本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑 % d( q9 h$ o) F0 M+ X# h
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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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) }* e+ Y3 V5 S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。
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# _0 O" s3 ]6 ]" l9 b4 x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。
1 s- b1 H+ X7 j一、HTTP网页服务器
2 Q. W4 L* e, y0 O1 a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)7 F0 S; m& [: w! j2 p/ K! q
- {
6 v: _& N0 `+ `2 D( Y - struct sockaddr_in servaddr;4 G4 v1 Z, x; p, z$ h
- socklen_t addrsize = sizeof(struct sockaddr);: s3 P- @. B8 d
- bzero(&servaddr , sizeof(servaddr));8 L* U# B, d# J
- servaddr.sin_family = AF_INET;$ W% B2 E- P7 E6 \' u3 T
- servaddr.sin_addr.s_addr = inet_addr(ip);
2 }/ R3 u; T: Z5 c/ w5 x3 a# U3 z - servaddr.sin_port = htons(port);8 G. B* {8 ~! W# R3 l/ h/ U
- int ret;
: _$ a( E2 j( g/ d* ^2 G% @ - IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)+ b1 F! E7 z( ~/ w' L7 F
- {# @) n5 h" X& T& E6 _1 D
- printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
: e) y- `; f' x8 n - return -1; p4 {8 t; ?% r9 h1 s
- }
2 n, O$ u N& J3 I" v( ^2 a - int on = 1;9 D1 M% I5 s5 w8 Z0 S
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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& G; z0 [% y4 ]" T8 w - printf("setsockopt error\n");
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- a. \# W- R j) [( C - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
& Z8 ~( Q! D5 O1 I( @. L2 v - if(ret == -1)- p8 Q: i& N5 X4 G# u( N5 p* \* X
- {
o3 I* {8 l7 Y+ ^9 u - printf("Tcp bind faiLED!\n");
) l% b2 s4 L: z: R# a - return -1;3 I- ]3 \7 y9 j& J# N
- }
, Y# c' O8 b3 N# `6 V: A! d - if(listen(*socket_found , 5) == -1)
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) s1 L v8 n& s: }6 | _ - printf("Listen failed!\n");% {" N3 p& ^' @# Q
- return -1;
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- return 0; F' R. A4 B& N9 l7 L0 W; l
- }
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);
Y* G& }- `6 d+ p7 X% i - void * Thread_TCP_Web_Recv(void *arg)
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- while(1)0 j8 ]1 p7 @ `( k8 ?$ H
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- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
& G; ?6 \+ q. ]. U3 @ - printf("fd_socket_conn = accept()\n");
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9 `. B( i: l9 B - recv(fd_socket_conn , recvbuf , 1000 , 0);: }3 f% \% F/ D( ^4 N
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- 。。。9 ?0 X( t6 f" G Z
- }
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);
+ e/ e! F7 U4 g - pic_tmpbuffer = pic.tmpbuffer;
5 N1 s/ l- f2 Q - pic.tmpbytesused = buff.bytesused;
- l- a B/ x% B; }# s$ P4 R - pic_tmpbytesused = pic.tmpbytesused;
8 l2 g- |; [' |' S. P( O# Y) x - pthread_cond_broadcast(&pct);
7 a* i7 }* Y+ X* Q* V# u% _ - 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( L0 i1 [. p& ~! Q' a
- pthread_cond_t pct;
) `& R8 @* P* I" y7 u2 y - int main(int argc, char* argv[])
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7 C' L3 J6 `9 o( L8 `4 Q; n5 E - ...
; |! Q# d: F: X4 X1 }$ a: z - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
# p% `, h4 i- Q( T7 Q. r - pthread_mutex_init(&pmt , NULL);/ L5 s4 K0 j8 l
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);
, C }& s* ?+ M7 i: a - pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);- k/ { {# K1 b% y+ u, W# D
- ...
( g4 z7 h/ R0 n2 C: m( } - while(1). k5 p/ k+ ] T1 g
- {
8 a6 Y' c* v- p. R6 i7 ]1 q5 I - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);1 H8 P" G) V+ M 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;">
. R0 D% Z/ b9 \: ~ - </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 Q/ ], o. l) M - "Server: MJPG-Streamer/0.2\r\n" \
+ U, k" d) a7 _* s1 O# O - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \6 _, P8 E! h4 n5 z0 H8 K
- "Pragma: no-cache\r\n" \
h5 _& }: r0 G: w+ o - "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
4 _9 U6 s, s, W - #define BOUNDARY "boundarydonotcross"8 O7 h! `' Z+ S& N0 ^
- printf("preparing header\n");
. Z2 V* R/ w6 d: n - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \# Z' u; l9 [8 p4 {0 l) a
- "Access-Control-Allow-Origin: *\r\n" \7 f5 ]( ?, K4 U( A2 \0 |
- STD_HEADER \. S! A9 s, v1 Q$ j" Y( V0 B5 _0 g
- "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
/ b' _$ J$ p0 U - "\r\n" \3 a& w& [, D1 {. q
- "--" BOUNDARY "\r\n");
, i0 ^7 F3 S+ t6 _) I. ^% z - if(write(fd, buffer, strlen(buffer)) < 0)
" _6 G" @- x. Z+ |7 r& r1 f) P! t - {
$ C0 R0 \7 d5 u' o7 d! F - free(frame);
* i# b/ U; ?' M5 {' u% N - return;
9 Y( t% N/ l- h6 [% T3 s - }
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" \# `/ {/ E7 S# A- L% R
- "Content-Length: %d\r\n" \9 `3 O% p* m8 n5 v* c
- "X-Timestamp: %d.%06d\r\n" \
: u6 |- D4 o& D - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
% _3 s; ^- C L7 d* x7 A - printf("sending intemdiate header\n");6 K6 |4 |9 [( ^8 ?& ~2 N
- if(write(fd, buffer, strlen(buffer)) < 0)
; j: @9 n* p% _& Z# l4 I - break;
7 t" \8 p* [0 F2 u" N3 j2 r; p - printf("sending frame\n");9 V0 g: K) C6 |- b& b: v' l
- if(write(fd, frame, frame_size) < 0)
6 k% O# M ^' M z% W2 x - break;) n' v2 c# m6 F
- printf("sending boundary\n");
' v8 R5 V& k# ]+ l9 O - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
' |- Z5 B8 c3 \6 X+ \& o - if(write(fd, buffer, strlen(buffer)) < 0)+ k4 r) I5 P8 B! ?( d
- 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:# g3 C3 _0 I% M
- 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);. d1 ?& o) W: Y& Z, ?# {
- if(*socket_found == (~0))
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9 P7 n+ H/ ^. c - printf("Create udp send socket failed!\n");1 g4 w2 V$ c$ T$ v, P k B0 ?; n. E
- return -1;9 w+ W; B2 \# B7 G2 K K. \/ \
- }
9 K0 k9 }! {0 D: y/ H - addr->sin_family = AF_INET;+ _+ ?9 c/ x/ L
- addr->sin_addr.s_addr = inet_addr(ip);' @: K1 {) A% Y% I6 i& u6 L; ^8 W% t3 j
- addr->sin_port = htons(port);
. J4 C& {- v0 w - memset(addr->sin_zero, 0, 8);
: `' d( K0 w0 {% j - return 0;7 r V/ z4 ?! T8 W8 J4 Z/ X
- }
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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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- while(fend > 0)5 }- H. T0 w: i8 x0 U. Y
- {
_% v( |$ d7 G: f3 t6 _, n$ l - memset(picture.data , 0 , sizeof(picture.data));2 j& A/ {) N# h# E8 q& U' W
- fread(picture.data , UDP_FRAME_LEN , 1, fp);0 d, L0 m7 _: X. Z/ Z# ~
- if(fend >= UDP_FRAME_LEN); v* v7 J. ^. R" d/ ?) V
- {
. d% A \! ]& R% u/ k1 E& t4 | - picture.length = UDP_FRAME_LEN;
9 m2 R0 r! n5 `/ t( D. ^ - picture.fin = 0;
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. g: d) u( m, |0 Z4 ?( ^ - else. `0 X9 E X6 ?
- {; k' F* \$ O4 I! u4 U
- picture.length = fend;
$ p8 u+ K% X4 Y Q1 b; ~# E - picture.fin = 1;
8 r _6 l- R; I - }- n7 A1 m8 F. H2 S3 g2 {
- //printf("sendbytes = %d \n",sendbytes);
# A9 l/ {8 J% Q% y% f! P9 X - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);2 X* M; Q+ \/ i) g/ C. ]
- if(sendbytes == -1)
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- printf("Send Picture Failed!d\n");
" |. j( i3 D/ h - return -1;
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- else
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- fend -= UDP_FRAME_LEN;
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复制代码 . H1 l' O& U/ w3 h. f
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7 K: ^3 ^$ n# N; |1 ]* q$ HiMX8MPlus 核心板: https://www.forlinx.com/product/136.html |