本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑 - b6 c( ?- C( i& R. J- t
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/ l3 R' ^# a) \) x% Q" \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; d4 Z2 u+ {& C0 v: w' W
( R& e. _3 M7 T6 y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。 4 }6 b( r+ [+ v$ }$ ~5 Z
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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。 - g# S5 n3 Y( c6 s O
一、HTTP网页服务器; _, E3 n; j" H `1 r+ u/ x, T. M5 X
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 x: `. K# ?/ r: k1 }; ?
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- struct sockaddr_in servaddr;1 R0 b5 `, k( R) q$ K" l3 |4 T$ b+ O
- socklen_t addrsize = sizeof(struct sockaddr);
2 Q/ F" n$ L" h( ^' D5 J) a - bzero(&servaddr , sizeof(servaddr));
) ]5 A; r( G" z' a+ g6 A - servaddr.sin_family = AF_INET;
$ Q" h% T( J# t# z; u C$ a% J! D! ^ - servaddr.sin_addr.s_addr = inet_addr(ip);& |# t1 e+ m9 Y- J P8 h
- servaddr.sin_port = htons(port);" D5 U5 e, m( R8 r: G4 b
- int ret;1 U! ?! C& O6 W- C* q# J: `6 K
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)
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' E& i9 m/ b1 R4 ^6 D - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);& m' ~7 _" L! y) f+ h* b+ v
- return -1;' I5 v W' e# C! _. K( S) e6 D0 I$ p" j
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- int on = 1;
" G U$ m! B" D9 {; r - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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, U9 I- u2 h4 O( V, P/ V - printf("setsockopt error\n");
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" Z% _% z1 A+ X" \" x. j - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);" m# r8 t( y; L4 E _0 ] [9 a
- if(ret == -1)
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- printf("Tcp bind faiLED!\n");/ I1 a. z- |0 u3 W' x
- return -1;
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- if(listen(*socket_found , 5) == -1)" i: V3 s0 L% c+ U X% C
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- printf("Listen failed!\n");
6 p4 k+ A6 ]0 Y3 R - return -1;
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- return 0;
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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);( S- Q4 v4 D6 a, K; p4 {! D
- void * Thread_TCP_Web_Recv(void *arg)
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- while(1)
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- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);8 i2 [1 {* o$ k3 t2 b- L
- printf("fd_socket_conn = accept()\n");6 c7 Z) o. Q0 A' I8 d& u) Z
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- recv(fd_socket_conn , recvbuf , 1000 , 0);) u1 Z! J4 ^* N5 E% 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);2 C9 g: P) v: y3 r- I& M: D
- pic_tmpbuffer = pic.tmpbuffer;
. N% e5 D0 T9 E0 Q- O - pic.tmpbytesused = buff.bytesused;! W* c) Y( F G# W
- pic_tmpbytesused = pic.tmpbytesused;, E5 ]( i) P! Z
- pthread_cond_broadcast(&pct);
! G5 t9 n" O' y1 i/ `9 }4 l' R. w - 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;
& j! K0 A# j9 R% F - pthread_cond_t pct;
# H# `; k" \# Y" R" \, L% ?8 _ - int main(int argc, char* argv[])
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- TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
# n: p3 Y, e# _* y - pthread_mutex_init(&pmt , NULL);
/ L3 G0 S$ S0 V - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);6 V# X+ F- U3 k$ B: i+ B
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
* y+ _% K' w- @ E ]( h - ...
: B# I( |- a6 z/ P! O: z - while(1)
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: ^; u: t# e! @ Z' S - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);7 | M4 U5 Y1 i
- ...
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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;">
1 P/ e: s I' O+ S1 Z/ j - </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" \
/ z( X4 Z3 p' M - "Server: MJPG-Streamer/0.2\r\n" \
$ c# {- \( v4 |6 {: G - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
5 C) ]' D# b2 U - "Pragma: no-cache\r\n" \' L( j6 `5 V$ J
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"4 C* i0 ^3 y; `) b3 [5 ~: `9 v
- #define BOUNDARY "boundarydonotcross"' w8 J% a+ c' v0 c2 H
- printf("preparing header\n");4 a. c) |# j# I$ J) ]
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
' b8 W; I; d% @ - "Access-Control-Allow-Origin: *\r\n" \
5 S: J+ H/ A- t3 F - STD_HEADER \9 A- E S8 d1 a, P* `
- "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
8 @; Q6 ~8 t* S - "\r\n" \
/ z; z3 C' a6 t: V( {) n - "--" BOUNDARY "\r\n");
9 b* v6 }: C/ g, Z' _4 G: z - if(write(fd, buffer, strlen(buffer)) < 0)6 P' T& j; N3 V0 k1 ?$ v1 m
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- free(frame);
4 A" w& Q. Y) z - 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" \
! z# Q. i) h$ A% i* f0 A, \ - "Content-Length: %d\r\n" \
% b% ~% o" m9 A! P - "X-Timestamp: %d.%06d\r\n" \
* f! F/ |% K8 j - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);* Z& V7 Q' t7 N, \' g
- printf("sending intemdiate header\n");
# ^% n2 G F8 A - if(write(fd, buffer, strlen(buffer)) < 0)
- S0 j! t* Q) z( O5 D2 Z6 o, q - break;
5 {' \8 X! l A {1 I: C - printf("sending frame\n");9 p9 ^. a4 k! G* D: B* S6 S6 O6 H
- if(write(fd, frame, frame_size) < 0)) `! s3 S: f, p R" R5 G
- break;
& D6 I0 Z3 f. m M. p - printf("sending boundary\n");, |' T& U* p$ L/ P) {0 m- J
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n"); R) z: I8 _* H& [+ p
- if(write(fd, buffer, strlen(buffer)) < 0)
' Q' ^0 ]0 \2 A& V9 I a4 M - 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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, i* E1 y' J' B二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:( e3 m$ Z, F6 R& \( n1 S& b
- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)2 ^* Y# s# N0 ]6 g9 C
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- *socket_found = socket(AF_INET, SOCK_DGRAM, 0);! _* D# ^8 c4 q! R6 @/ W) {
- if(*socket_found == (~0))
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+ y8 I4 t6 \" F$ Z# _( b2 z6 z$ g - printf("Create udp send socket failed!\n");
6 @; L1 M7 f T0 E0 j5 K - return -1;
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- addr->sin_family = AF_INET; _3 }0 i" W8 }0 Y6 J. Z, [# V
- addr->sin_addr.s_addr = inet_addr(ip);
9 Q5 x/ S3 D& I% a# N8 Y w% Q% X - addr->sin_port = htons(port);# V" E/ \6 ^2 w2 \+ z! O
- memset(addr->sin_zero, 0, 8);- H/ e/ x# L- _
- return 0;8 T6 \. Z% \* F. Y1 p5 Z+ a) }- p
- }
复制代码 ! k( @6 y4 ^4 O0 o. T8 N
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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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- while(fend > 0)
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- memset(picture.data , 0 , sizeof(picture.data));
3 ?* n2 r; q+ k; Q% i - fread(picture.data , UDP_FRAME_LEN , 1, fp);) U3 \3 E# r; @8 G
- if(fend >= UDP_FRAME_LEN)
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- picture.length = UDP_FRAME_LEN;
( l8 i4 k8 {. j8 f( A' p! b$ T O8 S - picture.fin = 0;
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- else
# @* J4 G, Q# ]6 c; l: H9 J - {
) G; _2 d: a: S - picture.length = fend;
+ L8 b& Z" H+ U# O7 U' g/ i+ t; C6 A - picture.fin = 1;
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, l* k+ h; x; ^! F; s0 k - //printf("sendbytes = %d \n",sendbytes);: F' v( h: h' K* |9 t* {1 O2 r
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);0 p7 L7 r" U# @! {4 v z! A9 U
- if(sendbytes == -1)
# C" G1 A I5 a& @4 T3 t1 I - {
: o. C5 M( O E% `6 ~$ a3 f - printf("Send Picture Failed!d\n");% L& } E. t- |2 w& Q3 W
- return -1;
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1 C& M/ S6 Z& s" ] - else' \& s% I1 N+ |: T
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- fend -= UDP_FRAME_LEN;
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复制代码
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* T7 z' E1 u2 z/ f. s Z- n. t' k! O9 ~iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |