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+ e) K9 A( J) D& z+ f8 t4 @1 l
$ V3 L. Z$ h' C( l. F8 j$ 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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% x; z5 a h- `% ?* s* p; I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。 1 X8 S3 Q6 h! r: X
一、HTTP网页服务器% G, ?/ u/ O( }+ ~3 ?
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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* G3 Z9 k& p2 r" o4 n* b - struct sockaddr_in servaddr;* |: j: V6 s, Q8 X5 O, r. e0 X
- socklen_t addrsize = sizeof(struct sockaddr);0 Z0 U6 s3 x) N5 P% L2 Z8 Z: d
- bzero(&servaddr , sizeof(servaddr));
4 r2 J( _3 o8 U8 k8 X3 c8 T1 [ - servaddr.sin_family = AF_INET;
- g! e/ s, J L8 b - servaddr.sin_addr.s_addr = inet_addr(ip);6 z( Z2 U/ f+ j; c2 [
- servaddr.sin_port = htons(port);
7 c9 x- G- B! g6 A5 K - int ret;
+ g1 G; B+ L# R7 g W4 @ - IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)
; R1 G O/ h: w/ L - {
* R+ r' b- P) E! Y2 r0 y - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);' S& J. |$ C% p3 M) v
- return -1;* d2 o0 ]; W. ~) o) D
- } [+ G; J$ d/ m
- int on = 1;4 t7 R/ p) `- _. [7 P( T# p
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0), x3 }) I/ e# Q7 C6 A. ~( n" q
- {
+ a" K8 q0 |* w - printf("setsockopt error\n");
+ I9 U1 N# V' ]+ S - }
6 {- ~: z8 N* w1 M" } - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);0 q n$ d: h$ y$ O2 r
- if(ret == -1)7 x8 J" g/ Y) \: u+ q8 N* p
- {& d* x2 Z8 C" e) O/ c' }
- printf("Tcp bind faiLED!\n");
! ?- I0 l8 s, k; V5 u5 v7 l1 ^ - return -1;+ O# |) C, f/ j% X$ n, Y
- }
* b- ?* X! O8 C! h1 \7 P0 ~, ] - if(listen(*socket_found , 5) == -1)# U9 |- X- u, }9 ^( b" S. z
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- printf("Listen failed!\n");. l2 ^8 {! q( e! M8 j6 q! T
- return -1;
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- return 0;; L1 K" u% P/ V" a: v
- }
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);1 J3 z1 u% w* B, J
- void * Thread_TCP_Web_Recv(void *arg)
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- 。。。2 M7 _) T4 Y% i8 g5 Q3 P2 Q3 W
- while(1)
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- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);6 J! w* z4 V' g4 X4 M- k( X$ w9 y
- printf("fd_socket_conn = accept()\n");8 |* m! m9 N7 ~6 a5 U3 B' g5 c. k
- 。。。
! b: v8 k; z- c2 G/ X1 N - recv(fd_socket_conn , recvbuf , 1000 , 0);
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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);
" I ^, f! I4 O' l - pic_tmpbuffer = pic.tmpbuffer;
: W0 e. t T. f3 y3 }3 w4 ?( s* e - pic.tmpbytesused = buff.bytesused;
3 }) F! ?6 G5 O - pic_tmpbytesused = pic.tmpbytesused;
7 z+ K# {0 j) K K - pthread_cond_broadcast(&pct);
4 v( y) b4 r* P, O - 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;+ F+ g9 r. N6 }3 n2 r( a* Z5 n$ c
- pthread_cond_t pct;
$ K4 Z/ D a2 y3 Q# V6 Y2 ? - int main(int argc, char* argv[])
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- ...
' D9 d% s8 o0 I$ _8 n9 ?' y5 Y8 R, V - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
* J: s( _' U1 n+ }, r: ?9 e - pthread_mutex_init(&pmt , NULL);
" L. E! K w; } - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);" q2 K) j% s6 |' A1 ]) w
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);4 x7 }- k5 M3 x& E* g, `5 |+ D
- ...% h/ }! v9 z3 b; j
- while(1)
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0 x, a3 L5 ?# E4 u' g) C - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);: f* e1 [9 Q% I8 b, f1 y8 c- W
- ...
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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;"># E7 R. i1 S; o) r1 c
- </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" \: T; h) {7 m! F5 |
- "Server: MJPG-Streamer/0.2\r\n" \# H* V H. c1 n% ?0 e
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \5 L' }9 z8 X: q; w4 w4 ]5 h
- "Pragma: no-cache\r\n" \. I4 ~7 Q" u; r! ^9 x
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
6 p8 E% P% A Q+ | - #define BOUNDARY "boundarydonotcross": R$ c6 B, Q9 j" U' b
- printf("preparing header\n");
' V& ]8 q+ n, W7 a' u1 f - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
% Y8 e5 ?! U, q8 h0 { - "Access-Control-Allow-Origin: *\r\n" \
( Z; U5 F v- h5 W' e( a0 p8 i - STD_HEADER \
7 F I& J% i8 F, g1 `' v2 a - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \5 w! @" f$ a8 _& N' J7 x+ \7 x
- "\r\n" \' L7 l8 ]2 O7 n: y8 W; n
- "--" BOUNDARY "\r\n");% C* R! ` `- s( x2 | B
- if(write(fd, buffer, strlen(buffer)) < 0), e4 P; ]2 E# T6 ]! x% W
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- free(frame);
9 Y. C4 d3 ]4 U4 s6 V1 r - return;% p$ a7 m& b, Q! v8 O3 W2 m
- }
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 A$ O# u0 V$ x
- "Content-Length: %d\r\n" \
: N5 U; J( L/ P; q - "X-Timestamp: %d.%06d\r\n" \
; @% o6 R, X/ h S3 x* o% e - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
% ~, V( h5 m1 j( n6 Y/ x - printf("sending intemdiate header\n");+ N$ s7 _7 ?) F/ l. B
- if(write(fd, buffer, strlen(buffer)) < 0)0 D' ]. Q3 e: R. g+ G% ~( M. t
- break;
2 d1 u+ K* p5 b1 Q' ` R% v+ l5 d - printf("sending frame\n");
3 m+ K( q% j2 s' g& c) Y$ O - if(write(fd, frame, frame_size) < 0)
9 E- Q( _/ N; |; F" p8 P2 J - break;
, _. r' d- L+ N: J: k s - printf("sending boundary\n");
+ \ p6 T8 f3 r3 m4 {8 c5 d3 M - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");8 m( m* |) T7 _: j) r
- if(write(fd, buffer, strlen(buffer)) < 0)) g: W0 W4 x) r! }. }
- 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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9 Q }& Q! l& A9 Y% E二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:, _: h+ a ]: r- Y+ o/ _2 f6 |1 t
- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)
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- *socket_found = socket(AF_INET, SOCK_DGRAM, 0);
& V' d$ h( p& h% e0 ]: f - if(*socket_found == (~0))$ p4 G2 k% w6 q: e
- {
8 x: Z6 v2 E( h9 y - printf("Create udp send socket failed!\n");
6 c2 k$ z. b5 s/ ~) K - return -1;6 @4 z& N7 a" k# J9 h, c+ {6 u! ]; r
- }
$ H" J" n3 T5 C3 @9 ?) f5 H2 p - addr->sin_family = AF_INET;2 |. a s( B( ^: Z" I7 J' ~
- addr->sin_addr.s_addr = inet_addr(ip);8 s# P! A7 R( X7 f: c6 M
- addr->sin_port = htons(port);# x$ G8 j P% e
- memset(addr->sin_zero, 0, 8);3 p, N8 p0 c' r) F# b0 C6 q* Y
- return 0;; k. c' J* l7 f, l2 ]
- }
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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:* b6 p& j9 L2 {- P* s0 |4 ], Z0 T
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- while(fend > 0)( p- r: Z/ F) @0 q% ~
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- memset(picture.data , 0 , sizeof(picture.data));
7 O( C' n2 I) d% b - fread(picture.data , UDP_FRAME_LEN , 1, fp);- Z+ y% A+ ] h+ O7 ?$ ?0 a
- if(fend >= UDP_FRAME_LEN)% ~9 y& b+ w9 {1 `2 Z" g
- {
& _. B( @* r2 }/ t/ `1 X - picture.length = UDP_FRAME_LEN;& H4 h* X ]: g) W3 B6 d* v
- picture.fin = 0;' @$ s+ X5 O z; P* e' X
- }
) f7 {) A/ k( H- r b - else
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- picture.length = fend;
8 P" V4 d1 t1 ?; e) U6 W - picture.fin = 1;
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- //printf("sendbytes = %d \n",sendbytes);7 P0 c2 ]& |& _/ _+ t. c
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
& ^9 Y8 F, ?7 R4 e% b7 o( G - if(sendbytes == -1)9 `6 B3 Z' _- `* `; o0 U
- {
N b/ Y8 \5 E9 p$ I. ~4 x4 K - printf("Send Picture Failed!d\n");
$ Y7 o; n5 k- s8 B - return -1;
- @- B/ Y. p8 i4 ? w5 d - }6 Y8 v5 r; _! L( {
- else
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E3 v2 R% a; @$ ~! [8 o Q - fend -= UDP_FRAME_LEN;
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- }
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iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |