本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑 & y* ]7 t+ i! m: s
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7 m: `, ]/ H+ N; o4 a/ h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" o* c3 J* Q A9 @1 @( T
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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。 ' y' j' `6 H7 m5 Z/ S; b$ Q: O; n
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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。
" K6 K# x& l8 `8 I' U* n一、HTTP网页服务器4 e$ l, h" \/ e6 `. C
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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- struct sockaddr_in servaddr;
' g0 f% |& `. U0 } - socklen_t addrsize = sizeof(struct sockaddr); e- \) A6 ]" e
- bzero(&servaddr , sizeof(servaddr));. e G& p* Q X8 L0 H1 z8 M) I
- servaddr.sin_family = AF_INET;
5 A o2 w, v# Y7 P* E# W - servaddr.sin_addr.s_addr = inet_addr(ip);
$ W" m5 V. ?. J; w+ @( R4 Z - servaddr.sin_port = htons(port);
; T8 _1 V6 Q/ ^ - int ret;0 O7 E$ r) Q0 B ?* n: Y0 \
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)2 W1 r) h( E+ P# `
- {) a. x- q( S* `; u3 i# i( S5 D
- printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
* ?5 Z; B/ E* ~5 n$ S `& `2 L - return -1;1 O# b* m2 L6 @" i8 a
- }
c0 V4 i P, O: W+ g1 ]+ m: a3 [( R. _ - int on = 1;7 k* R2 \; n4 _& ]6 F- E- c
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)4 V" o% Q; X7 W* _3 j; z: E
- {
4 e% J- {1 X9 Z) p9 ]+ D - printf("setsockopt error\n");
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- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);# y9 X" h5 H2 J7 }; [
- if(ret == -1)
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- printf("Tcp bind faiLED!\n");. Y6 F2 ~* m0 [9 u% v7 G
- return -1;$ B4 v4 z# X* q/ `7 n5 d
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- if(listen(*socket_found , 5) == -1)$ X' s3 L1 E/ u: `$ t( ~# }( `
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- printf("Listen failed!\n");; W0 o% X. j) t2 b- y% M T/ [, S
- return -1;
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% I" H2 S' C$ Z( Z$ r5 x) a - 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);
- v( ]0 e% n9 B+ G - void * Thread_TCP_Web_Recv(void *arg)0 J5 A+ K( o: ~
- {
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- while(1)% b" p% |1 c+ E' h
- {
! ` a: C" }- d* e$ U/ I - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);" ~$ U* b/ h% _8 Y. o
- printf("fd_socket_conn = accept()\n");* @* d0 E' R9 J1 S7 [( z
- 。。。
+ n) a- N; }) G1 m - recv(fd_socket_conn , recvbuf , 1000 , 0);
; {# }0 _) ~3 f# t$ x6 e - }
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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);
: n( i/ \, Y% S9 {9 w - pic_tmpbuffer = pic.tmpbuffer;! N; f5 X! o8 G j8 q. j
- pic.tmpbytesused = buff.bytesused;
' q3 |$ c" b2 e# Q$ J - pic_tmpbytesused = pic.tmpbytesused;. i ~; R0 W" O: P4 W/ B1 V
- pthread_cond_broadcast(&pct);) o2 p N, I" z; X+ b
- 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;
# B) f$ W! K& L- L1 [/ o0 M3 `1 y - pthread_cond_t pct;% v% ?7 l! T! Q5 Z) e2 m) p* q
- int main(int argc, char* argv[])
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* C' g6 H$ m, F) u' @0 u7 H - ...
) s, }/ [; j9 {1 B- P' s+ i9 H. | - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);+ K$ |7 t4 O' t- v
- pthread_mutex_init(&pmt , NULL);
$ e% @: b$ `9 ?: R+ O3 I - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);6 `" M( h4 p( e2 C
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
( D/ } [2 L% ~8 `1 V2 w6 O; c - ...
0 q; p# @* }; h% X$ x; \ - while(1)
( ]% }' b$ N7 T) l% B - {
: D4 }/ y4 Y9 H5 u' T. W- c - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);8 m$ N3 i& o( \" }+ i X4 R
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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;">7 S( h% H. `5 J. t
- </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" \
8 S8 r' T% h2 L. X. H9 ~ - "Server: MJPG-Streamer/0.2\r\n" \
' i# l" [5 n5 c& s/ R+ `9 w8 M - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \1 x' F4 Z8 a# T2 D# Y1 G
- "Pragma: no-cache\r\n" \* ^1 F. V/ x- Y6 J M. B
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n": P- F- ]$ ` I4 H5 m
- #define BOUNDARY "boundarydonotcross"
& [' }& a+ ^7 |! \3 Q+ \, g - printf("preparing header\n");
! f9 _ p4 f7 d4 \: D% r: R - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
1 a' Z" ^9 F9 m, q: ~; F T6 A* F - "Access-Control-Allow-Origin: *\r\n" \9 ?. K8 W* ?; y9 u5 y7 ]
- STD_HEADER \( I+ U$ v/ p; u8 a
- "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
i+ {5 l: I5 J+ V0 @ - "\r\n" \
+ n2 F% R9 y( d1 k4 L1 F; C1 i - "--" BOUNDARY "\r\n");) N% G1 D; k) V; ^
- if(write(fd, buffer, strlen(buffer)) < 0): Q+ s& U+ d8 P' L3 h9 b! w& g8 Z
- {
C# l$ @5 s0 d( Z, Y0 ^ - free(frame);$ j9 N5 j6 u, X. |" \3 X w
- return;& o7 } m- p2 l
- }
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 X! F; d( m- E3 A# T% w) L - "Content-Length: %d\r\n" \$ x2 ~: m9 p+ q* C' i
- "X-Timestamp: %d.%06d\r\n" \
$ Y6 N( O* p8 K9 O - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);8 i1 U) e- G3 n: r8 A
- printf("sending intemdiate header\n");
2 e5 D* F O6 k& e - if(write(fd, buffer, strlen(buffer)) < 0)
8 h2 a. [3 U2 j U2 U8 ^! m - break;
) z% N/ `9 @, j6 N9 ]; r - printf("sending frame\n");
1 q& F( g3 ~$ x - if(write(fd, frame, frame_size) < 0)0 H) f2 P3 k* ` K: ?6 Q/ u# p2 L
- break;# H/ y N1 t9 ?: P2 K' A3 S1 ]: y
- printf("sending boundary\n");6 K4 d! B) G* l0 I8 ]" O
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
; Z z: T1 q- ], r! E/ P, H - if(write(fd, buffer, strlen(buffer)) < 0), H& e/ ~+ k! f
- 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。  1 ? ]8 Y, R5 F, H4 B5 T

( j3 n! X) J% W; m2 y# w二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:/ R9 C& F1 ]9 x& n( i5 S& l
- 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);
1 l+ P' v. |: @3 ?, j/ q - if(*socket_found == (~0))
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- printf("Create udp send socket failed!\n");0 g& O* s& ~/ o2 W- ?: C$ l
- return -1;
7 p& {4 u) {3 \. s - }
/ u8 G2 f' R$ v3 A9 m - addr->sin_family = AF_INET;5 R% j4 R/ @( m% e
- addr->sin_addr.s_addr = inet_addr(ip);
4 \& ^- e' J# F. F/ Q" `/ V - addr->sin_port = htons(port);
& H1 @, m% S0 `5 v8 ~8 V - memset(addr->sin_zero, 0, 8);
( Q( M) X7 _! A1 g - return 0;
/ B; ? ]! E2 C- S* c5 `4 O - }
复制代码
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2 |. G/ g8 s) B9 o" _2 o$ l, T) X6 V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:" q$ W( I& U8 i% e& q: x& C' w8 l
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4 k/ P: L$ d& y2 J7 t' T* h- while(fend > 0); `' I2 R# \8 F% r% @, v
- {
$ Z4 w+ {% O6 U' K2 ] - memset(picture.data , 0 , sizeof(picture.data));
# W: l* @7 U0 A" c7 P - fread(picture.data , UDP_FRAME_LEN , 1, fp);
( N/ J! c+ | M! p8 o) ?0 t - if(fend >= UDP_FRAME_LEN)+ ~; R0 e# L6 n1 A3 N5 s7 N O6 r& `
- {
5 l) g2 F) _9 a' W6 W" K - picture.length = UDP_FRAME_LEN;& @% R W E, H( H" K( {) L% c
- picture.fin = 0;
- ]& }) O% |6 X; {( U8 P3 K - }4 Q+ m" c" X5 q6 x+ |: y
- else! U% }6 f. } w
- {
! y' v2 `0 n" M$ X. Z4 X; ` - picture.length = fend;
( v) S9 x7 ]6 S - picture.fin = 1;# v8 X8 J! U7 e# T. m+ l
- }) O5 d$ l$ {; l9 [: \
- //printf("sendbytes = %d \n",sendbytes);
" a% ?% r6 B- l - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len); p9 {) a( ^5 k) C
- if(sendbytes == -1)' N7 }$ e6 r( S2 f8 s
- {
! M& I. E, x, W3 |$ A - printf("Send Picture Failed!d\n");
% n1 v) _. L s/ j+ W0 Z! K# { - return -1;
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- else
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- fend -= UDP_FRAME_LEN;
" }+ H) Z' N6 p - }
/ m3 C3 D' f# ?7 u - }
复制代码 0 ^/ H7 I2 d) |2 E, f
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. V9 V) Z- ?4 j' t g, X# D) _! qiMX8MPlus 核心板: https://www.forlinx.com/product/136.html |