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 @ }6 p: `4 G7 Y
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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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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。 6 A8 h- }9 O4 I, R4 w
一、HTTP网页服务器/ I( k" f4 @: R8 D9 d
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;
8 c; o2 R/ R, o# \6 u0 B9 n8 { - socklen_t addrsize = sizeof(struct sockaddr);
5 n5 H3 z. U8 T1 `! h, x7 S - bzero(&servaddr , sizeof(servaddr));2 b( Z5 \6 w* g0 ~# z! n" r( h
- servaddr.sin_family = AF_INET;
: t9 y! G# q' m4 h5 \1 T - servaddr.sin_addr.s_addr = inet_addr(ip);
I3 i' O) e' `. {! N! J" I. [ - servaddr.sin_port = htons(port);1 R3 H9 _# K: |
- int ret;
8 o! ~5 o$ @8 M3 ?( {+ j - IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)- G% L t9 k7 q- H+ G" K& w
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- printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
/ {1 O: ~6 G% ^6 u8 x [/ O - return -1;
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- int on = 1;# m; W# V" t; r- N3 t N" p% K( J0 q
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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- printf("setsockopt error\n");. V6 u6 k K+ @: R! `$ x, x
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- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);4 O* x6 T5 ~: z+ A
- if(ret == -1)
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/ |9 m% b1 q% w - printf("Tcp bind faiLED!\n");. G7 l$ \) r2 d* b- x1 r
- return -1;# P3 i# {8 \1 `8 \
- }
" ]" D1 v4 Y- k+ _9 z: U1 N - if(listen(*socket_found , 5) == -1)$ V( | c6 i5 @% a0 U! I( Q0 w$ ?
- {
, \8 c8 j7 b7 @, G f/ O3 K1 s - printf("Listen failed!\n");4 i; H: Q E; F- P+ T! |0 c0 [( Y3 x
- return -1;0 |5 j" ` c3 b3 w
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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);5 f0 i' M* ~$ t; K) ^. b0 v( z7 T- s
- void * Thread_TCP_Web_Recv(void *arg)* F; @! `4 S J% ?/ N( }! l
- {
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- while(1)' ?1 A$ w6 ~( [8 H+ R H9 Z5 @
- {
; g3 [& L* X) a" v- F" a8 a - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
1 p0 F9 }! `8 X- R+ ? - printf("fd_socket_conn = accept()\n");; S' I) R5 `5 c
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- recv(fd_socket_conn , recvbuf , 1000 , 0);
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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);
& |* p' t) b9 H8 l! c - pic_tmpbuffer = pic.tmpbuffer;
1 e- G: h& d" Z4 }. r7 l2 M - pic.tmpbytesused = buff.bytesused;
& i% H6 H) @' m" o% z - pic_tmpbytesused = pic.tmpbytesused;& `) ]! Z4 b/ W2 B" {9 Z
- pthread_cond_broadcast(&pct);* f' d q, | b, E( s
- 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;" X3 A. Z6 g( H7 u; c/ s7 R
- pthread_cond_t pct;
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- TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
3 r# q% R! J9 e$ h0 g - pthread_mutex_init(&pmt , NULL);
8 R8 g/ S) k5 V) c5 y - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL); p3 c8 F) R$ n" K) V
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);# s& ~/ l& M# K9 f2 ?0 r- O) r' _
- ...
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- V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);/ Y6 X2 {1 m7 G# l
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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;">
$ [; ?6 U) C- y' f2 B" l4 V - </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" \
) J0 D. q5 ?# @5 A/ S" N9 G7 } - "Server: MJPG-Streamer/0.2\r\n" \
! q& s- A% v1 b6 X/ o - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \" W3 l2 d3 ?# _4 q' P
- "Pragma: no-cache\r\n" \3 O' s! I$ B( P+ i
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
$ J2 ]( n' h+ |. R" C; i; f - #define BOUNDARY "boundarydonotcross"7 V+ N2 i7 d6 z- O1 ^
- printf("preparing header\n");
7 v- m+ s& V0 E7 `) ?: @ - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
# K4 c7 f0 G7 c5 v# g l9 u - "Access-Control-Allow-Origin: *\r\n" \
1 o4 S# t; d( J. W2 F! f0 v - STD_HEADER \2 \1 T( D0 S" ?- U
- "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
- u& L* C5 Z0 w/ {. }9 P2 Y1 O; ]1 E' U2 e - "\r\n" \6 f( l. a# [! o" p1 z/ A& M
- "--" BOUNDARY "\r\n");4 _3 l/ T: [5 h6 j' L
- if(write(fd, buffer, strlen(buffer)) < 0)
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- free(frame);5 Q0 M, |8 r/ }5 P8 N/ w
- return;
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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" \; y9 r+ ^! n& \) H! F
- "Content-Length: %d\r\n" \; q3 k7 |. D. Y: U, f3 M; x7 p0 o
- "X-Timestamp: %d.%06d\r\n" \
. D' O6 U! G8 |; [. } - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);# B( F/ R4 d8 k2 R7 i( m6 @
- printf("sending intemdiate header\n");& `& |; ]; d, [- e1 S
- if(write(fd, buffer, strlen(buffer)) < 0)
# p `" ^0 ~; m% O7 ^ - break;
9 W/ [" O. H4 U5 _# C - printf("sending frame\n");9 `# D& o$ @( z. A2 j3 l4 `2 @ {
- if(write(fd, frame, frame_size) < 0)
- y- }* K9 c- F, d" h - break;/ D$ U+ A- p! ] k5 T6 k
- printf("sending boundary\n");
- t3 M4 \% ]6 K4 P4 e" e* I - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
, E! \5 p: U/ w* r* C' c - if(write(fd, buffer, strlen(buffer)) < 0)
! g! y* m }. r9 @/ B - 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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' F, M* `; ^. {8 N. }二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:
$ x* \+ z* c( w: s7 \- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port); e+ [0 |8 v" U; K$ ]! r
- {
2 ~. t7 {" L+ z& h, C( C - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);1 R( N" T' N6 X3 V
- if(*socket_found == (~0))! b, A! k! |+ ]7 z' y( p) H9 _
- {
0 j |/ e8 I5 u1 O8 _2 r* I5 i - printf("Create udp send socket failed!\n");5 W" S8 ?2 z" A8 o8 G
- return -1;
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2 U- X9 ]; Q$ s; [! | - addr->sin_family = AF_INET;
& N" ? G+ L8 }0 {+ t - addr->sin_addr.s_addr = inet_addr(ip);
, z) t# E2 o) Z6 D; f: F - addr->sin_port = htons(port);
4 |/ w( H0 Y" l4 f' } - memset(addr->sin_zero, 0, 8);4 ~! g* o0 i. p
- return 0;
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复制代码 / W2 ^. y$ }$ U5 S Y
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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:' Q& H. E* X8 c9 @
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1 r1 z5 m; R0 A. J2 k, Y0 {- while(fend > 0)
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2 z: C% x: Q, r+ X9 s$ m0 A - memset(picture.data , 0 , sizeof(picture.data));9 y0 L. Y! \: I- s$ r: ]4 Z
- fread(picture.data , UDP_FRAME_LEN , 1, fp);0 U1 A! C: u+ C6 e$ e2 H, O
- if(fend >= UDP_FRAME_LEN), ]. ~6 N6 b* ^
- {
% |/ o8 q; Y6 W# e" D' V - picture.length = UDP_FRAME_LEN;
3 S4 X% q* v; S* S0 \9 {( ] - picture.fin = 0;
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. h/ M% O6 V5 g0 D# t& I - else
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- picture.length = fend; f! Y) f- o8 h9 S1 @% P- s
- picture.fin = 1;
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- //printf("sendbytes = %d \n",sendbytes);2 `6 `7 _& ?( L9 r/ v
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
9 @4 c) S* r- ^* T+ f( f - if(sendbytes == -1)8 K$ P; l E; P( _. x
- {
# j# g$ e, \0 ?4 R - printf("Send Picture Failed!d\n");
7 T# o K+ o) |6 C+ D5 ^ - return -1;( p1 ?: o' c8 b! S
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- else" `, x2 G" n' i2 a( l
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- fend -= UDP_FRAME_LEN;' Z* J3 n9 ^, p1 K; ~+ K. @! x
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- }
复制代码
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9 _$ B# r( ?( l$ f$ _) A$ P% TiMX8MPlus 核心板: https://www.forlinx.com/product/136.html |