本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑 6 H! T7 }; w8 ?0 A2 u) |7 o* Y1 ?/ l8 @
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4 Y, Y: @5 h! M. P: J+ r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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7 P2 d5 H- _3 ~! Q7 k. D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。 7 u1 @: N; J8 d
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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。 & T, H9 w% ]! J7 V. K1 {, p
一、HTTP网页服务器# Z/ s% h4 m$ f( B2 ?6 `" R& Q
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)% _$ E- n9 v! Q' e+ q" }9 B
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- struct sockaddr_in servaddr;
: J7 S# Y- v1 C9 n( d; B- i% K0 P# t - socklen_t addrsize = sizeof(struct sockaddr);0 w1 T7 N k; B7 w. F; g) k0 A; z' D
- bzero(&servaddr , sizeof(servaddr));4 u& O9 o5 d5 n+ v
- servaddr.sin_family = AF_INET;
8 K1 C% s! A, U/ U - servaddr.sin_addr.s_addr = inet_addr(ip); s# |( p* ?+ Z2 e; `; S* ]) o- q) H
- servaddr.sin_port = htons(port);
5 Z5 n, F2 F8 j# b/ } - int ret;
! C, s* X+ } j1 T$ a! \ - IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1); z8 L4 f( f8 R8 g \, C
- {( }. G1 g2 U: ^
- printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);$ _& a- m+ Y) |1 z9 I6 F9 E
- return -1;6 e' l* G, c& P
- }
3 p- Y; W4 ^! u$ i+ D; r' } - int on = 1;
; j. t" I- v/ D8 C, _ - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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- printf("setsockopt error\n");7 j' } s. U) _% G
- }# l, _# o7 {% n& E% H# ?& F$ s
- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);' E$ y1 p3 C& s$ f
- if(ret == -1) k! o, t' ]4 U7 z
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- printf("Tcp bind faiLED!\n");
6 d; N# s; z$ F - return -1;
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- if(listen(*socket_found , 5) == -1)
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0 \' a) s" p% A* r, i& t - printf("Listen failed!\n");3 Q- K. V* h3 _
- return -1;
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- return 0;
1 A+ \0 K9 ?5 g# i2 e/ K - }
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);4 u% a: |4 O: o. A
- void * Thread_TCP_Web_Recv(void *arg)
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- while(1)
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\7 v% U; d9 q `$ n, w - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);# y' N2 A J; v3 O( ~! N5 c
- printf("fd_socket_conn = accept()\n");
7 T! ]' u6 ?, V5 { - 。。。
( k2 _: d4 L1 M; ^ - 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);) o- V! S2 F0 {. x
- pic_tmpbuffer = pic.tmpbuffer;
& U8 Z$ V8 c; x% ~: s5 a% a - pic.tmpbytesused = buff.bytesused;
, @! X) u. v& O( }& N0 N. R - pic_tmpbytesused = pic.tmpbytesused;
2 ` L: H8 G5 ~9 n - pthread_cond_broadcast(&pct);% {' |% `1 G* o9 w7 F& e+ w
- 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;, M8 G9 f& q# d! z: @' [7 F
- pthread_cond_t pct;
0 z6 U9 r- _2 E7 O( u - int main(int argc, char* argv[])
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- ...
) Q/ M+ e |) d1 ~4 d) r/ U - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);' V. s# Y8 ]3 r [! L; W
- pthread_mutex_init(&pmt , NULL);0 L# X& S, H' I" k: a$ k, O" O" b
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);" w" C8 a; U B- S) [* o2 f
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);) e( H; p. d' j! h
- ...
: k3 o& ~8 L' k5 b, ?" D2 E - while(1)( N( O8 y$ a' r
- {
# R6 q2 Y2 b; n% m& C& r2 C - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);
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- ...
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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;">
. B: u# K' m n - </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" \
% X H/ ~8 a6 t) f3 [/ E$ ? - "Server: MJPG-Streamer/0.2\r\n" \
4 d# c9 F; K9 q' U - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
' f6 j$ z. g3 O' i+ B* s% j - "Pragma: no-cache\r\n" \* Q2 l$ y( F v% C- f" Y
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"% R8 g) i5 A$ ~# m$ K
- #define BOUNDARY "boundarydonotcross"
/ S/ `* n7 h W5 @9 Q | - printf("preparing header\n");
# h5 @: N7 s: H7 ?3 P - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \$ s7 T$ q9 N2 ?- |. Z
- "Access-Control-Allow-Origin: *\r\n" \
! x) k" j1 l4 K {7 u - STD_HEADER \
5 Z7 X% S5 m& |% L% L2 {8 z4 } - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \1 l2 T+ m p- \) ^/ V$ a8 U5 N
- "\r\n" \
) |% r8 R4 u5 [; H/ V: G - "--" BOUNDARY "\r\n");$ `$ o- o* J2 d
- if(write(fd, buffer, strlen(buffer)) < 0)
$ }* z4 F. O; ?+ i" G' p% G - {
3 i" _. ^. Y2 M3 j9 W1 n$ p - free(frame);
' e) Z+ m0 ?9 F m( A - return;" j* q; G8 d& v/ ?' r$ w2 l
- }
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" \
* b5 X, ?0 P! v8 u* c% W: ?8 j! A2 V - "Content-Length: %d\r\n" \
" I, X7 `8 Z0 j1 F3 H& G - "X-Timestamp: %d.%06d\r\n" \& ]$ X7 ~! U! W) T
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
; B O- U2 Z+ @0 V1 Z - printf("sending intemdiate header\n");- |- | `# M0 B2 N
- if(write(fd, buffer, strlen(buffer)) < 0). Z% l6 ^8 k0 h+ ^
- break;7 D! C& f1 z, R2 R: S/ w
- printf("sending frame\n");$ T* Q5 f: M7 B5 U; t/ z7 a& S! S
- if(write(fd, frame, frame_size) < 0)
# X6 D" I5 F6 r& B# \& M0 z* T - break;. \" e7 B3 @3 I6 o% v' p0 ^
- printf("sending boundary\n");/ G# c; I. Q: Z ?! y, ]$ _! u( e" v
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
# k- i2 y7 w8 ? - if(write(fd, buffer, strlen(buffer)) < 0)
* }5 x* [/ ^4 I$ B3 N - 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:
' m% K7 l: R+ L* J o# ~( L) [- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)4 Z; x* w3 |; c& V
- {. `, W) R% q0 e
- *socket_found = socket(AF_INET, SOCK_DGRAM, 0);- o) }- j6 Q6 i4 v- ~1 `2 G% j
- if(*socket_found == (~0))* V3 O8 L1 ?, J$ q8 p, x9 Y
- {/ M9 x7 @* |, q% L
- printf("Create udp send socket failed!\n");
8 y) v6 _- Z3 b: i/ i - return -1; s$ x I0 L4 }- \; u7 l9 f
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- addr->sin_family = AF_INET;
* q8 m; h# B) z - addr->sin_addr.s_addr = inet_addr(ip);$ T: I0 t) k" x
- addr->sin_port = htons(port);
- V. |- _+ b/ s/ y+ [7 w - memset(addr->sin_zero, 0, 8);
3 c7 O- A5 f8 b6 ?# P5 Y9 x3 X - return 0;/ ~2 Z, P% b2 t4 u4 S; c
- }
复制代码 ( `. d6 f& m0 K4 A9 y3 T8 U0 r. K
/ x( t+ V1 G! C8 C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:! p; s: h/ i& c, Q/ n' X6 ]8 g! Q
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- while(fend > 0)
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- memset(picture.data , 0 , sizeof(picture.data));+ n* p# |: e, @' a; M# D1 B
- fread(picture.data , UDP_FRAME_LEN , 1, fp);( M9 a# q& R) B0 m: T
- if(fend >= UDP_FRAME_LEN)% c) h0 }8 n6 [
- {% @& m" s- E: K. A3 A, h8 d
- picture.length = UDP_FRAME_LEN;
) C) S# X0 R) Z& x2 a1 W8 C - picture.fin = 0;
6 D: K- H" C7 ~4 x& v4 k/ g1 f - }
9 X8 L9 S3 @! v: ? - else9 I3 f8 ~' U2 Z+ |9 G( q
- {
6 x t# b- L% t - picture.length = fend;
& Z1 y! c4 C3 D/ `" I - picture.fin = 1;9 }. q: u+ f/ {, s* s$ V# O
- }
! n, J+ B; Q' A9 T9 Q - //printf("sendbytes = %d \n",sendbytes);
& ?0 H9 T2 w7 h) L - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
% @( H2 M4 |$ ]0 x9 k7 h3 E - if(sendbytes == -1)
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- printf("Send Picture Failed!d\n");
$ U+ g8 T6 d" {. w - return -1;; C; s- n! ~$ h4 p* ~% x
- }
0 b1 P1 g$ m: e/ o7 o9 e T2 @) b - else, X2 O" e1 ]/ S0 G7 M
- {0 j5 r! C+ R# o( R# Q
- fend -= UDP_FRAME_LEN;
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复制代码 # I i4 l, k/ I( V+ C4 ?2 [& y+ R
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& r3 ^5 ?1 _/ Z* K) f4 N% h# XiMX8MPlus 核心板: https://www.forlinx.com/product/136.html |