本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑 ' m0 J+ }% V! u! p2 S( ^) M9 Z+ g% i
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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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' Y% H2 V& o0 W9 l7 n, N1 r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。 ^; w. C6 e* U

+ y5 Z% M0 V% Q# \2 f9 b* ^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。
% n! k" {1 c' d S一、HTTP网页服务器3 i8 |" M& C: Q( \; T
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;$ o' L8 y5 X* E6 ~- E* l/ g% \8 e
- socklen_t addrsize = sizeof(struct sockaddr);* S/ O, Z+ ^; y* k/ }/ N
- bzero(&servaddr , sizeof(servaddr));
: p0 o1 v1 x2 |) w; {7 f: j - servaddr.sin_family = AF_INET;
* {) H% s+ l/ l1 P! T# F5 p5 d - servaddr.sin_addr.s_addr = inet_addr(ip);
8 J; A' {7 b6 {% x5 \ V - servaddr.sin_port = htons(port);
% A3 K6 {. g2 @/ ]9 c, e - int ret;: H/ ^: ^+ I( m) y$ p9 b7 M9 Q
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)! `, e3 g+ F% p2 I2 D
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- printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
" q( I& S+ y* K" z7 ` - return -1;
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- int on = 1;8 O1 F9 i8 x) Q& ?! J
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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- printf("setsockopt error\n");7 P$ ], m, }; y9 H; ]9 F
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- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
' `, G1 z- P2 \5 c% r - if(ret == -1)
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4 C. I0 r6 q7 P0 u - printf("Tcp bind faiLED!\n");5 R5 e6 V9 }3 |( V
- return -1;
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6 U' W3 b; ]% ]3 t2 s0 t0 @ - if(listen(*socket_found , 5) == -1). X s& g$ _5 ?! q
- {
% j6 F \2 Y% t% b4 i7 M - printf("Listen failed!\n");- W- m! O2 ~$ f0 v2 X
- return -1; F; V8 z) v- f# M, H/ \: `
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- 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);
2 u8 `4 A$ d0 ? r - void * Thread_TCP_Web_Recv(void *arg); F. g' D- K ]0 q
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- while(1) T! }- L% Y: c! {% k# q, t
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- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);! y( @# Y$ a2 n8 G! N& g
- printf("fd_socket_conn = accept()\n");: v4 k- S' V6 F% |
- 。。。
) M/ S: ?1 w: l. ]0 I2 |6 | - recv(fd_socket_conn , recvbuf , 1000 , 0);
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- 。。。
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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);
/ z2 ^1 c% Z h a) `2 f4 F. \4 X - pic_tmpbuffer = pic.tmpbuffer;
& [/ Q [" M2 V+ P' Z f9 Z - pic.tmpbytesused = buff.bytesused;
: M, o* [# Y( `! e. Z& g' C R - pic_tmpbytesused = pic.tmpbytesused;
& b! o& i1 u/ C7 q - pthread_cond_broadcast(&pct);
1 R7 g w+ U8 Z9 l5 q: } - 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;2 w% [4 e8 m+ O8 N6 A4 `0 n/ o
- pthread_cond_t pct;( P% m3 T- N" K i
- int main(int argc, char* argv[]); F: P! I0 n7 p3 V
- {
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d" b: e6 Z7 V) S - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);4 ?! I9 k' j+ [# x/ @0 G% B
- pthread_mutex_init(&pmt , NULL);
' u' t# Y# z/ H' M - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);' @9 R. s) K( ]- U' W7 B. m
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);# ]1 V6 T3 w7 H T
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- while(1)9 Q3 M& t( e, _" g8 E
- {
2 Q$ w0 F! b) L0 ? - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);
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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;">
" q/ K3 e! A6 p$ P0 O3 ? - </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" \" r) t6 c. n* @6 l! T
- "Server: MJPG-Streamer/0.2\r\n" \
# Y9 g, X: V8 t& i5 e - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
6 ]( T7 M6 @& F3 Q - "Pragma: no-cache\r\n" \
# i7 G% g5 ^2 S3 J! ? - "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"6 x( M1 q# @- n5 O+ M/ ^7 `
- #define BOUNDARY "boundarydonotcross"
, B8 ~- K: [3 V- ?5 ^ - printf("preparing header\n");6 }9 Q# l9 {. k- d9 c8 {
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \" Y0 i5 }/ o, b0 j4 F
- "Access-Control-Allow-Origin: *\r\n" \
( L/ A2 D2 d( Q. A9 W4 C - STD_HEADER \& A# }5 S: x6 B0 e8 A \
- "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
* s4 ~+ U8 j! k - "\r\n" \7 Y, \& [1 U6 ~9 m+ f ^
- "--" BOUNDARY "\r\n");( x9 P3 j9 ~2 Z- k6 c
- if(write(fd, buffer, strlen(buffer)) < 0)
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& I9 f1 E8 s" o+ R9 f - free(frame);5 ^$ a, b) q1 N+ }' p2 i
- return;& S) x' |4 R& 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" \; Y+ |; u* g3 S! t
- "Content-Length: %d\r\n" \% Q& v8 ?2 C v3 _( m5 G7 L
- "X-Timestamp: %d.%06d\r\n" \% g3 Y Y# f& A) c5 S/ a
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);/ X# t) T' |2 j
- printf("sending intemdiate header\n");
8 w0 T! ]. R5 Q& H; ~# G) u - if(write(fd, buffer, strlen(buffer)) < 0)
- I8 B/ C: L+ M/ h4 `2 c - break;
) K, h8 }$ F: Q - printf("sending frame\n");9 H1 _7 G% e- C/ W% C4 Q, ~
- if(write(fd, frame, frame_size) < 0)
) [+ A2 _& |4 }) Z* K - break;) f. t3 O4 [- e
- printf("sending boundary\n");' `+ J9 G, F7 ?. n
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
6 U2 z/ X% z4 g8 P, n6 V - if(write(fd, buffer, strlen(buffer)) < 0)
) O; ~0 n9 x% C4 _ - 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:
( Y, Y+ F- |$ g- 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);+ a9 a- e8 L$ _3 A/ N* X
- if(*socket_found == (~0))
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4 f+ l' X: o' `+ Z3 W% m& x( p - printf("Create udp send socket failed!\n");& T* J; T2 [! e2 \" d* [
- return -1;
- C7 w' w3 \- d; y' ]* z7 z - }
( j4 M" {9 }5 l* c8 ]* y - addr->sin_family = AF_INET;% h. a. n# ?4 o) c; c( ?
- addr->sin_addr.s_addr = inet_addr(ip);* Y! M2 C( X, d. S6 l/ u" D+ F
- addr->sin_port = htons(port);/ j0 @8 B% ~2 | C5 |1 f, f
- memset(addr->sin_zero, 0, 8);0 P' A. P7 D5 U; G
- return 0;; p! H3 B* P# s8 x5 g
- }
复制代码 : w4 g" H) g8 z. c( g
8 c7 L7 X7 n2 v7 y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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0 s/ ]7 ~. Q/ k" p" K- while(fend > 0): n, ~6 v) |: s+ e4 T
- {% S; y! |* C& |& x4 z7 g
- memset(picture.data , 0 , sizeof(picture.data));" x) e* V* u; r
- fread(picture.data , UDP_FRAME_LEN , 1, fp);
2 j9 c) k( _/ U - if(fend >= UDP_FRAME_LEN)9 |" J7 Q) _' m8 Z: g- E
- {$ T6 h. c% O; A: E1 P
- picture.length = UDP_FRAME_LEN;
( j, i1 I1 V q - picture.fin = 0;
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- else+ m: {3 S# @" X) T% G
- {
( t% ^) ~! w2 K1 r6 \# P3 E - picture.length = fend;
: A2 k: e1 f) x! V' A% ^ - picture.fin = 1;6 E0 T5 S. w L) F
- }
, ?7 v2 W, ~& P3 [, {3 s - //printf("sendbytes = %d \n",sendbytes);
/ f: n+ H6 k% Q: P) W - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
( p5 X7 G- {! e2 n8 z3 Y - if(sendbytes == -1)
* T/ E! w4 X& Y! E3 ] - {
" C5 c6 ^# }* {' K# v/ r - printf("Send Picture Failed!d\n");
. f: ^3 ^1 c' R6 C p/ q - return -1; ^' A( v) i* F) U! z# |: `
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- else f9 t* @/ O, ] R( Z9 [- y$ P! O7 Q: ?
- {# a9 }, H/ }, e3 A
- fend -= UDP_FRAME_LEN;
* j+ j7 p, E2 M- i% f z - }
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复制代码
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iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |