+ I& ?0 ~* H
- if(write(fd, buffer, strlen(buffer)) < 0)9 j% k6 \: {3 }$ I7 z
- break;, b- _/ |, [0 ]" K. @" @3 K
- printf("sending frame\n");
4 Q3 J$ T% p$ B- e b3 O8 b - if(write(fd, frame, frame_size) < 0)
" P1 O1 X5 q, \7 L - break; D) r! l+ o. B
- printf("sending boundary\n");
. q! n$ y* R" z' w$ A/ ?; J - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");9 g& B: |% N2 ]% r
- if(write(fd, buffer, strlen(buffer)) < 0)
, u- `) e% M ` - 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。  - b" V, s& h! s6 g" {8 J
 8 `, B" Z9 @4 M
二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:
3 j: t5 q- m9 L: K7 ~5 M: E- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)! N9 u* E7 e4 F) ^; X( h
- {2 m9 ^) x) a) m/ c
- *socket_found = socket(AF_INET, SOCK_DGRAM, 0);
" ^ A a# ^( ]; h9 j# C - if(*socket_found == (~0))
) ?. M* K& o' N# y - {, R O' K9 _) v* x
- printf("Create udp send socket failed!\n");6 [+ V4 S* s; C7 F/ ?
- return -1;
# W! G3 Z9 a6 N, _- Z8 Z; a - }9 S/ [/ Y& t( @# z3 h# f& ?
- addr->sin_family = AF_INET;; c6 }& ]' |! P
- addr->sin_addr.s_addr = inet_addr(ip);/ y# ?, P% I* n' j
- addr->sin_port = htons(port);
+ _5 a) _0 K: g' k* Y - memset(addr->sin_zero, 0, 8);' B: X: U- i# S3 h. r
- return 0;
" E7 Y J: U* ^. T6 X6 @) I - }
复制代码 " o+ ~1 A" `7 ^4 u/ I {
$ _* ~* D- U9 J. E' {3 \7 B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:3 R9 ]8 T" z2 `# x4 V- R
4 m# \$ g: _: {) U* Z
; P) {0 {( w2 T1 w- while(fend > 0)- g( q i$ V2 |8 U0 G9 {
- {! [9 W r. o! u; |: \
- memset(picture.data , 0 , sizeof(picture.data));4 k0 F# U$ _; K; w) u
- fread(picture.data , UDP_FRAME_LEN , 1, fp);
! q7 O1 a* t1 B3 Z4 ~( c( b2 f+ ? - if(fend >= UDP_FRAME_LEN)
9 ?% c/ ^9 q5 p1 g3 W/ B! l - {
* x! {! J) q; G$ \ - picture.length = UDP_FRAME_LEN;7 k) F* C8 y$ d' }5 C
- picture.fin = 0;" I' _+ P f9 E
- }
3 L" o* l+ @: O0 ]* v* ] - else6 {" ?+ O8 ]8 f, d& t. |) G3 h
- {
3 J6 y5 \2 m$ b% ] - picture.length = fend; q: v# C* G o; J. |& w% g3 h
- picture.fin = 1;) }- K: w1 N4 N z
- }
0 s" `/ _+ t4 P6 [. w! S - //printf("sendbytes = %d \n",sendbytes);: Z5 L. j$ [& M+ {( u$ q9 A" r
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
5 w& m. p1 k0 F/ S$ a, s. O - if(sendbytes == -1)
* l/ e# N4 [* a& ]9 F* b - {+ y/ ^& f$ |+ U) x6 G0 [
- printf("Send Picture Failed!d\n");, n: [) P$ I5 ~( Z4 ~
- return -1;
$ u, ^5 j+ S5 M- K) z" j% s8 l! f9 O# R - }: q/ b6 | ^* ~ V, K
- else# w: r" f$ h2 c/ [% A8 G, O
- {8 D8 X/ Z$ T5 ?% E0 [$ ^2 C) U
- fend -= UDP_FRAME_LEN;
0 D0 k$ u r; w1 z' t) \ - }
! @" f4 s7 x/ _+ t6 w b8 j* p+ t8 } - }
复制代码
8 P; p0 A2 \: q" { E
% d9 v, _4 B# N. d1 \* v 7 f3 E* P8 t2 Y' n! Z, R
' _; Y3 }3 B2 X, G% ZiMX8MPlus 核心板: https://www.forlinx.com/product/136.html |