本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑 4 S+ q/ p% k1 B! V6 ^
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1 r3 ~8 s9 S6 j7 G/ O. s" L. z9 q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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( c: G, N8 l! n( O, S" M3 m1 G# M6 U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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/ _0 `* D6 ~2 E6 g$ ?, N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。 ; `2 v; X- }8 _6 B% ]/ S7 q* f0 Y! g
一、HTTP网页服务器' q, V- Z' t2 r7 }
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;; S7 i+ M$ f5 g8 g+ e d* _
- socklen_t addrsize = sizeof(struct sockaddr);
7 v7 i3 |- }: B) n5 @ - bzero(&servaddr , sizeof(servaddr));
8 L: R) C. I/ _% Q' b - servaddr.sin_family = AF_INET;: {; ^, z! V3 l( t
- servaddr.sin_addr.s_addr = inet_addr(ip);( h% f1 s; z- ?. j- [- X. T: ?
- servaddr.sin_port = htons(port);8 J. G3 V5 y2 y4 M6 p
- int ret;
$ i2 Z0 u5 ?! \ - IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)' T$ K9 B3 j' d# u/ B& }0 z
- {
( {; ]3 I' p7 A/ { - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
" N$ {2 t7 k& a, L - return -1;% |6 b+ t7 p* Q, u" V
- }2 Y7 x6 i! U8 ?- c
- int on = 1;& C5 n% r' x4 b+ b4 b
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)2 P' |' G* j; z) k
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- printf("setsockopt error\n");
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- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
2 D& q- [7 b1 G) o - if(ret == -1)' t3 S/ j4 X0 |4 V
- {
% C# u5 ?# I3 z/ H9 Q+ L; d - printf("Tcp bind faiLED!\n");
5 k3 t, p& B& e0 {+ O% t0 _ - return -1;- U6 i' O% n% V+ B! K# y. N
- }
5 x5 v1 | u+ Q; V2 L+ A8 k - if(listen(*socket_found , 5) == -1): m3 R, K5 a6 j) D. @& S
- {
+ S z/ y$ x& \+ X) X( y& A - printf("Listen failed!\n");) c7 v% Z) q9 _/ N4 x' o& k( r
- return -1;
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7 |1 ?0 c+ }5 m; L - return 0;# R& w7 D+ ^! ]' R/ l+ G
- }
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);: q6 c* B7 E1 y
- void * Thread_TCP_Web_Recv(void *arg)
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- while(1)7 C% w1 ^% K, g% A
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- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
4 D/ n; L2 S0 U. H - printf("fd_socket_conn = accept()\n");
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- recv(fd_socket_conn , recvbuf , 1000 , 0);% x# E* I& _$ @8 ~* t! z3 o
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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 Y$ Z3 i( A$ y' f, \! z8 t( ? - pic_tmpbuffer = pic.tmpbuffer;
& A! D" s. O5 q! D8 X - pic.tmpbytesused = buff.bytesused;7 k: s B; e: U. t" H, m
- pic_tmpbytesused = pic.tmpbytesused;
' e3 O# C' ?; s: j+ S! r* c - pthread_cond_broadcast(&pct);
; @* f. x* h2 r4 A- C- N2 N! T5 \ r - 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;
& c" n, p6 W x% s9 k: F# t - pthread_cond_t pct;
2 U* c ?! c$ ?: [ - int main(int argc, char* argv[])% Q6 u# t$ r/ U7 r/ l; y) b/ p: v
- {
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- TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
) ?, b7 ^+ i9 z! M% Y# E' T - pthread_mutex_init(&pmt , NULL);
) q0 N6 q; X0 m- W: `% Z! X - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);
: W/ B- K, g2 O6 W: ]$ X' | - pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
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- while(1)
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. |" I4 {2 Z+ u' ]/ z8 p6 V$ e - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);6 q3 s6 |$ \- A" i; V/ g& l
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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;">3 X$ d, i& o% O, x% l: h' \3 w8 v
- </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" \
: A$ X9 `+ e& N+ G - "Server: MJPG-Streamer/0.2\r\n" \2 D4 q' J7 r) a3 J& V2 k
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
]4 l; x; E: F2 R+ ]- ~5 _ - "Pragma: no-cache\r\n" \
8 Q6 [# S, ~: U0 d/ v5 s6 U- v! X - "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"0 z) [7 a, T: |/ V0 C( F
- #define BOUNDARY "boundarydonotcross"0 b+ r. p* h& T5 e+ I2 A
- printf("preparing header\n");- r4 z" p5 s+ S/ o" X+ n% `
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \" Q- H; |; n& G0 t5 ?4 M
- "Access-Control-Allow-Origin: *\r\n" \" {9 Z6 Q3 S; G, k8 l# U
- STD_HEADER \
y) Z9 c/ l9 |- Y5 e9 H/ ] - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
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- "--" BOUNDARY "\r\n");$ ]: G5 b0 [0 L$ g! I) o
- if(write(fd, buffer, strlen(buffer)) < 0)
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0 E0 v" p! U0 ~$ L - free(frame);& ^) {* h- g) S s& A
- 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" \
2 w0 e' Z3 J: k; l) }+ x - "Content-Length: %d\r\n" \
# e7 B& ^9 ~2 H$ W# ] ~ - "X-Timestamp: %d.%06d\r\n" \& m2 J5 t+ Z: }$ H6 o* c: W
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
7 E" ?- Z9 d1 _' k F$ V - printf("sending intemdiate header\n");
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- break;- E8 `# |3 L X/ _7 o
- printf("sending frame\n");1 r+ e" N! _6 n+ d$ E8 t
- if(write(fd, frame, frame_size) < 0)
3 i, r* v/ v! t$ g2 o* C - break;
7 p( M; P# P& I1 t( ]& T' ?0 i - printf("sending boundary\n");1 ^; y( i& o8 Y1 k2 {# h: N
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
+ X3 V$ r; f# d* ?) t Q - if(write(fd, buffer, strlen(buffer)) < 0)
/ x$ N% [+ X$ F; B4 A7 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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( p. j0 T! {7 H' S" z二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:
1 q! w2 o2 P( o- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)
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/ V7 R) r$ M0 L1 | - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);# b4 F4 q" R: G8 x0 O4 G/ z7 W
- if(*socket_found == (~0))
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- printf("Create udp send socket failed!\n");
1 k: z/ N- G& I! _: M - return -1;2 {9 ]1 _1 N$ M+ s! U
- }
' Y, v* {. E6 a - addr->sin_family = AF_INET;
' k" F1 \) j+ z/ |: a* B2 d6 l - addr->sin_addr.s_addr = inet_addr(ip);
1 s, Z, z2 U" t( R6 G0 [# x5 g - addr->sin_port = htons(port);) M2 f8 n# W: _6 d/ m" k W
- memset(addr->sin_zero, 0, 8);
2 d, Q" G* j! I6 a& u/ {4 C - return 0;, E4 S+ @9 V8 n% T% O4 Z6 ^
- }
复制代码
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- U5 I5 m+ l3 w0 B2 @: a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:4 x& p* j! F: j3 X5 K. L5 d) N
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- while(fend > 0)
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- memset(picture.data , 0 , sizeof(picture.data));6 k) ]( ?# x* d8 c
- fread(picture.data , UDP_FRAME_LEN , 1, fp);4 d0 C+ Z. y2 b, e; O" T
- if(fend >= UDP_FRAME_LEN)
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- picture.length = UDP_FRAME_LEN;
( W0 [7 Q: A! d - picture.fin = 0;+ o4 X7 w0 X4 v; }: U
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- else
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s9 o) s4 @, l: \- `& a - picture.length = fend;
2 J- w8 m- G! Y3 i) E S$ L9 l - picture.fin = 1;
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' a: C; a; j" m6 N5 a3 ^2 Q% _. ?0 H; \# r - //printf("sendbytes = %d \n",sendbytes);7 v7 x5 [; E, |" I/ B6 d( Q; M: V
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);4 }5 U3 t" c/ B
- if(sendbytes == -1)3 @5 p6 Z* F/ z; r
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- printf("Send Picture Failed!d\n");
. T) V8 c% J# Z4 L1 ? - return -1;( v* h3 ~( D5 |; _9 G6 E1 b
- }
4 h) s8 g4 }2 x& E - else
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, F u: m! `" w+ S3 p' o& C& p - fend -= UDP_FRAME_LEN;2 c: G; Q; p+ P0 X5 u2 c7 \
- }" D# i3 w0 \" @& W
- }
复制代码
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7 G B) f9 \5 |6 X6 O; o$ I( H5 giMX8MPlus 核心板: https://www.forlinx.com/product/136.html |