本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑
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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.html
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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。 4 E9 S9 j+ E7 P1 C- N4 G
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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。
3 l$ g. Z7 l! B0 |$ B一、HTTP网页服务器
5 c: O- B1 K v0 N$ X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)4 l3 W5 |/ z: T) Z5 L
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- struct sockaddr_in servaddr;' M) X9 t( c, Q: ^
- socklen_t addrsize = sizeof(struct sockaddr);0 e& b2 m3 e, c
- bzero(&servaddr , sizeof(servaddr));% J; `8 C! c, z% T8 D
- servaddr.sin_family = AF_INET;' a& y8 e! x4 s k& q% b2 E+ z
- servaddr.sin_addr.s_addr = inet_addr(ip);
6 Q. u6 V& [& v) [- a' F - servaddr.sin_port = htons(port);3 a- l5 \# q1 _$ t, O% O
- int ret;
* i X9 e4 Z+ c1 p - IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1) X$ ?! h( R( \6 J- W, {, E2 x3 q
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- printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);+ j& V+ V) S2 J, ?9 x
- return -1;
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- int on = 1;9 }# g" k9 c% L1 Y/ b- k% h) o
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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- printf("setsockopt error\n");
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- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);# `5 D0 c4 O, y: S) a! `2 R
- if(ret == -1)5 S$ U: y3 C3 N$ d1 b" m
- {
0 j8 X" D& ^5 L. Y/ P5 ]" t$ j - printf("Tcp bind faiLED!\n");
0 M3 a" ^8 r1 M( O: A! p - return -1;" C A0 F) ^: z8 Y% i! @0 S
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- if(listen(*socket_found , 5) == -1)2 c# q* w. g' t6 o% ]4 A5 f/ Q; k
- {
" p$ W. J, h0 l/ f% K6 b8 ` - printf("Listen failed!\n");
) g9 X& n7 J; `* F9 Q" Z; v9 A - return -1;* B W. O/ F$ ?7 j) D6 q
- }
( ] x3 ]5 X! Q+ y j5 O0 Z4 J - return 0;9 x, C2 f8 ]& [/ o" G% F0 t$ n- [9 v4 d
- }
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);' `8 F) c2 I! _% g
- void * Thread_TCP_Web_Recv(void *arg)
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# x+ [# P) \# ]3 {: Q$ l d - 。。。
8 C0 |# p' _/ |8 A6 ?. j - while(1)
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8 G2 q4 Z. d8 R1 J7 `8 n% b - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
& t! G3 `% z/ `5 ` H0 P& W - printf("fd_socket_conn = accept()\n");
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9 z# w) }2 i2 i1 D; l4 \' Y - 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);3 e8 ~1 x- e9 N1 d
- pic_tmpbuffer = pic.tmpbuffer;
7 a1 J" O- w. U/ g6 q0 Y - pic.tmpbytesused = buff.bytesused;
" \6 `' P/ V# e: | - pic_tmpbytesused = pic.tmpbytesused;' M. n2 o; k) ?- a2 k6 K* E9 p
- pthread_cond_broadcast(&pct);1 y5 v- s( J9 o' s8 _) m
- 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;
' @7 P. n; f! R1 v5 P, g - pthread_cond_t pct;6 a, B. m+ L5 B" Q; c- t
- int main(int argc, char* argv[])$ t' ]3 ^. E! I2 ~
- {
$ F# g5 H* `- S$ o- C/ S4 e+ G - ...
7 p! e2 e; g: t7 j: I - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
9 @% [0 i1 W$ F/ O - pthread_mutex_init(&pmt , NULL);' w3 X# B9 v. f# r4 V" H% j: E+ g
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);5 w4 q( K# U1 t, L# c+ ^2 R
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);# i1 M1 [3 T( Q+ n: B# ~# y
- ...
: U' p1 a! i% L2 J2 c - while(1)( h1 ^( V* P4 t% L( i
- {
$ @( J; o" t4 b) m - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);, z- w- c9 T$ v
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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;">
0 k9 l- j; `& 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 U" Y# d$ Y
- "Server: MJPG-Streamer/0.2\r\n" \
0 p% y6 D! d& R" w w - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \/ f- O7 r, L8 D/ ~5 I
- "Pragma: no-cache\r\n" \
0 Z$ Y* [" L# G' m k! {8 `; K - "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
+ i, F9 h ?$ a6 X; _+ l5 ~ - #define BOUNDARY "boundarydonotcross"( W0 M0 Q' Z: n! ]+ v
- printf("preparing header\n");
' f- A8 N$ |1 H7 M& o- u0 b) [7 F - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
' ]9 B8 O( Y) T& d# L: C* _ - "Access-Control-Allow-Origin: *\r\n" \
2 Q- B$ \0 j5 z1 R9 K( Q) C* |% O - STD_HEADER \+ l! [; m; l! o
- "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \6 @9 a' a: @, `0 o) [3 l1 T- S; M
- "\r\n" \
6 e0 C* R7 J: q- n) o - "--" BOUNDARY "\r\n");; o8 u( {2 b8 q- P+ z
- if(write(fd, buffer, strlen(buffer)) < 0)
) z* p6 o7 c3 Q$ N - {
l7 p7 X: o' G1 Z& T: q9 @$ m - free(frame);( ^8 B1 f$ u& u* {# b
- return;0 V1 Y$ U; f7 B0 K5 q0 m1 |
- }
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" \
5 Z4 n8 y2 O+ b/ R - "Content-Length: %d\r\n" \8 } u& f. Z1 c9 X1 l6 ~7 V
- "X-Timestamp: %d.%06d\r\n" \/ S" ^ E7 S# q! A; L* ~6 b# T# y0 Y9 J
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
* I% _7 D- P }4 Y4 u$ C - printf("sending intemdiate header\n");
/ K) t# s$ P+ Z, \0 a9 a0 T( Q5 a% P - if(write(fd, buffer, strlen(buffer)) < 0)5 L. O3 `& w& ~, n
- break;5 U! {8 a( F2 Q# r
- printf("sending frame\n");
9 m7 m/ k% J3 h' K - if(write(fd, frame, frame_size) < 0): g' \) l7 j* Z, z( F
- break;
# c' }! n, G- o B8 C/ V - printf("sending boundary\n");
% E; P* e6 G: h - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");1 p3 O7 y/ B( `
- if(write(fd, buffer, strlen(buffer)) < 0)4 K$ q6 t) X/ m/ G. ]7 R
- 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:
$ m' M- a1 _: }0 V3 d* s- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)( K6 Y# t$ L1 ~: U
- {
9 l6 P. D1 D* @- y# r6 ]/ ] - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);+ _) f- m' E- r
- if(*socket_found == (~0))% h1 d" O* Z4 c6 C# J
- {" n$ t/ _% k: N {1 T
- printf("Create udp send socket failed!\n");
0 [' A- A% B8 C- j* G6 E- M - return -1;
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6 |; L0 m- `& s - addr->sin_family = AF_INET;7 N" }7 E9 _. D, _' z9 m. n2 E
- addr->sin_addr.s_addr = inet_addr(ip);
2 U- U& q9 g* x% t8 H+ N% a4 M" j - addr->sin_port = htons(port);
* N* V! _5 R0 N) C! q/ v8 i - memset(addr->sin_zero, 0, 8);
3 h: U( l: z* D, [! r' k0 } - return 0;
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复制代码 ! i& p; h: O- s; }1 m1 s% q9 A
; u" [, Q8 y2 z5 S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:# l3 @9 Q8 R; n5 c ~4 `& a2 l+ s4 s
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- while(fend > 0)1 g6 ~/ Q, {0 t; E# P1 ^
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- memset(picture.data , 0 , sizeof(picture.data));6 h" E9 i- U2 Q2 E" w# S; ^
- fread(picture.data , UDP_FRAME_LEN , 1, fp);
4 }/ r$ E2 T) ~3 h/ X6 A4 x, L - if(fend >= UDP_FRAME_LEN)
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. c. p, r% S$ l$ @' W$ [. T - picture.length = UDP_FRAME_LEN; W# X( S; {6 w: R6 c2 f& @
- picture.fin = 0;
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- else
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- picture.length = fend;
7 r4 j9 q# a! ~" e/ K! x7 q+ i# O, l - picture.fin = 1;
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0 W/ X* ^- J0 G/ e8 e6 M: M+ ^; R - //printf("sendbytes = %d \n",sendbytes);
7 V, u. `3 _& i" n% { - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
( u+ f0 p& k- X* |/ y/ g Z - if(sendbytes == -1); M, U# V' t, J1 c ^2 O4 I
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- printf("Send Picture Failed!d\n");- x( o G- d1 {7 I( o1 O% N
- return -1;
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- else
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- fend -= UDP_FRAME_LEN;: |0 s; S' Y: j
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- }
复制代码 7 T% e; p3 p- n, v; w: S
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$ c) @: F7 ~2 N$ SiMX8MPlus 核心板: https://www.forlinx.com/product/136.html |