本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑 U6 W# U, ^4 {
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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" z9 O- i$ p( B7 l
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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。
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6 V/ Z \0 |) R" F2 z1 G; H/ b( w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。 0 A* ?' y. [3 j1 r F M
一、HTTP网页服务器
( Q2 J, i! s+ x' O/ v5 K( w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): A7 o0 X& g5 s% \2 j
- {$ n( `( H# T$ u" Q# e$ }$ C
- struct sockaddr_in servaddr;
; Z. t# x; J$ \ h& O8 {+ g% `4 t. x - socklen_t addrsize = sizeof(struct sockaddr);
( R7 X0 f; u4 \, ~9 A' k - bzero(&servaddr , sizeof(servaddr));
% X) a5 w3 B5 y. U5 b H' S4 T - servaddr.sin_family = AF_INET;
/ w O+ ]3 I- J0 S8 q - servaddr.sin_addr.s_addr = inet_addr(ip);+ \4 {# B5 u. q' W
- servaddr.sin_port = htons(port);1 T7 i7 C) ?, A& y8 V. W
- int ret;# {9 V3 A& M1 c
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1). ?3 r0 Y9 ^" b( y$ S. d. a
- {5 K( R% w+ W! }7 T" D9 z$ [
- printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);+ f! k$ P0 E5 v8 \! H
- return -1;
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8 g: l, y" N* o) v& t - int on = 1;) ]6 w. f( H, d" F0 b' ~
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)% ^) m0 y9 F% q3 g/ i
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- printf("setsockopt error\n");4 X2 I3 }* r! y7 \* d! A; c
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- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
; @. j; h$ ?- H - if(ret == -1)% U( x# Y+ p; p5 i
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- printf("Tcp bind faiLED!\n");) s \0 F* y3 G- u0 X% b
- return -1;
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- if(listen(*socket_found , 5) == -1)
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0 M' ~. _, h- o* N, v# b! w - printf("Listen failed!\n");6 q x) }- f3 O6 g
- return -1;0 m0 C& T9 c' K: u' @
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- return 0;7 o, Z8 U. o5 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);, G+ @4 D2 o" m+ Z: ?: p
- void * Thread_TCP_Web_Recv(void *arg)/ o0 z) K u6 r8 ]; F
- {
+ a! j9 Q$ ]5 ?& F) [ ^ - 。。。
! M1 ?" G$ b; W3 ]2 A$ l o7 F' ~ - while(1)
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- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
2 x9 g$ @# t7 i, A+ i: g! F4 W - printf("fd_socket_conn = accept()\n");% A) A6 p8 C6 v: ~6 X4 P
- 。。。. [9 a; E' |4 V: [5 x4 N
- recv(fd_socket_conn , recvbuf , 1000 , 0);% U4 w3 U" j w' l+ A# `$ z
- }( Y# A! z7 a5 {; E- ?
- 。。。
% |6 K- E8 W( B - }
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);: T# R1 d+ K3 ?5 L9 N& x+ H3 s
- pic_tmpbuffer = pic.tmpbuffer;7 W1 U; Z0 B& Z- t
- pic.tmpbytesused = buff.bytesused;
I! T: ]0 M9 b3 @! [( C, n - pic_tmpbytesused = pic.tmpbytesused;, h9 o: w4 p$ D' Y+ W! u% L
- pthread_cond_broadcast(&pct);
$ O* C; H: [3 W5 u - 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;7 V8 _# F2 s+ U+ ~0 {2 o
- pthread_cond_t pct;
2 l* K7 p; [; W: p6 B9 O4 T - int main(int argc, char* argv[])1 }- M7 ~- y* u& H% X
- {/ f8 G2 r. N( N% u
- ...
8 W" y. j7 f% a; M# l- u [7 m - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);( }, _8 F. F! X7 F, C; G
- pthread_mutex_init(&pmt , NULL);
: z( k0 \* H c& G - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);& K2 R* h3 K" [ E. |
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
2 z q9 \3 u% n% e. G, l - ...
+ J$ W& y4 f% ~8 i - while(1) y) F* C4 f( }1 W& i1 h
- {
1 w* w1 y5 }( f) U - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);5 \6 d+ {/ e( u0 K, E: q
- ...0 p0 K5 q" q, Y+ [7 Z
- }) D! n7 Z' f" O+ j0 i2 r$ M* j
- ...
