本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑 ( b" @0 t2 d( h6 H2 t0 `
4 {% U) X4 U& r9 d ; N' I. n; `/ @) 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
4 w0 `$ U/ Z; H* ?0 Z" R. P: E3 {% ^9 h- _6 r0 \) M
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。
; R) P2 K' A) x5 E - j6 G, d" V1 m. z. h( e: o
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 m/ i; l0 e. `/ Y1 A+ D
一、HTTP网页服务器) g% @) b' b% G6 s9 |
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), p( R" n# p% l* V+ ?4 A0 o
- {
. G, p6 m! _4 [ I2 c5 K0 @/ I* N7 F2 ^ - struct sockaddr_in servaddr;, y C* e3 T2 y" v3 ]5 r
- socklen_t addrsize = sizeof(struct sockaddr);( m; J# r! a C+ w
- bzero(&servaddr , sizeof(servaddr));
' N7 {0 P# T! h, u - servaddr.sin_family = AF_INET;
2 D7 o3 L+ {/ Y: U# O5 h0 B5 C: ^) | P - servaddr.sin_addr.s_addr = inet_addr(ip);# Q* g! Q' w2 S3 ?
- servaddr.sin_port = htons(port);
8 Q2 F) C* ]8 C. Z: V! ~1 d4 P; n - int ret;
4 J# { ^+ r! k: ~. U - IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)
8 ^4 ~) e7 @" `# G" O1 }5 K - {( _$ A; W. Q6 t% c, G
- printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
$ U, I6 U- S; _1 X6 k$ Z - return -1;
l1 p2 L& K% A - }
% H, B# D3 e( f* R4 z - int on = 1;* ]+ P9 Y6 M, c; L5 J, h
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
' P; U& ]/ {. c/ W9 ^! Q - {
- Q0 n9 h9 l5 k8 X: E! x' L - printf("setsockopt error\n");
6 k4 p6 y7 f( t - }
5 }+ |# ~7 n# w) s - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
+ Q7 Q( I' l8 Y4 W- k - if(ret == -1)8 w. u1 a( K6 D9 {" f0 h
- {% k, C6 y' Y5 E5 H- T& v
- printf("Tcp bind faiLED!\n");
* s+ }% T$ X) X& p3 R' L - return -1;
5 a3 _. u6 J2 W% | - }+ P' Z+ C* ~$ z) b+ R2 E
- if(listen(*socket_found , 5) == -1)7 ^3 K1 m5 U% I! I [. r
- {
( N& T- d+ m& r, A$ r - printf("Listen failed!\n");, w, m4 \( ^% L' c+ O& M+ c* g4 j$ A
- return -1;
- X$ v* m! S2 }, e/ m U; o - }
+ M" v# z+ \# s6 v1 M; O - return 0;( n4 ]7 ^; H. o- j# v4 C" ^
- }
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);
3 \& {" a+ q) \7 q* Z% i0 {( F" @ - void * Thread_TCP_Web_Recv(void *arg)( [1 V. T* U1 H1 [- C+ L
- {5 v+ \ U4 r9 N9 ~0 J! G
- 。。。
/ X7 L6 L) o& N8 F - while(1)% `9 ?$ g) R% u' {' X( v
- {% I, e5 j1 q! }+ R7 d U1 B/ |
- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);0 z6 }0 K# t1 ~; @: v; ~- e/ |9 n6 d
- printf("fd_socket_conn = accept()\n");
# W7 G9 \! d# N4 I; r6 l - 。。。1 ]' q4 V7 Y0 E4 r
- recv(fd_socket_conn , recvbuf , 1000 , 0);
( L3 w5 S7 v d; O - }7 L' i$ R0 g# G; m9 y% Q
- 。。。
: @- A$ H. A( E# c" T, R - }
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 S/ ^' p! ]. k, f0 R1 R8 L& ^ - pic_tmpbuffer = pic.tmpbuffer;1 l: ]% D# n7 m/ ~
- pic.tmpbytesused = buff.bytesused;
3 |+ x9 d: G3 p1 v+ t$ \ - pic_tmpbytesused = pic.tmpbytesused;! i, W1 u3 p% G7 O) m+ H' r, n
- pthread_cond_broadcast(&pct);
: R& ~" B$ M! [( d5 P - 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; I$ ]& [$ ^/ G, ^: j( H
- pthread_cond_t pct;
8 z) _1 f0 F3 t* L C/ K - int main(int argc, char* argv[])2 Z! i4 Y% x1 p( Y! ]. P, \5 z& W, A
- {! y, ?5 H Q* x. _0 x+ s
- ...
3 q- X5 z: a& m# l5 q - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
& c" @& x, i: |+ X/ o - pthread_mutex_init(&pmt , NULL);
; x! w6 j1 b, g) t8 | - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);" Q! p" V# o- ?9 |6 F0 ~
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
8 }4 e# e) B. t' s* a - .... K. V7 y$ h9 H! b6 ?
- while(1)5 J+ b2 J% S8 Z- W' l! A/ d
- {
, {* Y7 ?! W1 Q8 F" @ - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);
* f8 H! R' a) w8 ^+ `) N) s: ]5 W - ...$ j5 |; [6 p% ?+ {* _8 a
- }
. C. o, R% N5 F - ...
- y( s5 m C0 I/ x, T' ~6 h4 N4 W: O - }
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;">
% p: R) ?' }. w# ?! [! \$ W6 C - </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" \
8 W$ p8 \2 Y* c) Q3 l% N2 [ - "Server: MJPG-Streamer/0.2\r\n" \4 W9 F( g/ r$ p8 K, X7 e
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
9 |7 y$ E/ e# W2 m! O: t, p& ~( x( Z' g - "Pragma: no-cache\r\n" \
4 w$ A5 q" S+ l - "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n". y% h4 l1 B0 M/ H+ l. k& @
- #define BOUNDARY "boundarydonotcross"+ e F0 q4 f& g4 {! `/ o
- printf("preparing header\n");
# m* L: z8 U h2 M - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \: M0 Q/ j5 Q$ u8 i* W( f% V; o( u
- "Access-Control-Allow-Origin: *\r\n" \
2 t; p2 o+ j X" h - STD_HEADER \! i$ L- m, X" J' i1 g/ l* a0 H
- "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \5 H5 d! a" @, Q& }5 M' u
- "\r\n" \
+ H7 q: c2 e+ z6 i# z d - "--" BOUNDARY "\r\n");
4 b9 K4 ?+ e. D5 E( K3 ?# x" T - if(write(fd, buffer, strlen(buffer)) < 0)- e$ }$ z: W, J) F" M
- {! i* {+ Y1 l* e( h
- free(frame);
& O" J' g' d; ^" s - return;
8 W7 h5 p/ r# d0 Y - }
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" \8 b/ _4 U3 B4 y$ t9 S" a* O" ?$ |/ k
- "Content-Length: %d\r\n" \
+ h5 d( {8 {3 k: I9 v! q/ I - "X-Timestamp: %d.%06d\r\n" \
1 D' d/ s$ c u( Y( x - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
4 g! n0 d, ~3 l* S! s" j - printf("sending intemdiate header\n");- g: X# S; q2 @' V" R& q6 x
- if(write(fd, buffer, strlen(buffer)) < 0)
( X8 z; R- t& R3 |) E - break;
" Z) P( O9 N. _! J7 ?' n, c& N - printf("sending frame\n");
$ @! C3 q# U, n - if(write(fd, frame, frame_size) < 0)
2 y9 G! f7 E5 ^' j) K6 y/ a) w - break;
+ D( Y* w0 J3 L: E2 ? g \ - printf("sending boundary\n");
6 ?/ J$ E, D9 [6 M - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
/ V/ D8 |7 y& A6 u' J1 i) i - if(write(fd, buffer, strlen(buffer)) < 0)& b2 W' { K3 }: J$ v. \3 F
- 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。 
" ?! g/ Y; a) ^& a, V
2 E7 X6 q3 k# ]+ {二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:
" w! B7 Y/ S5 R1 q& m: Y- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port); Q8 g1 o2 \9 o: p& Q+ Q( t
- {
0 D2 @1 e( A! p. ~ - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);+ m' z4 i2 {. P5 s" f8 A K% m9 {
- if(*socket_found == (~0))
8 W4 B7 l# Z5 Y0 l. H- D- X v) L# e - { J8 E5 B% h% y- A
- printf("Create udp send socket failed!\n");! J& z/ t- r$ X9 U9 b
- return -1;! q1 m0 P8 Z, V# v
- }
4 j9 F& u9 } }6 X+ Q3 b. T - addr->sin_family = AF_INET;: @5 b3 g, Z, e8 b( f' ]
- addr->sin_addr.s_addr = inet_addr(ip);% z w4 ]5 f0 w' l4 X
- addr->sin_port = htons(port);
* g& N4 T" I$ w - memset(addr->sin_zero, 0, 8);8 J: P0 S+ V$ W5 d0 E
- return 0;
. G/ y% A$ ^7 H/ \ - }
复制代码 ' I P9 o2 y+ I' W8 s' X
( r$ t+ f& d. q/ V. F2 K3 J
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:, E+ [, r1 H6 i' _* c% c
3 `5 O& ?$ ]: R+ i4 z8 O m' f# a4 b- E& s/ A# c: l+ {% W
- while(fend > 0)
& s/ P' x8 K' M! V - {
4 \3 }# N) j# V O, ^ - memset(picture.data , 0 , sizeof(picture.data));
) q) w* [( C+ c/ h4 Q+ @ - fread(picture.data , UDP_FRAME_LEN , 1, fp);
5 }- o/ S* |2 q3 d$ v8 H) F - if(fend >= UDP_FRAME_LEN)3 }* V- z- V5 a, N% G' j
- {$ F3 u x+ G! q6 f5 P4 l2 m/ q t
- picture.length = UDP_FRAME_LEN;
$ h0 {* \. V% d2 t6 _ x! ~2 A - picture.fin = 0;7 j" C# e: ]# V% e
- }4 g+ m" e \7 R* E) F/ N
- else
% J% ?; C R6 p8 p8 X - {
1 S1 s1 @( b9 v8 @$ } - picture.length = fend;+ a$ x) }) m$ D& r$ g: {2 `
- picture.fin = 1;9 f- i4 }6 p% k9 s; b! x
- }, ` t2 [/ j3 t
- //printf("sendbytes = %d \n",sendbytes);
9 @4 u+ U! }& g0 k7 W, T6 [ - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
) Q# e7 L% Z0 u - if(sendbytes == -1) v9 F2 [+ M, W4 e
- {
3 ]+ ?+ S8 _0 T" S - printf("Send Picture Failed!d\n");6 j; q9 {! _, j$ r
- return -1;3 ]3 b: l; `* o) y: Y- I7 K6 v5 \0 L
- }
6 M) A# T& N# e' T9 d: G& q - else; o- N$ U! u7 I6 G
- {0 X ~( v4 ~) J4 }6 k/ b
- fend -= UDP_FRAME_LEN;
; {; K" `0 s( @( q0 _ w2 D - }
9 g' ~/ `8 `" R8 e" W+ G- L - }
复制代码 m" T! m0 M$ [5 Q) B$ ]
% H% x4 r' Y& t o F

# W9 Y0 z7 O% q* t1 b. C7 C0 g% F/ D3 Y. f- ]8 E2 e3 S+ t
iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |