本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑
1 F8 i( f Z3 C7 Z5 V
* M1 ^ y! P/ l) U
" H8 Q! G: S* A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" L" N& F X) F' l& Y
% v9 C* m7 s3 Y8 _0 g! u
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。
} r" s9 |& v: j/ F1 d }8 X5 @) f- }4 ? L, y
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。 3 V* {. j- S, W+ ^" g" I
一、HTTP网页服务器. n" W1 i+ \3 b# |( }- V
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)* @1 B3 v$ U5 ?4 z& `5 [( L
- {( A: \" S2 M `+ _, b
- struct sockaddr_in servaddr;
' C8 Q" p) Q5 d/ i2 N, q3 i - socklen_t addrsize = sizeof(struct sockaddr);: j. w0 u O/ G% w) G
- bzero(&servaddr , sizeof(servaddr));8 x! o4 p$ s6 z: m+ \$ G4 o
- servaddr.sin_family = AF_INET;) r5 u, `9 {; O/ A. g
- servaddr.sin_addr.s_addr = inet_addr(ip);
/ |3 d! o: [, d4 }0 z - servaddr.sin_port = htons(port);
; W0 _ c/ y% B5 O; F& l* b - int ret;
1 r$ J4 P/ L; v - IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)
7 z7 m# j+ i( ?) J* N& F9 G - {
0 q4 t1 [) D( R% { - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);$ g2 u7 |0 x! X* d4 p
- return -1;
% e7 q3 p" E0 A( ^# G - }
: c5 ~6 E6 @$ u7 r0 E7 p5 e - int on = 1;
; p3 v1 p* d d - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
) r E0 t3 h% T - {
% K5 s+ Y6 }' I - printf("setsockopt error\n");: q X/ ]5 O7 d% K
- }& b+ r" a( ]& c* k. x6 p
- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);- B$ P( M$ ?9 b r0 _7 `
- if(ret == -1)
3 s+ X% L+ Q5 M1 { - {" G/ G! E5 y& ~) R1 Y
- printf("Tcp bind faiLED!\n");, D& x' G' U: t9 k. J% H: i5 ]
- return -1;
. h0 {& }* l* z/ }2 A4 Y6 z; w, S+ C - }. ?" k8 }" P; h( x6 R
- if(listen(*socket_found , 5) == -1)2 R) ~5 k5 f2 i
- {: G5 y7 V1 q, |% Y5 T/ m( @
- printf("Listen failed!\n");; _* L Y8 D0 a6 M: B
- return -1;
8 q3 Z% b0 F) ~$ H% ` - }
/ A. p( l9 [. W - return 0;
6 F! I) [( G2 K1 i* E - }
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);+ I& A9 i- j8 i' l& k$ x4 J E
- void * Thread_TCP_Web_Recv(void *arg)
$ O5 } D& H; \* `; \+ j - {
2 F) o5 H G+ P. ?$ @. D - 。。。% u2 y5 ?5 `% O. }; G+ E
- while(1)
$ y" g% h$ p( L' z+ g - {8 `( w, w9 `, l
- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
4 i8 W* P B5 G2 ^ - printf("fd_socket_conn = accept()\n");
* ~) x% T4 b1 k* A. i - 。。。% u0 b: h2 w: F
- recv(fd_socket_conn , recvbuf , 1000 , 0);, R, k; ~, q5 A8 r" z0 G
- }
' K" D4 A1 a/ X5 Y r) O: s& ?2 u - 。。。
2 X, r9 T3 l; @/ ?- Y - }
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);6 x+ Z( r/ M- E
- pic_tmpbuffer = pic.tmpbuffer;4 c4 t0 }0 y Z, ^7 o* J
- pic.tmpbytesused = buff.bytesused;' a" u# t) ^6 ~8 \
- pic_tmpbytesused = pic.tmpbytesused;
- D& L9 K' a( c# ?& h( x - pthread_cond_broadcast(&pct);
8 x, N" P6 V& z; g8 _! h, m - 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;4 \7 _- @/ p% v6 J1 [
- pthread_cond_t pct;
9 E6 r8 c5 C8 B. R" a$ ?+ g" o. d - int main(int argc, char* argv[])3 c( h! ]0 H9 k* `8 B
- {
; j) D3 X7 I" h( A - .../ W4 S0 u' |( F& T1 G
- TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
. r x. N1 d5 q8 n& B# K' e2 C. f - pthread_mutex_init(&pmt , NULL);7 p; ^* G5 d- B- ^$ W/ F
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);$ v- ^; Z; ?: V
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);, N& c: k4 V( @- ` l6 ]1 f
- ...4 \% L {3 Q: d, M& E H1 u: x
- while(1)
9 y' N0 _2 }% f1 u - {( `" a3 Z% ?. k$ h) b
- V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);
O; H: T' n4 j% ] - ...7 L$ R, P* i. W5 n1 I
- }* V- ]. G* A. K0 ^( {
- ...
( j0 ~& \# |: U9 j6 J - }
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;">
/ A# y/ d) S/ G2 j. q" n% q - </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" \
3 L) y! r1 _( t2 v9 C9 n - "Server: MJPG-Streamer/0.2\r\n" \
9 h) |) f" o* c1 ]5 z - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \$ R" V8 g0 Q, t) T- z" o
- "Pragma: no-cache\r\n" \
0 ?4 F0 Z1 @% O# Z! }9 ]1 _ - "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
+ N- N9 M. s) q% y b/ R, e - #define BOUNDARY "boundarydonotcross"
; D9 W. W+ j8 \% W+ J+ C" i - printf("preparing header\n");9 X3 M: o0 J/ q- c5 R+ |7 j( V
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
9 T2 T5 q( K- Q& @) }' V7 a - "Access-Control-Allow-Origin: *\r\n" \/ F4 ?& V7 `, b4 M
- STD_HEADER \
% \: ~/ e9 W# Y+ u - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \9 E, `7 L" o9 L4 y% A; Q! y
- "\r\n" \8 D( f/ |, Y4 m9 n" n
- "--" BOUNDARY "\r\n");7 H; E9 t% b D' ^
- if(write(fd, buffer, strlen(buffer)) < 0)9 b+ ^- {% i9 s6 P
- {
' o8 |, U. y5 v% x - free(frame);1 v: s7 o, \& m- [/ W5 Y' k6 w8 G& I( F
- return;) o5 I. j1 K3 q; ]0 q- x9 k
- }
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" \8 q4 P6 _( V+ i5 d
- "Content-Length: %d\r\n" \' T3 Q1 s) I/ d4 \
- "X-Timestamp: %d.%06d\r\n" \
) ?$ r) ?9 M% P+ ` w - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
4 T8 n; _0 g2 a$ H - printf("sending intemdiate header\n");2 }1 p: ^8 R, i: O
- if(write(fd, buffer, strlen(buffer)) < 0)5 n4 B' w a3 z4 J4 C+ u6 {
- break;7 F' s7 S O% b% R
- printf("sending frame\n");
* A3 }3 o1 b x% [. K5 l2 F" q6 o - if(write(fd, frame, frame_size) < 0)6 Z+ j' m& X4 T+ q8 M3 J3 ?
- break;
2 n" z( I m4 s; c+ _# t2 ~) R4 K - printf("sending boundary\n");
' Y6 b1 c& g2 ]6 F& a. m - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");" v% w. g- M# |# Q r
- if(write(fd, buffer, strlen(buffer)) < 0), A, O, ?+ K+ u8 u
- 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。  - O8 Q7 r2 q& J8 E& D. d0 H
 - B$ |( Y. e) A e
二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:( z3 z" k" d% B! a# [' J* x
- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)
4 x( v5 } Y$ k9 R+ R - {
& [- k p" N" G - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);7 R3 T$ F# `0 y. C# s
- if(*socket_found == (~0))& N ]. o4 s* ^6 l. F
- {
; V4 u- {" i, I" w( ~7 l - printf("Create udp send socket failed!\n");
4 [& M/ X! e" {6 Q: A- ]) e' M - return -1;0 D+ \1 v" B+ F" Q- s0 g5 P; D' e
- }8 ~4 [/ ~' b% f+ J ]: X
- addr->sin_family = AF_INET;. {* H' H9 l, V h( C* c
- addr->sin_addr.s_addr = inet_addr(ip);' _8 U% J1 Q" n) N
- addr->sin_port = htons(port);
+ G% ~9 Z1 |8 a6 M - memset(addr->sin_zero, 0, 8);: D+ W: m% x3 Y
- return 0;- N: i4 m$ L& r" N
- }
复制代码
5 T5 o# D) Z# w6 |* B5 ]( @6 d/ H. B; y/ G0 Y& O2 E
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:- p0 G9 U4 K( z
7 K% |. h4 }3 p
- k) e h* u/ `
- while(fend > 0)9 g1 T1 J6 g3 U9 [. f7 w" w
- {" r# {, N( f% W T' }) T9 M* b
- memset(picture.data , 0 , sizeof(picture.data));3 Q- e0 g! P& q5 \7 K I$ o+ g
- fread(picture.data , UDP_FRAME_LEN , 1, fp);
% A W T( ~1 I - if(fend >= UDP_FRAME_LEN)/ d% d; Z) d1 z) X' G0 K( f+ p
- {
& R2 D$ i+ V! }" ^1 \0 Q! u- h - picture.length = UDP_FRAME_LEN;
" l& ?4 X! k' d" x6 l+ u5 s - picture.fin = 0;; U) m/ F8 \( D: |
- }! w# D8 A0 t6 m) _5 R6 E$ ` z
- else
( J/ [: p, q* n& c1 Y - {5 R2 z; ?4 C- m* p, |4 s$ Y& h
- picture.length = fend;
4 Z- h& P$ y1 z! }; r! P( O8 r - picture.fin = 1;
V- r/ o7 A6 `( \2 a - }, N7 r5 w: M9 }+ p* {
- //printf("sendbytes = %d \n",sendbytes);
5 a2 U# S5 a; V- C - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);; R; t+ }8 ^3 G4 _
- if(sendbytes == -1)9 d* L+ S! L, n: Q7 F i
- {
) k( w( P- j7 b1 @; v - printf("Send Picture Failed!d\n");
2 A: j& Z- j" g- E - return -1;+ {4 d" Q0 g5 ?; [1 E1 M* J
- }# \. s: \. r1 U" p ]
- else! t) t4 x9 L" \- y* y1 b# Q& O! O' c
- {, w- U# k8 L+ k- U: `
- fend -= UDP_FRAME_LEN;) `: {! J3 m& P, Q
- }0 o6 V; E- O( u9 f
- }
复制代码
: }" J; u& c0 G, x2 N( W. K) E. p4 J" ?& f

$ H' M1 Z; n, E2 [5 Z6 R7 f! @- C
, {. s0 H# \# R( `0 F2 UiMX8MPlus 核心板: https://www.forlinx.com/product/136.html |