本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑 ( Z0 Z! |' v0 A/ _
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, V: e" N+ b6 N" d* O5 H5 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
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% Q( x& y' c* Y; z8 e6 P8 q+ n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。 0 U' `( [0 L! u: ]3 i; Q

) L* ^% U* u r8 J N# Z7 c. n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。
' m6 a2 N9 p$ F- q3 c7 R* C0 j一、HTTP网页服务器
S& t# O+ o! U- s1 J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)( Y9 F J8 m9 |$ m0 `
- {
: N4 ~0 i0 L" J* c; H+ {$ {- K - struct sockaddr_in servaddr;- Q3 z4 o8 @' d2 I% a! a. `
- socklen_t addrsize = sizeof(struct sockaddr);( U' L& E5 _1 c e
- bzero(&servaddr , sizeof(servaddr));- x7 k+ m4 {) S
- servaddr.sin_family = AF_INET;$ T" F h- W- V; o5 x4 f+ h
- servaddr.sin_addr.s_addr = inet_addr(ip);
7 X4 v: C0 t& T1 C: W, z - servaddr.sin_port = htons(port);4 A# _+ `& V( C: O9 v/ r
- int ret;
4 {) B! P; t, g- t! 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);
" o! ~) r" g B) A: y - return -1;
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- int on = 1;
1 [$ g# W" a: h. b( a - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
+ J: n0 e+ L6 C6 Z; H - { u- @0 z+ \ i) ^6 X
- printf("setsockopt error\n");) ~( g, k7 S, L2 T' Y$ C. `
- }
1 d# w$ b0 h* ~, n3 o' i9 y: a3 ^ - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
+ g) b. I* X. J3 Z+ B - if(ret == -1)
+ B, e5 q0 H: Y3 P/ ^ - {
6 A |/ {% _! C. n, {) Y* Q - printf("Tcp bind faiLED!\n");
0 T$ g2 I3 F4 R* E! d& \$ y - return -1;
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- if(listen(*socket_found , 5) == -1)& x7 a; _; E7 h! ~
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- printf("Listen failed!\n");
8 O) h9 J$ K, ` - return -1;0 G% {) l+ d* N& [2 f/ i9 a
- }
- a4 W0 w* _$ C s4 o, ] - return 0;
$ |8 _) O4 x$ r - }
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);
, k9 S" W4 Y! ^9 ]6 s" j& K - void * Thread_TCP_Web_Recv(void *arg); e5 o, b+ u$ y: T
- {
5 w* P' B' |/ E$ }7 \; _ Z5 w - 。。。
! W$ R9 l5 e3 G4 b - while(1)% t+ P: T, N* w) ^5 i
- {
, I( X, `' |. G& h, ` - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
/ H9 e% ?7 M* t* u# [" G - printf("fd_socket_conn = accept()\n");9 K8 M! f! [! y' A& t
- 。。。
& e" R+ y2 H- `, p- Q8 T - recv(fd_socket_conn , recvbuf , 1000 , 0);( x+ ?6 ?6 i( i" k% u5 | E/ D. Y! q, U
- }
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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);5 D! ^: {' E8 j, c1 Q
- pic_tmpbuffer = pic.tmpbuffer;$ q& b5 s* h4 N- k0 y& t
- pic.tmpbytesused = buff.bytesused;
: p7 y: L% E' _3 t1 D - pic_tmpbytesused = pic.tmpbytesused;, i# m$ x( r, {8 [6 l
- pthread_cond_broadcast(&pct);8 _2 V% S$ U0 g; p- p- e1 N
- 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;" @' S; [: `- i3 M$ i
- pthread_cond_t pct;6 }6 s( Z: m* u' \' B& l$ k9 ~4 Z
- int main(int argc, char* argv[])
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- TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);0 g1 O1 r7 l7 c. u O- `' T4 }
- pthread_mutex_init(&pmt , NULL);
. f# ^1 u9 ^. {& J; `2 x3 v - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);3 W' \' g6 s" d$ b0 M/ `" F
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
/ w( B7 I& I% `+ \; M) u3 k+ E3 W - ...
$ r2 @8 v4 H* E2 W2 d: o" g - while(1): V3 S* ?9 m, ~5 E, C
- {/ h$ V: ~& \ u! P- p
- V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);
: }. y& Z4 q2 Z# X4 P - ...
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- ...
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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;">
6 S# q% U. E, f' L ~$ h* F - </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" \
% ]+ d6 U5 ?$ m# w - "Server: MJPG-Streamer/0.2\r\n" \. d1 H3 E9 ~; @0 x8 }+ h
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
8 {) D$ A D+ f4 H3 S - "Pragma: no-cache\r\n" \
# H7 h2 i( i- N! \: W1 l8 q - "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
0 T V$ A8 J) F- D2 {0 W5 q - #define BOUNDARY "boundarydonotcross"
2 p. m* g6 t" h, x2 B- c. ~ - printf("preparing header\n");9 q) u7 O+ ~/ `9 u, m0 V4 R
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
: |3 m' x, q: v. D2 z - "Access-Control-Allow-Origin: *\r\n" \2 r4 |0 j0 j0 J( M1 ?
- STD_HEADER \
/ c0 H- S" E7 V# p - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \, N% o7 H: ~, l7 m
- "\r\n" \
- t0 K4 w g/ i0 p& n2 K' x* h - "--" BOUNDARY "\r\n");' k3 t4 i2 |4 O; e1 T7 }
- if(write(fd, buffer, strlen(buffer)) < 0). s$ y% h# |$ @! G1 R% L/ V
- {
) s/ G+ C% w$ f, F - free(frame);# X7 t a0 t3 P" P- R
- return;
, I, e- ~- a% p: m. r6 c - }
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 `% u' M/ @ - "Content-Length: %d\r\n" \8 V$ I. ?3 I$ _+ O6 c
- "X-Timestamp: %d.%06d\r\n" \
; u9 ^: y0 Z5 L' d7 t ]$ w0 p - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
. ` s% f% t. ]* ^. C - printf("sending intemdiate header\n");0 P% H9 m+ w% [8 a% a5 l
- if(write(fd, buffer, strlen(buffer)) < 0) P: Z& _' N+ B1 T, X! o3 t
- break;% F, Y0 A7 L. L
- printf("sending frame\n");+ | j$ E0 J% i3 V' U2 Z
- if(write(fd, frame, frame_size) < 0)
: s7 W, W0 K% [. n( S7 V0 @7 M0 ` - break;7 b! Q% G9 d0 a2 p# M/ D, p
- printf("sending boundary\n");
; o2 @2 E/ \& y - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
2 O( a/ k9 @' k1 e( {: Q - if(write(fd, buffer, strlen(buffer)) < 0)6 ^) R, y/ C* R. ?' j! o3 o
- 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:$ z6 |4 K: Z* n6 l
- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)
5 W+ I9 t" _$ }+ m6 u' r. ^ - {0 w$ [& o+ f& K* p1 U+ `; `
- *socket_found = socket(AF_INET, SOCK_DGRAM, 0);
9 O4 L& W7 O# J* @: t. L - if(*socket_found == (~0))" Z8 j7 G7 u7 _' c9 Z$ e
- {3 [6 A# M9 Z0 c" k8 A; {2 N
- printf("Create udp send socket failed!\n");
5 }" _# N2 i& `+ ? - return -1;5 T; i' N! x, ^% _6 i
- }
* l/ C; F" |' @1 \8 B6 [ - addr->sin_family = AF_INET;( u0 M8 w9 A& H6 N+ m
- addr->sin_addr.s_addr = inet_addr(ip);+ G% Y3 g! s) ^% N4 Z* h. O3 |' a' Y
- addr->sin_port = htons(port); W6 l: o: I% @9 d6 T* M
- memset(addr->sin_zero, 0, 8);! V" g# `; t8 w* N6 \; `
- return 0;
9 o7 h5 B5 P9 w+ J - }
复制代码
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! y+ l4 I3 p* y, O. Y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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! f# L( w3 s3 E# s, P5 I- while(fend > 0)
% b2 B: X: F9 A: |; N- S c! n3 ` - {" I. s" Z1 p( W2 _0 F5 p5 `5 v1 C
- memset(picture.data , 0 , sizeof(picture.data));
: ?) F* y* ]$ P) t9 A4 Z& y - fread(picture.data , UDP_FRAME_LEN , 1, fp);
( U9 Y/ A5 P5 A! @ - if(fend >= UDP_FRAME_LEN)% I0 r! i/ z' d1 H
- {- f) k! m A& z. r Y( r: L
- picture.length = UDP_FRAME_LEN;
* }+ D% v8 N- Z$ p; F( t% T - picture.fin = 0;
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- else; D8 q, g/ L2 `* _! O
- {
# b9 n x; j/ \# @ - picture.length = fend;
- V! P( r, K1 x5 v' T9 W - picture.fin = 1;
) `# }3 I" I- C' a4 D9 [ r) C - }- m" [4 V6 O+ }
- //printf("sendbytes = %d \n",sendbytes);
4 |5 J7 D& E. X; {4 | - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);$ G! G/ Y l+ e4 x0 J7 f
- if(sendbytes == -1)* d& H& \/ v" @, {, }, v; t
- {
0 k3 F1 J: {! ?) \. S0 ] - printf("Send Picture Failed!d\n");' z* N/ v- ~. I2 X* d0 L
- return -1;
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- else7 M: U! `7 P s4 \% |# f8 H4 }9 W
- {3 B2 k7 W1 Z |6 ]5 s
- fend -= UDP_FRAME_LEN;
; \% f3 Y6 h7 b4 i# Q - }
& ^6 ~, `' b6 V - }
复制代码
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iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |