本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑
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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' L1 ]5 ~% j0 L$ O( C8 ~
; C4 r' n; J& B. t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。 ' a8 y/ g2 _1 e. Q

; e$ M: a9 e9 G' J# 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 m' p& f7 K0 o" `" T, e, t# c
一、HTTP网页服务器% n0 W3 z4 f" u: s/ R' p3 R
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;
2 ~0 E% i7 x8 g* Q+ S - socklen_t addrsize = sizeof(struct sockaddr);0 [ O' }% P; j2 @) M
- bzero(&servaddr , sizeof(servaddr)); F' }" F ^& f) h9 u! B; V' e
- servaddr.sin_family = AF_INET;# {# b- h) ?; H9 f3 d7 h9 l
- servaddr.sin_addr.s_addr = inet_addr(ip);
/ ?/ S* S) N) V* Y; f1 c1 Z" F4 F - servaddr.sin_port = htons(port);
8 [" i5 F" Z0 q; _2 z6 v - int ret;
. ?0 l% F/ O; P - IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)7 m. k$ q9 \8 `; b
- {
7 A+ Y& l( U0 b9 R' D/ w/ ? - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);* d! Y2 N G+ F c+ N- n! H
- return -1;
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E$ t2 s+ Y4 q. y0 _/ i - int on = 1;/ e0 |# t3 {5 O! A* d9 K
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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, R! G! H& X9 L8 l* N6 ^ - printf("setsockopt error\n");# G8 b4 n) I# J
- } Q: ]8 b% [6 C" T
- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
4 U' Y& e' g8 `, h - if(ret == -1)
+ F" `, N* o' l& e3 ? - {
: B# t. w& b5 J6 J - printf("Tcp bind faiLED!\n");* L5 B- S6 U @( {8 t. ?
- return -1;
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- if(listen(*socket_found , 5) == -1)
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! \! h# v( T- Z" S3 [# l - printf("Listen failed!\n");
( t; W# b3 U6 _# c# O0 q& s - return -1;. Q' I4 Q9 ^- J3 c* q' t/ }7 `
- }+ M0 @: l8 b5 G# l
- 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);+ T6 ]9 ]7 V! x) i3 O# X
- void * Thread_TCP_Web_Recv(void *arg)
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- 。。。
$ H- \0 p- v) \/ g( m) u - while(1)
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- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);% l6 W2 P$ U* K
- printf("fd_socket_conn = accept()\n");
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- recv(fd_socket_conn , recvbuf , 1000 , 0);
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- 。。。+ X. I/ S" `- c) g: y- f
- }
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);
" s% i9 x0 S) L* \; a5 `' S6 M - pic_tmpbuffer = pic.tmpbuffer;
+ H- q, Z0 s% k4 }+ x) d- X - pic.tmpbytesused = buff.bytesused;
- J9 u0 `5 N7 ?# }' G# ] - pic_tmpbytesused = pic.tmpbytesused;
& \. ^7 z7 i8 u ?! B - pthread_cond_broadcast(&pct);
3 v r P* {8 E" I' m( Q. g# e - 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;
6 \( Y U$ f% x a - pthread_cond_t pct;
( Z7 C2 |5 O% ~- w/ M- z. h$ i - int main(int argc, char* argv[])' }. o$ T1 e" G+ ]* j1 m' m
- {
& d I0 p" r. X. H U2 G. h - ...
- Q( P& F5 X. v( H: F2 v - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
; F! g: F! G8 |' x; o( G - pthread_mutex_init(&pmt , NULL);1 _- E# \4 e% q7 S [
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);, m7 y+ K7 @ G5 R
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);% z1 l0 @/ \% Y I
- ...
