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.html8 B4 G& j' }' m4 u
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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。 9 K, q! W1 O/ V/ T7 n& ]( h

( L. J% _" N# Q' f0 e; X0 V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。
+ v2 z3 c- e" \' P# z1 f% c: r4 _" j一、HTTP网页服务器
( v4 q" z; a; X: w3 l4 S1 M/ P5 l$ U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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, ^% I; N% _/ F8 `, i5 Z# j - struct sockaddr_in servaddr;) c9 ]% P8 v9 h2 k
- socklen_t addrsize = sizeof(struct sockaddr);
9 \$ O7 r$ l8 u& H- b: A9 a3 B - bzero(&servaddr , sizeof(servaddr));
0 i `. x, z; K, e. s - servaddr.sin_family = AF_INET;
, i' H7 \+ Y) \8 K3 X - servaddr.sin_addr.s_addr = inet_addr(ip);+ M6 k% Q* }2 J! T. j, y
- servaddr.sin_port = htons(port);( |& y- j }6 r6 j: Y/ [; j
- int ret;" n$ _& o4 y' J
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)
3 [0 j; l6 U. M+ y8 ]3 ^6 y, X - {
6 C7 P7 d# A; R6 _ - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
F9 R8 V/ Q2 c1 A! ?% H - return -1;$ R3 q! c5 u }4 ~! u! [5 l
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- int on = 1;
, q7 w9 E# W5 X2 G - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)- F R! R# H Y8 H9 E' J/ W6 G1 M
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- printf("setsockopt error\n");
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0 t3 z: R# u' s) l+ N9 F - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
% p( k0 Z; `: Q9 j/ ^3 o9 Q - if(ret == -1)- }8 H0 t/ X* {! y
- {
- j$ f: Z! _/ H% X! P& I8 {' n4 _ - printf("Tcp bind faiLED!\n");
9 y7 g; V6 Y# [: x - return -1;% `1 k! U9 A2 I, |0 C) O H
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- if(listen(*socket_found , 5) == -1)
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- printf("Listen failed!\n");
5 |: B/ Z( {% S; ^ - return -1;
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- return 0; M" o" l, U; @. ~5 P
- }
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);: g2 e9 R0 i5 Z5 \% d3 M
- void * Thread_TCP_Web_Recv(void *arg)
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- 。。。
, o7 {0 A. n. h; M: L# _2 @ - while(1). ^" d. {. }, L) \+ n
- {
5 c0 D, w. h% G, E7 @) L A! h% s - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);. M$ c6 E! v: [1 M' b4 C2 X' v* F" P
- printf("fd_socket_conn = accept()\n");+ |! \% V$ O6 B; S Q! y& y
- 。。。
8 _3 P9 d0 p$ l! S! K" f - recv(fd_socket_conn , recvbuf , 1000 , 0);7 N; Y( L" x/ q" W3 D7 V, s1 P
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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);
( L+ Y$ O! u/ G9 t8 G. h" Q+ ~0 S4 X - pic_tmpbuffer = pic.tmpbuffer;8 S. @5 i6 r* K0 ^ w
- pic.tmpbytesused = buff.bytesused;' _' F6 m# p0 [: n
- pic_tmpbytesused = pic.tmpbytesused;. X( m; w3 \# o* R
- pthread_cond_broadcast(&pct);
; W, g4 B! I! c" A2 w& u - 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;) w7 V4 h" [% d `" G$ T
- pthread_cond_t pct;. T3 B8 L5 \9 D* _
- int main(int argc, char* argv[])' t t6 e+ n, F7 e8 {( {
- {
: }* S+ ^( {8 V4 j0 \) X - ...
4 h9 ^$ X/ d6 K/ |2 L - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
f0 g; o% y' T6 W P - pthread_mutex_init(&pmt , NULL);
/ Z8 \1 d, Y4 o3 [- ~3 }; p - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);
3 U1 a1 C9 I2 M4 v - pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);6 B9 w1 K/ ~8 q- q5 X3 k/ Z; r# T
- ...3 i5 a) u) H2 j
- while(1)
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- V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);* w' a7 d1 \4 Y/ b
- ...- j) [' C7 b! p. H" K) {, I
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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;">0 N6 ]6 n6 B' a0 {/ \( d1 t
- </span></p><p style="box-sizing: border-box; border: 0px; vertical-align: baseline; line-height: 26px;"></p>
复制代码- #define STD_HEADER "Connection: close\r\n" \7 F# H, Y7 s# ]! E1 C
- "Server: MJPG-Streamer/0.2\r\n" \
1 }0 \, p$ K: R1 ^& N - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \0 ]9 M& G: v, B# b; D
- "Pragma: no-cache\r\n" \2 M+ U) G" H! w# U" Q m4 [
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
) x5 J {8 f1 M/ w: v( J* ` - #define BOUNDARY "boundarydonotcross"6 q! `, S' F5 E- N
- printf("preparing header\n");
" D& b1 L: W" d. S' a; M3 ~0 M - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \) _% Z; I, T- Z5 e v$ d
- "Access-Control-Allow-Origin: *\r\n" \9 l8 C% }0 ?# ^
- STD_HEADER \
- V* w2 _% W+ z/ o5 X - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \: p& n3 U7 X( O, r D
- "\r\n" \
% u! k' t3 t; E - "--" BOUNDARY "\r\n");# z. \5 Q/ G0 M& f2 w2 M) y4 K. Y
- if(write(fd, buffer, strlen(buffer)) < 0)
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8 N G# T% M0 E# E! ^. D# U - free(frame);9 e* N; ~* c. y# q
- 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" \
- ^! l F3 {! d) ] - "Content-Length: %d\r\n" \4 Z% s. l8 A& R. h% c) q7 Q+ n# @
- "X-Timestamp: %d.%06d\r\n" \
/ N! \. R3 }/ T, U3 q - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);6 a' E% \7 A3 u
- printf("sending intemdiate header\n");+ s6 V' R C+ H
- if(write(fd, buffer, strlen(buffer)) < 0)# Y6 l7 ^0 P! x( W
- break;
- u: P7 g, n9 e: _% m - printf("sending frame\n");2 J2 ]. \, w* `5 h/ z1 _: N; j# z) M' H$ {
- if(write(fd, frame, frame_size) < 0); e0 P0 H7 y% @2 y, O
- break;, ~5 K; G( i2 G" l
- printf("sending boundary\n");0 K$ l- C! P5 W8 \
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");' a; D( O; v+ S9 U: ^" f" {) n
- if(write(fd, buffer, strlen(buffer)) < 0)
' I8 ?5 H+ _9 v- Z X6 K0 p1 r - 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。  7 _" I6 H O$ o
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二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:
- D' C6 X4 ]3 N) z5 F. v- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port), @ W+ q6 I0 ~5 `
- {
+ R0 d& [$ K" D$ d - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);# E- A& c+ q+ c6 o; Y% \& i
- if(*socket_found == (~0))
6 v( m+ @; V, y e) W - {
( {3 @& m) Q# T% F7 ?9 ~ - printf("Create udp send socket failed!\n");( U1 t" m' _, ?" u
- return -1;
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9 ^7 f" K4 x ^# u o! e - addr->sin_family = AF_INET;
7 m1 W. C# E. ~ S9 X/ S/ Z - addr->sin_addr.s_addr = inet_addr(ip);* O7 V" n$ C( B% V
- addr->sin_port = htons(port);
, ^. W5 I# X8 U% a; d - memset(addr->sin_zero, 0, 8);3 [& G8 P3 Z* Q6 ^5 G
- return 0;
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复制代码 ! O& ^7 L* ~; g: V& [) ?
3 {0 R9 { [7 u7 Q: k* v g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:$ L) K. l& X( B
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0 W5 }/ w4 k8 Z- while(fend > 0)
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. d: y3 D b/ {( B - memset(picture.data , 0 , sizeof(picture.data));8 x! P6 r. Y. Z/ I7 ~( n# f6 c5 u8 Z
- fread(picture.data , UDP_FRAME_LEN , 1, fp);! ?2 Q3 g$ ^% ?# h: l
- if(fend >= UDP_FRAME_LEN)" [" P" f, J, B' d0 m- d
- {
Y/ [9 v; m0 c - picture.length = UDP_FRAME_LEN; v/ I2 N# P7 b ?" ?, y& X0 H
- picture.fin = 0;
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- else
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- picture.length = fend;
3 f( l; \. ~' E+ `# a - picture.fin = 1;5 [& |* ]/ _2 D/ c3 W' x- S
- }
, d) l& c! |3 Y a# W7 H; m - //printf("sendbytes = %d \n",sendbytes);; r- ]- W# z, |% H5 z- M/ s
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
" c: b) O- S% G5 l& C2 w - if(sendbytes == -1)
6 x% J. `- s3 p7 I - {
' ^. W3 s5 [- t% e0 ~1 D+ ` - printf("Send Picture Failed!d\n");
6 Y X) K! O0 f- |; I - return -1;# |1 h; q2 v4 f
- }
8 e& o* G$ V, Z& r6 _1 | - else1 \5 ]; H: J8 Y4 {! u
- {
' R$ M; [" G& q9 n+ l - fend -= UDP_FRAME_LEN;
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- }
复制代码
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iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |