本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑
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" R4 |3 l5 A9 o; 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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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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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。
; r1 c8 c9 F) S' p一、HTTP网页服务器# M) U. ]: e$ N0 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)1 a$ F3 z2 D: |8 f9 T
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- struct sockaddr_in servaddr; ?! r! o" h* X0 C# T- G
- socklen_t addrsize = sizeof(struct sockaddr);
/ s9 G W# z/ a4 C- n$ y - bzero(&servaddr , sizeof(servaddr));) F |8 D1 a% r# Y
- servaddr.sin_family = AF_INET;, C5 }1 O1 A% o; n) E6 U
- servaddr.sin_addr.s_addr = inet_addr(ip);
0 r: c4 f0 b$ i: ^/ v - servaddr.sin_port = htons(port);
# {5 n. b2 {0 L% w" ]' _ - int ret;9 d8 B" h2 A+ e4 w! T- R
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)
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. l; B3 {, R2 T E - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
% Q1 P" [" i1 G# e2 ^4 s - return -1;
; [" h: Q6 N2 O8 w, x0 J - }
2 T0 I0 N% [; d5 q - int on = 1;
- e# ~: ^3 G; p3 a+ w - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)! S6 W9 a p2 i" b
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- printf("setsockopt error\n");
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- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
" C4 U' I& i( L+ \5 ]& e5 I) |1 o& a - if(ret == -1)
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- printf("Tcp bind faiLED!\n");
' v9 f+ U# d; L: o - return -1;
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- if(listen(*socket_found , 5) == -1)
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6 Z$ o* Y" ]0 A: L9 T& J G - printf("Listen failed!\n");
/ j/ x+ M9 {0 m+ T - return -1;0 J$ i- N! t0 ~" ]: d/ o! z% C
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- return 0;! |! q' U- N0 K1 p* B
- }
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 X6 K Z0 |% e; a' q" g
- void * Thread_TCP_Web_Recv(void *arg)1 _ _- z N1 p9 o
- {
- } s, d/ p! K) ~6 \ `; M - 。。。
6 X, k0 B0 k) S0 ^0 F - while(1)
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- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);: ^2 D8 g9 W/ R" y
- printf("fd_socket_conn = accept()\n");% R' L# B% _5 ]6 |5 r+ l7 E
- 。。。
% N. Q! D& U* p4 v, e- O3 q - recv(fd_socket_conn , recvbuf , 1000 , 0);$ j% t6 f' d8 u1 |
- }
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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);
: _3 A% Z0 u- T! F7 j - pic_tmpbuffer = pic.tmpbuffer;
6 g. b- f4 {; r" y1 ^4 Q - pic.tmpbytesused = buff.bytesused;$ f/ \* S8 i8 ?3 a1 h
- pic_tmpbytesused = pic.tmpbytesused;
6 k4 q# Y* R( j, H6 Z1 z* Q - pthread_cond_broadcast(&pct);7 m$ [: L5 q3 q1 R- c. T
- 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;4 j5 G& z. g Z& ]
- pthread_cond_t pct;" R8 T3 u" w5 y5 A) A6 g: m
- int main(int argc, char* argv[])
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- ...
& N. K% i) r2 ^5 g" w T - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);$ q0 A" ^' ?/ Q t: [5 K
- pthread_mutex_init(&pmt , NULL);; h0 Z- u: b+ I s
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);4 c% A5 E! \* L+ I* t
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
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- while(1)
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- V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);4 ?# U2 F0 G7 u O
- ...
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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;">
5 P/ \5 G4 \1 F% I9 Q# G6 G - </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" \
. J) G3 Y- t: ~2 y- b - "Server: MJPG-Streamer/0.2\r\n" \& v+ L* W% z/ _+ }$ \$ P' N( Z
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \( e! b" a6 F: u5 F* b1 C6 \: \1 b* `
- "Pragma: no-cache\r\n" \
4 C0 M, S6 h/ `8 G - "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
- `7 Z3 D0 a2 I) o3 J# p0 o/ E - #define BOUNDARY "boundarydonotcross"3 Y! E$ W" s' m7 F0 a# S' Q! ~
- printf("preparing header\n");
# v: _4 g# x0 q# U% u b5 j5 ]- |/ ^) @ - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
/ f# h% A' r; t' j2 U - "Access-Control-Allow-Origin: *\r\n" \
; S' Q8 n1 w, W+ ] - STD_HEADER \2 F( a* T1 {5 D* J
- "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \7 D2 v6 S) ]& `! D+ l3 p$ j
- "\r\n" \
, L& ^# `! X- q5 ~ - "--" BOUNDARY "\r\n");
9 M( S: n$ m" E) s3 v& g( w4 K - if(write(fd, buffer, strlen(buffer)) < 0)
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- free(frame);4 m1 s7 ^) r6 ]" [ @; T7 D' r
- 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" \
! m+ }/ _( {' I: h5 g+ F# X) I - "Content-Length: %d\r\n" \, S$ U' j( ~+ h& x7 \+ E2 T
- "X-Timestamp: %d.%06d\r\n" \
?1 Z9 U4 d5 Y( A/ K - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
0 ^/ n- X% k/ g# e/ A - printf("sending intemdiate header\n");
/ ^! J! x. D4 t1 G# [1 }( p - if(write(fd, buffer, strlen(buffer)) < 0)6 j R2 w6 ~. O. U* F0 k
- break;7 L. {' u+ O. r/ P7 F
- printf("sending frame\n");
" ]( O! `. e4 k$ ` - if(write(fd, frame, frame_size) < 0)
- s+ X/ v' x: i& k7 r, h8 Z" B - break;- r4 w/ E1 G( y! x/ j/ _
- printf("sending boundary\n");& L7 L `5 \% U/ p
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
. B7 P0 y- ^/ g' ?2 Z* L' q6 { - if(write(fd, buffer, strlen(buffer)) < 0)
9 W2 s& @$ t7 g" ^. i - 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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, S0 y1 Z- D3 _/ U% a二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:7 o- W& E$ e( i) b, G& k
- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)( r% ^0 v! @# Z/ H
- {% ]9 K( r* p2 Q
- *socket_found = socket(AF_INET, SOCK_DGRAM, 0);6 y, C( A$ A3 c5 m
- if(*socket_found == (~0))
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- printf("Create udp send socket failed!\n");
T) l8 Y7 B) V7 [ a& B. [ - return -1;; `1 V3 l2 `6 M5 n: f! l% k
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- addr->sin_family = AF_INET;1 P) Y8 F2 }* w9 @- s
- addr->sin_addr.s_addr = inet_addr(ip);
; m7 A" N8 u0 l7 |% Q - addr->sin_port = htons(port);
5 o% [/ X) X8 Y5 P6 r* k - memset(addr->sin_zero, 0, 8);
" s1 x7 X! Z; U# v& M - return 0;! Y8 c( X9 L8 W8 p2 n
- }
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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:/ W8 A4 s& l- z
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: {# d9 m0 i1 j5 F% f6 R N- while(fend > 0)3 h+ w0 @0 V9 A- _- _# _
- {
5 r: \, J4 M9 `' H/ @$ x* x$ z - memset(picture.data , 0 , sizeof(picture.data));
0 a- h6 g8 e9 K7 E9 q4 v) H; A* Y - fread(picture.data , UDP_FRAME_LEN , 1, fp);
) P' _, k' f% n; z l' V$ d - if(fend >= UDP_FRAME_LEN)
! U5 I+ M$ \7 Q# m0 n" w! [ - {
( S! N8 E' e( z8 s* y9 W- o - picture.length = UDP_FRAME_LEN;+ Y# Z4 U8 y, y9 D) R: \
- picture.fin = 0;
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* S$ L% {" n% n, K5 j6 W' I9 l - else
# g3 N# {( U/ g }1 [6 X2 Z' L1 W - {
: j7 {8 E2 J" T: m- f1 `! u/ c - picture.length = fend;
. Z6 q% {' i! [ - picture.fin = 1;
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- //printf("sendbytes = %d \n",sendbytes);3 M$ Q( e% W& `
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
, z; U# K5 e* a$ u: J' @ - if(sendbytes == -1)
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3 t% ?; Z. w, f/ @4 Q7 B - printf("Send Picture Failed!d\n");, }7 I" i6 j* K3 Z( ]1 p0 n
- return -1;
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- else
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- fend -= UDP_FRAME_LEN;. d$ m3 Z, o( l2 |) }+ E
- } n& t% S4 G6 Q5 {
- }
复制代码
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! t. j) I, D) s+ k; D2 [0 ciMX8MPlus 核心板: https://www.forlinx.com/product/136.html |