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- {* s6 m& Q5 G& g! o
- V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);
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- }
复制代码然后是发送的细节,发送图片文件之前,需要先发送HTTP标准头,这个相当于给发送图片或者其它类型的流数据铺路: - <p style="box-sizing: border-box; border: 0px; vertical-align: baseline; line-height: 26px;"><span style="text-indent: 32px;">- I+ A5 B" r1 w
- </span></p><p style="box-sizing: border-box; border: 0px; vertical-align: baseline; line-height: 26px;"></p>
复制代码- #define STD_HEADER "Connection: close\r\n" \
8 R% `9 R2 `* U+ L7 z0 l/ C - "Server: MJPG-Streamer/0.2\r\n" \/ `; p) z7 |$ f3 R
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
8 C; T5 h% Q( [ J - "Pragma: no-cache\r\n" \9 E) b# u7 y% F8 ~$ ], X5 B! I
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
6 T2 O6 ^# w. v- | - #define BOUNDARY "boundarydonotcross"2 c' Y+ j2 ?' f
- printf("preparing header\n");0 a9 t% v% C6 ]; W
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
' D: L5 P% e9 y" @) N - "Access-Control-Allow-Origin: *\r\n" \
7 W" G! U' R: W - STD_HEADER \) G) c, f6 j! |* y: w; [- U# j
- "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
8 }7 R0 X7 B7 ^ - "\r\n" \
% C. U1 X! S6 o) z3 i - "--" BOUNDARY "\r\n");
# x! v4 n" s0 U - if(write(fd, buffer, strlen(buffer)) < 0)
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- free(frame);
. @- M& b% F4 k* { - return;+ }0 ]. e7 R) Y4 ]5 A$ V2 D
- }
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" \ o7 w+ R' c# K( q$ f4 K+ m
- "Content-Length: %d\r\n" \8 g, y" z" H" ]. B
- "X-Timestamp: %d.%06d\r\n" \7 ]0 W& C6 r0 b% f( e+ X
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);& U. k* y! k, B" P6 s" `8 d. [5 \
- printf("sending intemdiate header\n");, a. w; g- A4 T$ P9 `; W
- if(write(fd, buffer, strlen(buffer)) < 0)
9 p. T' v" h+ p - break;
5 h" t- M2 o0 B4 E9 M O - printf("sending frame\n");* j0 M5 D, H2 P: d) u. g. }
- if(write(fd, frame, frame_size) < 0)
- L( k9 K( F: I h4 B- X/ d) e - break;8 {' _: T/ W* I2 } X+ u. n5 ]
- printf("sending boundary\n");! Z/ y: t$ p5 V1 Z
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");/ ]3 a' I `- }1 Q" q- {, Y
- if(write(fd, buffer, strlen(buffer)) < 0)4 J) G5 Q! q3 s' F0 `! l o6 L
- 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。  & O5 z3 b8 P0 c) q

8 g8 U# u% w& j二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:4 r u5 M, a4 B$ ]
- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)
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* r! ?8 n6 v8 f. i - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);; T( M6 Q( m+ o f9 S0 d) [) a6 w8 s
- if(*socket_found == (~0)). t: e5 o4 v5 C" ^
- {
! E( [( v) s) A& Z9 f; a - printf("Create udp send socket failed!\n");
" C g! Q( s" F, b3 |, W: x4 } - return -1;! c- w/ K0 W- X) A, O4 l+ d( M
- }5 P. m0 D( V; _& X& [
- addr->sin_family = AF_INET;, w. ]: ?2 }1 n: w; _. |1 O6 U K
- addr->sin_addr.s_addr = inet_addr(ip);
, J5 z' N0 q$ t# j, r - addr->sin_port = htons(port);
& K: z; w: s. _5 j - memset(addr->sin_zero, 0, 8);
# d% D! R5 ]2 r; O& F) C7 g C - return 0;, h w6 r$ m* P' X8 Z4 E
- }
复制代码
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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)
" Y0 z0 ~. {- r2 r4 K - {
" U5 A/ r5 P6 a+ A7 V! l - memset(picture.data , 0 , sizeof(picture.data));
- v0 ^4 h; q- z# s! V! s1 `; A - fread(picture.data , UDP_FRAME_LEN , 1, fp);
1 P9 C2 L0 D- O k - if(fend >= UDP_FRAME_LEN)& J' ^9 Y/ s# v* B% R4 t8 z- b
- {; [4 g" p" H" d
- picture.length = UDP_FRAME_LEN;
; e. C/ h" ]6 v+ D3 W. f& \% C - picture.fin = 0;/ }/ \; M; V# e" M, v% A; ^+ Q
- }
x) J3 v+ n2 c; ]( d9 y6 ]$ {% A - else
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- picture.length = fend;$ P0 Z: Z$ s. o7 c' h1 G* Z
- picture.fin = 1;
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- //printf("sendbytes = %d \n",sendbytes); K: R1 U/ `4 s; ~: Y( _
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
. B8 }5 H" T* e/ K+ J - if(sendbytes == -1), j5 Y$ B) W9 w( s! \
- {
" ]" j3 Q/ z# U* I - printf("Send Picture Failed!d\n");; K1 H. N# L& [5 d/ }# g# ~
- return -1;7 l; K7 O8 [5 V% W
- }
# A+ [0 ]* J& ~* O' ]+ m - else
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- l4 Z7 c1 Y* v( q: ?) {; H- \3 N; j - fend -= UDP_FRAME_LEN;' w2 E* ^& _5 ?
- }
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复制代码 ! a& z, c1 n. Y/ p* n, |
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. m- ^' K! E' c0 _/ f- RiMX8MPlus 核心板: https://www.forlinx.com/product/136.html |