本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑 2 q# Y9 r8 k; M' v
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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.html7 c* m4 Q( ~- E6 m
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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。 / v- G/ `3 }4 ~3 i# C

4 ~# L/ D6 e0 ^0 o& A! R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 j0 L P8 M: M! p; o+ o; N' t
一、HTTP网页服务器
9 U( G F9 u; I9 V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); p0 a8 g& V& S
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- struct sockaddr_in servaddr;: w b' p# L: U6 |: j
- socklen_t addrsize = sizeof(struct sockaddr);0 e' N/ F# S0 g" o4 h$ O8 e
- bzero(&servaddr , sizeof(servaddr));2 k% u) v8 h% G7 L% m7 Y6 ^6 b
- servaddr.sin_family = AF_INET; u, F: B+ W- T6 e
- servaddr.sin_addr.s_addr = inet_addr(ip);& g2 l V3 s! {' u$ e/ o
- servaddr.sin_port = htons(port);
: x" p& @6 H H1 C$ Q - int ret;
4 Q. H0 B) F1 ~" O; j$ F - IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)1 w" V* }/ D" d
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- printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);8 g2 ~) p$ e0 n1 t& @) _/ X) O O
- return -1;' N3 Q$ T& T9 D$ N k
- }
5 ~. p, @8 ^0 q/ R- y' n5 ^ - int on = 1;
% f& ^$ r: Z9 n. w+ a! n' v9 Y - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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- printf("setsockopt error\n");* P6 ^; x! e! j
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- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
f" w% a+ w0 a0 o' ` - if(ret == -1)3 q: c" J) ~ i0 T; b/ p- A( k$ k
- {
- j: m$ Y* Z( t- x0 y% i: I - printf("Tcp bind faiLED!\n");
& A! |9 D# d0 @ - return -1;
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" ^9 I. `: u8 t, R1 k/ T+ ^& j" H - if(listen(*socket_found , 5) == -1)5 P" Q8 t+ w0 m; C' h! F
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- printf("Listen failed!\n");9 B8 \8 E# X7 n+ ]9 ^
- return -1;
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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);, W d/ g* k2 ~
- void * Thread_TCP_Web_Recv(void *arg)1 k% ?$ B' E2 a1 ]7 z# P6 A! k$ W
- {
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- while(1)
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8 I: f4 J K, g- l) e - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);% F; Y* o9 W. @/ Y) c
- printf("fd_socket_conn = accept()\n");5 Y4 k, y- n. D! B; d& R, M
- 。。。3 ^0 J, ]/ [4 s$ u$ |" H5 ]
- 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);
! d2 m6 }, e' W - pic_tmpbuffer = pic.tmpbuffer;3 N1 F6 Q; H& |7 w9 M
- pic.tmpbytesused = buff.bytesused;
i2 _8 J$ P8 q2 {! |4 i7 } - pic_tmpbytesused = pic.tmpbytesused;0 R! n) @1 P( C T/ L* m1 N9 h% w: Q
- pthread_cond_broadcast(&pct);2 [# Z5 R$ L& q$ ^" T1 h5 s
- 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, ~3 Y5 ?0 M C- \8 i2 J - pthread_cond_t pct;5 U& E0 ^( j$ S/ r! i+ n' U% P
- int main(int argc, char* argv[])
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- ...
/ g$ ]/ `7 _3 u; @: r' } k# L - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);% O9 d, _0 u* i$ j0 m. u4 W
- pthread_mutex_init(&pmt , NULL);
2 c- M' ~ }" z: N! Z5 I6 Z - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);
5 z) A7 Z' C. h2 u. m% ~# A" }0 f - pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);* L+ j' A; Q: |3 x$ F
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- while(1)
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! @. [$ y7 J1 C% R0 L4 w+ Q - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);
- ?8 g3 R& Y* Y9 g8 l. K - ...
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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;">/ ~3 F) V+ X9 @7 ]% |
- </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" \8 T* D1 n+ w; { p* J. g* r: Q
- "Server: MJPG-Streamer/0.2\r\n" \- J( c- r0 v; k4 ?, \* o6 }8 {
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
) U; @+ `. D* B5 g - "Pragma: no-cache\r\n" \$ y' }* u$ y& G5 s* Q
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"' K) Q( A0 D5 _2 N [
- #define BOUNDARY "boundarydonotcross"9 t* I/ q, ?% [0 t& F6 a1 M
- printf("preparing header\n");5 W. B6 ?# M" R* c
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
, n U* A: u6 ^5 t - "Access-Control-Allow-Origin: *\r\n" \. J. }( H3 _$ x% M" i
- STD_HEADER \! H3 w) ]9 Y% n$ v# @# A; [5 W
- "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \( T, a2 X0 ]5 y( J3 n2 M$ d0 L
- "\r\n" \
4 B0 j) O% g9 T, }( h; x - "--" BOUNDARY "\r\n");
: E: p) l ^. h* E/ q9 n5 ~# L. k - if(write(fd, buffer, strlen(buffer)) < 0)
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- free(frame);+ |8 {% r# I$ `8 Z' C9 H
- return;4 y+ U( c) |! x" `$ O5 N$ 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" \
, C% F$ K K9 s2 Y2 ^% x* F - "Content-Length: %d\r\n" \
7 f8 \; E2 Q% [6 ? r6 \5 W - "X-Timestamp: %d.%06d\r\n" \
$ U+ V2 w6 F g( O' i - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
& F y7 q' y; S - printf("sending intemdiate header\n");
, V$ o/ g- z8 O! b - if(write(fd, buffer, strlen(buffer)) < 0)/ y" ~5 b7 G' Y% z5 J
- break;
/ s/ B+ d& p j% d6 K& H& D - printf("sending frame\n");+ h8 ?. v: n9 e$ B$ |% s; a8 e
- if(write(fd, frame, frame_size) < 0)& e; K) C# {8 G8 R: S
- break;7 E* q) n8 H- i, L+ C
- printf("sending boundary\n");: F4 a& ^4 L* a S- I
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
8 ~! G% s7 Y( K; l. [ - if(write(fd, buffer, strlen(buffer)) < 0)
! n! [- p0 l4 u7 p& C0 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。  2 t% X e* G/ e% h: Y

0 A. ]: X( C5 }2 f2 T& W0 O二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:
3 A+ R3 U }; k9 j! C- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)$ l% s" U2 ]# U9 O4 \$ D) D
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- *socket_found = socket(AF_INET, SOCK_DGRAM, 0);0 m- V3 e; J& C# b# K
- if(*socket_found == (~0)) a ?# t2 J8 I* R! d% D6 a$ {
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- printf("Create udp send socket failed!\n");
2 C4 i/ i6 ^: a( c - return -1;8 E9 ]6 }. g, X$ ~8 \1 t) \
- }
: U' C3 ~: n6 E( @0 U4 L0 ?0 A5 X - addr->sin_family = AF_INET;- y" N2 n+ O0 N! G& K) t5 g
- addr->sin_addr.s_addr = inet_addr(ip);
4 D( A+ n+ i3 M" Y, c - addr->sin_port = htons(port);
1 v# c* I5 i0 H1 s4 | - memset(addr->sin_zero, 0, 8);7 j% M& b, A' R/ n
- return 0; F& L. q, z; O9 E; ~* g, S+ P
- }
复制代码 0 T7 I: g9 J5 o# I
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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:
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2 n$ ^( d. k- [, B" p/ j- while(fend > 0)
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- memset(picture.data , 0 , sizeof(picture.data));
& D' c5 M! l( D: h( B - fread(picture.data , UDP_FRAME_LEN , 1, fp);
M: s0 u* ?0 M3 @$ U# I/ {4 w - if(fend >= UDP_FRAME_LEN)4 [5 P4 _1 v9 u* P1 t6 U
- {
/ \ D u* O) c6 z9 g - picture.length = UDP_FRAME_LEN;
1 ^8 o* P! A2 v% b" Y0 l9 G4 J5 r% j - picture.fin = 0;- @$ e2 |! O/ y( h
- }
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- picture.length = fend;
8 l9 a- y+ F# ` - picture.fin = 1;
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- //printf("sendbytes = %d \n",sendbytes);/ A! N/ k! @/ J! ^
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);1 V3 f& L& E; I0 M- g7 N
- if(sendbytes == -1)
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- printf("Send Picture Failed!d\n");1 H" |4 [/ L% a& i8 B2 g0 O
- return -1;
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- else' I! e0 }1 l' S: E+ [
- {
0 ^! G/ u$ [+ E, i9 e - fend -= UDP_FRAME_LEN;' ^ ? C' I$ E+ }, w1 m
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- }
复制代码
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iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |