本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑
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' ^* G! S/ ^3 C2 c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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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。 1 j g% O# C+ h* d% E% h

/ O f3 g: T: @) Z' }+ t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。 , E* ?/ @! l; ]8 [% V8 P3 g" S
一、HTTP网页服务器
# M( @; `$ u+ Z% t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;3 i- O S5 ]! c q& b J6 ?
- socklen_t addrsize = sizeof(struct sockaddr);4 J7 |% W# [8 \1 Y, A5 b
- bzero(&servaddr , sizeof(servaddr));
- D, B# `3 \* X; b; U, G0 Q# m - servaddr.sin_family = AF_INET;9 F1 S' a0 f% Z8 q% E& x: ?) y: U
- servaddr.sin_addr.s_addr = inet_addr(ip);
: T3 r1 ~- ]" X5 w - servaddr.sin_port = htons(port);8 T) z; `( f- `' \: ^1 G- w
- int ret;" z8 M3 T) K, d+ ~- I( D
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1) |2 r- H; d J T; k7 B$ o6 W5 A
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- printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);+ i+ D1 y6 h x* |
- return -1;" R8 a# U4 r) Z7 d A
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- int on = 1;* q" V! c* r }1 w+ ~- {
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)0 h! n0 k7 a/ S: z- m9 A! e
- {
* z# q0 v+ N, M - printf("setsockopt error\n");' v7 t! j# q, m; c
- }
6 ^# o! | x1 q/ r7 e - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
* M9 n: ^% h9 i7 ]2 `, @1 ]4 m - if(ret == -1)
! x" f) N+ H0 d/ \ O8 k - {
* `, \5 t" m% C; ?9 V - printf("Tcp bind faiLED!\n");
. }& i' O7 m0 @5 w9 X - return -1;
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/ n- l+ W6 f2 H, X* I - if(listen(*socket_found , 5) == -1)
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- printf("Listen failed!\n");
8 p: B& b7 t* N% t; Z/ c - return -1;; v5 V* c2 N: v; L; S
- }
7 a( C8 k! p* i - return 0;) x5 Z. s4 c% l# z' Y& Z. ]( M- Y
- }
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);
8 a8 B9 V4 W/ C8 h; v- y$ x - void * Thread_TCP_Web_Recv(void *arg)0 o# P4 @! T: M# Z, X1 v$ @
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- 。。。
' c- N2 Z2 M5 E) L& f7 z - while(1)) \9 G3 J) q+ J5 I ~" s+ I' Y
- {
( i7 j( ~/ K! ? - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);$ H* |; W% W% w& U3 X: R6 A6 A
- printf("fd_socket_conn = accept()\n");: i; z8 e+ N, E* i, `/ c; o+ ]# b
- 。。。
, E* b4 q5 o0 A& q& \ - 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);% |, V& I) e; i/ C& j, a
- pic_tmpbuffer = pic.tmpbuffer;
% H3 W6 Y8 ~2 L! v - pic.tmpbytesused = buff.bytesused;
. J p( S1 b( u, | - pic_tmpbytesused = pic.tmpbytesused;( }3 c5 i M8 d5 G3 @3 ?& ^8 X
- pthread_cond_broadcast(&pct);
9 L( T) G+ Z: Q9 T, L3 F - 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;
7 R- c+ p c/ A& x( s - pthread_cond_t pct;( g4 x F: D. A) K
- int main(int argc, char* argv[])) v; K; M# b7 [2 _, j0 H6 X% J' E0 x
- {
k) O0 } q3 E1 x - ...
% F3 ~- _1 ]( j - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
6 `2 j4 Q9 K. J2 ?5 N - pthread_mutex_init(&pmt , NULL);
* I: |! o: r) i0 r( G: a - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);
( |+ O) d+ }- V: J0 E4 H: n" A - pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);. i3 B) H V* n+ S0 x, [3 U4 @
- ...& X# |/ g6 _; P8 ^4 k
- while(1)
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$ c; o$ P( O% z o/ O - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);5 w4 u0 G8 O# \2 v8 l& s
- ...
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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;">6 G$ }( P/ h% |' c5 g- C. E
- </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" \ O/ x I! E$ D! J+ @8 j
- "Server: MJPG-Streamer/0.2\r\n" \- }/ x9 i) b" b8 V/ J0 L
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
9 H* Q3 e* Z3 A( z1 E/ ~ - "Pragma: no-cache\r\n" \+ {' i6 a9 Q7 m9 Q R/ a
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
g1 ~0 [# @" X7 o1 C! b9 L# E" B - #define BOUNDARY "boundarydonotcross"* y4 j2 T6 H& G, Q/ q. L
- printf("preparing header\n");' `% l1 Q/ j6 L3 r. \8 Y
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
& g* v6 U$ X: Y0 a8 y - "Access-Control-Allow-Origin: *\r\n" \
( I6 G7 a- s7 _! |" N - STD_HEADER \
& ~* @' I T6 G - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
, |' j" ^9 O& Q9 A/ i - "\r\n" \3 P) J2 e/ W+ F( \; V5 j% l
- "--" BOUNDARY "\r\n");8 T+ y+ a5 L* z3 O& P7 a" L
- if(write(fd, buffer, strlen(buffer)) < 0)
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- free(frame);
' a, [- w0 s- z - return;
9 s1 N8 l: l6 u - }
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" \: @- S# [/ I s8 [% V
- "Content-Length: %d\r\n" \
- U( b8 w+ s' W z9 S9 f( Z - "X-Timestamp: %d.%06d\r\n" \
2 K. m2 c1 {. }% r+ ?: V9 D# S - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);4 t ]2 p+ M. S2 D V" g
- printf("sending intemdiate header\n");
, A& p* u5 q1 r# b - if(write(fd, buffer, strlen(buffer)) < 0)4 w% C% R" w! B T1 U8 P8 M
- break;
6 f4 U4 | u8 u# J( Z# |& m - printf("sending frame\n");- [& H2 k" u( |, f/ y- b2 l
- if(write(fd, frame, frame_size) < 0) A, }# ]6 {; v, M. S
- break;% q3 h8 A% U( z* {5 C3 z
- printf("sending boundary\n");
' E+ V0 U$ t& H/ F! Q - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");8 g& ?" i. V1 z* M/ I
- if(write(fd, buffer, strlen(buffer)) < 0)0 w* f7 A) P* q. ~9 K
- 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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5 A. a8 T2 q9 B3 n( x3 a1 F二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:/ ^+ G7 R' y8 g8 T$ d, `" M' `
- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)
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8 Z% _1 A! a+ z. h* r, b9 A - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);
6 S1 c) |, U8 ~, H9 R - if(*socket_found == (~0)): x6 a5 D2 }0 A) T* N1 w, b: H
- {6 t9 {/ _. q, ~0 X4 H( B
- printf("Create udp send socket failed!\n");
* M1 b. r+ s& k6 a4 l* h6 l" B - return -1;, O1 ^+ ?( I( g" @' P+ E
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- addr->sin_family = AF_INET;1 ?6 T# P8 W3 N# @- I
- addr->sin_addr.s_addr = inet_addr(ip);
* u& f Z- ~1 P) P w0 Z4 W. g - addr->sin_port = htons(port);
5 W! \8 K1 Y! D8 X& P0 f) x7 g - memset(addr->sin_zero, 0, 8);
2 t. K+ @: x7 J- a - return 0;
& u* V- F& v3 t8 l! W - }
复制代码
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3 x" _* y* P7 k+ m1 o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:' `, {: ~6 h0 M. Z. H5 m
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- while(fend > 0). `% `: W: b, S' s' M
- {0 O( l( l: g* K7 D$ @1 e3 D( M
- memset(picture.data , 0 , sizeof(picture.data));
# r3 X. p4 s$ t, ]; F - fread(picture.data , UDP_FRAME_LEN , 1, fp);
- Y% ~" ~1 x3 G$ U4 R6 u/ q9 {5 c& f' Y - if(fend >= UDP_FRAME_LEN)
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- picture.length = UDP_FRAME_LEN;) ^/ }' \- g0 z" W0 g' J
- picture.fin = 0;
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4 s% u: N7 p' _; H8 A8 l; V, a - else; j1 ]1 x4 z# H/ @! T1 r) d/ T
- {; R3 ^& I% O9 |8 y/ F4 `1 E5 U, |
- picture.length = fend;8 }0 m7 c& s5 z4 U( d1 s
- picture.fin = 1;3 F% [/ G2 w Y! r1 g; ?
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- //printf("sendbytes = %d \n",sendbytes);
9 }+ e( g8 ^. r" @ - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
1 a |; L! s. T, K/ k. t - if(sendbytes == -1)
; N& E9 K# W/ p& g- m - {
+ z8 D% J& ~) @3 ` - printf("Send Picture Failed!d\n");
: m! j( F" N/ p5 |% l0 i6 y9 [0 ~ - return -1;
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- else) v% y7 @4 e0 S' _# N, l( ~9 X
- {
8 M- u- S( n5 y: P7 c - fend -= UDP_FRAME_LEN;
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- }
复制代码 3 W% T& x7 \) c6 X& Q- J$ z) k
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8 B+ g: ~; x4 r& P" @iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |