本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑 ) v: l, ~7 d% @
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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.html3 ^1 b! Q: p' C
8 K; g' V9 Y% [2 g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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8 _6 E( T( u6 m) g0 d. ?9 T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。
: {; E& ~7 o; O' l7 h9 K; U一、HTTP网页服务器
& Q8 ^& {* p/ R( S3 Q; ?8 Z4 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)) @6 _" u) G2 P( o2 c/ j4 x
- {
& e$ L, Y8 Z& H: l$ J: X( B - struct sockaddr_in servaddr;2 N' {5 f) Q$ E
- socklen_t addrsize = sizeof(struct sockaddr);/ [; H' [3 l U Z# ^. t
- bzero(&servaddr , sizeof(servaddr));
6 ^+ l' B5 L" {; U - servaddr.sin_family = AF_INET;, O) G/ W* x# X5 Y* L' ^* a
- servaddr.sin_addr.s_addr = inet_addr(ip);
X, r) ~; @2 |) D - servaddr.sin_port = htons(port);
; f7 n; K$ v/ d6 ]* `" ^ - int ret;
) t k5 ^+ O+ a - IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)
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- printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
, V" e- u* H" J' R - return -1;
2 r7 I" `/ ~/ R8 m2 C# C2 g - }
; ]& o/ e& R! i- U% I! m4 J - int on = 1;' b( s+ g7 c. D2 J; ?
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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- printf("setsockopt error\n");
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. K4 W/ L5 }) _7 v! N - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
9 S' e W, T8 X/ { - if(ret == -1)- A4 z, k) |2 j, w" x1 v
- {5 F' C7 g" C( S& e5 y% P' I
- printf("Tcp bind faiLED!\n");% B/ F, G6 m% V, }7 o2 t n5 T
- return -1;0 M: ~6 s3 g8 E- y- } G9 J
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- if(listen(*socket_found , 5) == -1)
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+ g" y! @( H x( K& K - printf("Listen failed!\n");4 R3 o* A4 r/ T% C& h& n
- return -1;0 a4 W8 C5 ~) c1 Z, c" } a
- }
% s9 ^& @1 o% T: p/ O - 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); D' p' o3 N w+ p
- void * Thread_TCP_Web_Recv(void *arg)- j$ j; ^ Y4 e
- {
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9 N, g0 k5 @0 Q - while(1)( o j* ^2 o: @6 E' V$ @. c
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- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);. n. F. S! v# x. Y8 Z: l1 g
- printf("fd_socket_conn = accept()\n");7 g! x# a% w7 y2 L) ^
- 。。。3 t8 w9 {. c- K7 \' O6 x' ~6 ]! P
- recv(fd_socket_conn , recvbuf , 1000 , 0);
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- 。。。
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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);/ a$ t7 `8 C; h( g8 d
- pic_tmpbuffer = pic.tmpbuffer;: G, N5 Y, J2 b6 v5 X( q9 Y
- pic.tmpbytesused = buff.bytesused;$ {0 E: T2 [" b. I. g. t+ U2 A- J
- pic_tmpbytesused = pic.tmpbytesused;' p# F( \' {( \ C
- pthread_cond_broadcast(&pct); X+ E0 l4 q; ~5 a8 q4 e( d! r9 K% n1 s
- 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;
2 U t! Y) r( a - pthread_cond_t pct;
' ~$ p4 a# ]" \! o+ [ - int main(int argc, char* argv[])+ j0 A6 U& @% X4 @. d
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- TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);9 L! b, M. _. S1 ]4 c% M
- pthread_mutex_init(&pmt , NULL);
& F2 q( j! P6 y5 y - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);3 `) ?+ O0 k. Y* O9 |, H
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);# X1 \8 T6 N( I: p# B0 T# T4 E
- .../ n3 v; A3 F" Q, @9 }8 T! h, p5 T m
- while(1)
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2 X. T$ i" k0 P - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);
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- }* g3 {5 A' n4 S9 \; k3 g1 \8 V
- ...
' q5 m, h0 V! D. p7 q/ Y - }
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;">
3 Y! J& c/ E3 a( B: s - </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" \
7 r \9 [" W1 K' Y - "Server: MJPG-Streamer/0.2\r\n" \
, [* v4 G$ |/ _ - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \& e2 [* r" v |+ M1 t' @& Z
- "Pragma: no-cache\r\n" \5 U) \) I6 J- A8 e
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"9 ]* {' r6 Z; d0 V1 e, k- A( i
- #define BOUNDARY "boundarydonotcross"4 t) v: b' n# }/ l8 k
- printf("preparing header\n");
% n! D+ B( b9 E! X" M - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \0 D. Q, b& b: S2 q9 c9 W/ }
- "Access-Control-Allow-Origin: *\r\n" \
$ d, `0 Q" d8 ]! a+ b - STD_HEADER \
! A8 f, J' F9 B8 o7 a, O- d - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \# S. J3 d' S+ I" x1 O7 g0 e
- "\r\n" \$ \5 m3 d; j5 T
- "--" BOUNDARY "\r\n");
1 s/ t8 L7 s& ?1 w6 T - if(write(fd, buffer, strlen(buffer)) < 0)
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- free(frame);: l8 J- a. Y$ U; N+ c$ b7 w( ]
- return;6 O/ X4 d* c/ B7 n$ M- Y
- }
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" \
. I& S5 W2 _. @/ Y5 m. F - "Content-Length: %d\r\n" \
: C* ?# N" r8 J D- v - "X-Timestamp: %d.%06d\r\n" \
6 L+ J m) s+ v& R! P7 u - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
! y+ W6 K' {0 N) r* ^% i; j- G2 P7 \ - printf("sending intemdiate header\n");
/ v7 }! C& {+ t/ w6 y8 P - if(write(fd, buffer, strlen(buffer)) < 0)
9 U' k% j# @$ `$ x! V9 T) ^ - break;
( b% \: G+ O+ n( u" v7 S V- i - printf("sending frame\n");
. `. R u3 F$ j w2 f# u! x; a - if(write(fd, frame, frame_size) < 0)
8 v. [* p& Q! T; V1 d9 f2 p9 t9 J - break;
7 D; |0 U; R7 ]' w' U4 \ - printf("sending boundary\n");
5 W3 b" M* B" U4 h7 h - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
# w6 o, D' C& R6 M - if(write(fd, buffer, strlen(buffer)) < 0)
2 K: H- T N, {2 j: X3 |/ c7 H - 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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- v( d! X9 x7 ^3 @ D3 r* S( O二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:
: u) I6 N- \1 q: q# G4 \- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port), E6 W4 W. h; b7 R/ D0 { g
- {
3 {( N" A3 z4 V9 } - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);% }: g* R5 Q/ d* k4 {
- if(*socket_found == (~0))0 I3 w* S6 B1 k. W2 T3 M
- {4 }9 y7 `: ?+ H
- printf("Create udp send socket failed!\n");6 I3 f) D' u) {+ i! K7 |- r$ i
- return -1;
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- addr->sin_family = AF_INET;, A/ f4 W( e) y; G1 B9 `
- addr->sin_addr.s_addr = inet_addr(ip);
- Y1 {$ V- w: Y( X( Y: @# ? - addr->sin_port = htons(port);8 n$ A" v: t2 o" X. E! i) w
- memset(addr->sin_zero, 0, 8);7 z0 K2 ~& ~. A
- return 0;
- z5 I9 p$ c4 ?4 D - }
复制代码 5 B! p& c7 G! D1 m; r, W! R
9 t9 F% w4 _9 k: {3 `2 j9 L; ~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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0 z2 P( n1 b6 h/ H4 c, b- while(fend > 0)+ ~- v6 R9 _' ~# O% ^ V" J
- {) b1 @, t5 W1 u, F! n w2 @
- memset(picture.data , 0 , sizeof(picture.data));
/ w: I. k- Y: X6 i4 ]3 n: R - fread(picture.data , UDP_FRAME_LEN , 1, fp);
) Z4 S3 ?5 L6 K# i - if(fend >= UDP_FRAME_LEN) c( [: q8 { M, ?5 y; \; W
- {* P$ d+ i1 c. A" u# h' B, A ^$ s
- picture.length = UDP_FRAME_LEN; { W( R6 ^. A# \& M* N% w
- picture.fin = 0;
! |0 D C0 M! }, c; H/ e - }
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- {
$ _+ I7 W. j: q8 W$ G7 `" i - picture.length = fend;
! h3 B# r W3 A1 d) y& n. M - picture.fin = 1;9 Q, d- h% O; D% x0 s
- }/ S0 G' g4 ]; N# v! N
- //printf("sendbytes = %d \n",sendbytes);# P# i) n$ f* _7 o+ c
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);" I: w* ^; e0 Q$ s1 o0 R- j
- if(sendbytes == -1)
- F5 U6 s# ^% [( B/ c4 \; S - {
! ?, |, g: F9 t, C" ` - printf("Send Picture Failed!d\n");: J1 Z9 k) T: u9 \) d# j
- return -1;
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- else& |$ H6 S3 p3 b7 y/ I( F* O) i
- { x$ ~- P* q. C' ]+ m+ S3 H
- fend -= UDP_FRAME_LEN;% i; I8 s+ n% S G e3 r+ L
- }
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复制代码
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iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |