本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑
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/ \! B& y' `% w% @' D7 I% _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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( |9 C. c3 H. O- U# P7 ?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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7 R. V4 q7 g7 N$ \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。 $ T. u+ C9 p$ C! h0 V0 W9 p( I: M
一、HTTP网页服务器
1 s. A) F- C6 t$ E. E: |2 U9 h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)9 j3 O( B4 X: r
- {
2 j; S* S0 v/ K- A* I - struct sockaddr_in servaddr;+ D* K+ a* u& G; y% n( z& K% Y9 a
- socklen_t addrsize = sizeof(struct sockaddr);
: o6 C0 i+ ?+ ?! ^6 {! s2 N- J - bzero(&servaddr , sizeof(servaddr));
; V5 H' _" ]6 \7 g+ M+ V4 M - servaddr.sin_family = AF_INET;
* t( d& H6 ~/ S7 ^3 f4 H; A - servaddr.sin_addr.s_addr = inet_addr(ip);
& B- F" f8 j- k" }$ U- j% @ - servaddr.sin_port = htons(port);
' ~2 v& m" @5 x6 ~0 r - int ret;
" E. f4 t+ k! d0 T% s - IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)
; r& Q4 |1 }: L - {
& O5 l* v! w5 s6 h0 p4 t6 K - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
9 I$ D" f5 O4 d* N0 v - return -1;
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- int on = 1;
- a. z# b) ]6 l- D( ]1 [ - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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- printf("setsockopt error\n");+ ^4 ` z) i" T) D& u$ r5 Y
- }
2 {& ?% A' C$ J+ V! ` - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);# ]: E& x+ L& f) I3 z! H7 c, s4 C4 M
- if(ret == -1). ?, V; ^7 M9 Z# H0 k; r; b
- {. h* l, \' d& |- O) u
- printf("Tcp bind faiLED!\n");
4 `7 v b: c7 o - return -1;
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- if(listen(*socket_found , 5) == -1)' |% z9 G4 Q4 h. |3 g6 x' T+ @
- {
+ ~1 o/ f* U; ? - printf("Listen failed!\n");
0 e6 l* w, X1 N, ]% w3 q8 F a - return -1;; ^% \( `. W( } i* U3 O4 C& N, E4 T
- }
3 B2 A0 i( S' ~, t% T1 [ - return 0;' {6 c: `2 ~) e7 o' q: c" `$ N
- }
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);
- i7 h4 Q2 n& t3 I5 s# C - void * Thread_TCP_Web_Recv(void *arg)' D7 v6 x: M) i! ]# y% r
- {
4 v! J6 q1 f6 j2 Z6 b8 F - 。。。
" e0 Y7 `- {+ v0 f* c - while(1)
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" w$ S6 }& q/ T, \ - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
! K+ V* H+ \0 ]" n - printf("fd_socket_conn = accept()\n");
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- recv(fd_socket_conn , recvbuf , 1000 , 0);
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- 。。。7 g; u5 w! l0 G6 t. O( _
- }
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);
7 y( P" W: |( T3 D( a( L) @( y5 ~ - pic_tmpbuffer = pic.tmpbuffer;
! X- m! p! c2 W6 y4 F' O' ^ - pic.tmpbytesused = buff.bytesused; ~/ M7 H, t' t( P, ?
- pic_tmpbytesused = pic.tmpbytesused;1 {, b1 k& t- [
- pthread_cond_broadcast(&pct);
, y6 ~% k+ `3 `* S- X- Z# R% ? - 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 N7 w$ \! }* P; E
- pthread_cond_t pct;, @* @9 j6 W3 W9 c
- int main(int argc, char* argv[])
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- ...
$ i; I# |/ }* ?& U8 S: r% G - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
- B4 m- g& g' e - pthread_mutex_init(&pmt , NULL);2 n# t1 f" z5 r
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);0 r$ x4 q$ p* `- n D8 X
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
U. Y$ ?8 e ^0 q S - ...
4 J9 j3 _& T$ Q( @! @7 l - while(1)5 s& D2 R% t8 U5 S4 x
- {
e' N( G8 }5 l - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);
. Z* P2 W u& A5 \) h- r - ...
- S% O) \; ^9 y. y- k9 K - }
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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;">* w7 N9 F0 z. p- A1 B
- </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" \
) A" w& m$ p1 N - "Server: MJPG-Streamer/0.2\r\n" \2 [* B) m8 H2 C' n0 @6 w" ^
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
7 y6 s" O" {) A" @1 d - "Pragma: no-cache\r\n" \
; h4 l* H- Z; k' t, D - "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"6 K/ f8 J, ^ a1 F8 b I \
- #define BOUNDARY "boundarydonotcross"
8 y8 C6 n G2 y! u8 \ - printf("preparing header\n");
) [7 W9 H7 M" X$ _ - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
, j/ p4 j% j! P - "Access-Control-Allow-Origin: *\r\n" \9 J! m5 r! t6 d r, o! ~3 ^
- STD_HEADER \& W0 l. ~8 M# K) V* Y2 R
- "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
4 M6 p2 c; ]- f* J5 { - "\r\n" \, Q) e5 E4 E# b6 ~0 W6 p. l Y
- "--" BOUNDARY "\r\n");
2 U% B0 ]# d+ z; ^$ G - if(write(fd, buffer, strlen(buffer)) < 0)
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- free(frame);0 t& D H# p- ^' z* M
- return;* w$ u' m! K- p+ u1 C2 {
- }
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" \
. A# B3 V$ k! I5 N0 E; W5 H - "Content-Length: %d\r\n" \
- s$ l4 o+ P& J2 n1 M1 u - "X-Timestamp: %d.%06d\r\n" \
6 E9 G+ `* H. H% c4 r - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);+ L; a9 Q1 `8 M. D7 c2 W
- printf("sending intemdiate header\n");
6 h2 j& a( Q0 K; j - if(write(fd, buffer, strlen(buffer)) < 0), i: |7 H t# z
- break;4 R7 y; R+ e5 y0 L0 w
- printf("sending frame\n");
/ @% W' w6 K0 [+ Q* u - if(write(fd, frame, frame_size) < 0)5 o$ x/ E$ `5 S8 C! G
- break;
p0 d+ w* g T0 _! |/ u - printf("sending boundary\n");
2 d+ q/ f/ X6 N) {: A% F - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
" c1 r( M' t4 t - if(write(fd, buffer, strlen(buffer)) < 0)
" r5 v$ B( `4 T, a& P6 H - 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:( {+ s2 O X2 t) G: N
- 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);7 o# ^0 h$ c& r/ [3 ?3 \
- if(*socket_found == (~0))
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- printf("Create udp send socket failed!\n");9 ^* W' r' n( {7 D
- return -1;
: `6 X* ]' Q" U/ \& c - }
8 w9 X/ S; n# E- s2 {& o: f% v. x - addr->sin_family = AF_INET;
3 u% Y8 Y5 O% g- W: D - addr->sin_addr.s_addr = inet_addr(ip);
: @; z& Q( _9 ^2 X9 L- W* d4 ]0 P - addr->sin_port = htons(port);* L3 F$ M% u3 \8 L
- memset(addr->sin_zero, 0, 8);# n3 i% G0 T2 ^5 \
- return 0;
4 Y5 i6 Y; b2 B7 I - }
复制代码 : r* k0 d0 I2 x5 G9 }; e+ s
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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:; c, S- W7 S7 T3 J$ i2 d& j6 Y
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- while(fend > 0)
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- memset(picture.data , 0 , sizeof(picture.data));& D- d; ]$ X: y+ b& E
- fread(picture.data , UDP_FRAME_LEN , 1, fp);
0 I& N6 j/ }: q: W7 n& O& k# l - if(fend >= UDP_FRAME_LEN)
; l6 y' \+ N; l% q3 T6 o1 x* q - {
7 p% k* z& I% r! w2 |5 g) K/ y - picture.length = UDP_FRAME_LEN;
1 X$ X4 W# X! O9 }- s: i+ c" J - picture.fin = 0;
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- else' g) W( O& ~/ Z# l$ t1 z
- {
# o. g! S# E. Q4 P1 a2 D* y0 Z - picture.length = fend;
8 w6 A- ?4 {/ g* G+ ?% n4 e9 p - picture.fin = 1;
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& `* ], m- o. @" x9 @! Q - //printf("sendbytes = %d \n",sendbytes);( m0 W K/ _/ q& E& ~
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
" c" q/ i c; J \ - if(sendbytes == -1)% g, q+ v! u( X: D+ ^) ^; j5 u9 L. M
- {% H+ c4 [, \% q4 I2 j
- printf("Send Picture Failed!d\n");/ @8 k9 N7 a4 ]( A4 K' O
- return -1;. I) T% M' n4 q. N/ Y- ]
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- else
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- fend -= UDP_FRAME_LEN;
' u( L( c* O, J) Q8 y& Q9 p - }
# u: C F5 v- Z& z - }
复制代码
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@" Z/ f v% c4 q. d6 T% h3 QiMX8MPlus 核心板: https://www.forlinx.com/product/136.html |