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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;">8 I i: P* {- o9 z
- </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" \4 L: h; c1 `& U. R
- "Server: MJPG-Streamer/0.2\r\n" \) E& J5 m5 E4 O* h
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \* @: X4 T, W8 g7 |- ^9 n
- "Pragma: no-cache\r\n" \, e" {& C( E" p0 k7 d* k
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
4 O- F5 n" E# l2 H4 C+ u - #define BOUNDARY "boundarydonotcross"
' F' B7 G4 l$ E5 w4 S; ?/ t' S - printf("preparing header\n");2 X3 A3 M9 P& T/ e' R6 V
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \* P, O+ F( T" L% H
- "Access-Control-Allow-Origin: *\r\n" \
* W" Q7 r% f9 s N% G8 a: [ - STD_HEADER \ m% s# b4 i' b9 f
- "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \9 {' |3 K) ?7 p9 }9 g/ b# R
- "\r\n" \8 X6 `# e' u4 C% F8 X6 @' e5 O
- "--" BOUNDARY "\r\n");- w+ A5 C0 w2 p/ X
- if(write(fd, buffer, strlen(buffer)) < 0)
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- free(frame);
/ H5 m, M3 P% j% l! y; _ - return;' R9 R0 z$ C3 o6 t2 U1 K
- }
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" \
7 S* S a5 }, D+ |- \2 {3 X. Z - "Content-Length: %d\r\n" \
& E4 a' q: m b) P2 K9 t8 ~/ s - "X-Timestamp: %d.%06d\r\n" \8 v/ y" k* b( O
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);* v0 t; y. [' B6 f5 b
- printf("sending intemdiate header\n");
- g* ~5 ]/ w. g A# v - if(write(fd, buffer, strlen(buffer)) < 0)
# l) R, H% G8 k% Q$ h4 Q - break;
, W) r! ]3 _' j2 y5 }7 N$ Y$ Q - printf("sending frame\n");
6 T- {4 V' y ^3 q$ M, U6 C - if(write(fd, frame, frame_size) < 0)3 E$ {7 h! @/ x# z& f u
- break;" Q0 O h) W* O i
- printf("sending boundary\n");
7 | f9 u0 y, Z) i- @0 o2 v - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");, H3 c* e" |( N. @
- if(write(fd, buffer, strlen(buffer)) < 0)
' D1 S& \: p# ~# U8 P7 V4 T# G" e6 v - 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。 
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二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:
1 c0 D( U8 c: v9 ?) b% l$ \ d- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)
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- *socket_found = socket(AF_INET, SOCK_DGRAM, 0);4 A8 l# Y! Z4 N: J% x- n* _" t
- if(*socket_found == (~0))
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- printf("Create udp send socket failed!\n");6 P; z1 x+ D( c- C; w: [, i
- return -1;
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- addr->sin_family = AF_INET;
/ L9 L+ O$ W: S( B - addr->sin_addr.s_addr = inet_addr(ip);, _, D, R$ R+ s4 M9 p6 W; I; R! l2 f7 G
- addr->sin_port = htons(port);
; X) W I7 k H; f4 S# {7 ^ - memset(addr->sin_zero, 0, 8);
3 {' r, k/ L9 a - return 0;1 j) `6 F" [+ v8 b8 W/ a2 o, U5 L
- }
复制代码
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! r2 u& C9 r+ l! X- `# T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:) T/ A/ F2 g% B/ `
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, v* V" W7 d, S/ K- H9 a- }- while(fend > 0)
7 _* [' x$ y; M% q k# p - {
! U8 V; u7 _4 f5 p @' `1 D - memset(picture.data , 0 , sizeof(picture.data));
. ^2 ^! L1 J/ V# C5 e6 J - fread(picture.data , UDP_FRAME_LEN , 1, fp);- j6 X; z2 }8 Y4 R, A
- if(fend >= UDP_FRAME_LEN)% u) y/ W" P7 H0 ~9 \% S; b% a' _! Z
- {1 X2 Y' Y% N4 X+ p
- picture.length = UDP_FRAME_LEN;
' `7 b% o) X7 k! c! o+ y - picture.fin = 0;
" \- a1 j$ E9 y4 d - }
0 {% u/ c- w7 k8 J" ?8 y- X - else2 f" w" m, x' ?. n* ~
- {
: ?$ T3 Y. j: k4 }, ^- g - picture.length = fend;
5 L9 f, p3 f6 ~- b+ _+ v - picture.fin = 1;5 c: t( c) m- |) z$ _
- }; R6 _& X+ A# C* e4 a8 B- f U
- //printf("sendbytes = %d \n",sendbytes);
0 Z2 n* j8 H0 J - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);0 F9 o: W7 W) u @/ F; r; C( X
- if(sendbytes == -1)
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% _: ?) @; H4 O& v6 o4 S& z+ D: g" G1 \ - printf("Send Picture Failed!d\n");0 {+ g6 y, x9 k% m* m7 l
- return -1;8 A; x, |* A# O. X
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- else3 O: Q4 B- \7 G; [6 K) d0 ~& A; q/ ~6 s2 |
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- fend -= UDP_FRAME_LEN;) O* z& k7 K% E6 O9 x! L
- }
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复制代码 ) X% k5 X S* t5 N; K
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# \/ u8 t; m7 I7 `iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |