本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑 ) o0 p- n/ m. N) |5 Z; _
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. W" |: k6 e3 @+ o7 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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8 p. H" M Y- b$ S6 F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。 : Q! O# s, e ~+ j

0 n& \7 ^4 X" }; ~/ ~& n9 x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。 / S( I; w: Q4 S
一、HTTP网页服务器
5 s/ F9 b5 u9 G1 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)
$ v6 \+ }# b3 j - {
( ^& H% J6 ?4 \0 ?& L - struct sockaddr_in servaddr;$ h: [! N. Y& R* ^, j/ y; h
- socklen_t addrsize = sizeof(struct sockaddr);! M! p8 b! `- M; p, L9 j
- bzero(&servaddr , sizeof(servaddr));8 W- w8 { f- O4 t+ r
- servaddr.sin_family = AF_INET;$ ]7 C" b" Q. H
- servaddr.sin_addr.s_addr = inet_addr(ip);
6 u7 [: \+ }: R6 `& O0 Z. j - servaddr.sin_port = htons(port);- e, ]9 u0 Y6 n. {' a1 _
- int ret;
1 h2 q0 ^ F6 I [. N$ T$ @7 P8 ? - IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1) f3 h3 l9 B, U8 p. ^( K
- {! G; a0 z* L1 C
- printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
4 ?; P% K1 b, c# O - return -1;" _& r4 Q7 Y- u; E: b/ X
- }
; ^3 A/ _, h& n8 T/ u, f6 s - int on = 1;
" G1 A# g* H( I2 v; ~- K" D - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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- printf("setsockopt error\n");
" M+ A; w! l0 m, t3 _9 q - }
# f1 V1 `- b$ i! w2 T. y - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);( j0 O* m9 d' S# h% j
- if(ret == -1)5 ~4 Y% N7 e5 H$ j
- {
% n9 b$ K; I, a - printf("Tcp bind faiLED!\n");
0 U$ `; T8 j8 p. d8 i* R - return -1;( w. e$ @1 K1 Z( V
- }
9 d6 O5 D- Y8 P4 ?( B - if(listen(*socket_found , 5) == -1)
/ F: l, C5 m) _+ a% V, u& N# j1 g - {
% U% ^- `5 k3 W% {* w! ~( N1 f0 d - printf("Listen failed!\n");
+ e9 C* c+ T. D" P6 p5 o: z6 r) E- ] - return -1;- Y6 P) ~3 `: h* y. W9 D& r
- }
! J4 g- f2 V$ ~# [ - return 0;( T$ l h2 o; C1 u" V9 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);+ |/ W2 R3 @. k
- void * Thread_TCP_Web_Recv(void *arg)2 f6 b" l( v1 |/ x! U; E
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- 。。。8 i6 M) K$ U0 C) }' p
- while(1)( d( L/ W# p' R* }0 F1 Z, e
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- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);" p7 z2 G% X( B$ j" C2 ~0 D
- printf("fd_socket_conn = accept()\n");
- u* y: w8 p, L& v: s3 m - 。。。
6 q( C+ ?6 e+ G: J! a - recv(fd_socket_conn , recvbuf , 1000 , 0);, z/ a# W# n' ?& A4 p4 w
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- 。。。
4 r3 M s: T+ C8 M" o - }
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);% I- Q( p( o+ h- \- _
- pic_tmpbuffer = pic.tmpbuffer;! B" B# l1 q1 M: G4 F" C, T Z
- pic.tmpbytesused = buff.bytesused;/ t: ^% @( _& {/ L5 }
- pic_tmpbytesused = pic.tmpbytesused;
: x8 f8 {2 j6 D g - pthread_cond_broadcast(&pct);
% w% B( Z+ j* C3 _1 v7 O - 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;( G& Y3 L- v. \7 x' e
- pthread_cond_t pct;
0 c* _: C, p$ w2 C- e - int main(int argc, char* argv[]), y8 ]5 q" n0 s& H& x g
- {
2 ~+ e3 h$ b/ t' j6 [5 n( K( x" b - ...
" X- C& G1 U7 `6 F# H6 S - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);+ g3 S n7 i. p: N& A
- pthread_mutex_init(&pmt , NULL);3 m: B% h; I/ b
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);
1 S% {9 q# V( c# ]; c- K4 p - pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
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- while(1)
- n1 k; f8 E' x% F9 O - {
8 a: N: f: I _: }% y - 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;">
2 s/ l4 ?/ Z( T9 [4 J9 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" \" L$ Z; Q' v" U1 M {0 R& d
- "Server: MJPG-Streamer/0.2\r\n" \7 z8 a: t. e) W* Y, \
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \: r# i1 C; H J+ W2 q: m' W
- "Pragma: no-cache\r\n" \+ j; x( u1 z5 g" `
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
6 P! @1 v e6 w - #define BOUNDARY "boundarydonotcross"
# T, z$ t: O# U& y1 i - printf("preparing header\n");0 y' X' |1 N3 t" r6 ]
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
& p0 H( \! A( L) i" S0 Z - "Access-Control-Allow-Origin: *\r\n" \
: {1 |- y0 N& q5 M( C3 Y - STD_HEADER \
6 D! y5 c- Y( K - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
. V1 {' v% u8 F2 ~0 g3 ?6 I S - "\r\n" \
# ~& L$ |1 W1 ]9 x2 ^ - "--" BOUNDARY "\r\n");. R- y/ w# B0 |- P8 l
- if(write(fd, buffer, strlen(buffer)) < 0)3 y* ^8 w% y( |2 z. e
- {- o$ `2 Z7 Q+ z9 D3 U$ D' k. f8 K
- free(frame);
1 k7 g; W/ @9 n* y - return;
5 t5 S- f. O3 {0 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" \* I' t7 ]# r* }
- "Content-Length: %d\r\n" \
& r/ O9 c: I* O- U' z- G7 ^1 j - "X-Timestamp: %d.%06d\r\n" \
: y2 e5 x5 h! K; Z% H - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
9 `4 y o) T4 c - printf("sending intemdiate header\n");4 F, C4 J# M- o! v: e4 y
- if(write(fd, buffer, strlen(buffer)) < 0)% x0 V/ C) {7 T9 `4 V. y, D
- break;
. i9 }" P; ]9 \" o% i - printf("sending frame\n");- s4 o- D. `* Y. h {6 y
- if(write(fd, frame, frame_size) < 0)
, J8 x9 Y/ J! u/ ] - break;
8 c# s- M$ S0 d% A! i: ~- [& a - printf("sending boundary\n");+ ]5 z8 Q7 E0 R. ^$ ^. ?+ e
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
I* y7 J" L5 C% j - if(write(fd, buffer, strlen(buffer)) < 0)6 O/ S- b; x8 f' P+ l
- 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 z" g4 c* Q, c5 Z9 [

: c. Q X( X: G0 U$ E7 k% T二、UDP上位机UDP发送操作,同样需要先建立UDP Socket: \: l2 Z. P5 |+ y" ?
- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)
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- *socket_found = socket(AF_INET, SOCK_DGRAM, 0);
C$ f/ V- ~7 m, q - if(*socket_found == (~0))& O e/ u9 K" x6 ^4 s6 J
- {& I# ] }; z. r6 @: f$ V
- printf("Create udp send socket failed!\n");) S% Q- o M# o5 |: u, f
- return -1;+ J8 ?; c: K% n- p4 |6 \. n: l
- }
, j% v8 C- f& N8 Y7 z+ H G - addr->sin_family = AF_INET;
0 b; f8 n4 E" `1 T% M( M$ W - addr->sin_addr.s_addr = inet_addr(ip);0 z1 j* R) h" ?
- addr->sin_port = htons(port);
- V2 G% F9 b3 V% f& W - memset(addr->sin_zero, 0, 8);
/ c8 {' Q& V6 Q; r4 t' } - return 0;
, i! r$ h( K& G1 n/ [) o, o& P5 B - }
复制代码 % ^$ W: O1 m: h4 ]2 b q! ^: {) A
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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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7 L( R( O! i) I8 _, p9 l- while(fend > 0)! `7 Q1 M, s6 }3 \3 x) O1 T
- {
' Q; c- g# X2 s8 g - memset(picture.data , 0 , sizeof(picture.data));& u0 l* x' u" v
- fread(picture.data , UDP_FRAME_LEN , 1, fp);
1 T% O' T: N& d - if(fend >= UDP_FRAME_LEN)
m. [1 n) ^# q% ~( I+ i8 w - {
4 m4 S& R5 t$ L' M E: ^# _ - picture.length = UDP_FRAME_LEN;) g. n4 k5 f d
- picture.fin = 0;0 O! C9 B( n$ b2 H% m# K, Q- [
- }
: w+ @+ F+ w H9 [4 N - else
! t/ F& q! q) [8 { - {
( o+ k! L2 x" t6 e! }' E# H - picture.length = fend;+ w, B, K" ?; Y8 s, a% R9 D/ i" e
- picture.fin = 1;0 V! p7 m9 n; @1 v: {( W) ^& v
- }
: H6 s) z" h" U( m+ d0 g - //printf("sendbytes = %d \n",sendbytes);
; q- y: h; m2 d% s3 f7 s - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);9 X! Q) g% ]- P; f) D4 \6 R4 Y
- if(sendbytes == -1)
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- printf("Send Picture Failed!d\n");
3 f6 ~7 J. \# M, N& g2 w D - return -1;
' K2 m G% M# {8 ?1 U& Z - }
8 R* S+ ]( \' B - else
" b S- _* s% c. c" W5 ]) x* Q; D* G4 j - {
3 k1 A+ Q8 p0 F+ ] - fend -= UDP_FRAME_LEN;
4 y p, @4 Z# c. s4 F- O" S7 I6 F - }
- `' y9 z0 T9 }7 H) K - }
复制代码
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2 e8 r }( F5 f; J' W+ GiMX8MPlus 核心板: https://www.forlinx.com/product/136.html |