本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑
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: s, ] U1 ~, W n8 J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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3 y9 m Z- X0 k0 z5 [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。 3 s; J+ u; l- z+ G

- t! @" L' G, R6 r0 X7 r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 ?4 T/ l# J" p4 Z: Y
一、HTTP网页服务器
$ ~% \% n+ a+ S& c# \, D$ b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): q- h2 p( R N. ^: m7 o
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- struct sockaddr_in servaddr;9 m7 z1 y- F T k/ E
- socklen_t addrsize = sizeof(struct sockaddr);6 x, t0 m5 V5 H
- bzero(&servaddr , sizeof(servaddr));) `1 R1 C' S6 I. y* r, S! p
- servaddr.sin_family = AF_INET;
; L; O- p, Q2 b3 m2 [; _ - servaddr.sin_addr.s_addr = inet_addr(ip);
$ A# a& B5 ?: o* T1 y R0 _ - servaddr.sin_port = htons(port);
5 i) r% H6 ^1 S. m - int ret;" [* {5 g' s3 E9 k1 `
- 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);
, u! }" ~/ s2 [7 R0 ]8 H - return -1;
7 W) P1 c4 B. N! t) N - }
3 ]: ?; d# `4 x6 _: ^8 q( Y - int on = 1;
9 d+ l8 P4 `9 C1 w M+ r - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
! Q7 q1 G T& P+ G, p - {
5 Q& |" V3 j5 k5 s$ T' v - printf("setsockopt error\n");; g0 v3 z, Q9 b+ k8 k' a% Z
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- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
^9 j* ^' k- @0 ? - if(ret == -1)
; O/ _+ {& b3 W4 r& R) t9 B - {
- ?1 _8 c8 N3 X$ J - printf("Tcp bind faiLED!\n"); ]# V# i3 K7 B- g. @8 V
- return -1;. P, M+ z- B) Z1 `# T. @$ x
- }
# G9 O9 [- H: i - if(listen(*socket_found , 5) == -1)" u4 T3 j, c" p" s
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- printf("Listen failed!\n");
" x0 f. r( s* Z7 h' L1 ^ - return -1;, a" i# g4 ^5 ? e! u% r) J8 {7 D
- }
- \7 u) w; e' v1 R; {; u" n - return 0;4 g9 ^$ z! [) w) V- X
- }
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);0 m8 u; v0 q" H- J, ?6 F
- void * Thread_TCP_Web_Recv(void *arg)7 C# A$ [: x" y! @( t
- {" x; u* x) n, u7 \
- 。。。
], ] @# W) {, n9 [ - while(1)
1 O1 y! `& t, F$ r; @ - {
' j9 b9 }7 G* B! d9 i P) l0 }. V - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize); e4 I- j; v' {6 @
- printf("fd_socket_conn = accept()\n");
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- recv(fd_socket_conn , recvbuf , 1000 , 0);
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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);! ^* n9 d% R" W4 o/ A7 }
- pic_tmpbuffer = pic.tmpbuffer;
5 t) z9 P/ _3 J7 W - pic.tmpbytesused = buff.bytesused;
* n2 n3 k3 @1 `6 C* ?- R - pic_tmpbytesused = pic.tmpbytesused;# l: [ ]9 S p* ]2 M Z; |
- pthread_cond_broadcast(&pct);5 d, w- C% Q4 h) L- F8 ^8 a
- 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: U$ y' |/ v
- pthread_cond_t pct;- M" c5 i+ ^9 D/ C3 R- \
- int main(int argc, char* argv[])
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- ...
2 M. b6 F5 u" z* k( Y$ \ - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
+ I+ W0 q7 s- D- F# o - pthread_mutex_init(&pmt , NULL);. q8 T$ K. {2 N3 F, \5 @
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);
}0 r8 i8 J/ V - pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);7 k- n5 V, C" ?8 i; E2 {
- ...
# H8 {# Z9 L' n* t J - while(1)
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- V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);+ f! z. Y0 {( c" G( ~ K+ V0 v' X
- ...
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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 |- C- l; e$ O9 m
- </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" \
4 H! y. n* |: P8 ?5 x" {: R' w - "Server: MJPG-Streamer/0.2\r\n" \
) C* |: w( d- Z; X6 I- N - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
j J" n1 w, ?% o9 ]- @ - "Pragma: no-cache\r\n" \4 D: N2 T. q/ B# w3 A; O" H
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
: ~1 I5 B; J% v8 }5 S - #define BOUNDARY "boundarydonotcross"
! X% y5 w& W- x6 _5 R C- U' e c - printf("preparing header\n");7 X2 ]5 x4 d7 M/ J) W
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \( c$ R- ~) a" |, o2 J3 l8 Z
- "Access-Control-Allow-Origin: *\r\n" \& R' f- H6 Q3 w( H3 T0 W( E
- STD_HEADER \/ x8 {* ~- G5 U
- "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \# ?$ F9 u$ a( l x% P# \
- "\r\n" \0 p3 p) c8 V6 }: L3 j. ?
- "--" BOUNDARY "\r\n");
" m) y, H" S2 U7 u - if(write(fd, buffer, strlen(buffer)) < 0)) H7 l1 {0 _+ \8 I$ h" r* D7 ~
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- free(frame);
1 z0 ^/ J a) T - return;0 y9 h* k1 K9 h% E. b
- }
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 S) }8 X6 K. P4 z( ?! ^3 Y - "Content-Length: %d\r\n" \7 g& ?/ F/ ^4 V( q0 ^/ Z8 }6 H% f
- "X-Timestamp: %d.%06d\r\n" \1 L$ T8 N# m. J* I
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
0 I1 O7 Q4 \" ?4 M1 l7 o - printf("sending intemdiate header\n");: }6 m* r2 Q) [$ X: }
- if(write(fd, buffer, strlen(buffer)) < 0)) H! r: g6 z" ` P, [: y- J" U) J
- break;
# J( G" e* @/ y5 c# r9 @2 Y - printf("sending frame\n");
! R4 U, x( P4 L- l7 a6 `5 F - if(write(fd, frame, frame_size) < 0)5 d% \8 d0 `) i* E. Y
- break; S* X+ L }3 M% D. `& Z1 F. I) n
- printf("sending boundary\n");9 k! \1 _( K1 c3 F
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");0 w" Q0 _9 j8 G8 ?& ]4 {$ w
- if(write(fd, buffer, strlen(buffer)) < 0)
* c0 d- }% _ q8 Q( x( z - 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。  6 N- o N9 ]) ?* R9 `0 q) S
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二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:3 U3 P, R. I& G0 _/ r% C" R+ @
- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)4 K% t) _0 \: G1 D" i$ g
- {2 T, u$ g+ Y3 S {& P1 p4 S* t. l& b3 |; ~
- *socket_found = socket(AF_INET, SOCK_DGRAM, 0);8 x1 H9 e X u: a" N* R2 T
- if(*socket_found == (~0))2 ?- F* v' A, E- d f! N6 Y+ o% E
- {
5 z& J9 a- _3 b c2 h - printf("Create udp send socket failed!\n");
$ t% u0 d. g3 N3 ~. _( | - return -1;/ N1 h- P2 q3 u3 C
- }
8 C/ |! o3 d0 Q" W - addr->sin_family = AF_INET;7 [0 T1 }; ^% k; O; ~0 z7 l
- addr->sin_addr.s_addr = inet_addr(ip);* W% ~4 Q2 N2 f ?7 g7 R% \
- addr->sin_port = htons(port);
& p2 m4 w$ q; Y- ~6 T - memset(addr->sin_zero, 0, 8);
2 j3 l9 e5 i P- W. ~ - return 0;
& v0 p& |, ~+ e - }
复制代码
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" K) ^) n# X& w7 s5 c2 Z6 R0 {& }- V. j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:" p! H) H" l5 o! y5 D! x# F
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- while(fend > 0)
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- memset(picture.data , 0 , sizeof(picture.data));6 o- S3 p# F9 V! g! N
- fread(picture.data , UDP_FRAME_LEN , 1, fp);
/ B" }% q7 w+ u# `+ q( B6 F: l - if(fend >= UDP_FRAME_LEN)0 u8 s( g/ ?) X# Z8 A) w
- {, Y- W- J! L2 q- [ r2 H' R6 ?
- picture.length = UDP_FRAME_LEN;
$ O9 N' \6 Z) T2 N6 o1 p( L - picture.fin = 0;
) M+ j. Q+ L0 t# E. V - }
5 D' H( r+ N1 t7 t( w - else
' {- N3 B3 B! p7 O - {
N$ M3 M& G8 m* G2 t4 u - picture.length = fend;
6 [8 V8 B# {2 g - picture.fin = 1;2 ]2 }/ ~* Y6 Q' M% {8 s
- }
, M, N& |3 ?- A- e - //printf("sendbytes = %d \n",sendbytes);0 Z; }& |, s% m# S
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);* u: `! v; U2 J/ c j3 g% T; W
- if(sendbytes == -1)
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- printf("Send Picture Failed!d\n");
' z1 |7 c+ L1 V5 o: N, l; D - return -1;
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- else
5 g" P Q0 W4 ^4 g) p) C0 d - {
8 B+ N- g8 C6 O0 N( `. i( P - fend -= UDP_FRAME_LEN;
' V; X5 d" L4 h% f/ \ - }
3 K7 P3 G J" B7 Z( x% w - }
复制代码 $ u' A. D) r |5 M# j+ T
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iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |