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.html
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6 g1 b2 ]% l+ I2 f2 c! {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。 + Y* S* x- ]& [! S" R
一、HTTP网页服务器
7 ^! s0 Q8 J, {) m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)' A+ E! H) ~4 f* A7 V6 l# `
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- struct sockaddr_in servaddr;
. c. q) `8 {% `& t# y - socklen_t addrsize = sizeof(struct sockaddr);
: ^6 `# O; C H: C - bzero(&servaddr , sizeof(servaddr));
; f) l" n/ N6 Q4 {- Q - servaddr.sin_family = AF_INET;
' }8 x9 g1 n1 O8 v9 d, P - servaddr.sin_addr.s_addr = inet_addr(ip);
8 u: {* G8 X1 D1 A: [ - servaddr.sin_port = htons(port);3 U3 K; X+ [1 q* Q. `9 O
- int ret;+ f- c. E- G' j3 m
- 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);
9 e/ Y! i7 A# t$ @ - return -1;! p0 U- Z i. Y4 e6 h
- }! B3 s3 ]4 \; \- q+ j/ P
- int on = 1;
( l( m! G5 ?2 D" i& c9 z - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)8 {% P( E+ M) y3 l5 _3 g
- {
1 ^$ I9 @$ p }" a6 [! C - printf("setsockopt error\n");. Y' Y0 J( @- `1 x. Q
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- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);; p, C: e4 ]1 n/ [7 }% a
- if(ret == -1)
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- printf("Tcp bind faiLED!\n");
1 @& v( h0 T0 R5 ~, H% x - return -1;! ?( R" X1 H- u& N% q% K3 ?
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- if(listen(*socket_found , 5) == -1). y$ l( }8 h/ |7 G
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- printf("Listen failed!\n");
0 \- N. B6 V/ T' N8 e# G% M( O - return -1;+ y8 O; c0 P3 c3 c, ~
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- return 0;
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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);6 P4 |0 C9 ]5 Y% b: d
- void * Thread_TCP_Web_Recv(void *arg)
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- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize); l! \3 [' q$ k+ r
- printf("fd_socket_conn = accept()\n");9 k M9 c7 Z( s6 c
- 。。。
V( U4 n( I X4 S4 J9 N9 d - 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);
4 o, U& n* A* y4 ~ - pic_tmpbuffer = pic.tmpbuffer;/ f& E. V) ^, [# d( H+ H# G
- pic.tmpbytesused = buff.bytesused;( n& b n- T$ b, V6 h6 f
- pic_tmpbytesused = pic.tmpbytesused;
3 h" r! t9 Y# f! h4 a - pthread_cond_broadcast(&pct);9 d! k9 V; a4 {/ ]; w& `
- 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;
2 ]# T5 \5 e4 o" V' I- I - pthread_cond_t pct;, p6 S( U" _! B
- int main(int argc, char* argv[])- G. D) i0 L X2 Y
- {
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7 Q! z/ l& i2 L! C9 j0 g- C: n - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
# Z2 J+ J+ o7 W C: ^1 {2 b - pthread_mutex_init(&pmt , NULL);
0 ^) \, d- E' z9 O# ` - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);2 ~) ?$ E Z S: F% w( _+ X, k
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);! e- }# X* ~. I. z+ i4 V% S
- ...+ o" i: D6 {5 o! V3 ~
- while(1)9 [2 ^0 q S" X5 @0 f4 P/ D/ @
- {
, ?$ [4 b* m6 G- { - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);) y, U2 q1 V8 Q V) `+ G/ u8 p
- ...
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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;">
% k6 k6 u; s) n1 b2 h/ |8 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" \% g; m$ Y) H9 O* N
- "Server: MJPG-Streamer/0.2\r\n" \
* I* z7 B7 A9 g% I( o" S* b - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \3 y( I) E _% N% t& Z$ l. L6 M
- "Pragma: no-cache\r\n" \9 @2 k# d- U Z
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"5 D4 b* k! { m. p2 |8 k
- #define BOUNDARY "boundarydonotcross"
9 ]& b* [ Q2 P( W( Z - printf("preparing header\n");5 E1 ?4 u! d' O2 c
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
& }/ ]$ m6 |9 a1 v1 B3 j - "Access-Control-Allow-Origin: *\r\n" \6 P: O- `, F; a! P) c, M: W
- STD_HEADER \
F- P T& T- r1 E+ |* y' A: [ - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
4 \! z: ]( g" d: k; M! v" f$ E - "\r\n" \4 p6 y1 J( Q4 U
- "--" BOUNDARY "\r\n");7 Z& @* q) p& A3 f6 ?0 i5 l/ r
- if(write(fd, buffer, strlen(buffer)) < 0)! J# Y# y( c* V5 o* \9 x9 [5 U9 `
- {
I- x5 o( n8 R- p - free(frame); {, O/ z `/ x4 J c* H5 i
- 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" \
+ q: J3 g4 N: g$ ?, b - "Content-Length: %d\r\n" \! a4 P' _+ I/ V7 f2 F R/ ^2 n
- "X-Timestamp: %d.%06d\r\n" \
* l( j' z: ^7 _9 \ - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);2 P& K6 C4 m# P' G9 s. g2 g" d3 O
- printf("sending intemdiate header\n");
; D1 c' k5 ]* n' k - if(write(fd, buffer, strlen(buffer)) < 0)
x2 ^1 L- M5 c$ w! I - break;
4 |- ~0 p8 A' o; J9 z7 O - printf("sending frame\n");
f/ j5 Q$ h; v$ p }- o2 W( J - if(write(fd, frame, frame_size) < 0)
$ W2 p5 W- e: A; z - break;; x0 `0 H$ D. W8 P9 E* c {1 _
- printf("sending boundary\n");
' v9 H: M& G t1 I! z - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");5 \/ p0 Y1 M$ o0 P
- if(write(fd, buffer, strlen(buffer)) < 0)$ K! \* w* Z# X3 M0 {. @3 V
- 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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二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:2 z3 u; v' k& q& V
- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)
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9 \- T' L5 j, ]8 I1 O7 o - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);
! {" s2 t% E; q8 J6 ]+ p7 { - if(*socket_found == (~0))+ U- i2 s a8 l8 {+ B( _
- {$ ]2 g% h7 n, o/ a' R
- printf("Create udp send socket failed!\n");' n% t2 Y$ }4 t3 c6 _7 P) d
- return -1;% y5 `2 P5 ~0 E* C6 A4 p2 A$ {
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- addr->sin_family = AF_INET;4 T5 c: e6 C$ v5 ]' \2 ^
- addr->sin_addr.s_addr = inet_addr(ip);
6 K/ M# R+ M, q3 l) r; j3 k - addr->sin_port = htons(port);4 V2 _. M0 h: B+ }( k
- memset(addr->sin_zero, 0, 8);
+ k2 }- p% b4 s( n - return 0;. F( K5 i. Z! L8 O* g- Q
- }
复制代码
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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:4 ~- [- G+ d9 A/ }3 {" c
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- while(fend > 0)
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( \( e( |5 y+ w. R - memset(picture.data , 0 , sizeof(picture.data));
9 s, {" `* g( @ - fread(picture.data , UDP_FRAME_LEN , 1, fp);/ r! l E8 f/ Y3 }
- if(fend >= UDP_FRAME_LEN). e' u7 }" P" g; i& k
- {
! A) N6 `. G9 K1 |5 c7 n% R, l2 e8 Z - picture.length = UDP_FRAME_LEN; N! l& D, K% ^% {1 Y( N* k) B" U1 I. e
- picture.fin = 0;+ B3 d3 W4 I" j9 D' i
- }
9 Z; G' o1 M' J - else
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- picture.length = fend;. h$ u9 `4 A3 x o
- picture.fin = 1;
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( q( }! K4 Q: T" g% t - //printf("sendbytes = %d \n",sendbytes);- t/ H0 G F; s+ y( }
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);# {9 `# X/ [1 {6 S7 j
- if(sendbytes == -1)
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6 Q0 @, l0 |7 u1 E$ t2 r - printf("Send Picture Failed!d\n");6 P3 r- m. |& _: `) b; o
- return -1;0 V. x0 P+ q( j8 u
- }
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- {
& W- G' A8 H& j6 e) U - fend -= UDP_FRAME_LEN;
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复制代码 / s, W/ u7 A% T1 h3 I0 k3 y
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iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |