本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑 ; \1 W3 x# R( J
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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& t D& n; L: C# i
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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。 % `2 q% O8 D# }% ]1 e% A9 ?

s+ S1 g/ e5 Q4 N0 x* R" x7 N+ k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。
- V' a Y' p" I4 K: Q一、HTTP网页服务器
9 q( G _8 `9 f, |. \; a. J* e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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+ r, B: k0 C: S+ s4 ? - struct sockaddr_in servaddr;
% M- L8 g- F' ]; j3 c" r0 C! [- X - socklen_t addrsize = sizeof(struct sockaddr);
+ z6 T' R' j5 F+ z! X - bzero(&servaddr , sizeof(servaddr));/ O+ v5 D) M' ?4 m9 J2 c
- servaddr.sin_family = AF_INET;
" Z2 b4 f; |' u; d' }* b - servaddr.sin_addr.s_addr = inet_addr(ip);" @" }2 |5 M7 ]2 k* g1 R
- servaddr.sin_port = htons(port);9 X" _' W% {& r4 l+ r1 W8 t9 O
- int ret;
. u6 l- F0 j* K* a - IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1), ~4 J" \$ ~( J F8 n6 Z% C
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- printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);, a1 ^: ?! [7 R6 ], s% q0 N. S
- return -1;/ ~6 ^! O7 T" m H- h
- }
5 s) s& Y$ K. S6 j9 S - int on = 1;1 B( X; Q5 q o' t9 B
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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- printf("setsockopt error\n"); K" X/ W5 J2 _( W
- }
4 x5 }9 h5 M% k) D1 ` - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
, o8 _4 W$ F; w - if(ret == -1)" w7 A) q* C! a, I2 G3 S7 ^
- {
# S7 d3 ^. h8 \" N - printf("Tcp bind faiLED!\n");) l) O! O: I( z$ L
- return -1;
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- if(listen(*socket_found , 5) == -1)
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- printf("Listen failed!\n");
" P% b. P0 B' F8 c! X( E! t - return -1;
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5 M! W' {2 ~* D6 U - 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 ?/ ~ b3 A' }4 y7 \ |: [; r# O
- void * Thread_TCP_Web_Recv(void *arg)
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- 。。。( f+ U# u0 u G6 c9 _; U
- while(1)& d: k% x* v& E0 F7 i" y+ r7 {
- {
/ O! Y% V' W) S$ }: G+ B( _9 Z8 n, p1 ? - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
0 T- ?$ i1 C) O \) d - printf("fd_socket_conn = accept()\n");5 _( l0 _- w! g. s) F
- 。。。
& V5 F6 |. G. e* w, z9 p P" P. n - recv(fd_socket_conn , recvbuf , 1000 , 0);$ g! f" y+ h0 x2 b' q _7 N
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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);
& J4 s+ J0 C% O% R9 A( ? - pic_tmpbuffer = pic.tmpbuffer;
1 d4 A% K7 E6 ?( Y% ~+ O# {" g - pic.tmpbytesused = buff.bytesused;
$ p9 [' m: F! X: T' v0 j$ J0 f - pic_tmpbytesused = pic.tmpbytesused;
+ P4 ^4 ]: `4 U$ P+ @6 O' O - pthread_cond_broadcast(&pct);
: i3 k, F" N; \9 Z* d" K - 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;1 C5 D1 L4 Y* b
- pthread_cond_t pct;
! D }3 q& f: u$ x" [ - int main(int argc, char* argv[])
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- TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);7 x. C& l5 P' f) Q7 X& N9 F
- pthread_mutex_init(&pmt , NULL);. ~6 }9 e3 P, Q0 [, _' V% t
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);
7 q: K- B' y" x7 } - pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);5 @5 |! {2 e3 [6 K$ f. X( t
- ...
% U) m0 p: ]1 {8 E: Q# ]- ]; \, f - while(1)
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; U( A+ K- @ t* { - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);
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- ...5 r" z% ~9 ?9 Q4 Y. |4 f
- }
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 b/ S" J, P* v$ Z S
- </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" \" p7 H# b; q3 O
- "Server: MJPG-Streamer/0.2\r\n" \
8 b6 Y0 u/ o0 L' V# c! M t - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \0 t! ^& b w4 H
- "Pragma: no-cache\r\n" \
a- B; ~" _) i3 X! }* h - "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
+ G O, v- v/ c - #define BOUNDARY "boundarydonotcross"3 _6 X6 h$ F2 ^5 _6 Y% u
- printf("preparing header\n");. r" O6 V# S4 D. f; D& g( L1 D' i$ U M
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \# A; E" y+ D9 k! w+ G6 F3 P1 s
- "Access-Control-Allow-Origin: *\r\n" \+ o4 F4 \5 D- n* _+ S5 d% t
- STD_HEADER \! b0 I5 Z3 u6 o4 m' f- P- S/ U
- "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
9 O5 ?9 x7 X K+ @6 I& g. H - "\r\n" \' m. i+ P2 w4 m7 v. N
- "--" BOUNDARY "\r\n");9 m5 \$ J- @! h
- if(write(fd, buffer, strlen(buffer)) < 0)4 r/ M' f( Z3 P' E) Z% S1 w! W
- {
0 L& W: B( j0 J# y% \4 O; k - free(frame);7 _; V* O6 ^! u' t8 }
- return;5 d3 l H) g- G* ~7 f2 V1 j
- }
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" \
; Y) B9 i" Y' [5 a% |% x7 c5 { - "Content-Length: %d\r\n" \2 o! B/ T$ n5 w# |; u% u
- "X-Timestamp: %d.%06d\r\n" \
9 p9 k6 e/ V4 } Q2 F - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
# L4 c4 O. z0 V. F - printf("sending intemdiate header\n");
* j/ H# f5 t: z4 a3 @7 u/ s - if(write(fd, buffer, strlen(buffer)) < 0)
& l R" S6 d0 }. l, H - break;$ L* e$ I8 d. c; a1 F" f
- printf("sending frame\n"); k3 U& B' ]8 t
- if(write(fd, frame, frame_size) < 0)8 @7 C3 J8 Z2 p% q6 Y+ Z2 c; y
- break;/ p* k' I7 e8 g; g# w' G
- printf("sending boundary\n");5 l8 R, V+ m; P. u
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
: ]5 K4 k8 { n' q4 h+ ]# R - if(write(fd, buffer, strlen(buffer)) < 0)+ z" e4 B0 i% P
- 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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$ y7 u9 ~- C# {3 p+ s/ W二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:
- ~ O4 F6 ^8 W7 D$ i: D4 g' O- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)- ~9 D- C$ `0 G& q6 @7 U- F, f
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- *socket_found = socket(AF_INET, SOCK_DGRAM, 0);
% _5 j, f) H6 S6 h' u4 e5 t - if(*socket_found == (~0))8 O0 ?* J5 Q+ @7 o) L- A {0 F
- {
1 e# x& J% ]6 M( M - printf("Create udp send socket failed!\n");
- e" D5 {+ O* }1 j - return -1;! h$ B8 ]9 w. {5 p) J
- }3 W# Q$ P& D- v
- addr->sin_family = AF_INET;9 W1 e5 a: ]' U( ~2 C
- addr->sin_addr.s_addr = inet_addr(ip);3 Q6 C. S& _! _% ]8 u
- addr->sin_port = htons(port);
8 o3 e+ ~0 J/ B, r: I$ x5 B4 p - memset(addr->sin_zero, 0, 8);
( M/ s2 A2 a4 B# p% e7 L - return 0;/ `& K) j9 R$ m! p( A+ L5 u
- }
复制代码
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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:- Y8 D4 C0 F1 Y8 F/ D+ s# V
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- while(fend > 0)
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- memset(picture.data , 0 , sizeof(picture.data));: [! ?1 Q3 l' ]
- fread(picture.data , UDP_FRAME_LEN , 1, fp);% b& ~6 D/ i( F$ Z: J+ e( |
- if(fend >= UDP_FRAME_LEN)
: [6 u5 ?8 J4 c9 W - {
- D* d; ]* B' I! g: ]+ Z - picture.length = UDP_FRAME_LEN;5 D! r4 N. m9 ^- B; e8 H
- picture.fin = 0;( \1 B& {. g g _7 i' p1 e
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- else; W! {/ d, Q& T- h& f
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- picture.length = fend;
1 L6 }7 g% o) Y" K, |! U - picture.fin = 1;
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- //printf("sendbytes = %d \n",sendbytes);8 y+ j5 L: p; e1 T, `
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);* D: e7 r4 |6 @/ e( j# b3 T9 d1 a, h+ ^
- if(sendbytes == -1)7 K+ G7 k4 O- k& s3 l
- {+ g$ h, s" J& i n" c9 i
- printf("Send Picture Failed!d\n");8 N; b' W- m) v7 e
- return -1;% J0 Z( e% I/ {0 k. F. M: D' i
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- else
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- fend -= UDP_FRAME_LEN;
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复制代码
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" ]. t$ L- T P( W0 Q. M2 N2 c, B, ^iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |