本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑 6 u, U/ }& t/ N; n! q( u
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0 E" @1 s0 y) c; i6 r. l# [4 g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% R' B m6 g9 N7 e& v. B [0 K5 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。
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/ m" i* ^! d% `- D+ J9 M2 M* ^) {( 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。
5 w# x/ c$ g4 F9 e1 S G一、HTTP网页服务器1 V r& K# R) v, p4 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)8 j1 \" O6 E6 ?/ _0 r. v( M
- {
! g1 m. V4 _5 k) d% B - struct sockaddr_in servaddr;
. c# m2 B9 ?% F& i% j. H N - socklen_t addrsize = sizeof(struct sockaddr);! \1 A1 C" k }! `4 u
- bzero(&servaddr , sizeof(servaddr));
l1 D) Q+ ?( t2 {) q. |# o - servaddr.sin_family = AF_INET;
; n9 J2 Y/ W! k5 ~$ m R; ?; G - servaddr.sin_addr.s_addr = inet_addr(ip);
2 ^/ \5 k/ o: g4 G' P - servaddr.sin_port = htons(port);
- P* }" U& J, e" }( B' H& j - int ret;$ t( _* T' T2 I$ K
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)
) ~' h8 f/ V. A, @: c - {
; W+ G! ^9 r, d- d# ?$ q# z - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);# \# S% A( f' b- n
- return -1;
e. L E! Q' }% L: V7 L - }
3 S0 S* C1 `6 j - int on = 1;
, J7 a7 W' z6 ~5 i2 _$ {* L2 S - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
. w4 c; N) X9 h# O% ~ - {
4 d i* g' L, P7 A - printf("setsockopt error\n");
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- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
- v& X! P3 I# f5 A; M8 ~$ U - if(ret == -1)
4 z( @ T2 z0 T# ~4 q - {
% A/ m6 c$ s5 l( x! s - printf("Tcp bind faiLED!\n");9 N; G3 b7 h% o- k B! O4 G+ w5 z
- return -1;
3 S1 G# o G- b5 g/ h - }
1 V% N, z) B+ Z: D1 `' Q4 K, f% E* W) K - if(listen(*socket_found , 5) == -1)
" V) _: h7 H/ G3 ^1 ^1 O - {
& x! w1 L/ n1 C2 u! M! I( j - printf("Listen failed!\n");
8 C1 V4 e' P5 I' X - return -1;
% T% z+ A8 D+ n - }
! [4 g0 T6 |/ {9 u - return 0;9 F( h+ r9 m5 v3 ]+ K
- }
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);" }% H8 ~ n& ^$ J F# Y9 ]
- void * Thread_TCP_Web_Recv(void *arg)4 S( S7 _3 f, \* R. m. N
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- 。。。
/ F& V I7 y- p% j - while(1)
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- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);6 E: { R/ { [( b( `2 P' E
- printf("fd_socket_conn = accept()\n");
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- recv(fd_socket_conn , recvbuf , 1000 , 0);) e. h3 G% i6 e4 ?9 q
- }
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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);
, j& V7 d+ m6 D - pic_tmpbuffer = pic.tmpbuffer;* i- S r6 l* ^2 U
- pic.tmpbytesused = buff.bytesused;; ]9 r8 E1 k# k3 _* }
- pic_tmpbytesused = pic.tmpbytesused;
4 a( c5 T. a; C6 v6 b( ^# p0 t; ? - pthread_cond_broadcast(&pct);" [; ^, H+ Y% g6 U4 ?. ]) Q% ^
- 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;
' s1 o/ I! L) P4 }% e) m2 Q& S - pthread_cond_t pct;
* F' I4 l/ |/ n- }) R - int main(int argc, char* argv[])
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- ..., Q- i4 |# `8 c! N
- TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
3 d3 K2 h ^0 u! _. r+ x5 F - pthread_mutex_init(&pmt , NULL);" U# H8 S/ ], P& G) S
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);' u( Z L9 Z8 e
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
2 m( }( G7 i- V3 F; i* o - ...
- V; I# [( I( y; ] - while(1)) _9 T6 z; H3 J+ @
- {
1 s% O0 r( q9 a - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);5 J% B+ {% Y( D: B
- ...
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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;">
6 I8 V5 w/ u* m% Q2 L - </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" \) D1 Z6 D. V/ W& Q
- "Server: MJPG-Streamer/0.2\r\n" \. x+ O. C2 q+ k3 V7 ]" B) ]
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \; d$ {" B3 m! C' Z
- "Pragma: no-cache\r\n" \% y% s) o+ t9 b4 C/ W
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"' S% Y: V8 k- o$ Z9 `5 v
- #define BOUNDARY "boundarydonotcross"
9 \6 h3 w8 w- k1 ~$ n0 V5 Q' e - printf("preparing header\n");' E5 @0 r6 y- E% O
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \: i& p$ W' r4 A8 z: }5 }! c
- "Access-Control-Allow-Origin: *\r\n" \+ ?1 e9 _8 J) {. v: E9 | u
- STD_HEADER \
$ _1 ?( O8 t1 b- U- S* u- R - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
2 m. w0 }5 o. b' p - "\r\n" \
# v2 q! `1 Y: e9 s3 {7 n& G$ v - "--" BOUNDARY "\r\n");2 E! d# P4 k: H$ j$ a) {0 W3 k
- if(write(fd, buffer, strlen(buffer)) < 0)9 X# a( j/ L5 D
- {
( _" I7 m( v0 b$ g' Z- Q4 m9 } - free(frame);& c% u7 R$ a% @, p9 F. }( ~5 k
- 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" \8 F5 M- ~8 Q0 @# u
- "Content-Length: %d\r\n" \& ~/ ?8 Z" h1 F7 N; ?6 L. N
- "X-Timestamp: %d.%06d\r\n" \, ?0 P# R' l' _! n- o
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
7 ^9 }5 Y8 v5 s8 l - printf("sending intemdiate header\n");
- Q6 H, f( A" h/ c L2 k - if(write(fd, buffer, strlen(buffer)) < 0)+ w/ o) b8 a v% `3 u3 a
- break;
. W% y8 A& _/ R) U$ l$ g - printf("sending frame\n"); ~ }7 c7 f- G5 |5 ?
- if(write(fd, frame, frame_size) < 0)4 ~1 b( F: W% f3 f$ Z
- break;9 [8 W0 i+ k, X/ {' c9 W) a* {/ e
- printf("sending boundary\n"); H$ N! }) n1 k6 O
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");/ k, ]) _' H" A
- if(write(fd, buffer, strlen(buffer)) < 0)1 I" N) c/ Z- @ A) o
- 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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2 i4 c- V/ b9 a5 ^+ W; i& W二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:9 Z' w/ b' p1 q
- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)& ?) }8 J7 k- x4 }$ H7 \! k- u
- {
3 [7 l) e% e2 A2 _/ P- ^! k/ V' X - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);9 j: l$ {6 S, P" _
- if(*socket_found == (~0))
" l# v. a) h$ R5 f6 j# f, v# I - {
6 `* K/ J% v8 C" _% A+ l - printf("Create udp send socket failed!\n");1 E! ?) s5 A- @. Y' A( ~
- return -1;
$ L& M% U* S: u+ b7 v - }
+ L" u" \" t4 `9 w - addr->sin_family = AF_INET;
/ M" E! u& ^* l! y7 x# q - addr->sin_addr.s_addr = inet_addr(ip);; Z, f) h* p6 u
- addr->sin_port = htons(port);0 Y9 y9 \7 y) y( _+ \
- memset(addr->sin_zero, 0, 8);7 {* |3 M* V3 S0 I0 b
- return 0;
/ ]9 ?. J' ~& n/ O. o - }
复制代码 5 \6 @1 g$ t6 K$ T7 ?
5 v5 r2 `- J+ @* }: L6 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:
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- while(fend > 0)
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- memset(picture.data , 0 , sizeof(picture.data));
, c7 [/ ] S* s3 G `" M" J - fread(picture.data , UDP_FRAME_LEN , 1, fp);
4 B( X3 }. p. F3 L8 \5 v - if(fend >= UDP_FRAME_LEN)
. g: G0 X0 d, K* s - {
/ j% R8 E, q/ L, o, o. t/ @3 [2 E - picture.length = UDP_FRAME_LEN;
. }7 Q6 u& c4 W I) H. G, Q - picture.fin = 0;
- \5 ~; l1 k% y3 G2 b3 D5 g - }
. c' E# V5 }$ l0 H5 N6 t( P/ w3 v& N - else. X) v. |# s2 C
- {
n- o) {7 y0 b, w - picture.length = fend;
7 v4 ^$ u( J& _* [& i - picture.fin = 1;' l( J5 K) @" N* V" [. J
- }
+ `% n6 W6 n* i \% X/ K f1 z - //printf("sendbytes = %d \n",sendbytes);
# g5 M* x9 O+ C& s5 Y - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len); o' p. e3 h" O3 M+ R7 m- u
- if(sendbytes == -1)( d' U. @( W' A9 c @( D9 ~
- {
9 z4 Z: C. Q! \9 }. _* ? - printf("Send Picture Failed!d\n");) `4 U4 x+ U, H& B, a
- return -1;3 ~: c% |) V0 D" J
- }
9 c- f9 M) c9 l" T) c/ P# l - else% a4 a- R' T: i: h2 W
- {$ ^% b; u! d, L0 |0 k& m
- fend -= UDP_FRAME_LEN;
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复制代码
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8 H# k {) b+ A6 O! TiMX8MPlus 核心板: https://www.forlinx.com/product/136.html |