本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑 7 ^9 J# i% `8 K& M
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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! L4 Z# k8 [2 G1 ~
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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。 # k9 z- Q e; J) x6 A* v- } a

! A3 H0 c+ ?" I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。
( ?* c2 Y- f; X6 a一、HTTP网页服务器8 f, w/ H: p4 f3 r" O! [
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;
! g4 A( ]% f/ D4 G6 O - socklen_t addrsize = sizeof(struct sockaddr);' D$ l& B! u' t. }6 q
- bzero(&servaddr , sizeof(servaddr));
( t \" N0 `$ L - servaddr.sin_family = AF_INET;
' ?; e! @0 D- }4 B' N3 a - servaddr.sin_addr.s_addr = inet_addr(ip);) a+ H5 Q! f# x* O
- servaddr.sin_port = htons(port);
( L3 E1 G1 d9 {! I: j - int ret;
& e. N8 T6 a6 g. P4 u - IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1), l0 N9 t( f$ \% m' I% }$ h3 }7 g' t
- {
; @6 q( Y' T# b& X- F9 d; h& Q - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
8 M+ L9 J+ y$ }4 a7 |+ O - return -1;+ ^9 h4 Z6 [" v
- }
& G& f Y8 F9 e% k - int on = 1;
/ ?) }4 K8 A* X; m' X2 {: c - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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- printf("setsockopt error\n");' r. D% L$ t8 H, x# R7 S( A/ l1 w
- }
2 z1 N( p% r# { - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);; H7 k& W) q7 l3 U4 r
- if(ret == -1)
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- printf("Tcp bind faiLED!\n");% i" h% w# A C9 ?
- return -1;
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0 Q- |, S2 I3 ^+ z" g3 X: i& Z - if(listen(*socket_found , 5) == -1)
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) W4 [; s2 C8 s8 W, Z7 Q - printf("Listen failed!\n");
/ h# ~* N* d# j! J6 _! I3 E - return -1;
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- return 0;7 y. t9 o. H6 i5 o$ H
- }
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);# N, F$ Y. F; P9 J, r8 }; b* H
- void * Thread_TCP_Web_Recv(void *arg): A/ A3 }! ?( N% I
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- while(1)8 N. F. J! C r0 ~- }
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- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
: P. ], D1 Q2 X - printf("fd_socket_conn = accept()\n");1 |/ n# O- }* A1 _/ H$ s
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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);! F8 X, `: C4 j, A- \4 c$ C) t
- pic_tmpbuffer = pic.tmpbuffer;
1 c3 j4 Y/ C# N' X4 t2 e9 i - pic.tmpbytesused = buff.bytesused;
0 Y2 b+ X' P0 { q" N5 _( U8 u/ @ - pic_tmpbytesused = pic.tmpbytesused;
& |: U" i( E- u0 v# J - pthread_cond_broadcast(&pct);
+ E; M. r! ]& [6 ^" g P: G - 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;! x& f M/ O& ?0 S0 ~& s$ T
- pthread_cond_t pct;
# _' G' ^) _+ H* g% \8 S0 i - int main(int argc, char* argv[])
3 D1 e1 B; I, b+ B; _6 Q/ w - {
& A! i* O; b8 U3 t4 v( c - ...
, F1 g+ l% O, n8 K - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
/ `: R1 j6 E6 r5 y - pthread_mutex_init(&pmt , NULL);
2 A) q- Q/ T o' A - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);
; D9 }! i& a1 X, ?1 D - pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);0 t! k0 V8 M* m9 \& P6 T1 V8 E( B
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- while(1)- C/ p8 d) s* q" T: H, F" |
- {
9 F2 m' V# ?+ |0 G7 W - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);* K R! n5 ^3 c6 \3 `' [
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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;">8 K& C5 ~' o% t3 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" \4 {* [/ S$ ?8 [1 l5 {! b. e
- "Server: MJPG-Streamer/0.2\r\n" \
& x5 A8 x3 Y. t: o - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \# H' w: l7 w# h5 ~$ q& k$ Q
- "Pragma: no-cache\r\n" \
# l) Z- x$ z! y4 r# ~) y1 U - "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"0 v# D& f3 Q8 z* C7 E6 Y C* I
- #define BOUNDARY "boundarydonotcross", t$ D3 T: e+ `- _# r; D% @
- printf("preparing header\n");/ q; A$ D& m9 W0 z: S
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
& M# v h5 D0 F/ ` - "Access-Control-Allow-Origin: *\r\n" \9 U. ~, G0 [/ H; f' \3 @4 y
- STD_HEADER \0 W8 V7 v" O& X' ?. W; Z' T
- "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \) j# k! l3 K- |5 U3 H/ v
- "\r\n" \% T( r/ K5 G4 I
- "--" BOUNDARY "\r\n"); W) o/ L) p% q, Q# A
- if(write(fd, buffer, strlen(buffer)) < 0): T+ {$ Y! ]6 U7 q& J4 x
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- free(frame);; B+ W: q+ X- |# K# |! q
- return;, c, p, ~! Z* Q6 c
- }
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 X+ K5 {- O4 D
- "Content-Length: %d\r\n" \0 j' I, n) i. n2 o. Q1 P
- "X-Timestamp: %d.%06d\r\n" \# x+ ~+ n4 M i# C! R% n
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);; j2 D$ r2 Q7 v( Q9 X# K9 q9 \! R% Y' o
- printf("sending intemdiate header\n");; ~* R; ]/ S8 @* ~7 n; M* d: }
- if(write(fd, buffer, strlen(buffer)) < 0)- x4 A6 M a$ A4 {: C7 w8 \, t. C
- break;
# W( _) D$ C- w% F/ c) J - printf("sending frame\n");
8 \& \! ~0 b# r - if(write(fd, frame, frame_size) < 0)
" a; N0 i& P% c0 m u K% H6 c - break;
- r) ^ ^* ]" i2 C - printf("sending boundary\n");
8 }" C3 n$ `) C0 }! p1 C2 T+ O3 K - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
6 O4 _6 }1 y+ ]" E& q1 Q - if(write(fd, buffer, strlen(buffer)) < 0)
1 L% r- Y5 d6 F% m( N9 c - 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。  ! |5 k0 U3 U& ]: E0 ?

$ b$ M& z% [4 L3 H* N二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:
/ i+ j+ x- U3 Y$ l- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)$ f# ?6 J# E% P# _, z
- {
0 g* `6 R3 ~% }& \5 H3 _ - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);( b2 j( p6 i" z9 r5 L# K0 u% i- W; D
- if(*socket_found == (~0))1 F5 h# {% ?+ l% k2 }# N
- {
- E- Z* k0 @4 ?" ~' o# z+ x k" _ - printf("Create udp send socket failed!\n");
* v+ K8 ?5 Y& S - return -1;5 k# A( a0 n/ G$ Q @8 ^
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- addr->sin_family = AF_INET;5 |* [6 J/ y( e! g. n4 B' V; M5 A8 {
- addr->sin_addr.s_addr = inet_addr(ip);6 a5 \: L3 j! O# _
- addr->sin_port = htons(port);
7 F5 A$ z o+ W' B4 t0 @ - memset(addr->sin_zero, 0, 8);
/ C+ Q: A. |+ p9 \) w& t% S [( [2 @ - return 0;
. O9 W7 X! `0 V - }
复制代码
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( I- l9 Q" t; G! R5 X/ H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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% b4 |. Y: U J3 P- W& d- while(fend > 0)# w( x- f* ~3 ], C) T6 @& G- p
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- memset(picture.data , 0 , sizeof(picture.data)); z5 Q3 B$ w, y$ W; b( T
- fread(picture.data , UDP_FRAME_LEN , 1, fp);
' k# h4 I- d6 F' F9 o) K - if(fend >= UDP_FRAME_LEN), p. B# O9 K: V
- {
6 B1 e7 r2 x- C+ k% r - picture.length = UDP_FRAME_LEN;
1 p" U* O$ L' D+ w8 y* K2 s - picture.fin = 0;
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4 F% f" W& R; a$ s- V% N - else
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- picture.length = fend;
]5 g; ]1 ^6 U {: w6 W9 k ~+ P/ ? - picture.fin = 1;
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# J0 n; h) Y- G8 p - //printf("sendbytes = %d \n",sendbytes);
( l2 y3 r/ m8 K) |# K% r - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
9 k5 ]- u9 N a) a - if(sendbytes == -1)
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- printf("Send Picture Failed!d\n");/ f/ o) _7 [/ t8 ]' S$ c* `
- return -1;
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- else1 k! y' M# t/ e3 u% F
- {# \+ s5 k. J7 M/ E! Z
- fend -= UDP_FRAME_LEN;+ h. j3 R" K; \5 h1 ?/ B) d) G" x
- }
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复制代码 7 J2 i6 I l* d" O# ^
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- y4 F: u7 E8 s( A9 HiMX8MPlus 核心板: https://www.forlinx.com/product/136.html |