本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑 + i3 A* L- |5 M; m; O& z
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9 R; I( O8 D, k: Y) E1 R+ u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 v& e6 t6 V2 S) _
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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。 6 U2 O' ?- y2 \5 u8 B9 J. p1 q

% u1 g- k3 P3 D! Q6 ?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。 - g$ M; F" b7 o$ x$ m9 l5 z) T
一、HTTP网页服务器
# |( e5 o1 u/ n+ v, r. k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)
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- struct sockaddr_in servaddr;6 Z1 p. k6 Q. {2 R# J m# `. ]
- socklen_t addrsize = sizeof(struct sockaddr);
& ^; D: ^: l- n+ e8 m- ? - bzero(&servaddr , sizeof(servaddr));
4 y- C+ D9 p# @ - servaddr.sin_family = AF_INET;
L9 ~" x6 ?# ^ D u4 o6 P1 e' k - servaddr.sin_addr.s_addr = inet_addr(ip);" n# e; A- R2 n' m) o3 {
- servaddr.sin_port = htons(port);
, e$ i0 a; z, l - int ret;! v1 Q; @. K1 }+ \$ n
- 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);; T* q2 M: @7 ^% u& h# y# {* f% `
- return -1;6 `3 u+ k c7 H* p4 b
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- int on = 1;
& p0 r( I" z6 f+ O$ } - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)3 L# ~; y/ O7 s
- {7 C3 T+ w/ z2 m( F9 P* p5 l
- printf("setsockopt error\n");
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- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize); r7 P% x& J& a% ]
- if(ret == -1)# w! K0 [' O+ M/ a B t: S
- {
0 L @1 r6 T. t* W - printf("Tcp bind faiLED!\n");) |) u( `! {. X6 b, ?+ ?, y
- return -1;* B. E* } o% t; R) g% H
- }
* G1 Y4 F& M [6 A3 n - if(listen(*socket_found , 5) == -1)
6 q$ ]/ ]* u* |. { - {
' q4 V; S% j( [, S - printf("Listen failed!\n");
( _$ c1 \, }# @+ l, S/ ^8 n9 t3 | - return -1;
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- return 0;
- A, }* q9 Z. c$ X - }
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);% k$ H" M9 J* F1 R: v- y
- void * Thread_TCP_Web_Recv(void *arg)
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5 A0 n# w- T2 e- k9 d - 。。。8 {2 B8 N; z5 U& V7 S
- while(1)
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! @! I: D6 _( w: A1 C - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);- V2 w5 j" E1 A, n$ x$ B
- printf("fd_socket_conn = accept()\n");
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2 m% N! s7 N1 v' b9 q6 u3 G - recv(fd_socket_conn , recvbuf , 1000 , 0);/ M$ r }& ^, A7 a% \0 J; \) B
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- 。。。* Q2 D% }* T4 w9 p* \7 {9 H
- }
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);
5 C, g! {; ~0 ^2 b - pic_tmpbuffer = pic.tmpbuffer;6 R0 Z0 m) \1 H
- pic.tmpbytesused = buff.bytesused;
; x2 b/ k4 ~$ w) y - pic_tmpbytesused = pic.tmpbytesused;! Q7 M1 |/ w, d5 O9 a' z) J
- pthread_cond_broadcast(&pct);
6 \* i T y" v! _2 n1 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;
; {. c$ X/ w7 |: x8 b" ^% A# w3 L - pthread_cond_t pct;
( c+ l& i+ ]$ f - int main(int argc, char* argv[])
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8 y0 _7 v- G' }5 J/ a4 r - ...
* f" ~, H$ e* D$ ~9 Q6 S - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
3 W5 T8 @ R: n0 u: y8 h% P# o - pthread_mutex_init(&pmt , NULL);# k" {) V3 y2 X* e+ u5 s$ T
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);6 a" k; ~, E; _ C; o
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);4 @# d2 V6 `# `) Q; H
- ...
' s H0 K, z6 X5 F' u5 D+ X4 z - while(1)
" P, e; x: w' f - {
( W% H3 M3 u* I/ U2 s U2 g - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);! v n- A8 p' J" j) |) r2 D
- ...7 M+ n+ N* }6 _: E$ s
- }4 I" U" [' O- B% {
- ...# {( \0 m5 d* m2 g# g& f
- }
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;">& C5 G: N( t; i% I5 s
- </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" \
0 c" V5 A( I- e5 U$ | - "Server: MJPG-Streamer/0.2\r\n" \
, b. W- e N) a - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \, I9 q* K" e# J3 h
- "Pragma: no-cache\r\n" \
" ]$ c' `! j0 w+ l | - "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"! G; a/ a4 k" ~% j, I$ d T& D
- #define BOUNDARY "boundarydonotcross"4 R8 r4 r0 C- [# z9 q3 m2 J
- printf("preparing header\n");
$ x, B/ e2 H) n" t# u - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \7 K' |. P3 [" y, b% l
- "Access-Control-Allow-Origin: *\r\n" \- Z& v! \; U6 \" l, u
- STD_HEADER \
* z5 H( ^6 T; _ - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
9 k- U! d2 A' B" c - "\r\n" \
: J$ H7 j- w' {; \ - "--" BOUNDARY "\r\n");* T. S- v* X2 h) x9 w6 |6 ]
- if(write(fd, buffer, strlen(buffer)) < 0); E7 d5 n9 f; o: d" r3 L" i$ L1 h
- {
2 w5 a% V+ x m; n8 j8 P' ` - free(frame);
! Q U1 P/ g6 X9 v( w5 }2 I3 K - return;
8 U: D& i1 j' x+ w- `& V7 D3 {! D0 Q - }
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" \6 Q- @: \" J; j9 v9 [0 i
- "Content-Length: %d\r\n" \
! ` r) I4 ^: @$ K3 [; K - "X-Timestamp: %d.%06d\r\n" \
& O# j/ p+ w: O7 J2 ^8 O - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
R' t2 l; w% A$ B! F9 W& j - printf("sending intemdiate header\n");) g3 {6 A- ~' w7 x z: c* ^
- if(write(fd, buffer, strlen(buffer)) < 0)
U( ]: p! Q' p: u1 O9 S+ ? - break;
, A$ [# m& t- ?) N) G - printf("sending frame\n");$ S& s5 X2 D5 |9 m- c- X8 l
- if(write(fd, frame, frame_size) < 0)
1 P3 ^( v# d, Y+ p - break;
s; E2 m% X5 g% I - printf("sending boundary\n");
4 m$ w& F+ N( V - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");6 u# p0 Q0 p& Z! h
- if(write(fd, buffer, strlen(buffer)) < 0)
- U2 @, X+ p/ j0 T - 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。  * g7 }9 P9 e3 B9 Q# d
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二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:
8 B6 k5 h, `1 N; _& @- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)
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- *socket_found = socket(AF_INET, SOCK_DGRAM, 0);
1 Z- p3 E5 l0 r# v1 | - if(*socket_found == (~0)). q/ ?" y1 y' ?
- {- k( Q q; b3 g7 V4 d& S9 f* u0 n
- printf("Create udp send socket failed!\n");
0 k; R3 p+ D0 A( n0 t% I0 ?, O9 S0 d. }$ l - return -1;
4 k' b; W Z u/ w. U* ? - }
% K4 @" }* K" P8 r) l Y& w' Y - addr->sin_family = AF_INET;
% v& @8 N0 K$ U! x' `+ i7 i; ~. T: y - addr->sin_addr.s_addr = inet_addr(ip);. h5 v4 o! J0 y2 \# m
- addr->sin_port = htons(port);
1 Q5 i, M0 f) p9 V. V - memset(addr->sin_zero, 0, 8);* z5 ]' d1 h' f4 b. B j
- return 0;5 V( e( r7 E# A: \( q6 n
- }
复制代码 . P0 y, \4 `' S, Z) b
! w6 l, p+ p/ S! Z D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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6 h8 E) w+ Z+ c& }/ j2 O% B; A- while(fend > 0)
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- memset(picture.data , 0 , sizeof(picture.data));
( {8 N% X1 w, \7 Y( J, P - fread(picture.data , UDP_FRAME_LEN , 1, fp);
" z0 P' {) A, X! ?5 n+ o - if(fend >= UDP_FRAME_LEN)8 N1 d% |4 K3 i+ G; G: ^( K
- {
- j. [, s+ ?. r! S6 V; A# K - picture.length = UDP_FRAME_LEN;
7 l7 b3 U* ]0 e4 e; L. ^3 Q - picture.fin = 0;
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- else# D3 |$ ^2 y0 m7 G, w9 @
- {
c1 y; w; J; w! J0 ~+ q - picture.length = fend;
4 ~ r- N: w, G5 k, ?) {3 t) d - picture.fin = 1;0 P. i5 U' M' e% s r5 @0 G: J3 l
- }0 [- Z5 E% n# ^/ e/ X u* a, {: c
- //printf("sendbytes = %d \n",sendbytes);
) r+ w4 M! F# A. _ - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
% v' `& J) L& j2 L1 @ - if(sendbytes == -1)
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- printf("Send Picture Failed!d\n");$ z# f& g2 P: u6 D0 I+ ^
- return -1;
7 D" o1 j* j9 k - }
" ^# c1 w6 H" m# [ - else
. }1 z' r5 q& |! ~3 k - {
' q# V( A) y4 o3 v7 |6 r4 n* f+ A9 Z - fend -= UDP_FRAME_LEN;
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- }
复制代码 7 t5 p, {6 D3 |
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# T' w$ l) B3 JiMX8MPlus 核心板: https://www.forlinx.com/product/136.html |