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
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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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2 M/ `# |8 W! Y# n1 b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。
q% I& S1 _* _! k7 s, X* k7 ^; y一、HTTP网页服务器9 b- B3 d! W; q" x# b) \4 ^
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;6 m( a" f( X5 b8 }* \! C
- socklen_t addrsize = sizeof(struct sockaddr);' p' q8 o" H3 m0 u
- bzero(&servaddr , sizeof(servaddr));7 Y) K. j6 Q) X5 Q0 q6 s% ]) B# Y/ B
- servaddr.sin_family = AF_INET;" y# {- e+ `+ A. {- F: W
- servaddr.sin_addr.s_addr = inet_addr(ip);
( n: @( s" ?, C( m# j - servaddr.sin_port = htons(port);
/ U2 W( l+ c: E - int ret;4 ~3 C F, T `
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)' [1 e$ |; v( ^1 O
- {
" P) c9 k* k( V. m: c4 p- e - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);( H5 E6 y$ N. V! l) u
- return -1;
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- int on = 1;0 t$ k7 \: Q2 E9 t7 ~5 L3 ?
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)- S+ V/ T- i& |4 B+ E
- {
3 u: \0 l8 c" ~ - printf("setsockopt error\n");- w4 R6 Z# m2 @" {. `# f9 l) e z
- }4 d: J8 j& P$ J: l, _, z
- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
' W- n5 w& ]2 E$ ?( X5 V1 i - if(ret == -1)
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- printf("Tcp bind faiLED!\n");- i( a7 k3 i5 c+ A- h! V
- return -1;
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3 |: M- [$ Y _, V - if(listen(*socket_found , 5) == -1)7 }9 F9 N4 P0 X
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- printf("Listen failed!\n");
+ E1 \9 C3 o: Y/ d. _5 L - return -1;
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8 @3 _# V- R, S9 r$ I - return 0;' m K% D- @( b7 d9 j+ K# n% H* s1 a
- }
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);; ^( U0 e% L% U- S$ R2 L- `- G
- void * Thread_TCP_Web_Recv(void *arg)+ @( I$ ]9 w9 j2 u4 e8 k
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- 。。。! W4 U& t$ }5 c4 Z5 A
- while(1)9 p4 x. r. A& Q5 u1 ~: t8 c
- {
( Y- Q; @) W0 m; `% M - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);6 Y' R( s X d/ D9 b
- printf("fd_socket_conn = accept()\n");
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9 i, p, u2 S+ Q, i0 D! s - 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);
, [( X6 M" ~* l. o& o; W - pic_tmpbuffer = pic.tmpbuffer;
7 o. ~8 V( [5 t3 Z- @9 D, j - pic.tmpbytesused = buff.bytesused;9 x4 r7 ~' x3 s9 e4 a
- pic_tmpbytesused = pic.tmpbytesused;
' L$ o6 k; @6 I1 D H) a, V - pthread_cond_broadcast(&pct);
1 f$ G; ]% x2 I/ G w" m5 B+ D - 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;" [' y5 n$ p# I
- pthread_cond_t pct;
! i1 N2 x) p( \0 c - int main(int argc, char* argv[])" G& x: n# b% C( J4 Q, ~9 g
- {9 \. `8 W: c$ {. X
- ...
8 C4 C0 x/ l3 t* ?8 w% Z5 b - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);8 t. k( E3 E; m- X d; w2 `- B
- pthread_mutex_init(&pmt , NULL);
% m2 y) [1 S: ] - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);
5 a6 r# A3 m$ O' W/ f( J( s - pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
& Z3 d) P: W# G. ~; `1 ? - ...
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- {
, m& N9 A5 S6 u' y5 A0 O - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);
- b2 t" ~# z+ O7 X- d: e - ...
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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;">
' m, S* `! A; ~9 `: p3 ?3 k - </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" \0 g$ j' F% f2 o
- "Server: MJPG-Streamer/0.2\r\n" \
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- "Pragma: no-cache\r\n" \
7 V" k& f4 o' W- N4 n - "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
% J% e/ |1 C, r! K - #define BOUNDARY "boundarydonotcross"# G- W! K3 [& n4 V
- printf("preparing header\n");
, g! i' K; n+ {. w( A) N" E - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \0 P( o5 @' R1 E8 `9 W
- "Access-Control-Allow-Origin: *\r\n" \+ [) L. |: H0 p; p0 B' s+ |
- STD_HEADER \
7 u3 h2 j7 } u. J - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
% H6 g/ t/ @+ E/ V! L - "\r\n" \
: T7 K2 C. Y$ z- l7 g! r6 G - "--" BOUNDARY "\r\n");
: ^% V z5 n. B& J) h4 t, } - if(write(fd, buffer, strlen(buffer)) < 0)
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: ~" O3 f+ d8 M- V7 A& c2 \ - free(frame);
; p; y/ m+ c5 K - 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" \
6 i. c" I F6 H% o# ] [/ F0 [ - "Content-Length: %d\r\n" \3 ^7 A; `+ p4 a, o+ `& A
- "X-Timestamp: %d.%06d\r\n" \
2 i" m3 R7 ?$ z Y$ X- q - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);+ B+ V' m0 @' T, \: A: }* E
- printf("sending intemdiate header\n");. Y" ~1 J' v0 G1 I
- if(write(fd, buffer, strlen(buffer)) < 0), r& R; o" F% h9 S
- break;" n S$ [; G2 J
- printf("sending frame\n");) V* I( d6 y- e, d
- if(write(fd, frame, frame_size) < 0)+ O D4 d3 ^( F E: }
- break;
$ B% T$ K l( W. m" A- ]* D1 W - printf("sending boundary\n");# \) T( w; X0 _1 R; i) a
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");0 _. ~ i, G9 w! l5 N: W5 `/ E
- if(write(fd, buffer, strlen(buffer)) < 0)
0 K2 u) q& @! w9 K - 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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/ m( C5 l( p) z# r. j二、UDP上位机UDP发送操作,同样需要先建立UDP Socket: N. u7 `) b5 X1 j1 H8 ]( l
- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)7 |- y/ | J0 P6 J
- {
# A( _5 N" _8 O) l' q: J - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);
/ Z* f, E2 k G9 X - if(*socket_found == (~0))/ H' I3 O. ]# ~
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- printf("Create udp send socket failed!\n");# V$ O$ |8 o% `! O+ A, }, {3 `
- return -1;
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5 c `, @1 D( Y/ I4 `9 S0 b2 D - addr->sin_family = AF_INET;
9 {( p4 M, w' B: n - addr->sin_addr.s_addr = inet_addr(ip);
( E) j7 j) ]5 S+ o2 L. W2 q - addr->sin_port = htons(port);# @8 S7 `6 m9 J) B* \
- memset(addr->sin_zero, 0, 8);# w$ _9 D8 z% w* k f
- return 0;2 y7 f2 }9 C1 G& ?' p$ Q% H
- }
复制代码
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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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- while(fend > 0)/ m3 c$ l, W# K$ y7 e
- {1 l, \/ x4 `+ i( h
- memset(picture.data , 0 , sizeof(picture.data)); x) f& W0 t9 i6 `
- fread(picture.data , UDP_FRAME_LEN , 1, fp);# P# Z8 _& B% F4 s1 [
- if(fend >= UDP_FRAME_LEN); y$ S0 l* z( k
- {
* M' P T& q; t7 { - picture.length = UDP_FRAME_LEN;3 u) Z& Y+ {' W; {* `! k
- picture.fin = 0;
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- else& J# u2 V0 k) o3 s
- { z. J) G' O0 u E8 Q: l
- picture.length = fend;
$ O! {9 R6 R2 r- \: s+ b4 V3 _) y+ t, W - picture.fin = 1;
/ Q; k$ \- S) ~- C/ } - }
: B* ^1 E/ e2 H( O$ r - //printf("sendbytes = %d \n",sendbytes); r7 h( k( O1 n3 }% x
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);8 k$ M% Y: w$ B
- if(sendbytes == -1)
# V1 h; w; I# G% v# J: b$ u9 @ - {
v8 y3 X; Y3 n0 \# \ - printf("Send Picture Failed!d\n");( B8 ], _. ~' T
- return -1;
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- else' c- N5 t, O5 R. i
- {9 q0 N( t7 }1 D' |: ^, Z9 t A. [
- fend -= UDP_FRAME_LEN;$ N, H: k {; Z( v/ ?' M
- }3 w [9 Q5 F: A
- }
复制代码 $ ?7 \5 E" z: u* ]3 J
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iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |