本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑 & R6 F- j) c- F X9 g
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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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4 Q+ F: s( J) t1 D, g) e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。 % S4 Q R% r! W+ A# F

9 E6 V7 Z" A) v$ {! m% L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。
8 J$ ^+ |+ n7 g" H& l5 O- A4 Y7 k一、HTTP网页服务器
& c1 Q- @1 H# F* f# Y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)
; G& b9 m0 z/ s. H) K - {
- [4 L3 o/ I, S! Q - struct sockaddr_in servaddr; o. |" n9 V r; F
- socklen_t addrsize = sizeof(struct sockaddr);+ U- g1 B" ~1 Q, Y# j
- bzero(&servaddr , sizeof(servaddr));5 u9 G+ J- g* d6 W- L' a
- servaddr.sin_family = AF_INET;2 e' @; e# l( d
- servaddr.sin_addr.s_addr = inet_addr(ip);4 A" n7 g) B8 `, X
- servaddr.sin_port = htons(port);/ Y& C$ p8 o' o, g
- int ret;
" I$ i6 }$ X. _; ~( b - IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1). d- A% D, G2 X8 T, ^, y
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- printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);7 T- V; {) d2 W1 g: ?9 [
- return -1;
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- int on = 1;
! l. N) J& o5 P! B4 Z4 B3 }( B+ K - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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- printf("setsockopt error\n");
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- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);7 L) x7 d$ ^3 o! e: y+ G! l
- if(ret == -1)
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6 I, `# w k0 k( q4 P - printf("Tcp bind faiLED!\n");7 B. [" f4 L6 M, {5 t
- return -1;1 w: c" M+ u$ V
- }
0 F; S3 d1 R" n6 @5 c - if(listen(*socket_found , 5) == -1)' g Z2 i: H/ [
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- printf("Listen failed!\n");
) M! A/ V% c* o( u' A- c9 Q - return -1;
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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);3 L9 M* x W) ^) ^
- void * Thread_TCP_Web_Recv(void *arg)/ T1 _* X6 f" j( e& d3 n
- {
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- while(1)
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0 A; }. ]) Y9 {( ~' } - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
( b+ p6 V4 \8 |6 a/ S; \ - printf("fd_socket_conn = accept()\n");6 G2 | @* u8 L# e/ a
- 。。。
/ D5 O" t6 v7 s - 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);
3 Q* f; `( S0 l2 j+ J6 p, {/ `# {3 P% h - pic_tmpbuffer = pic.tmpbuffer;! |' b- H8 L0 n' ~/ k" F( b
- pic.tmpbytesused = buff.bytesused;
5 O+ t2 {5 N! ]1 T - pic_tmpbytesused = pic.tmpbytesused;4 u' Q% e; K. `5 Z
- pthread_cond_broadcast(&pct);+ Y8 m& t1 G/ u. N/ i% c! O& X6 Y
- 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;) `) j5 Y$ ]( t! U1 ]: P
- pthread_cond_t pct;
3 u2 L3 l5 w ]( y% } - int main(int argc, char* argv[])" x- }& d, r1 k& v u
- {" t* o; O7 I# n B) @
- ...
# ?9 A0 I1 ~8 {& N8 j* R - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
7 Y1 D. m. K( ^" ^ - pthread_mutex_init(&pmt , NULL);0 x- m# W1 B) f- _
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);
+ h3 O( E" }- o7 V' \0 s6 [ - pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);8 H# q. ]0 _$ s$ a6 {* \/ S
- ...
" l# r$ K3 x( ` M - while(1)
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- V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);
( H% l9 k! l9 x0 u/ Y - ..., N0 A( }0 V6 b6 x: T4 T9 a6 E
- }
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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;">
0 ]. h4 s( m" H/ M/ ^ - </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 g# q J: `) J6 e
- "Server: MJPG-Streamer/0.2\r\n" \1 O! Y7 O4 p C% h# p, ] O
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
3 H2 @! L& j' U# y2 K! w' E - "Pragma: no-cache\r\n" \
D) F" T! e& g; p: \7 m9 {$ Q - "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
, w* i! X6 _3 ^: X' [' _1 m - #define BOUNDARY "boundarydonotcross"% \/ {* _2 T9 z! f, h( v
- printf("preparing header\n");
& D( O" C: _$ S$ ]( h - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
$ x: G7 e5 a5 Q" }9 T( a - "Access-Control-Allow-Origin: *\r\n" \8 ]$ q d7 M! F" E1 y: ^
- STD_HEADER \/ b/ L7 r9 V9 O& E8 R/ Z/ x" v! A+ @
- "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
5 A# d) I8 {7 n. t, `" N6 Q( G7 q R - "\r\n" \/ p9 e+ \9 q. g- z: g2 P# d0 M
- "--" BOUNDARY "\r\n");
8 p! U. j& D3 B; F6 K - if(write(fd, buffer, strlen(buffer)) < 0)
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- free(frame);
- C. F2 A1 T; T7 N6 [2 z7 L - return;
. |2 y0 T! i( }$ ~8 V9 \ - }
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" \
4 j0 H( t' I' e" r/ a$ \) L a7 Q - "Content-Length: %d\r\n" \5 g9 u, n4 c9 g5 R6 u8 Z
- "X-Timestamp: %d.%06d\r\n" \) a' C9 l; o( k) j- f# e/ r
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
& q& e7 e9 t- L; f1 [; D0 t - printf("sending intemdiate header\n");' N$ i' H# l# L
- if(write(fd, buffer, strlen(buffer)) < 0)8 O9 m8 M7 F; a$ y& D6 A
- break;$ s( G$ i8 `1 T* V
- printf("sending frame\n");- c6 X K" Q ?9 O6 c; P
- if(write(fd, frame, frame_size) < 0)
$ ~$ \3 Y& H6 j ?0 L3 F - break;' V- `7 P4 l" v5 t b
- printf("sending boundary\n");
8 Y2 u* N+ k; N- h5 n3 w: y - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
( J& y5 l8 W. _2 s1 t& @ - if(write(fd, buffer, strlen(buffer)) < 0)
2 q! k) E/ E& h1 H0 u& s D) U - 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:* z! _0 h- z5 }
- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)0 ~# g, I. m- o' H* h1 x5 t9 B& R
- {- a; g: N1 j0 a3 D
- *socket_found = socket(AF_INET, SOCK_DGRAM, 0);& {. E' n9 G0 o$ N! ]
- if(*socket_found == (~0))
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- printf("Create udp send socket failed!\n");
! B1 }, r* \. j1 l, ]/ [ - return -1;
* \7 k2 d( g9 z3 O5 p. C. F - }
( R* B9 A4 [3 w1 n - addr->sin_family = AF_INET;6 E/ z0 p0 f' J0 m
- addr->sin_addr.s_addr = inet_addr(ip);
$ Q. D; X' h- h5 c1 i4 r - addr->sin_port = htons(port);
7 y; P+ U" V& [. c0 l - memset(addr->sin_zero, 0, 8);" O/ S7 `' ~( \+ y) o% O. J4 z& H
- return 0;
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复制代码 X6 U" t, a' l+ C/ p
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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)3 j8 n( `. V. G* @" e
- { s i9 E8 x( Q6 O q' F
- memset(picture.data , 0 , sizeof(picture.data));
5 E4 k: ]# b' C- R: t9 Q+ J' I% N - fread(picture.data , UDP_FRAME_LEN , 1, fp);
5 z. i7 B* k* J- f, ]4 ? - if(fend >= UDP_FRAME_LEN)
3 Q; R2 E; y& P' v# H - {
" E7 @( k- ]" h9 Y* L$ A - picture.length = UDP_FRAME_LEN;5 l. _. X. F0 E3 S' t5 d! r+ a
- picture.fin = 0;" B% u$ k5 i3 [! m/ p
- }. d; o0 W2 Q" y5 i8 w
- else' n ^# y9 r: O7 v) a
- {' p. H F! C' x' M7 E3 C
- picture.length = fend;: K3 E' ~1 y+ b1 C6 C+ ^9 ]3 U
- picture.fin = 1;6 t+ r' l) V) Q* |! k! U' F8 c
- }
( K* x3 O' s C6 |1 g - //printf("sendbytes = %d \n",sendbytes);4 B) e8 X. x& g4 C! ^/ x
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
3 w# g' v+ M5 h$ u4 Y( y( Q" S - if(sendbytes == -1)' _2 u% m9 s1 d5 `7 @
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- printf("Send Picture Failed!d\n");" ~5 `3 G$ m+ u: Q3 m
- return -1;4 e% x$ [- }% m& i' X8 K0 C
- }
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- {! ]. l! p4 [$ a- m7 ^
- fend -= UDP_FRAME_LEN; r: h1 y3 L+ `: J
- }
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复制代码
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! G5 G$ V$ A' p8 S5 t* miMX8MPlus 核心板: https://www.forlinx.com/product/136.html |