本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑 & q2 L/ [& j X9 i, s
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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.html8 y' t2 x( S5 x; z2 W. @" d
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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。
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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。 9 X# \4 Z: E" p( V4 e+ n7 K
一、HTTP网页服务器1 T" O9 D" |+ @% h2 r" d
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)- ?( K2 g% v) b2 R
- {
* S7 y r; [2 N4 O - struct sockaddr_in servaddr;/ T. z6 }2 o; Q( N
- socklen_t addrsize = sizeof(struct sockaddr);; L# `* }% G/ f% H0 C {2 [
- bzero(&servaddr , sizeof(servaddr));+ w4 P2 t2 M: p
- servaddr.sin_family = AF_INET;$ F5 V+ @) x, f8 e
- servaddr.sin_addr.s_addr = inet_addr(ip);
- }& k1 J$ V* k! x# r/ } - servaddr.sin_port = htons(port);& q7 q9 J& m2 e( G% R+ @9 X
- int ret;
: |, L8 ~& t/ n( [ - IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)$ L f/ ~% l. ~6 O% O! s- x; ?
- {+ i- U& D' i& J7 ~
- printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
5 ?0 \5 P+ M- \; w; e( {+ ~ - return -1;
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- int on = 1;) F: X4 t8 l( _+ b
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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- printf("setsockopt error\n");3 l" g0 D! W$ M9 {% v/ ` i& d
- }- }6 |. R6 Z' G \
- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
, |& `; u, s: ~: ^) x) b" p) {" E - if(ret == -1)4 V: u& T$ ~; f- Y8 T
- {
- i+ |- i! Y" P/ _% f) W4 A, C - printf("Tcp bind faiLED!\n");
% M; L b/ f! S% l' h Q - return -1;
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- if(listen(*socket_found , 5) == -1)) V7 I) I) g! O& X$ c# m) @
- {
( W. }; Y2 U/ d r - printf("Listen failed!\n");( b* e: B" f5 n3 l, d# r
- return -1;4 D& m# _0 F7 _" u2 \7 C0 Z+ K& g
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- return 0;
, v1 l0 {; S! ]' D; _ - }
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);& ^5 ^- f% Q/ ~3 H8 z% Y. Z
- void * Thread_TCP_Web_Recv(void *arg)# J/ i/ E. t4 H# q! L; z4 M
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- 。。。( u5 H8 G* U: k+ g" W" h/ ]8 Z
- while(1)+ g! D' y! |0 n+ T
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- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);. [9 ~ d: N5 i0 |+ Y; t8 ~. ~& ~: \
- printf("fd_socket_conn = accept()\n");
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2 Z% n% d9 s6 r( M. W- _! ~ - recv(fd_socket_conn , recvbuf , 1000 , 0);" }. s: k0 a8 ]5 L! W" z2 }
- }
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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);" L0 q0 s7 R u2 Y4 Y$ @
- pic_tmpbuffer = pic.tmpbuffer;6 h q$ B/ a! f2 M& k9 r8 \
- pic.tmpbytesused = buff.bytesused;6 z+ a* c! W0 U0 ?5 d$ q% |# g. J
- pic_tmpbytesused = pic.tmpbytesused;
1 k6 t* }3 L! D& L - pthread_cond_broadcast(&pct);
Q% @/ ?* m0 c+ a - 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;4 k5 g; s6 W( Z, p
- pthread_cond_t pct;
8 s2 y. A7 N+ y0 ` - int main(int argc, char* argv[])0 b5 z( i8 Z1 B; p f% q
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- ...+ Z7 {1 T; P5 t* t9 y5 p8 y/ D% R
- TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
0 |9 `. |5 V- o! f( @6 z - pthread_mutex_init(&pmt , NULL);+ b8 Q& c# K& v" P
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);
8 ~/ ?" o8 \( _7 W* o% d! M8 K7 f6 m4 I N - pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);3 y, Y2 s$ B* ^1 _
- ...
) B" n7 N3 b9 Q7 }2 J B; z - while(1)5 J* a% i( D. A" D: M J3 _
- {
7 ~6 o M6 K6 q4 ?7 g - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);, U# @9 [3 x4 D0 m) Y3 k7 J, Q$ O" {
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- }
% I( c1 N; |3 _7 B, n - ...
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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;"># l1 U& d9 V& I W" ?/ A( }
- </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% `' @% q9 @% B& y! C8 _* A m* w - "Server: MJPG-Streamer/0.2\r\n" \
, @! o& m; Y5 x4 \( Q' P - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \( ^' L( S7 s! ^% B# h8 n' C
- "Pragma: no-cache\r\n" \
! x# X, k8 ^2 E* a - "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
3 t9 c% A% G( v - #define BOUNDARY "boundarydonotcross") v- f v' h/ W4 ?
- printf("preparing header\n");# r8 y" f+ B8 w% q3 q+ Y8 G
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \3 V7 [+ J9 f1 [
- "Access-Control-Allow-Origin: *\r\n" \* t$ B0 f/ _5 f) `% x
- STD_HEADER \* y d+ _8 i4 \% `9 [
- "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \# C. z3 o! H: O* N
- "\r\n" \
# l! D$ O& B) b( w- N# M: t& Y0 \8 g - "--" BOUNDARY "\r\n");
, f- w# u# e1 q - if(write(fd, buffer, strlen(buffer)) < 0)8 w" | G% a' A0 n9 F" l; K* P
- {
& T# A7 j3 ^2 L' g9 m. R - free(frame);
5 A. q" ^% B8 O' ?- P/ j - return;
' [' U$ l9 a- W) ?- m1 O& I1 W - }
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" \
3 K: q* i h' r! S% G! \2 [ - "Content-Length: %d\r\n" \
2 Y( @: `+ W2 i( I# O - "X-Timestamp: %d.%06d\r\n" \2 ]1 E7 L# L3 |/ C1 d
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);1 g( h/ J a% i/ n/ h) f
- printf("sending intemdiate header\n");, j9 v5 h) T2 k& x8 P
- if(write(fd, buffer, strlen(buffer)) < 0)" t$ P [, _8 ]2 E# j
- break;% A" N. `% ~: m8 Q
- printf("sending frame\n");$ d/ ]$ I: J0 y7 G# N) Q
- if(write(fd, frame, frame_size) < 0)$ t1 f. o$ {6 {& k4 @
- break;6 f5 D" d2 ` t) }- c7 X5 ]" v
- printf("sending boundary\n");
. i- q4 }* W y" Y j - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");! f# D. C: t; b c, x
- if(write(fd, buffer, strlen(buffer)) < 0)- Q. S! x9 c0 M4 p
- 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。  3 G% N! B* e( O* Y* g; z" A% u
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二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:8 q$ A# Y& V' A4 D: D
- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)
3 J8 M K3 ]1 U8 @9 u3 s - {
3 C6 _: u( F5 K0 n+ w+ H* [ - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);( ]* f9 C3 c5 G3 s% I# U$ z2 ]
- if(*socket_found == (~0))
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- printf("Create udp send socket failed!\n");
* s/ R |% ~, W9 i/ { - return -1;
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- addr->sin_family = AF_INET;4 y4 O5 c, e% L/ u8 q
- addr->sin_addr.s_addr = inet_addr(ip);
2 w+ d7 _# s$ t) Z! h& q - addr->sin_port = htons(port);2 M. t3 e! Z* E! \
- memset(addr->sin_zero, 0, 8);
S) _# L$ h. w3 h - return 0;
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复制代码 " {7 J! d- P4 G7 y2 G. X- \; o
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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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1 x0 Z% D: G: Q" E- while(fend > 0)
) b+ y& N; j) M3 S3 n) B( } - {
+ c0 c3 i% F* _ - memset(picture.data , 0 , sizeof(picture.data));
6 v! U% t# _6 F4 k+ O - fread(picture.data , UDP_FRAME_LEN , 1, fp);
6 y! [) d% A% f% r" b - if(fend >= UDP_FRAME_LEN)
' _' E+ k7 c- p& F- _% b5 m' \- r - {
+ Q! V( q( J0 H+ T. p - picture.length = UDP_FRAME_LEN;- w) T- Y( k( V
- picture.fin = 0;
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- else
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- picture.length = fend;
+ n% ^+ W) E; E0 @9 T; y7 N& E - picture.fin = 1;
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- //printf("sendbytes = %d \n",sendbytes); N% D! s' M) ~2 A
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
+ R3 {2 B0 i' V" l4 V+ [ - if(sendbytes == -1)
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- printf("Send Picture Failed!d\n");3 ^3 K2 y/ I% O S J
- return -1;
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* r. X0 b& J7 j- s - else
. D% H2 B3 t$ K: t, C - {
4 q; o! M: B2 c& d9 I; p - fend -= UDP_FRAME_LEN;
% E/ U0 G" a+ G. p: ^ - }
3 V' Z/ G/ n# O2 k6 o9 }) j - }
复制代码 . X( ?6 C' t" [* M/ e9 v4 _4 C7 d
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" S; P1 Z/ D9 [9 TiMX8MPlus 核心板: https://www.forlinx.com/product/136.html |