本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑 : K3 W# A. u8 }
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1 B: o. j6 K+ G! H6 m% v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.html1 N0 y( U' }7 D F0 U( L8 c. j( y
3 ^! T- u1 K5 r* r; J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。 & L/ w4 m: j/ D6 _% f! b+ ~
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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。
- B! c- g* o, E6 x( a, o* \一、HTTP网页服务器: n9 Z: Z# h8 v3 |
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)
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. }2 T! y6 Q" i' c3 u - struct sockaddr_in servaddr;
# @$ Q, w/ U( h( j. ? - socklen_t addrsize = sizeof(struct sockaddr);
* m! f) G+ t H1 E - bzero(&servaddr , sizeof(servaddr));- R- N4 |$ z5 E7 q
- servaddr.sin_family = AF_INET;0 D- X* {1 G; X' r0 x
- servaddr.sin_addr.s_addr = inet_addr(ip);1 }. h7 U% b+ B$ F- h+ ]1 s8 y) g
- servaddr.sin_port = htons(port);' b; `+ Z* E: f; L* p
- int ret;
* P, `' @: x$ v - IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)6 @3 f" A3 R' R
- {# F# S3 _/ h5 |0 e2 r4 ^9 ~# [
- printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
' ?& a j3 ]" [' W - return -1;3 L( k0 \% y% j. t! Q
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- int on = 1;/ K0 o. M! S6 Q! N! {
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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- printf("setsockopt error\n");
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# U, Q+ J( O8 U* \) i- {6 V - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
4 \& A' N" @+ I, M2 c - if(ret == -1)0 a9 l0 ^" P/ V, _0 k
- {/ \# }# h' o( A; \2 J. g
- printf("Tcp bind faiLED!\n");+ Z" [, s$ N1 t5 k( U; o( J
- return -1;3 o- Q0 R# e. k4 t( Q
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- if(listen(*socket_found , 5) == -1)
2 _2 w; Y! w5 G0 f+ M - {
( J. Z7 M! N# L5 ` - printf("Listen failed!\n");
9 g. g( ?9 p: F, c3 H% ] - return -1;
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" n* g* D$ t& y9 S; o. Z - return 0;
# @/ z0 H# W6 g! w# r& r - }
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 Y, o' G" _- k0 v& J
- void * Thread_TCP_Web_Recv(void *arg)
% N2 J/ k, k( j* i- C# G" V - {
: l5 t2 g( _, `9 `; w: P# i8 k+ H - 。。。
' r. K2 v5 r2 H9 v9 I" R5 |+ f - while(1)
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" @' h4 s, {0 \! X - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
+ @% x0 _) i4 B/ q$ t: b* A - printf("fd_socket_conn = accept()\n");; Y4 Z& x! j. A& d8 \' ^
- 。。。9 z) B7 i% K+ w) o
- recv(fd_socket_conn , recvbuf , 1000 , 0);
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- 。。。3 \# V' k! [( N1 T1 }
- }
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);
. P. s( I b7 \0 w6 Y - pic_tmpbuffer = pic.tmpbuffer;+ h9 q5 ?6 I6 g. X4 n, v' x
- pic.tmpbytesused = buff.bytesused;% Z( h+ a- K$ |4 e" m
- pic_tmpbytesused = pic.tmpbytesused;
4 d; e" X- `) p - pthread_cond_broadcast(&pct);
5 ^: N( ]+ a, i R2 z, w$ Q: Q$ I - 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;$ ?' C$ T3 k; E( V/ A2 ]7 F, `
- pthread_cond_t pct;
+ D% Y3 t& O: m1 y2 r - int main(int argc, char* argv[])
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- ...
1 ]' V/ s: |/ W, \6 Y2 y* b - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
& P2 |$ l3 D1 S1 n6 \+ b. ~1 m" } - pthread_mutex_init(&pmt , NULL);
9 O( a$ J1 q4 z. _' x& Q) P& D - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);
9 L+ D- x% n5 t N$ Q$ T7 h ], r - pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
5 ^2 c0 ?, G/ S' t - ...
4 C$ Y$ Z4 G# P% ~: s7 q5 k* H, L - while(1)
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; p7 U' N/ [# ], Z2 z - 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;">6 b1 @9 {" G# ^+ W" [5 }! |
- </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" \
4 R4 ~( J8 `+ H. k( e) Q0 a - "Server: MJPG-Streamer/0.2\r\n" \9 ]* e% `5 U# ^; e) q
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \- b6 c; @* ~" ?/ [2 w9 D
- "Pragma: no-cache\r\n" \
7 @. B" Y; Q9 F/ r1 Z% J - "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
0 a4 C$ s9 M- L: A, y! L' z - #define BOUNDARY "boundarydonotcross"
]# ^/ c2 i/ S - printf("preparing header\n");$ _! w4 V: n r3 W5 h/ I/ M8 g4 Z
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
9 I8 a8 E! D. l( e. C( m1 U - "Access-Control-Allow-Origin: *\r\n" \
" W$ n' A$ s2 ` L$ u - STD_HEADER \0 F. d, ?3 E, H# J& q
- "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \+ y( ?# B% @$ X5 }2 o( A4 b
- "\r\n" \8 X( U0 u2 ?) P2 M8 N
- "--" BOUNDARY "\r\n");
, F! ]/ ]' ^0 u9 ^% p0 N - if(write(fd, buffer, strlen(buffer)) < 0)" X7 R) |! U: `/ |$ v
- {; L" _; }# D# O+ j2 c
- free(frame);
' w; C( ]. j2 x# R" N. q - 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" \
, c7 r+ C; ?1 \: n7 a b - "Content-Length: %d\r\n" \
( q8 |7 g3 W, k1 e: i2 z - "X-Timestamp: %d.%06d\r\n" \
9 B2 S2 D! \3 n' H T - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
/ M3 U% u \5 C: X! v - printf("sending intemdiate header\n");3 S" @# k! H5 x! T; a" I4 S U# K9 e K. _% L
- if(write(fd, buffer, strlen(buffer)) < 0)0 J. p; [$ c! u, q1 O
- break;
+ j9 t6 x2 E9 K# r' ? - printf("sending frame\n");- i& W0 q, j. `3 K" S
- if(write(fd, frame, frame_size) < 0)6 y8 x- Z8 g: V" T2 M5 q
- break;
* @8 }$ p; y' }7 D0 t" r - printf("sending boundary\n");! c" d1 L! G4 ~/ p
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");3 G9 @9 |- v! v8 M5 s
- if(write(fd, buffer, strlen(buffer)) < 0); J# D+ Y. W: b p( J2 t7 q
- 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:
( o d( k* U6 n9 {( ?" P- N3 l- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)
( f0 [& f1 m# e# s - {
. \% R/ Z- w% J - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);* X8 q& M) z" c" z( |4 w
- if(*socket_found == (~0))
( G2 c8 ]. Y' }7 A! l* h' p; w - {
H9 u) {' R$ |6 y$ D, D# }0 e - printf("Create udp send socket failed!\n");
2 A! N' Q' S1 [/ X/ [% P% M - return -1;
* }& o* m L! y3 w4 n2 F3 V: y# D - }' O5 i/ ?8 C: x7 j3 C8 W3 i
- addr->sin_family = AF_INET;
8 d5 H6 Y' ]% z! B0 H - addr->sin_addr.s_addr = inet_addr(ip);. k- Z% f) ?) |
- addr->sin_port = htons(port);
1 H, e: J' q2 O- {, R6 n - memset(addr->sin_zero, 0, 8);
) f* \0 R' H+ \- x& P6 { - return 0;
& A2 q) T1 f# {7 \' K - }
复制代码 3 f' A3 Q2 H* [9 o/ K3 i" F
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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:/ n4 m6 J: L4 O' {
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; W5 _- \$ _( W: W- while(fend > 0)
: v+ }( n0 t) F7 [& f' d - {
5 G- \1 i G7 \! s" n1 X9 Q/ v5 @ - memset(picture.data , 0 , sizeof(picture.data));8 \, Q) z' f' y3 e# c7 o9 s" Y
- fread(picture.data , UDP_FRAME_LEN , 1, fp);
: w. ]; Q W' o - if(fend >= UDP_FRAME_LEN)
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- picture.length = UDP_FRAME_LEN;
# P6 g5 \/ M4 C" X4 F ~ - picture.fin = 0;- T' b" l4 N+ J6 s
- }
7 W$ [ j4 e/ a/ O3 V - else
( u. E) t# M3 [( x3 X, }2 P - {
+ [! ], n! s0 k* v. ]2 w6 R - picture.length = fend;0 I3 k. r6 O, p/ g$ v. h l
- picture.fin = 1;, A5 S( @4 b* l3 ]. u( G
- }
; i0 e( J: i1 Y3 `+ T" u" _ - //printf("sendbytes = %d \n",sendbytes);
/ B7 g5 e2 I6 m% o' K+ S" f& y6 k& P - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
3 V- F/ V0 |+ o. i - if(sendbytes == -1)
1 ]: a" M, q( E' M5 e - {
" u4 p5 E3 k: e( H5 |5 g - printf("Send Picture Failed!d\n");
3 r0 e$ F0 y2 n$ u6 ~% K- S - return -1;. l8 e" d1 ~+ v
- }
4 P4 h" k' w/ N8 a! e7 K) G7 S - else
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- fend -= UDP_FRAME_LEN;3 ^# U) Y0 v1 a% _8 t
- }& X5 G7 u; _5 T2 J" B. z1 }4 F
- }
复制代码
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" \, f9 {- |3 `. r. z5 `& y9 ], _iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |