本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑
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0 Y& y9 s. X) A4 f; x: A4 k: Q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- ~/ h' }" ?0 ?' E m4 x( X
" u0 k9 `: L1 V1 i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 i' w; x; o7 E, X: Y: a( N$ [4 X) B

( L0 D- d) `6 I* ]3 E3 P" }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。
2 b/ i* m6 u8 d( b) a6 T9 E) B0 A一、HTTP网页服务器7 F9 g v) K, ?! y
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)0 T$ {( b7 ~7 ]9 a
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- struct sockaddr_in servaddr;: N1 e4 C) j- s5 z5 u8 z
- socklen_t addrsize = sizeof(struct sockaddr);
& X0 c; a. u# k% _ - bzero(&servaddr , sizeof(servaddr));# z/ L9 O& r# u2 ?
- servaddr.sin_family = AF_INET;
4 n+ j+ g+ T1 X% o6 L5 ] - servaddr.sin_addr.s_addr = inet_addr(ip);
: A5 e( J5 k9 {+ K s - servaddr.sin_port = htons(port);/ n8 l1 k9 ~( h R) |
- int ret;
) m. q( v% g$ ] - IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)3 m4 e* B# a9 A D I
- {
: p9 G1 \8 i0 r1 f( x8 Z" z - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
/ ]! r+ ^) c% [- ?2 _/ `5 ^ - return -1;
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- int on = 1;( D+ J4 M. u+ P+ U8 `& w& A6 R' n+ J
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)7 x0 Y4 i5 ~7 B1 q. F3 T
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- printf("setsockopt error\n");- D/ f9 O8 X* G
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- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);$ e& K. r. q; ]
- if(ret == -1)- }4 M( L* Z# H# h. [9 `
- {& V; p1 o# B4 Q- V6 A
- printf("Tcp bind faiLED!\n");' i/ {' d4 D/ _( y/ }
- return -1;
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- if(listen(*socket_found , 5) == -1)
% L8 {* [0 s0 Z% s4 { - {
6 ~7 _: e. L- Y$ ?6 Z2 R - printf("Listen failed!\n");7 T% `1 t. {( q7 N
- return -1;- C" a0 k* R4 q$ O1 J6 ?# m( v2 J
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- return 0;# B4 H% y5 o: {
- }
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);6 m% p, p9 J( _, z! [0 m0 |) l
- void * Thread_TCP_Web_Recv(void *arg)0 F0 r& c: p" a" P2 c; b& V* b
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- 。。。
( [# u5 W) {9 ?' |: ]+ B, }4 w - while(1)
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2 B! h6 t* ~* V - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
* F2 p) F1 G, W, X - printf("fd_socket_conn = accept()\n");0 c' [2 \1 |5 ~8 W- I2 _
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- recv(fd_socket_conn , recvbuf , 1000 , 0);; a9 p$ ~( J* E7 p d: {
- }
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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);
( L. |1 f+ s! Y" Z4 o - pic_tmpbuffer = pic.tmpbuffer;
; C- v) j. E2 d) f% e6 x- E: C1 k4 |9 d - pic.tmpbytesused = buff.bytesused;
3 |8 }) t- R) ] - pic_tmpbytesused = pic.tmpbytesused;4 j4 K& ^( O# A" e0 P! \
- pthread_cond_broadcast(&pct);
9 e; x b% O0 K2 f; T# d - 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;) ^+ K/ G, v" D1 M
- pthread_cond_t pct;# X3 ^0 e! @7 n3 e0 |) q
- int main(int argc, char* argv[])
; z- {4 W y W* z - {
' U5 B) l# c0 d- o* }' a7 | - ...
! _8 X* J3 f! \ - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);# K) c1 L; w2 h1 ?6 X
- pthread_mutex_init(&pmt , NULL);1 `# c; i! u6 r' O* W
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);
7 a9 }+ g: ~* J6 R4 y [$ u - pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);5 H7 ]0 p3 t9 \1 p/ l( u# W
- ...
% ~, ? x( v) a9 h; s0 B0 ~ - while(1)( S3 X! D Y b5 e" r/ q) @; `* t
- {
# B7 u& P5 b9 M7 q - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);
+ Y" S! c/ `' h* ]& A - ...
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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;">
, h4 a( b; Y8 q6 O+ h - </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" \
# i) E( k$ |* Q8 t. X - "Server: MJPG-Streamer/0.2\r\n" \ J8 f, G7 J5 A7 O, @- [; @
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
4 R8 u. ^: \: [5 v& A9 z1 G - "Pragma: no-cache\r\n" \
, Q) Z' ~5 v# n - "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"6 a) J, L2 ]- Q! L3 H
- #define BOUNDARY "boundarydonotcross"5 `" K% J5 A- A+ b
- printf("preparing header\n");
, b! z* v: \% ?5 N: b% ~ - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
- `; D3 S0 Y S3 J - "Access-Control-Allow-Origin: *\r\n" \
& L2 R6 c+ o% s7 w/ H' l - STD_HEADER \
. |) |6 G D, X8 J# f - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
E- K# m0 \2 o - "\r\n" \
; {& d1 X) `. x2 o, C& h - "--" BOUNDARY "\r\n");
% }" M u; A9 P k1 J( P% {: L% { - if(write(fd, buffer, strlen(buffer)) < 0)! r) ^! h% U" a) Q8 G
- {
$ |' i/ n' S, i w+ `& a' O* t - free(frame);
4 V/ M+ g3 V, q( E: y - return;( l& u9 r# _+ b0 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" \' D; `% ?$ B5 P' ^ j
- "Content-Length: %d\r\n" \1 {, H) r ~' L
- "X-Timestamp: %d.%06d\r\n" \
- U) n5 j2 i8 E2 O" s" x" a7 O - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
7 ^1 s5 K: |* j2 z; F% X6 b - printf("sending intemdiate header\n");
( U* u- ]$ } c( N! C' y2 O - if(write(fd, buffer, strlen(buffer)) < 0)- e( j6 f# ?: R' h i5 Q
- break;
5 C2 S+ c9 A/ V. z - printf("sending frame\n");/ _9 F6 P# ^1 u; e2 v- L
- if(write(fd, frame, frame_size) < 0)
% [! J2 N# X+ E% m6 L - break;
4 a$ l9 E, s& A2 F - printf("sending boundary\n");7 q) O1 z. I# R
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");% `1 O$ ^5 B8 D7 G4 r; }: k
- if(write(fd, buffer, strlen(buffer)) < 0)" m h: f! Q3 U \. V: y4 z
- 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。  3 X8 X7 n2 I( i+ D1 J" V! w& t% F

$ {# s, @# Q" {9 Q+ ?, e二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:
8 b2 v. C& g! B9 q, [# I- 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);
' \! S# }" o7 h8 ~& o - if(*socket_found == (~0))9 A5 {+ o# ~7 \' `9 u" P6 h" v* N/ Y
- {
% B- T( | w* a4 r; U2 U - printf("Create udp send socket failed!\n");
5 ?; p8 C( Y: n2 u6 J! u - return -1;% K& n. m. D3 F. b
- }; I& Z/ V0 {# A" F. M
- addr->sin_family = AF_INET;, q; ^& \, v" a. H* @
- addr->sin_addr.s_addr = inet_addr(ip);+ `6 _/ v! k* \( M" p
- addr->sin_port = htons(port);5 F' w/ t% }+ s8 I
- memset(addr->sin_zero, 0, 8);
9 p: }$ I7 M% Y7 g& y3 Q - return 0;
" W1 E* J/ P4 w# @ z" l - }
复制代码
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4 F T8 D# p! C# M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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- while(fend > 0)
* y6 w" l Y! n, D' r - {
3 v6 Y! I, N4 w4 Y' d' d - memset(picture.data , 0 , sizeof(picture.data));# M% A: x5 f1 i: z9 R1 }
- fread(picture.data , UDP_FRAME_LEN , 1, fp);
: ~" T. P; X) g# r - if(fend >= UDP_FRAME_LEN)
& ~$ s% N1 K4 c - {
9 b; l" E/ R/ c4 ? - picture.length = UDP_FRAME_LEN;9 V; A2 {5 o3 o- T$ Z3 N- B
- picture.fin = 0;
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. ?$ O. d9 b8 E! w9 T( P* u+ M. R7 \4 y- H - else
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, `7 y/ Q, n+ g$ z2 f - picture.length = fend;
& x7 u1 ^* {& }$ a3 i* X - picture.fin = 1;
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3 u9 j4 U8 U# {7 _$ ]; k - //printf("sendbytes = %d \n",sendbytes);
% B0 X9 f0 c; l8 {/ G. v - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);( w7 f/ y$ X* w) b) A% Q4 E0 z
- if(sendbytes == -1)4 b6 n u1 G5 }; Z \3 b* D
- {5 A' R5 ^) b; g" t+ w: m( Z* e
- printf("Send Picture Failed!d\n");: s5 C6 N( P/ C$ s" J% P/ Y6 m
- return -1;3 j. ?7 u' v/ e# e$ x' X
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- else* ~# V( g6 O1 J
- {5 k: O9 w0 {! f4 j% u f
- fend -= UDP_FRAME_LEN;) D6 a1 u; c( V: a
- }
: S9 ?/ f4 F& q T- o) b8 p& V - }
复制代码
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iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |