本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑 ( I5 j- h4 @) P# Z6 h
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/ d. E" I7 |& 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# L) n7 G2 S9 Q8 D) W
# P* l* H' b% X& S2 L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。
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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。
% t" M/ Y1 y& w. `4 X一、HTTP网页服务器1 l+ k% f. ]7 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)9 d t( l- v+ D+ J
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- struct sockaddr_in servaddr;9 B3 i& A4 K2 M6 D8 q( q! ^5 L. j
- socklen_t addrsize = sizeof(struct sockaddr);
# I; a2 H" @) n# D; u - bzero(&servaddr , sizeof(servaddr));$ ~# R1 S7 ]- o. u
- servaddr.sin_family = AF_INET;, b3 l, \: m/ ~5 t
- servaddr.sin_addr.s_addr = inet_addr(ip);+ ?* S6 Y. z3 D5 Z7 R' s2 J& f7 P' G8 X
- servaddr.sin_port = htons(port);7 A, z x$ v, e" A$ k; {
- int ret;; \1 y; }! V$ L* L3 \# u7 N
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)3 k2 f" M6 L0 {. q
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- printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);+ p2 M c# _0 A9 E3 v: P/ V
- return -1;0 x( z' F4 D+ o3 [# d" x( v8 x
- }
2 w) u9 G8 e' B/ W - int on = 1;
0 q3 h4 _( W: w: s - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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- printf("setsockopt error\n");, L9 ^& m0 y; H6 D! y6 `/ p% z
- }
5 e9 m; M7 M, T, D" k - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
% C! l+ ]% D' }3 V9 u. _8 u+ l0 ^ - if(ret == -1)0 z- I2 {/ u2 J4 r
- {% F& q* {2 Z1 s* J, o
- printf("Tcp bind faiLED!\n");) b$ n. z- v8 j5 |0 I7 y7 V) g
- return -1;# o3 T3 K3 M7 f: E* m
- }
7 L# ?5 L; T0 }, W/ q4 H - if(listen(*socket_found , 5) == -1)
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- printf("Listen failed!\n");
D2 p+ z0 D+ h C9 v- m - return -1;
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- return 0;9 `: a$ V0 M' o& a% ~
- }
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);: ~6 z7 R4 Z3 _
- void * Thread_TCP_Web_Recv(void *arg)) Q2 n0 Y* C/ ?, a7 X. g
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- 。。。
: c, N1 U9 X0 X0 A- T1 Y - while(1)
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% [" X Y$ ?. p( O6 ~- X - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);- q- _1 u B2 ]7 N/ F# v3 n8 s
- printf("fd_socket_conn = accept()\n");
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- recv(fd_socket_conn , recvbuf , 1000 , 0);8 N$ d/ v( `5 B& j
- }
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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);! V7 n+ @8 L$ w9 g0 x& l! c
- pic_tmpbuffer = pic.tmpbuffer;9 y- R. _8 n7 r6 W0 W+ X
- pic.tmpbytesused = buff.bytesused;
6 l4 E2 f) `/ F0 V4 G: y. j - pic_tmpbytesused = pic.tmpbytesused;
! b8 W0 }1 B- b - pthread_cond_broadcast(&pct);2 Z5 c. ]8 j- \' a( C) ~- m5 [
- 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;% Z8 I: r3 t6 b* M0 ^' u5 e: t7 H
- pthread_cond_t pct;
1 G/ ^; \, m$ W - int main(int argc, char* argv[])
. e6 R8 Z( P0 D, | - {
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- TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
& W! t% p8 P+ n$ d6 ? - pthread_mutex_init(&pmt , NULL);" L+ U+ m% @" l* E$ T _! U& R
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);4 {4 ^8 C8 ~3 b/ i. f6 C/ b
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
5 [, \# s( I4 ^9 n5 s - ...
! ]: g8 `) v( W# F4 L - while(1)
3 v, |) D$ R) m& A% F. q0 m - {
9 X2 ^* O3 d0 G( F - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);5 Y5 M/ A$ ?2 u7 @0 J7 ^
- ...5 J* Y5 t& o+ L
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- ...
7 c0 q/ S- [8 } - }
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;">! U) Z3 d- z6 S3 {) V
- </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" \
. _8 E3 U) @5 N2 O8 k- A - "Server: MJPG-Streamer/0.2\r\n" \& d1 d: J" Q& D
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \) ^4 n, s1 J$ d% t9 ?5 z
- "Pragma: no-cache\r\n" \
( q ]8 S" V6 X* r" M- h o* ~ - "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"3 A6 ]4 Z0 I4 m/ Z- M
- #define BOUNDARY "boundarydonotcross"
6 g( u( y1 B8 M - printf("preparing header\n");$ ^ q! p/ L/ \ D# s. c) [7 P
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
7 P% A; ~* z6 _1 D# ^ - "Access-Control-Allow-Origin: *\r\n" \8 N& ?: D: ^/ M9 s: ~6 l3 j ?" g/ q. T
- STD_HEADER \
1 O" j8 a" ]# k* R6 s9 u7 T8 h - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \$ D1 n' l" K6 l2 P) G1 ^+ A6 x# R
- "\r\n" \
0 i" \: r; j- q- f - "--" BOUNDARY "\r\n");2 d7 k: I4 Y7 }5 \, ^' X7 g
- if(write(fd, buffer, strlen(buffer)) < 0)
$ S* w/ f+ y5 a( T" a" ]$ x2 j - {
) X8 v3 v" \& Z; q5 i - free(frame);
5 Q, ?: e. M! | - return;. {( s5 D* O; B4 a+ `4 v
- }
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" \
9 o! g( P3 P! {4 a o3 z - "Content-Length: %d\r\n" \
/ Z) d& }( Z; A1 u1 V - "X-Timestamp: %d.%06d\r\n" \* J8 B- a( `! S: D# U1 A& E
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
4 _" @7 g% q2 O N% M$ e2 g - printf("sending intemdiate header\n");/ s& k6 x) f1 [6 d: m, }
- if(write(fd, buffer, strlen(buffer)) < 0)
: J4 Z; Y7 X' n! |0 `4 b' Q - break;
a) x5 o% ?9 R - printf("sending frame\n");$ K( I0 b" {& Z& S
- if(write(fd, frame, frame_size) < 0)) M( V6 u( z8 @2 q
- break;3 K4 V+ R. q9 @7 ?6 V
- printf("sending boundary\n");
+ A; n0 ^' j B: A- m( B# n: ^ - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");) m) Y1 u& b" E
- if(write(fd, buffer, strlen(buffer)) < 0)- I; D* F. l6 i. ^+ z. z) A
- 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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' g8 K4 d) x2 ~ T3 G6 G X二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:
! ?1 D2 Z, B) \9 L- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)2 l* q6 G* J0 [, x; D+ l: Y
- { J2 \* ?* {# ^) V: {: V: O
- *socket_found = socket(AF_INET, SOCK_DGRAM, 0);+ i; N% W$ n. Q" k
- if(*socket_found == (~0)) p( |0 h/ E1 I. s u
- {
& U L/ ^5 i, \! ?5 R - printf("Create udp send socket failed!\n"); U8 W) K8 K! h8 g! r( r2 z
- return -1;
$ {' k+ a3 E& l% R! E6 t4 P" G# b - }
1 j; [: r9 |; Q9 g# U - addr->sin_family = AF_INET;: ^3 \& k5 l/ R+ t) s0 C4 ?+ r
- addr->sin_addr.s_addr = inet_addr(ip);2 l( U# J9 M: h$ ~! Z! k( n) u" \
- addr->sin_port = htons(port);
: }6 M8 v" ]6 m9 I# I, k K3 f5 \ - memset(addr->sin_zero, 0, 8);" U: U6 l& E n# h
- return 0;/ K/ D* D/ ~, B J5 y% P; r, s* Y. T
- }
复制代码 , n2 Z+ P+ m7 o( |8 `7 @
9 c8 N9 }% r: D8 t# o: N, ]1 Y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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- while(fend > 0)* v' e; Q# _" `& L
- {
7 i7 n |/ u. a0 g# z% @ - memset(picture.data , 0 , sizeof(picture.data));' r: f2 B) F+ S' {
- fread(picture.data , UDP_FRAME_LEN , 1, fp);+ X1 S8 G5 X& J$ T' t! Z; ?
- if(fend >= UDP_FRAME_LEN)
1 `( H% F3 a0 @; g s - {# {8 f4 h9 }: y
- picture.length = UDP_FRAME_LEN;
9 @- d) n/ w3 R% r3 E - picture.fin = 0;* p9 v$ @& k3 J) x0 w5 q& r
- }
: E& J! Y; }6 [% ?" R - else
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- picture.length = fend;8 f; i" D9 Z3 A+ B2 u2 o
- picture.fin = 1;3 c8 D7 |+ Q( F7 w+ P7 C
- }) O( T: \; H4 V& _4 c% _
- //printf("sendbytes = %d \n",sendbytes);% X/ e: a; q% \( u
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
0 i; U! d- e J: u - if(sendbytes == -1)# Z) b) N# t% X9 i/ l
- {
5 e0 S; h8 `0 T3 O5 v - printf("Send Picture Failed!d\n");# w3 u8 g k& s0 t2 z2 O2 a
- return -1;" _* t n8 v, f; G+ [: a$ n# `
- }
5 F g. ^' T) D) Z/ G$ C' A# M - else) N% y9 X- d& @% c% W0 w6 r1 m
- {
3 P' B+ Z+ D" t - fend -= UDP_FRAME_LEN;
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- }
复制代码 3 f! ^* x8 G* o9 M6 g1 K# w
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$ v: x. H6 A2 n' j& u$ AiMX8MPlus 核心板: https://www.forlinx.com/product/136.html |