本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑 4 o5 r* k8 K' e/ H, M5 a* q8 P
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0 b: a: ?' J6 t: q8 S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; o d7 Q# s6 B" ]/ v2 P
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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。 " p$ |' p" I3 q' W; W7 q% P3 A
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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。
" ^9 b4 y2 w7 R3 N% | W) B一、HTTP网页服务器
5 h" q$ o' p3 R' c) I7 @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)
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- struct sockaddr_in servaddr;1 @; g) e: k+ i6 \
- socklen_t addrsize = sizeof(struct sockaddr);
2 M( J. p8 D! ^6 F$ R- a - bzero(&servaddr , sizeof(servaddr));
8 m) S D, N3 t6 I+ y& k( d - servaddr.sin_family = AF_INET;/ Q D c7 l; `1 t4 z' g! H7 q
- servaddr.sin_addr.s_addr = inet_addr(ip);7 G/ O, b. }6 r% V' f! ^
- servaddr.sin_port = htons(port); X" D# W' U- @2 t+ C7 O; k) B' B
- int ret; M/ [( v' Z" `9 S; G# b- C
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)4 Z6 a0 J( W4 D9 U/ X: N t9 v4 m
- {
4 g3 d1 j8 Z7 Z8 y4 [3 _2 ]- _ - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
% r. ]+ @: E; U- D* {. P+ o$ ^# i - return -1;) s" u F( L3 h% b" {/ t' H
- }! R& h% ]: F; x
- int on = 1;- z& F, P5 y+ I
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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- printf("setsockopt error\n");
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- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);+ _9 J# p* L0 H$ y1 {
- if(ret == -1)
& S1 N5 s# y3 h9 { - {
4 L: G& F& W# H2 T k! O" g - printf("Tcp bind faiLED!\n");: {& R; D% V' J( D7 G) k
- return -1;8 {/ s. b, }% Q
- }
5 p. L4 S" ]1 ~4 k - if(listen(*socket_found , 5) == -1)
/ }6 k6 l3 @* G; @& [ - {
) n- ?- |! x& b! y - printf("Listen failed!\n");* h2 k. J7 W; W
- return -1;9 @4 m: B8 R# `7 t \1 i( [
- }
( a- x% B1 `( A- q& K2 c. p - return 0;
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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);
! R. e+ R' h8 Q/ X4 n Y - void * Thread_TCP_Web_Recv(void *arg)
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- 。。。7 a* j& f+ F& p3 z3 k& O
- while(1)
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' q# \; b9 N% ^, B$ M8 z - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
+ `; E6 W9 N& w. W$ F: f6 g9 M - printf("fd_socket_conn = accept()\n");! V1 I* f2 J g. H9 ^# W
- 。。。/ s' ]1 s# d$ q9 w* X) F# Y" |& H
- recv(fd_socket_conn , recvbuf , 1000 , 0);! F, ]1 l* y) G$ A/ {
- }
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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);" A5 n$ d: G' T; v' e
- pic_tmpbuffer = pic.tmpbuffer;
( A! @; A5 q9 i( m0 i - pic.tmpbytesused = buff.bytesused;+ m& c& g4 Q+ g; [
- pic_tmpbytesused = pic.tmpbytesused;
9 ?# L3 M$ h$ X. z+ v E - pthread_cond_broadcast(&pct);
" _' k Z! V# c* U0 w. c - 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;" s- t0 o- M9 a1 _( [
- pthread_cond_t pct;! Q6 h- O. f; r" e( \1 y) D
- int main(int argc, char* argv[])7 ?* q: D; k3 K) ]3 T
- {% w1 e+ O7 i4 c1 y0 M! ^" {
- ...# ]! \9 B- u& `7 a1 @" J3 g* ]
- TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
& K. Z' |/ I3 q3 g1 E; v - pthread_mutex_init(&pmt , NULL);7 m; R- ~" |0 ^. k
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);, x; D; d% `% Y% P% H. z
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
2 F& a! R$ n% U! W# B - ...
0 G! S' V v! g - while(1)
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- V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);# [: y" W7 ^, J
- ...
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- ...5 I+ s8 @/ k" ?
- }
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;">
. t2 n9 x$ n' c# ^0 v' Y1 N% I - </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% o Z ?. _ - "Server: MJPG-Streamer/0.2\r\n" \' a/ j3 K; F$ y5 m2 J5 K* u
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
; t# K4 V: V% E/ S7 A. N5 G - "Pragma: no-cache\r\n" \& [+ y! T. e; A' ]8 o3 B
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
3 ], m: a# j' O - #define BOUNDARY "boundarydonotcross"7 v' `! U0 G% J! `' ?; p
- printf("preparing header\n");
% {8 f- l s! K$ o g% V - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
! r& Z( I- ? k - "Access-Control-Allow-Origin: *\r\n" \, j4 {; f" R1 y5 d+ K1 O
- STD_HEADER \
1 ]. t0 d# d; |2 H w - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \" b8 }, B3 Q1 v q
- "\r\n" \
4 N8 R! F2 y$ g5 I/ i; x/ O - "--" BOUNDARY "\r\n");6 d3 q- T1 c4 K0 D6 M7 D7 S* v2 F
- if(write(fd, buffer, strlen(buffer)) < 0), ^& H d5 O. `) J9 x& D+ q) n
- {
; V* N7 @! c" |0 ?0 x - free(frame);
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- }
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" \
1 \: Q" u8 O3 N. y6 E% l. E+ B! t. K - "Content-Length: %d\r\n" \3 j2 m' D$ N- F, w
- "X-Timestamp: %d.%06d\r\n" \
* E; I% C- G/ u+ H" ?, H( ]* G% f - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);/ n4 L) z, h5 a8 v1 L# u, G L8 N' {
- printf("sending intemdiate header\n");
# a) S$ @ G% \# q8 E/ g - if(write(fd, buffer, strlen(buffer)) < 0); U5 g( ? Q, Z2 M$ t( J! k8 G
- break;
" c' f/ x, E0 h% \- Y2 W1 q- F9 { - printf("sending frame\n"); ^, S2 a6 t. L& x( v
- if(write(fd, frame, frame_size) < 0)
" _' R2 E3 N5 c - break;
( @9 Y/ L/ m* g; ` - printf("sending boundary\n");4 d7 v- G3 m+ J% ?( a$ `
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");& L! Q& K$ U z8 A
- if(write(fd, buffer, strlen(buffer)) < 0)
& L5 `' [/ C' E - 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。  9 t+ ]' ^3 Q8 m8 r' U0 V6 T0 j8 m
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二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:6 {: A. X/ j3 H
- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)
+ R1 x0 w0 x) D, O* P) j z - {( g: Q9 | g8 f( G6 e! ], O
- *socket_found = socket(AF_INET, SOCK_DGRAM, 0);
. I7 }8 }# e$ t: N' { - if(*socket_found == (~0))7 T! T9 d0 a8 o4 S$ [
- {( `% r2 i) ]9 F9 f4 O
- printf("Create udp send socket failed!\n");
4 N. n/ @" |* m# X" e - return -1;
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- addr->sin_family = AF_INET;% [7 B! T6 t' f2 G, u
- addr->sin_addr.s_addr = inet_addr(ip);
6 e1 c# i& g0 e# _; i5 F - addr->sin_port = htons(port);
) n" {5 _; a: A9 j& \ ]/ U - memset(addr->sin_zero, 0, 8);. O% l5 V! f. I# G
- return 0;
" S* e) y3 ?& T( v - }
复制代码 5 B; \+ L6 H( A/ L% j+ R
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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:
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- while(fend > 0)
0 V0 f6 c* G" x v' F/ D - {
0 Y3 X6 x, x, t6 { - memset(picture.data , 0 , sizeof(picture.data));
- c ?( R& C8 b- Y5 v! V J; b/ M - fread(picture.data , UDP_FRAME_LEN , 1, fp);% p9 I) Z* o3 q% r4 Y
- if(fend >= UDP_FRAME_LEN)
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- picture.length = UDP_FRAME_LEN;
; t4 G( x+ {# D p$ Q& T9 g - picture.fin = 0;
( A2 u# g) [' s8 U0 y" @0 d) p2 O - }
) ]& ]5 `( V9 W/ L! ?0 z% p- R - else
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- picture.length = fend;, I0 g! q6 d! Z
- picture.fin = 1;+ R! S# W* ?3 b" m# e& u
- }$ _) ^; G0 W7 }+ h
- //printf("sendbytes = %d \n",sendbytes);# t9 U+ j" C2 `$ ?4 v Q) D
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);6 f$ P5 \7 f& n8 H0 [4 j: n, B
- if(sendbytes == -1)
2 |& v) b0 y5 g& } - {
* h+ q, L- n( f: ^ - printf("Send Picture Failed!d\n");, U$ G' S: c+ @, i
- return -1;5 R, L9 y2 E2 w9 G
- }# x( t+ f$ d6 O1 ~/ r
- else& E; R. S- q. V
- {7 Y& S, r: @ B6 n v& i ]5 `
- fend -= UDP_FRAME_LEN;3 a1 U/ C( v; l% [& @: W! Q
- }
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复制代码
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7 ~$ o. R; S4 h* }$ X( H5 W, \/ ?iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |