本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑 ! v$ D d6 b- c, U0 z/ C" c
- s o6 U' m5 S$ j* u' v0 L

+ V' E& i9 x3 t' Z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
+ M. N' d7 k/ h. s& C, g% P
5 O( h3 q; ^' H* D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。
% h* ]. `: f# t! i+ s : s8 i+ Y1 _5 T) |6 |$ n; K
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。 , W, S2 H0 H5 B+ Y
一、HTTP网页服务器/ ~) c& S) {: K# T' G
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)
3 i4 i$ m1 l$ Y - {) E$ e: X3 B, m1 p0 r
- struct sockaddr_in servaddr;
/ t) x2 q8 `" R. T- n - socklen_t addrsize = sizeof(struct sockaddr);5 x( Y4 _1 A% p6 U- k
- bzero(&servaddr , sizeof(servaddr));4 P0 s5 {; ^! W- [/ X
- servaddr.sin_family = AF_INET;
0 g4 e; ]/ D) K, }. ~) r - servaddr.sin_addr.s_addr = inet_addr(ip);
' }# C1 I5 O6 m - servaddr.sin_port = htons(port);1 X ?( U, z- K% F
- int ret;- }/ a. j* m& B
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)
$ Q; W- ^ Y+ h2 D1 o& h6 H - {
4 O/ V+ P: T2 P" O V - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);9 O, |! w7 k2 v6 `
- return -1;
1 u" H) ~! C$ l - }
. E4 s0 H2 i! O# O - int on = 1;
( L! T6 |/ y( T8 J - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
) D$ M' \ d& t% b$ O# \ f' u - {& T4 }2 x9 Y" Q" }3 p: z, l
- printf("setsockopt error\n");
2 h$ n4 x, n; ]- f' B& M - }) K& c. s6 t3 ^/ |5 H# a
- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);9 R+ C5 Y& ?- F
- if(ret == -1)
2 o9 X& k; h: ]' ?6 h$ _1 ] - {
$ Z& s, b* _, o( P2 p& L; l% I1 z - printf("Tcp bind faiLED!\n");/ R( R3 M9 z3 f% W; R* q$ H; i5 V" e
- return -1;
^+ L% ~ J C: ^: h% N6 J" I - }6 x7 ~6 F0 k: R5 w$ h# K8 H
- if(listen(*socket_found , 5) == -1), ?; \8 Y |- A3 S- I+ q
- {
2 ?8 ~6 \! d0 U& i2 k! t0 u# f! Y - printf("Listen failed!\n");
. h+ M$ E) C; q0 s) D- ^ - return -1;
8 K( f- K/ p$ h& f% y. Q$ z - }: x% z! R- L9 v0 o
- return 0;+ Y& F1 `, h5 m
- }
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);- H" Q2 E8 I) T7 K8 Q/ U* E4 f" X
- void * Thread_TCP_Web_Recv(void *arg)
! J3 N+ w( T3 ~- ^& o/ j: C d - {
3 ^4 N3 ~8 Z9 ^! k - 。。。( ^' g2 T) [# k; A- ~4 L
- while(1)
5 t3 E5 c# O( P2 O - {) b1 d$ @% X7 N3 I' y3 v5 E
- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);: j# b7 C5 i$ a& j) P! Y+ `
- printf("fd_socket_conn = accept()\n");
# Y8 N7 `: d8 _7 z2 |# ~+ t! s - 。。。
# K# b8 u5 f# W, Z% T - recv(fd_socket_conn , recvbuf , 1000 , 0);
$ ]) D0 t9 Y# |/ f B9 ^ - }
) k# O% N1 K/ [; T- G2 a - 。。。
5 E6 J( q0 F0 |0 t - }
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);& A6 ?7 S1 N6 Z5 F/ Y" h
- pic_tmpbuffer = pic.tmpbuffer;
' A- J7 b% P; r ^- r - pic.tmpbytesused = buff.bytesused;& O# i a3 H$ S/ J3 \& H+ x
- pic_tmpbytesused = pic.tmpbytesused;+ W. z( ?& F7 m" [: V0 Z
- pthread_cond_broadcast(&pct);
5 x5 S' N; n8 c: {! G% z+ z - 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;( D2 M, A0 B) D! Z' C
- pthread_cond_t pct;
0 x6 e" g* ]" D S( G9 y - int main(int argc, char* argv[])
1 A* B& [( i( p" K" W: ` - {# Y% G7 i+ B' K* I7 K5 Y
- ...
9 \1 t, g4 ~. @1 @ - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
. b+ K6 D2 F h - pthread_mutex_init(&pmt , NULL);
# A1 h( |: c, k, _- d& R - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);
( s- M3 M( o' G# y - pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
8 v9 h X9 ]. G3 q - ...
8 r' m M4 F. p" }! x) w+ P6 a - while(1)
{5 K# s# G( p8 c: h0 H - {$ l: B1 X/ s' _/ X2 p% y
- V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);, s( h8 o/ Z# d7 S9 [ V
- ...
2 a3 F; n- v: P# [2 Z, x3 k8 b N2 k - }
& a! b# u3 y; @. s5 m" n - ...
7 s* W) N; A! z/ T: P - }
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;">4 T5 q4 a% `% K2 | [$ i
- </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" \
# k4 B+ D# P" C% `: L. ` - "Server: MJPG-Streamer/0.2\r\n" \; }4 o& ^7 o* n C# d- d% R
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \- \2 y: z5 K& E6 G
- "Pragma: no-cache\r\n" \- C2 u9 J7 E% x% Y/ U) v% v2 {
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"& Z; O& i# \; d. V
- #define BOUNDARY "boundarydonotcross"9 c& T& [1 b i% E6 f
- printf("preparing header\n");% N2 A' g. N( J) d9 ]# R1 K
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
2 B; K, F+ B5 X( T7 S9 k - "Access-Control-Allow-Origin: *\r\n" \
& ^! T1 A6 A0 S - STD_HEADER \: q$ o% f x$ ]( x% U, K* s# w
- "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \4 E+ S: q5 B- H
- "\r\n" \
6 Z% j& r% ?3 X! h! x V3 g - "--" BOUNDARY "\r\n");
8 e% n% }; D* Q' ^& e0 x - if(write(fd, buffer, strlen(buffer)) < 0)
: h9 k3 t8 f0 _% ?; q - {/ P) v6 V0 h9 ~! p: s# n+ C
- free(frame);7 {% A. B# h/ L. P& |
- return;
% S' L7 k7 l. C. Z6 u! F - }
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" \2 [3 ?' S) C+ H3 T8 b
- "Content-Length: %d\r\n" \
; I7 c# {# z3 u. _ - "X-Timestamp: %d.%06d\r\n" \6 ]( x! j3 K) N. q& e
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);, n W8 t0 O' n" l$ x8 r
- printf("sending intemdiate header\n");* `3 ?1 O. p' y- T! k8 ~' d6 W
- if(write(fd, buffer, strlen(buffer)) < 0)' ~1 e# v& @* v
- break;0 t6 R' c7 T" d% }
- printf("sending frame\n");
+ F9 p& B3 Z6 ~6 l7 E1 p! L - if(write(fd, frame, frame_size) < 0): y. g: Y5 }+ p) c( i7 t
- break;
5 M- o# m5 T5 u - printf("sending boundary\n");
1 T4 I+ K; C8 o - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
2 Y. U* x4 h8 I3 |% y* s% Q' M - if(write(fd, buffer, strlen(buffer)) < 0)* T. ]) \+ K- t; L+ 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。 
* l/ b2 \+ D' B; b6 `& ?
. o! p2 T5 R$ o; w二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:
3 p: ^& V# i; Z2 f& h" l3 N0 o- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)0 U, [ @- N1 {5 n; J \1 w
- {
( l0 S3 k- h& U } - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);
& P! |* s1 X4 F - if(*socket_found == (~0))3 p ~" e# K D: f
- {
! J, ?+ \3 q& p4 X) } - printf("Create udp send socket failed!\n");
4 F' j E5 K$ S( E$ N- o - return -1;
% h% f7 A* |! i/ `+ e1 P4 H - }: k: O4 V' {& M, X N9 P7 O
- addr->sin_family = AF_INET;
: N" V$ y: {2 Z - addr->sin_addr.s_addr = inet_addr(ip);8 T" p6 E( f+ j
- addr->sin_port = htons(port);2 M3 T, ?# @* L$ _
- memset(addr->sin_zero, 0, 8);/ D; s! j6 u/ h5 S
- return 0;% b( I$ X0 J/ D8 D
- }
复制代码
5 n( K; q2 `. u X9 x- W6 n/ |
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:
& }9 Z8 { c( m3 [7 X' u( ~5 A
3 U( p2 y) q: W
* e2 ?: r8 \. @1 y6 _4 D- c- while(fend > 0)3 @8 W4 H$ A9 A- u- D# J" ^
- {! x1 c* k; d; y
- memset(picture.data , 0 , sizeof(picture.data));
8 `; c3 o* E5 ^/ H( V4 K - fread(picture.data , UDP_FRAME_LEN , 1, fp);
0 L" j; D- W6 U0 X* q/ R - if(fend >= UDP_FRAME_LEN)
& I3 Y1 C: f1 A/ r+ ~0 e - {
' G) z' j. H5 D" v6 d - picture.length = UDP_FRAME_LEN;
( x: d/ @* g3 R. }3 z - picture.fin = 0;
: V6 E/ }. s9 @ - }3 V: W# s# g4 R! h: o# X
- else
3 y; v6 _/ L: a1 N - {, t+ g/ M7 h2 M+ H' `! G
- picture.length = fend;
5 y9 k2 ~" h: G9 `4 R! r# Z# D - picture.fin = 1;0 h0 Z n# A( }+ k2 f* P
- }
# I$ y3 o# P. F+ U9 a - //printf("sendbytes = %d \n",sendbytes);
6 a: d1 n2 f/ @ - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
: t8 c" g* \& D - if(sendbytes == -1)( c! N3 @4 R6 D5 @5 l4 H* L& E8 C
- {
, ~3 L" \, e% m3 j - printf("Send Picture Failed!d\n");
& M |, z% W W* U* H - return -1;+ B% q5 q/ D+ {1 U
- }# l" b4 R) ^0 L: a9 [
- else
, i, s" r/ @9 l5 l- {+ ~ - {0 Z! z3 v* {: V0 O/ H1 F# K
- fend -= UDP_FRAME_LEN;
0 d% V' J8 R" _0 ] - }& a4 ?/ `* v% O$ Y s' o8 w
- }
复制代码
9 _) K( N) _! g8 d" i# K q/ i% ~
+ }" C4 y: ~4 v( @& x1 P* v
! A* M( O2 ]; M# V1 M
/ i% ?1 B5 X7 ViMX8MPlus 核心板: https://www.forlinx.com/product/136.html |