本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑
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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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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。 + u" q0 m9 `2 p3 U% j

& I3 S& `, ]; u% 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。
- y- {) f* d6 x0 \' {) J一、HTTP网页服务器
$ c2 c0 [6 s% L! _, F/ t& I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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! m( K1 d P; ^4 \- f' _ - struct sockaddr_in servaddr;$ Z' i3 v" x( R
- socklen_t addrsize = sizeof(struct sockaddr);
: b# ^# E% \) N$ U+ m - bzero(&servaddr , sizeof(servaddr));
5 u# \5 f9 k6 m- e* N5 l' | - servaddr.sin_family = AF_INET;
* M: F9 v4 D& A# ^, F1 U2 ^ - servaddr.sin_addr.s_addr = inet_addr(ip);
8 c, R9 G4 k7 O1 ^+ c# j - servaddr.sin_port = htons(port);+ C& Q( X1 N" M% S
- int ret;* B9 n1 j7 v# ~1 u1 D% a/ J
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)
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- printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
5 X3 G% y' C0 u6 h - return -1;
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- int on = 1;
0 R" B( r8 S$ U - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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* K9 z" S* j5 f0 E4 T4 w - printf("setsockopt error\n");
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- G6 D) m5 a8 c% } - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
% v' H: [, E, x" P# q. R" [7 D$ m - if(ret == -1). z0 _# b d$ H/ }
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- printf("Tcp bind faiLED!\n");
. ^8 [" k1 l: U - return -1;9 @! U4 w/ a) d x9 O2 ] C
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- if(listen(*socket_found , 5) == -1)
]+ A N* S9 N - {
7 d- h6 s1 z6 M1 ^3 d - printf("Listen failed!\n");& R }* d$ [2 X% k5 B
- return -1;
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. @* v/ P& U0 ?. i6 V - return 0;" M& R! N$ f Q; v" g
- }
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); d3 J2 o/ W+ D% n
- void * Thread_TCP_Web_Recv(void *arg): x: G) X$ n/ ^3 S
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- 。。。
. q6 b8 E; s- @! l, f% j - while(1)
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6 u! s2 ^$ G4 o* A - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
& y) [: F8 s& w- R7 u* I5 Q# ^ - printf("fd_socket_conn = accept()\n");. Y4 R" j: ^! V8 U
- 。。。, u4 I, U7 k' t# T6 P9 ^
- 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);
9 n! t( ?' g& y8 S - pic_tmpbuffer = pic.tmpbuffer;
0 s+ l2 M0 u7 H, u5 } - pic.tmpbytesused = buff.bytesused;
1 j! h( p4 i, x! v6 n: V - pic_tmpbytesused = pic.tmpbytesused;1 k! J) m3 T2 _' L+ s3 `: p1 A
- pthread_cond_broadcast(&pct);
+ g' K- {4 p1 f4 {, |9 V - 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;
; s F0 f8 v% k8 P - pthread_cond_t pct;# I6 E% {- h$ Q( x- z
- int main(int argc, char* argv[])3 t l5 C3 ~% G) F5 d
- {
% A$ b0 p( O+ h3 R$ V - ...
5 ?0 Z9 K' v& L1 b6 O# k9 [ - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);/ n/ s' Z! y1 @8 m& N
- pthread_mutex_init(&pmt , NULL);
$ @" p/ G& S7 L - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);9 J+ K& Q& v* W* y/ C/ C
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);! z+ m7 h' F# |9 H+ M( T
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- while(1)8 [8 j4 J+ c! R! a) w2 [
- {
6 Y1 P& E& Q7 B7 u0 p; g& a* l. H$ | - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);
+ ~0 X) A+ \, ~1 B4 |% {% w6 P: q - ...
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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;">
# F) ?, Y7 `. G- G - </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" \
& p+ s/ P3 r8 v( i, z - "Server: MJPG-Streamer/0.2\r\n" \! z4 ^0 q0 ^- A4 l9 Z4 T, P. F
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
# H6 C3 n3 N# C5 X - "Pragma: no-cache\r\n" \
& h' U/ t5 I& K7 G/ p - "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
- t W3 l0 S( J$ b2 r/ E - #define BOUNDARY "boundarydonotcross"
3 P) X; L9 `) K' Y - printf("preparing header\n");9 G: V/ `( E. X) I& t3 j8 ]' [
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
; k9 O; u: X. ?$ B" b6 N2 L - "Access-Control-Allow-Origin: *\r\n" \
: V# ]6 Q: u- s$ ], l3 M - STD_HEADER \' _: o/ P( U' z% a; [4 p( u) n
- "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \0 r8 A1 N6 G4 T* @8 Z9 D2 c
- "\r\n" \
' [1 L; q M6 x! u! C2 S* L - "--" BOUNDARY "\r\n");: I$ A6 ?4 @9 L- B# V; l
- if(write(fd, buffer, strlen(buffer)) < 0): ?/ O. ^ l" @. l! j) z
- {
9 w1 ?4 f p/ A& z9 X% g* X - free(frame);
9 x1 t+ ?. w) i - return;
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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" \
V* [6 k: a$ J2 R4 G - "Content-Length: %d\r\n" \ |6 v2 n4 J# R, ?& ^* l4 {
- "X-Timestamp: %d.%06d\r\n" \
. B+ N, W L, h0 {9 J - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
& r5 \, `9 c% `8 {/ s2 c+ F: f - printf("sending intemdiate header\n");% A, e6 d; z) m) i7 f& v
- if(write(fd, buffer, strlen(buffer)) < 0)4 p2 ^ g% A6 t8 u4 u! x& }# |3 ?
- break;
2 R: w7 w1 P5 @- b. @9 \3 M1 h - printf("sending frame\n");
5 F3 F/ p# m3 K5 B+ J - if(write(fd, frame, frame_size) < 0)
! t: g; L# Z7 P* i/ T7 y5 Z - break;
' O! t2 t( `: _" @4 Q' l - printf("sending boundary\n");
& `. U7 \; e6 A) G' U$ ~! W r - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");) s, V6 z L% C- }( t
- if(write(fd, buffer, strlen(buffer)) < 0)
/ n C( B( [% J. M& E8 U. u) W - 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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+ o* b, p' s; n二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:9 j( z$ M9 W3 }5 A
- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)/ W8 z& U4 W0 O7 b! g! D
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- *socket_found = socket(AF_INET, SOCK_DGRAM, 0);
3 K( h7 y9 k8 b+ w) i' X% z7 f - if(*socket_found == (~0))
/ O7 @8 k. B3 Z6 C( j# Z1 o - {
9 v" t: i9 J3 j$ q! U- l3 r7 p - printf("Create udp send socket failed!\n");
- z2 }; L, ]3 s8 h1 B/ L& ? - return -1;2 f2 n" R: Z9 v* y/ u+ m; ^
- }
$ d8 E$ O$ ^6 D/ \9 L7 l9 l) s - addr->sin_family = AF_INET;
8 T: D# i4 t7 x& m0 k+ h$ I - addr->sin_addr.s_addr = inet_addr(ip);
) I3 w8 ]! w% B& q - addr->sin_port = htons(port);
5 R: U+ h2 _6 f/ p - memset(addr->sin_zero, 0, 8);9 G: D& r1 R' q+ W. C
- return 0;
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复制代码 " a; H/ \7 T& S' A; Q' Z% k3 q
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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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9 }2 _% l# ]! S9 o& S- while(fend > 0): N) d* H7 c z9 t! {
- {
: X* P/ J9 N5 T( r9 Z" I - memset(picture.data , 0 , sizeof(picture.data));% F$ b- r* W i8 z
- fread(picture.data , UDP_FRAME_LEN , 1, fp); I0 }8 q3 C0 n5 Z2 B! y- @
- if(fend >= UDP_FRAME_LEN)
% u: y! x* J2 J, P1 c" K& d% ^ - {
N" Y8 u3 Y* g - picture.length = UDP_FRAME_LEN;
2 u2 k3 f( R: J! Y - picture.fin = 0;& f2 E3 f8 w I. ^1 V
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- else
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- picture.length = fend;* v6 x0 a6 |: Q Q/ O5 p4 a
- picture.fin = 1;$ _& @) V. M8 C- C7 d0 e' Y* f
- }
2 G7 z+ r2 ?+ {( `5 N1 Q - //printf("sendbytes = %d \n",sendbytes);
, h/ H" H' w0 ^4 ?" j& u! Y - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);( ^8 ]! e, n* S- K
- if(sendbytes == -1)5 q$ O$ O( D' _& w& K4 i3 y4 |' o
- {- B @2 ^9 T# Y& u9 z
- printf("Send Picture Failed!d\n");
; n7 Z: j% H9 F1 {, K/ n6 ^ - return -1;
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- else
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- fend -= UDP_FRAME_LEN;; J& A+ c, ~8 F: o1 k1 [
- }6 v5 u" b- h T6 y7 ]
- }
复制代码 : j8 `! o5 m' E! D8 U0 g
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3 P8 [3 d" h/ n, ^4 {* f. e! MiMX8MPlus 核心板: https://www.forlinx.com/product/136.html |