本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑 + S5 Z0 d6 I1 W) f9 Z3 Q! O
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2 a4 r7 S' u/ \$ Y! J) x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/ m/ a0 g1 [ d) N2 A+ q$ ~
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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。 ! q) S) J$ B2 ?, g6 u7 b+ y& K8 e
一、HTTP网页服务器
6 S' I: e$ s# M+ n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;, H( R6 B) u% J/ B% C0 n
- socklen_t addrsize = sizeof(struct sockaddr);: t! F+ M" H" e- m
- bzero(&servaddr , sizeof(servaddr));! g% P4 K0 c( L: K" A
- servaddr.sin_family = AF_INET;
8 c& {9 F+ b H+ p - servaddr.sin_addr.s_addr = inet_addr(ip);
6 G! t* s, G& ]- m: X- { - servaddr.sin_port = htons(port);: B- i# k4 y5 t* _) z
- int ret;0 b! y! l+ K C
- 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);
/ b$ O( N" |, C3 g6 a - return -1;. @! c2 K2 c2 w4 r, b9 J+ Y. N. u) [
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- int on = 1;/ y# ]6 c+ g/ e! Q! }4 p
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)7 L: P8 h; S8 Q: s3 @
- {
* b8 M- J, S2 p8 ?3 } - printf("setsockopt error\n");
3 K) Z3 B% u* u4 L& ~$ h4 I - }
& F2 R) C1 L0 A - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);* F' [0 q! y, E! y& @
- if(ret == -1)6 m, |$ B, ^4 A) X( e" _6 X; ~
- {
8 |( ~+ I' }0 F) M: i6 q. k0 x, X, Q T - printf("Tcp bind faiLED!\n");, s+ t( _1 f/ b. o
- return -1;/ ~, Q L1 X0 z% z/ e! L; y# }
- }
; C! @- ?( I2 Z0 R! C' o% p+ b& K0 [& ~ - if(listen(*socket_found , 5) == -1)
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- printf("Listen failed!\n");
# r7 q' S0 B: P ^+ U; O - return -1;
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^$ ^/ Y$ s! X/ z - return 0;- P7 Y; R6 Q( R. w; ]4 _3 w
- }
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);
6 b$ a. P( a: ~8 Z - void * Thread_TCP_Web_Recv(void *arg)9 g8 O+ w# D6 s/ D6 L1 J0 N/ k; n
- {
5 [( I0 f4 I6 q# [ - 。。。
8 b' ? K! l5 N7 q - while(1)
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. @( t4 X# e, f5 s& T% l! [* z( Q5 y - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
4 R; h5 }7 _6 P( L - printf("fd_socket_conn = accept()\n");
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& W+ j, q. C! |' P' b0 v3 |0 F - recv(fd_socket_conn , recvbuf , 1000 , 0);; E, {7 N' _- U; A4 O+ I( h' {
- }
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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);
4 _ I( a/ N; ~( n3 b - pic_tmpbuffer = pic.tmpbuffer;
2 V, g7 I0 _9 e& P$ |! y) Q - pic.tmpbytesused = buff.bytesused;
" v, g- `% a( q' L - pic_tmpbytesused = pic.tmpbytesused;
+ K6 Z9 D+ l5 n3 q# H% B% |6 m - pthread_cond_broadcast(&pct);
6 \9 x* H9 D0 l9 G - 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;
" @: B6 L1 y x3 M8 A' d s - pthread_cond_t pct;
J# h) v3 C q" F" H! z - int main(int argc, char* argv[])
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- TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);8 M* `$ w' q) `, M* l* u! x
- pthread_mutex_init(&pmt , NULL);" J u6 j2 D, M8 U j4 p
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);. g. F, |: `# m8 ~0 _
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
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- while(1), I* A( L7 R5 G0 _2 \
- {
# w8 u( b/ o( f! h1 ^" @; C v - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);
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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;">
- P D/ B/ F+ |" g9 c$ N - </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" \2 s0 C' e7 y8 ~3 l
- "Server: MJPG-Streamer/0.2\r\n" \+ m. E$ ~3 ]; _- Q2 U
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \4 t7 F1 z9 K- t( p3 t" [1 s
- "Pragma: no-cache\r\n" \5 L+ K9 L2 N3 k: H f4 ]. N
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
5 ?; T6 @3 [) k3 ~% B5 e - #define BOUNDARY "boundarydonotcross"
% P6 o# k ?0 f. l" @ - printf("preparing header\n");& U0 `; p9 A2 A& \
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
9 t! k' N; ^* v1 s6 O - "Access-Control-Allow-Origin: *\r\n" \/ `( y' u" p, I! T1 N8 I: M! d
- STD_HEADER \
. S8 V! L8 s5 [6 j- [, F - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
8 G1 G( Q; }" X0 B8 M8 y - "\r\n" \. @% J, m; K( A+ y. O8 K# n
- "--" BOUNDARY "\r\n");3 h- Z9 ~. s5 ]
- if(write(fd, buffer, strlen(buffer)) < 0)
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- free(frame);
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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" \
, f% m* p) I6 N" b; ^/ ~+ C - "Content-Length: %d\r\n" \+ M9 O8 n) E) m8 X
- "X-Timestamp: %d.%06d\r\n" \
4 N! \& l/ d/ P H9 z& k h - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);' u: T5 r) Y7 R
- printf("sending intemdiate header\n");8 \( B( ?1 E& e% V
- if(write(fd, buffer, strlen(buffer)) < 0)
0 Z( w: y$ i8 D7 B - break;5 ]6 J$ Y A e3 _( b+ n7 B. ]
- printf("sending frame\n");
+ W! n3 [5 B( t; H. w - if(write(fd, frame, frame_size) < 0)
9 U2 K6 y; i- n1 R0 E - break;
; R O) j( m; Y - printf("sending boundary\n");
# x/ D. H, \' z, b6 L9 y - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
0 w. @& ?$ ]* P% K - if(write(fd, buffer, strlen(buffer)) < 0)
3 q$ Q6 i' s r% o' K3 e; U+ Q - 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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二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:- E0 H1 r1 C) L. }6 V0 X
- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)
: b3 ^) W; z1 y) @1 E! K# [2 d+ b: | - {
1 C* M; m: _' f4 l+ Q - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);
2 E- X8 }1 d1 z3 f, ~: M' C - if(*socket_found == (~0))! A$ W+ F& J, A3 ]' r- ~: z6 a
- {
1 T/ m- }. H$ |" R) c - printf("Create udp send socket failed!\n");7 a" Q/ A; r% @; V' o' [0 g
- return -1;
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- addr->sin_family = AF_INET;
+ L0 {* n7 J4 X7 V- H8 a1 b1 _ - addr->sin_addr.s_addr = inet_addr(ip);: p- Y- n1 h/ U
- addr->sin_port = htons(port);+ k1 [6 J/ B$ A" p- o- i/ F
- memset(addr->sin_zero, 0, 8);
- O" N% r8 k6 a' y - return 0;
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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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6 J( V. a4 _7 r+ B8 i0 _- while(fend > 0)
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- memset(picture.data , 0 , sizeof(picture.data));
' {9 J/ D0 K: j3 j" z1 j8 S- e - fread(picture.data , UDP_FRAME_LEN , 1, fp);
! x8 E1 d( K# ~" c - if(fend >= UDP_FRAME_LEN)1 Y8 a4 y# Y% i! O3 T' i) ]
- {
) F+ D& {, `8 K - picture.length = UDP_FRAME_LEN;
4 g* s) P' B! @9 O) r - picture.fin = 0;
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7 G' H2 @- q" v/ ]7 | - else
: F9 |' g2 r- _* A# Z" j2 D$ f - {
& t# I3 B( ~6 i' r - picture.length = fend;
: @$ T. H, n8 `! @* e - picture.fin = 1;
: ^, A4 G% J% @/ Z - }
+ B; w$ j/ E* x; k4 Q: }5 v, | - //printf("sendbytes = %d \n",sendbytes);
& ~& D. T, Y; x! X/ T$ K5 W - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
2 g9 K! w0 p. |- n/ X4 ] - if(sendbytes == -1)4 F# ^' \! p7 f* i$ F Y
- {7 |: t* K3 [9 v( u+ q
- printf("Send Picture Failed!d\n");
9 r) W& Z- P5 g2 H3 h3 i" S - return -1;. Z- ?7 Q: F! R6 E: H- A
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- else; {% }( w, y6 t! h
- {
+ v& |4 \! R$ n. U, v - fend -= UDP_FRAME_LEN; N- X+ @8 M7 p: _3 H
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- }
复制代码
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iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |