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: n) G1 t. x' t

7 ~9 w8 r( P3 k$ K! G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。 : L- c; A* u- k+ ^" k
一、HTTP网页服务器/ | B/ Z, w' @' v c) U5 d" j
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), s& Y& E5 S+ }9 R( T$ L/ w
- {3 |1 B# ]) e+ M. @! a3 }1 g6 q
- struct sockaddr_in servaddr;# e: M8 E8 k9 s! \" n, V7 N
- socklen_t addrsize = sizeof(struct sockaddr);
$ Y J' ~% L m( c$ Z) @( Y" R - bzero(&servaddr , sizeof(servaddr));
8 w- [0 ?: u/ [1 y! \! j - servaddr.sin_family = AF_INET;8 P1 C- r9 q* b/ S3 S
- servaddr.sin_addr.s_addr = inet_addr(ip);
% d$ x1 }, J% J. ?/ C2 X - servaddr.sin_port = htons(port);
9 J0 {& u c& d) s7 L, G* E) S - int ret;
2 ?$ S; I: f% o( K$ v2 l: P, L - IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)+ v, q' M8 K S
- {
: V) }6 s- [ Q" G - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
& o7 y6 r% q& q0 | @' D3 w - return -1;2 V3 w1 o u8 h& h5 B$ j2 c
- }
+ t/ {: X O. D* | - int on = 1;9 O4 l6 ^# ]! r h$ X/ W
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)! P" e' |% J9 @, t7 U* m# \% H2 |
- {
# e8 v3 M4 u- V) T" g$ H3 j/ X5 g, D - printf("setsockopt error\n");: ]) _ C% v! @" j# z( Y
- }
/ s, p# N. m1 B, R% f$ H - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
, m* k! k" v7 z; _' {6 A1 J - if(ret == -1), x% y, ?1 J5 a2 m
- {
% h O2 J3 K- h - printf("Tcp bind faiLED!\n");# f/ Y z$ b+ t: \, {
- return -1;7 V! F9 ?+ z Q" K7 P" F! d$ f
- }
9 F/ L- u, x3 u. i# {/ C$ c$ K# { - if(listen(*socket_found , 5) == -1)
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- printf("Listen failed!\n");
6 p& O( _9 H# c! p# K - return -1;6 x! v9 C: U1 V
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- return 0;$ x9 T. i& C; [# q
- }
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);
3 R, H! w e' `0 ]* W& _+ a$ o - void * Thread_TCP_Web_Recv(void *arg)0 I5 M' o4 Z. q/ _$ U' w' t2 p
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- 。。。
. ]+ B0 X0 X/ Q: T4 s+ _ - while(1); y/ V+ m5 H/ Q, u8 m
- {
l! I6 I* D- e$ ? - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
. w/ N0 _4 w" z+ G" N+ B# h4 r - printf("fd_socket_conn = accept()\n");1 n+ x `5 i% G- a3 M
- 。。。8 s) W: e5 K+ B# |
- recv(fd_socket_conn , recvbuf , 1000 , 0);& \- I! V3 Z5 y( W4 k+ r" y4 y
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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);$ \( `" o- z, X( f3 r
- pic_tmpbuffer = pic.tmpbuffer;( m$ `/ [. g& s, `& P
- pic.tmpbytesused = buff.bytesused;9 ~/ l1 H* Y) }$ |+ h3 \
- pic_tmpbytesused = pic.tmpbytesused;0 d, |( _; c) q/ ~+ K) W5 Y! s
- pthread_cond_broadcast(&pct);
8 d) j2 ~) x% f0 T# U - 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;" m, F" ^0 z6 F6 w- x
- pthread_cond_t pct;
; t% V. k0 M: M, H3 Q8 z - int main(int argc, char* argv[])
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- TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
' A) f, f4 Y3 @9 v - pthread_mutex_init(&pmt , NULL);
7 a" L+ Y0 z4 w; P% u/ B( D) _ - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);. i A* p, P/ U
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
- R5 Q. P) ^9 b" Q" B - ...
) n" a- V7 X1 u$ h" J - while(1)! }3 E! z4 p% u) U' {8 J* g
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- V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);
' `4 u9 j5 c2 w' e - ...
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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 M( [+ Q5 H( J' F* X$ 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" \- A# `2 O% [! J: ?
- "Server: MJPG-Streamer/0.2\r\n" \
; C* t: [2 O- E7 Q) P* u - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \& F6 z3 [! j1 N5 r) P
- "Pragma: no-cache\r\n" \
: q. }) {1 H$ z9 B2 G+ M, G - "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"9 o* _/ z+ l$ \8 [/ k, P( k) f( o
- #define BOUNDARY "boundarydonotcross"* k9 x% k2 h" V) W: O$ g; T3 e
- printf("preparing header\n");3 K" V! u; T% b+ ]( T
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
: y8 ?1 j0 ~( s0 m- s3 y - "Access-Control-Allow-Origin: *\r\n" \
j2 E, @: @% R1 [- Q - STD_HEADER \) t$ f7 ~0 m( I+ q' C' n, `
- "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
& E* v+ [7 D9 p+ I* [" S - "\r\n" \
" l! Y7 r+ L- S% l/ @ - "--" BOUNDARY "\r\n");: B+ K- g+ n! T0 i8 |$ j3 `# R
- if(write(fd, buffer, strlen(buffer)) < 0): S0 \! \7 G- E) z8 a* G
- {' G- F, y* j1 _* }$ r8 \
- free(frame);. X' t* Z6 r3 G9 p6 K {! }
- 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" \; T3 G# R$ R3 n
- "Content-Length: %d\r\n" \& o, C2 d% j! [1 z( |6 z
- "X-Timestamp: %d.%06d\r\n" \& `; H. F5 ^) s) u% _
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);! C( G* X/ x- s$ U+ e4 T/ a
- printf("sending intemdiate header\n");
0 S* _: u0 @( y6 r4 M2 F - if(write(fd, buffer, strlen(buffer)) < 0)
, O- P4 E* T( b& v5 R- P - break;- x0 R# _ f" t& [% `. S% X
- printf("sending frame\n");2 o) g# C* E& S4 l7 N
- if(write(fd, frame, frame_size) < 0)
6 b2 a6 s9 `" p) |1 ?) C, z0 w - break;
3 x7 o5 _) f i& } - printf("sending boundary\n");+ S2 Q# N! A {! F5 r8 v6 ~
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
3 c% g: U; P" w6 |2 T0 s - if(write(fd, buffer, strlen(buffer)) < 0)
2 A# S. T- b. k0 _/ ~ - 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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二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:9 K! A5 ^- ` G8 u* G' h0 h9 q
- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)1 p5 W1 y# W' ~/ A3 }$ p
- {
h* I) \' B' | ?' `- `+ N' } - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);* n+ q& ^9 D* O: j- W. J
- if(*socket_found == (~0))
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- printf("Create udp send socket failed!\n");8 t. c+ `9 c# @* `# q: h9 d
- return -1;
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' O9 s- X7 A# V3 c+ Y$ r' B/ f" C) _ - addr->sin_family = AF_INET;
& y. C$ q3 H! b0 ^( e# B - addr->sin_addr.s_addr = inet_addr(ip);
; J) E' ^! a, d8 W6 K4 l3 B - addr->sin_port = htons(port);- \% }& E7 @$ c0 ?( q
- memset(addr->sin_zero, 0, 8);' X9 m2 R' O ^: }4 l) D6 ^& T
- return 0;6 D: h: R) ^" S
- }
复制代码
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- \. }2 A b& M H! a" f# s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:9 T8 G1 |0 d* R) r4 C6 ?
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- while(fend > 0)# J, c7 b; s# s/ Q$ Y0 N! Q
- {6 z$ q$ _6 h" {6 G# l: }
- memset(picture.data , 0 , sizeof(picture.data));
* Y# b4 Q% Q: x - fread(picture.data , UDP_FRAME_LEN , 1, fp);
" Y0 [( |! B/ D9 N - if(fend >= UDP_FRAME_LEN)
: G. `- Z" u8 d/ }* b - {
4 [. u8 ^9 G& L$ C! _+ K9 i8 R - picture.length = UDP_FRAME_LEN; y2 D4 a4 A$ V% u) b8 A
- picture.fin = 0;, k' D& ^- o3 i( _) X! J
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- else
7 w4 x+ y* q" b' V - {
9 C+ Q+ Z' d$ i2 K - picture.length = fend;
, h- u+ s' S2 I7 b* }: R/ h - picture.fin = 1;
. O% r. y$ Q! {1 }! I# ^- | - }
9 u7 k- f A4 j4 ?' h; M2 r9 v - //printf("sendbytes = %d \n",sendbytes);. b j2 e2 Q6 p( O3 V. w" f
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
! Z5 C4 R) j$ ?" Q$ y - if(sendbytes == -1)
: u G! _' B& X4 W2 P" t - {
! ?: W0 }0 ]; V0 e - printf("Send Picture Failed!d\n");# h$ n, F. P: m3 L4 q# {! w
- return -1;
4 [$ [! c+ i9 j; }; ] - }
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- {1 ^9 m) t: O4 S; R, [2 y
- fend -= UDP_FRAME_LEN; ~8 c3 r0 r( N& ?8 U& z
- }
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复制代码
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8 r6 L( h8 V# niMX8MPlus 核心板: https://www.forlinx.com/product/136.html |