本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑 ( D$ K6 b h$ m7 g+ n+ n- S5 Z' i
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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% u5 V' M9 r0 i0 _
) Y6 W5 L0 I2 f$ ?8 l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。 6 }- o$ l2 E0 o% ^

3 X- Y U0 l7 x( e7 h/ @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。 6 q& A4 [4 C0 W: l
一、HTTP网页服务器
8 O0 P4 u) p; _7 _) u$ a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 E" H+ W6 \) a& r ]4 D/ m4 I; P
- {
4 g: b- k1 F2 G - struct sockaddr_in servaddr;9 b% W# X' f) D4 `5 ?: `( r
- socklen_t addrsize = sizeof(struct sockaddr);' x" j4 Y: |5 q1 U* Y
- bzero(&servaddr , sizeof(servaddr));& D& n0 f5 t k4 w( N( o
- servaddr.sin_family = AF_INET;$ w2 g, r; c2 O4 W P: H$ t
- servaddr.sin_addr.s_addr = inet_addr(ip);
- T/ O% L3 y" F- `- ?1 | - servaddr.sin_port = htons(port);
% Z8 _/ P& @; E. i9 A) b - int ret;4 S- T B* E. }4 D3 U4 ^6 f
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)2 y: S& {9 @2 [; ?
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- printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);5 @" T* }" M5 |+ }% a: v7 Z
- return -1;& Q, K2 T( Y6 F+ S, e
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- int on = 1;6 I: m4 m# T# A+ N/ N0 C1 j
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)6 K* g2 K, y; J0 z
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- printf("setsockopt error\n");: S% m+ j% h2 [
- }
% }0 a0 C7 k4 Z4 N - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
( d5 J. s* m5 r* y, i+ R" s! R - if(ret == -1); J) \6 e0 y. J& _1 r; ]
- {
$ `6 x/ T) H: P1 q5 ? - printf("Tcp bind faiLED!\n");
7 ?8 M- @$ _3 K - return -1;5 x; r9 V- G- F
- }
) T$ C. K" E, S - if(listen(*socket_found , 5) == -1)6 `; n8 e/ g& g7 f" S
- {
! e( `& [4 b7 l% A) [9 G - printf("Listen failed!\n");7 f& c! ]1 A& s/ F1 [3 D
- return -1;
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5 u7 j, o" }7 Y9 f7 r" y! \8 f% \ - return 0;
/ w' E% x+ d' M - }
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);
" G5 c6 [" s. p n - void * Thread_TCP_Web_Recv(void *arg)7 ]* z# F7 i7 l( R8 B
- {
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. v* A( f. W- ^4 O; l - while(1)
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- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);# N& m1 u; Q3 ^4 O2 I
- printf("fd_socket_conn = accept()\n");
7 G' G J. ^9 b! h4 Y - 。。。
! \* ~) \) E$ q9 [/ ^% j/ v - 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);) J* {5 M& P# J& X4 Q
- pic_tmpbuffer = pic.tmpbuffer;
/ t# U# n2 ?, w& @* f* I! [ - pic.tmpbytesused = buff.bytesused;
; U+ f( K* L ~5 a* @# a! w3 y - pic_tmpbytesused = pic.tmpbytesused;# J% R% {# B# G6 e- H
- pthread_cond_broadcast(&pct);; Y. P% l) M- L
- 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;
" y$ l5 A: ^# P9 k! g - pthread_cond_t pct;7 w x5 @8 W! m! P" R
- int main(int argc, char* argv[])) H9 I/ q, d4 ^9 u1 ~% r8 Q/ i
- {
/ ]/ | e$ P1 }! n& e - ...
1 \5 D- T' D' ]4 L1 x - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);: k+ K9 F) T1 I8 A* u% A
- pthread_mutex_init(&pmt , NULL);
9 \1 f# ^+ w% q% X - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);# s$ T; G8 I6 z5 ^
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);$ J- `1 L/ E+ n3 A8 R
- ...9 P: F. w: k9 E U7 v
- while(1)0 u0 O. H* L z7 L
- {
% ]" Q- \) Z; k: b - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);' M! F+ E: l: t4 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;">
' A5 d4 R7 d$ k y - </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" \5 V$ d' \9 b9 p7 A: a/ Z2 j# \
- "Server: MJPG-Streamer/0.2\r\n" \
' }; `% ~' P4 U6 ` - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
: n- J4 E6 S* p }% Z( K$ f - "Pragma: no-cache\r\n" \
R3 w% D1 W' C$ R0 ?' F. F - "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
H! z" w0 \" e) c& F; T* q2 S - #define BOUNDARY "boundarydonotcross"" L4 j0 e; i2 X' e4 W) R
- printf("preparing header\n");
0 }, E# q3 g' x( Q - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \1 k1 X/ ~/ }5 v" r% a4 @3 E
- "Access-Control-Allow-Origin: *\r\n" \
4 O* Q$ y- B. x$ {6 @: r - STD_HEADER \! \) `' q3 O+ B8 e
- "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
( S- y6 c8 n- Z3 A1 T3 i - "\r\n" \" Z% ?4 |. [) {; d
- "--" BOUNDARY "\r\n");% T* Q, t b% B; R
- if(write(fd, buffer, strlen(buffer)) < 0)
, {( _, T5 U3 V4 v - {
% ?& `! e' ?! h0 T# L- ~ - free(frame);
( p! N7 h$ c/ ^- U - return;- @' p% |' y7 {/ O& t. H
- }
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" \. v- T5 e+ ^! n% W4 b' H. Q
- "Content-Length: %d\r\n" \9 d) c. r' w" [& y U$ |
- "X-Timestamp: %d.%06d\r\n" \
( p4 U0 O X2 o1 K. p3 |' i" i - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
! v; {1 C' l, d% {0 q Z" V - printf("sending intemdiate header\n");/ G4 m9 T/ h# e1 \) a. e6 X
- if(write(fd, buffer, strlen(buffer)) < 0)
{9 m9 N$ b" p S - break;
1 g' F8 B) r6 n* n - printf("sending frame\n");
' x3 Q6 |) z/ f8 h4 Z7 A0 C - if(write(fd, frame, frame_size) < 0)2 S! E/ W5 U9 g( t+ ~- |, v
- break;
7 Y+ e! r5 p7 U c) `1 Y - printf("sending boundary\n");9 a* d( Z8 R. Z- e
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
3 `! G3 D. s. y8 N - if(write(fd, buffer, strlen(buffer)) < 0)
2 G2 P7 b, c6 m% [! L- w# l Y6 R9 u - 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:3 Y- v6 @3 p9 k7 C" [
- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port) i$ q/ [. o& M& Q
- {4 @# K! c7 Q9 `" H4 `+ j8 q
- *socket_found = socket(AF_INET, SOCK_DGRAM, 0);
. l2 a0 \: ^" K9 Q8 Y& @2 o - if(*socket_found == (~0))
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- printf("Create udp send socket failed!\n");$ U& m1 U& S& q0 D# N6 ]
- return -1;7 C2 |; V7 L7 o1 F" G4 u; T, a
- }
i- ?' o) ]5 }) Q ? - addr->sin_family = AF_INET;
5 S x. k% ^9 s& @' ]( s - addr->sin_addr.s_addr = inet_addr(ip);& W' x1 e7 T4 l$ }3 t( l/ T" y S
- addr->sin_port = htons(port);3 i* _: U2 H% m5 n/ l
- memset(addr->sin_zero, 0, 8);
. n1 B' d- Z1 ` W - return 0;* u9 X+ f5 U& }) A. @
- }
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:. r; O q7 m, _8 z
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- while(fend > 0)
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- memset(picture.data , 0 , sizeof(picture.data));
9 q D% h& \4 j" N2 S. T4 Q! k - fread(picture.data , UDP_FRAME_LEN , 1, fp);
3 p! c/ @3 L" e5 q' Q9 k; q - if(fend >= UDP_FRAME_LEN)
! E% b4 r: o# \5 l6 p% H1 L1 j4 q - {
$ M9 \5 t& w- e - picture.length = UDP_FRAME_LEN;
3 b" u2 h+ r( Z! h9 Z - picture.fin = 0;% f1 p u* X+ d) Y
- }' R. M; @; D) m* S- Z
- else' b$ O0 V) N8 E; N! Y8 D' g
- {" x2 g5 |$ L6 ]
- picture.length = fend;
4 C, x9 `4 s/ w$ Z, d7 w) I - picture.fin = 1;+ O& l& b2 G) h N; w7 A
- }
2 N* R8 h2 Y9 A7 h$ a0 p) Q - //printf("sendbytes = %d \n",sendbytes);* M5 |6 j9 }$ C
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);- [* U! `' z5 M/ d ?
- if(sendbytes == -1)
& o: b7 }( D- C1 Z - {
; z) U3 q; ^/ d+ @* W, i- E' A0 ]; | - printf("Send Picture Failed!d\n");
! Z1 J( K0 k! O8 _ - return -1;
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! K% k) _7 Z/ N- V/ j - else7 P0 M* Q6 p3 V, s! p9 c& j) P
- {
1 F% W% R" G( p ` - fend -= UDP_FRAME_LEN;
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- }
复制代码 ) O( M" C% ]# b* N
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iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |