本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑
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/ ]5 w6 Z, ?" l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: C4 n, K& i& @2 [" A
5 F E+ q) n& D% G! s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。 , }7 w S/ o, g. m2 h: X( r

4 l4 N/ e9 N- A! ]4 f/ q# A; Y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。 . u. @$ r/ k4 S. |% a! O/ h v
一、HTTP网页服务器% G9 I- C2 X- m3 l& b4 y4 B& G
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)" n- e1 M+ `! X2 C$ j. |6 F
- {
. N; t; B* l& Y. I8 k - struct sockaddr_in servaddr;
+ y3 I* ~! U; d& _3 r - socklen_t addrsize = sizeof(struct sockaddr);# {. Z* {: T' X( \* s; s, _. I
- bzero(&servaddr , sizeof(servaddr));+ w% y# S3 m8 @0 b2 f7 C0 {- L& u
- servaddr.sin_family = AF_INET;
7 ~. _4 s/ W. M w1 K* {1 Q - servaddr.sin_addr.s_addr = inet_addr(ip);
0 Z. X9 v4 Y8 P# ] - servaddr.sin_port = htons(port);) z( H5 Q! U9 o @
- int ret; R3 N& O' [" j# r9 l" W
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)
* d# u ~0 s8 r+ ~& h8 d( E$ ^ - {
2 x) W1 n X: K3 {3 w ] {5 [ q - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
6 S' u/ \0 e) @: o+ w0 h - return -1;- m- y Y# ` e" d
- }
# P3 P0 ^ S1 q8 V. F8 o9 x& S - int on = 1;3 S& X* o( r8 A) Z3 M
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
. W1 S; }# x: f/ @! ~4 O - {
# }3 V# M7 a6 N - printf("setsockopt error\n");: B; {& z! ]) a' E G
- }
1 i; n3 ]: Y9 G6 \ - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);6 S6 _; ~5 n# r1 T7 w/ K- H
- if(ret == -1)
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- printf("Tcp bind faiLED!\n");
8 K+ ]- V* c7 ?, m - return -1;
- ^: f2 h& C1 h& w1 g! J: J' ` - }" g$ u7 d) g4 b0 v1 Z+ g
- if(listen(*socket_found , 5) == -1)9 a( z! ? p; _7 _3 U
- {
N2 }; i8 k3 T - printf("Listen failed!\n");
, D( m( F- x1 C, D5 O6 T - return -1;4 _* g; R( T1 k0 A% w
- }
( O% @; U! U- i3 L1 E0 x7 r - return 0;
6 t/ K- `6 b- g- p0 a4 } - }
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);
! \) D1 U( |/ n6 _ - void * Thread_TCP_Web_Recv(void *arg)+ S" N( w' y H& j
- {
' V; \5 \5 k) \ - 。。。
/ s8 _& n2 l9 N$ x - while(1)' r$ V$ q% e* D* o: X% A* `, f
- {9 ~) r" Q7 }% d9 ^. {
- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
8 h( @0 K% ^" l4 u - printf("fd_socket_conn = accept()\n");3 T# S6 b( t; v7 `) B9 X
- 。。。; w! q- ? f2 O F
- recv(fd_socket_conn , recvbuf , 1000 , 0);
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- 。。。
5 B8 U# O: U" @$ F) T3 L2 T - }
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);
* z D* r+ b3 c: s1 ] - pic_tmpbuffer = pic.tmpbuffer;* P- v) T+ V |, F" A1 Q
- pic.tmpbytesused = buff.bytesused;
4 j* W5 @$ T6 h8 D - pic_tmpbytesused = pic.tmpbytesused;
/ i* _- d) V1 c( N& f Y) m3 Z0 K. I - pthread_cond_broadcast(&pct);
2 b; Z/ A/ \% E9 [7 o6 G - 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;9 c4 z4 Q! y1 @2 w3 o1 s
- pthread_cond_t pct;9 n( V. o9 d4 { T4 f, K
- int main(int argc, char* argv[]); m v7 I! ]8 V0 O5 |
- {
" k. I- G$ _8 y) Q! b/ ` - ...
+ [+ N0 u' Q; S. c - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
* _! D& |. s& \; a" V - pthread_mutex_init(&pmt , NULL);
3 u8 D; |/ |% n7 C9 Y - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);* P2 z8 M+ N5 |9 q
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
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- while(1)4 g) V/ |$ n4 h; g, h
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- V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);. j; N. `6 Z. A5 V
- ..." T; H* I$ _' k2 m) p
- }
* s i. T( U6 ^$ O" i - ...( h' P) X \- b
- }
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;">9 k2 C8 l/ q8 C6 b; H& p/ C
- </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" \- q) ~+ s5 {* W1 P$ _. \! L
- "Server: MJPG-Streamer/0.2\r\n" \1 r) y7 T( M8 h
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \) i8 I& E8 k! N* |' ~
- "Pragma: no-cache\r\n" \3 I1 ^6 u" t4 q& V( P
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n" N# a7 C. p8 t2 q) s
- #define BOUNDARY "boundarydonotcross"
6 b6 [3 `$ \ y" Z; q - printf("preparing header\n");# o. s6 ?3 r" w0 |7 c. i
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \1 u& m, d3 |; u' ?. y+ L2 L! Y+ J
- "Access-Control-Allow-Origin: *\r\n" \+ F, @( @' T. k+ a& [$ W
- STD_HEADER \$ ?" C! S0 @/ I; D7 F
- "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
- W! @% G) _6 E' G- g - "\r\n" \" O7 n! g* ]* Y0 a1 T5 v
- "--" BOUNDARY "\r\n");
5 N5 |( Y4 B' J8 p - if(write(fd, buffer, strlen(buffer)) < 0)
. \4 G- c+ l0 D8 `' q! p - {
( A3 f5 T9 c/ K* r x - free(frame);9 g" V6 Z, L. o; W2 ?% n* H2 j
- return;
. ~$ H. R! B, `! e f" e - }
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; H C( U9 Q* { - "Content-Length: %d\r\n" \
1 \5 L7 L7 Z5 V; P' T7 _ - "X-Timestamp: %d.%06d\r\n" \. V$ n7 R# ^. Q8 _" M! p
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
! x I# g3 v- Y1 I - printf("sending intemdiate header\n");
0 S* Q$ D2 z* R) v9 x) y' n - if(write(fd, buffer, strlen(buffer)) < 0)
" [1 ]0 L/ |' M( w q9 f5 i) j - break;
|" P5 t/ H; Q9 S - printf("sending frame\n");! {# o. Z$ R' a* Q; y* k9 @& u! f+ b
- if(write(fd, frame, frame_size) < 0)
8 a5 d( J% E: Q6 Q; V7 o - break;$ I+ J* Q' p( q
- printf("sending boundary\n");
! Y7 N! e. c- m, I - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
% o8 a- E+ [' O C$ ] - if(write(fd, buffer, strlen(buffer)) < 0)1 u- |" d3 s$ @6 d; Y
- 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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) L* f# w" A3 x- S二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:; R8 \5 A+ b# e
- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)
" D, u; ?. o( O% [% V6 B$ r - {
' \: M6 R: A3 F, j7 ^3 G1 i - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);- |8 V) y) y/ S$ a2 V
- if(*socket_found == (~0))0 P; K1 S9 o, Q- C# C+ N' D; j3 W
- {
7 g6 Z& B- Q3 u7 D) w2 a - printf("Create udp send socket failed!\n");2 F4 V, W; ?2 I
- return -1;
0 [/ P7 z: V1 K' G7 H; z- B - }
$ R I- B2 N7 u3 b E; m) | - addr->sin_family = AF_INET;
8 S8 t- H+ D# C" r- ]6 y: A6 F - addr->sin_addr.s_addr = inet_addr(ip);
% j$ r1 W8 q9 r" d - addr->sin_port = htons(port);9 y9 R% S" { s3 _
- memset(addr->sin_zero, 0, 8);
; c% \; m' \) d - return 0;
4 V+ L/ M( d5 o" g. g - }
复制代码 ' d9 ^' i, K9 g7 q% D" m) J
( o3 y/ U+ \; p" @+ \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:3 S c+ U& M) K! \ R: u8 h
% y" M& _6 k' o" ]# D/ ]
4 N% P' b' x3 b4 U; A" ~- I- while(fend > 0)" Q4 o+ R/ e6 A! [4 i v$ e
- {
3 U9 r% r$ O/ F# p2 I) C' e - memset(picture.data , 0 , sizeof(picture.data));
, z$ O* k# f# t - fread(picture.data , UDP_FRAME_LEN , 1, fp);% Y; @* B) g: i" x
- if(fend >= UDP_FRAME_LEN): C6 X& G: o0 m# z
- {
0 P! e R5 `# o/ f - picture.length = UDP_FRAME_LEN;
0 z. `/ Y& W, N - picture.fin = 0;: b# |% p' g* ~1 H& V
- }
- L8 I; J4 ?$ g) ]+ @ - else. e8 M+ {$ b" t- }2 d1 i3 F' z
- {* {# w1 n7 s+ ~0 A7 ^& g
- picture.length = fend;" _. }% F) ^8 a; I% |! ]8 z
- picture.fin = 1;
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2 F3 q- F7 Z1 j' [ - //printf("sendbytes = %d \n",sendbytes);; J8 @3 v: J5 ?& k1 d0 V' o
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);& M( @* p# m# e+ [% Y$ r" m$ U
- if(sendbytes == -1)
0 [! G: s* {& o, ?, D+ s4 \- c( U4 y - {1 k, j# l, E p
- printf("Send Picture Failed!d\n");6 I3 k2 j0 p% [/ N' M) k9 \, G
- return -1;
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- else1 G+ p, g& H. H4 `% M8 e
- {
8 O/ z9 d% w" `+ J, P - fend -= UDP_FRAME_LEN;
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- }
复制代码 4 a8 L- R8 @$ F: u3 E
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iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |