本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑 : e+ L6 T+ M( o# f& i2 c" O/ S/ z! e) O
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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.html3 c L' w) N0 m) \, c
2 y) a4 F( F; [% M; D) t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。 # x8 |1 m& |% t. t
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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。
8 L& u7 N7 s( }& C6 e% t一、HTTP网页服务器
1 r( B' m! q2 r; s" @2 Q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)
8 A- v V! x* P' m1 J Y& K - {
5 J$ S+ B' ^" g3 ?4 ]) V6 D - struct sockaddr_in servaddr;
4 C8 M( p* \- v - socklen_t addrsize = sizeof(struct sockaddr);) B |. d$ O* s3 N, t3 l1 q' k" j% n
- bzero(&servaddr , sizeof(servaddr));# k6 j) [7 h/ \) h+ y6 w; m" Q9 i
- servaddr.sin_family = AF_INET;
2 ^- C g- a7 M) O - servaddr.sin_addr.s_addr = inet_addr(ip);/ |+ X# K/ K+ E7 {
- servaddr.sin_port = htons(port);& g* ]6 v! t: b) F9 \' z! f, W; }3 W/ K
- int ret; G& I7 ~5 w* b9 n. m/ W# k/ A
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)) N; E2 Z9 m& L; l' ^' K
- {
0 z: c- t& O0 o; W. J. r/ n - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
+ e1 f0 V. _6 I/ h - return -1;% m2 t9 }0 `6 Y9 B# i- T
- }) _% z* J& @: U, ]. g
- int on = 1;
& P, ~1 ^) c$ t: b3 a3 T. @ - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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- printf("setsockopt error\n");
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1 c# i2 A! }' `, F - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);" V2 u p0 W6 U8 W$ G
- if(ret == -1)
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- printf("Tcp bind faiLED!\n");/ G4 ?8 Q" P" Y. _8 U; }: r
- return -1;5 ]3 n3 C% ]' N- |1 a
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- if(listen(*socket_found , 5) == -1)) k, n: U( f; |* A
- {
8 Z! z! T/ p$ T; b1 K# K - printf("Listen failed!\n");( }' G S) @7 K. N9 x( Q
- return -1;
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- return 0;
- |( g2 u6 \3 A, M8 D3 A; m1 Z9 F - }
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);
- E8 g9 e4 M# E) b - void * Thread_TCP_Web_Recv(void *arg): D! w# j) N( R5 u( G* {
- {
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- while(1)
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) [, r. V' A- U. T - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);8 `; S6 ~; N* ]" ]! m# j
- printf("fd_socket_conn = accept()\n");
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w A8 @5 L+ @9 ?) u! E - recv(fd_socket_conn , recvbuf , 1000 , 0);" T, t) N' `! x/ I
- }
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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);
5 U3 V3 ]9 s- m; g& Z; r) X. D - pic_tmpbuffer = pic.tmpbuffer;
- @ c$ P$ z, d9 P- q - pic.tmpbytesused = buff.bytesused;: W+ i a) P! j2 ^1 D
- pic_tmpbytesused = pic.tmpbytesused;) C8 ]- r9 G" H# r
- pthread_cond_broadcast(&pct);) U% H- M/ }" K% I. `1 g! w
- 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' ~" `* S* v5 _3 G2 O
- pthread_cond_t pct;# C! ~/ x2 W& k2 [, l% c5 E& U+ F
- int main(int argc, char* argv[])
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- TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
0 H5 d) P+ N# q# w - pthread_mutex_init(&pmt , NULL);- F( o) f" `. q
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);# P' ^! t1 ?- @
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
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0 k' y. [2 u! o6 }) c0 R# a - while(1)
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- V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);. P8 _" T& N, V2 T( D3 j8 f
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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;">) ~ ~! C, t1 f; l/ G( ?3 [1 g( W' P
- </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" \( u7 W3 j3 I4 ^
- "Server: MJPG-Streamer/0.2\r\n" \
" D; S, F$ Q2 b% k - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
0 R, E; }$ Q+ K/ a; S( v - "Pragma: no-cache\r\n" \- X! Q. J9 g( b
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
8 q6 x* ^0 S+ b1 y7 [1 K - #define BOUNDARY "boundarydonotcross"
: z/ d) e" Y: k5 e+ h. E - printf("preparing header\n");5 P9 q5 D; ~1 {7 h% X4 y6 `' k
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
3 o' T$ q2 V7 l - "Access-Control-Allow-Origin: *\r\n" \( l/ V& W& }. b% N' w e" j
- STD_HEADER \7 s% E( p0 T. e& |
- "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
/ m9 N6 J. E1 {" K1 d. L - "\r\n" \- q/ c- h5 O" _/ i+ v. t3 X! z
- "--" BOUNDARY "\r\n");
9 V C2 n7 Q, H$ |; U% K$ } - if(write(fd, buffer, strlen(buffer)) < 0)
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; E( C* r f' C" C& B - free(frame);1 L5 h8 u1 n5 O
- return;7 `& N$ w% c& f/ N0 t* s
- }
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" \( f9 }1 K1 U" `& V2 L
- "Content-Length: %d\r\n" \& u, o% C( d: v( a& }
- "X-Timestamp: %d.%06d\r\n" \9 D" W8 f; X9 ~5 R3 J
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
' B5 V6 H" y% H- c8 G q - printf("sending intemdiate header\n");
* l5 S9 z2 v2 K; ?" A- L$ ` - if(write(fd, buffer, strlen(buffer)) < 0): {0 P: Z2 c5 U3 |( t
- break;
5 d( F. d8 f; J9 b - printf("sending frame\n");
. l8 a g# H f% B9 Q( z% m4 h' } - if(write(fd, frame, frame_size) < 0)8 L6 R" g6 W/ `+ G$ ^
- break;
9 D2 E" M' u6 F! }( I; v3 Z - printf("sending boundary\n");
9 B/ ]0 Y- I# S* v# q - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");( }' N& Z" w8 z9 r3 h, J
- if(write(fd, buffer, strlen(buffer)) < 0)5 h5 a2 Z6 J1 b: l
- 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。  4 }& @9 L1 G+ l; g/ J
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二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:
: k6 C, D) q5 L7 {- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)4 J& ? X* {' Q: d' o
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- *socket_found = socket(AF_INET, SOCK_DGRAM, 0);
# e& u) ~% |3 d, m" R - if(*socket_found == (~0))+ f6 q, M2 k5 ^$ R* E0 P) h5 P3 _
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- printf("Create udp send socket failed!\n");
, L8 {* J' N+ l! _- m - return -1;1 R( D. Z8 N2 c2 i& Z, i$ p
- } j! u! v! A/ S3 y' q2 Q* O! s- {
- addr->sin_family = AF_INET;3 R, f9 ?) z! T- P2 |
- addr->sin_addr.s_addr = inet_addr(ip);
7 C$ E; f& Y' g, \& }5 d- _* S - addr->sin_port = htons(port);, n8 r2 S4 Q7 J$ Y8 i
- memset(addr->sin_zero, 0, 8);
3 ]/ g% `6 I! O - return 0;2 U! S7 {) W6 S( x: i2 F
- }
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)9 a8 {( V- B+ S0 F- @5 j5 Z
- {
" w( d2 E! M* P, c2 {" [3 o - memset(picture.data , 0 , sizeof(picture.data));
1 J2 r! h3 l" C: q( A, L; ^ - fread(picture.data , UDP_FRAME_LEN , 1, fp);
, L2 p4 l% E* n- c; x - if(fend >= UDP_FRAME_LEN)
' l" ^, u0 p6 x+ D - {
( v' a' R( o- {6 U - picture.length = UDP_FRAME_LEN;5 r% y: d3 w/ M. B0 {2 x
- picture.fin = 0;) O5 z/ t8 _6 b' _$ l
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- else+ c5 v( y, m6 w9 R8 P
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- picture.length = fend;
6 l# S4 r2 }7 \( d' E0 P& ^ - picture.fin = 1;
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. N& b+ f4 @3 u0 \ - //printf("sendbytes = %d \n",sendbytes);
3 I: i6 l$ Z& @' P1 V5 F+ W - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
/ s2 P" _$ S- n6 r; G1 u - if(sendbytes == -1)' v" {# X, J5 W! K
- {8 D; Q/ y9 B2 b: r, I3 q
- printf("Send Picture Failed!d\n");
S% J% c! J! U1 d0 s - return -1;- [+ `( m/ Y- M% `, f4 L. L2 _
- }
& O8 }: I* g( Z" u5 P: m - else
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- fend -= UDP_FRAME_LEN;! Q8 Q7 N" V. j6 t, j* |
- }
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复制代码
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iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |