本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑 ' l. f8 ]2 \; U6 V2 y. L
) o, g) |4 ]1 Y

! Y4 t) V. m9 o& L5 g# k4 d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.html2 e+ `% [" r% g5 {7 C+ k
3 e- a) _: r, @+ e s% h
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。
) j3 [, b+ v( W* h% ]8 W# O! [( D
& `5 i u; t: M6 T0 W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。
9 y$ c% F9 d/ p% W2 F一、HTTP网页服务器; @" l" V9 j$ V; I
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). {) S$ Z, m6 t) ~
- {
/ B* g' `, Y) [' M - struct sockaddr_in servaddr;# j" g9 Q( C9 J2 W9 b
- socklen_t addrsize = sizeof(struct sockaddr);% N5 l: x7 z* f6 F2 e
- bzero(&servaddr , sizeof(servaddr));6 E* h/ @3 s6 I. `1 W3 l
- servaddr.sin_family = AF_INET;5 K: ^8 n: l5 ]. j& Z% ~2 a
- servaddr.sin_addr.s_addr = inet_addr(ip);$ H/ J: F6 c) c% m; ]+ q$ h
- servaddr.sin_port = htons(port);
/ B* @( r: g8 t7 O+ W& g - int ret;) N9 [/ ]6 U/ O, |9 x' ]
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)1 e& r9 O; s5 l: L
- {
: `- E9 S9 N1 Y( ` - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
* _3 u2 ^1 w' t; {3 d - return -1;# o3 |3 N! U5 Z( f4 P$ P9 s+ D
- }; h5 D- Z$ ?/ y) W) p' j9 N
- int on = 1;, p9 j/ X( V6 R
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)' E% I) o! X: W4 ^& ]! I2 I2 [
- {
6 q' J! I) n* L0 s3 z - printf("setsockopt error\n");7 _6 N$ Z! h+ K; o; L9 n- p/ p, Q! O
- }7 ~! k+ P4 z6 |7 | P" }9 F+ L
- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
7 p/ ^6 e; S& i6 m - if(ret == -1)0 @; t& o4 j9 d9 F: {
- {
6 M9 X; |0 B3 w+ J3 I3 b - printf("Tcp bind faiLED!\n");4 g; l( @% C+ u. i
- return -1;
. c: f' t. y, E2 l - }. {: d' w) O D/ C5 U
- if(listen(*socket_found , 5) == -1)
& `! R f/ ~1 C: S - {7 X* `* _/ @1 L, _/ d+ F7 x# O
- printf("Listen failed!\n");# l1 n" o& c5 z- l/ G
- return -1; t5 D+ ]' E3 n& t& ?
- }
$ m/ N. H9 G5 ^; Z - return 0;# T8 _5 w/ `3 U4 e
- }
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 N5 T$ c! }6 B3 s5 [
- void * Thread_TCP_Web_Recv(void *arg)! `$ p U3 _) _/ V4 {
- {
1 p2 U- H, }' k: O. k - 。。。 a, Q8 f$ g3 X6 B1 y5 }
- while(1)
/ a- A l% V0 H; A% ] - {
' @+ D, ?- E% S0 X - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);, A, n3 {2 U2 e B- K' B
- printf("fd_socket_conn = accept()\n");
# j4 `: |8 M: x; ] - 。。。# n. |8 w* Z7 I; ~
- recv(fd_socket_conn , recvbuf , 1000 , 0);
& S6 _# U6 i* p; o% \7 j" n - }
: Z2 i$ q/ m* ? - 。。。
7 U* Q Z9 o7 q! p" p. v7 Y* X - }
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);
) I: i& Y) e. {& A0 S( O- X0 j - pic_tmpbuffer = pic.tmpbuffer;$ |0 v* P1 S7 O. o& p9 ?
- pic.tmpbytesused = buff.bytesused;
% T2 k' d9 K8 g) E - pic_tmpbytesused = pic.tmpbytesused;
0 Q) s; y3 r7 J% t2 s - pthread_cond_broadcast(&pct);
- A9 ~1 g$ k" b - 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;
* E' f- j. ~2 t+ M) h. ]- K0 E - pthread_cond_t pct;
. z V: g; d# A5 t. c - int main(int argc, char* argv[])- |% ~8 [, `0 ^) m6 q# [) x# Y
- {
+ S7 S: ]: E& E5 N4 K7 G/ k8 S - ...# s- \- Q' u, b3 E
- TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
( p$ ?; p8 G+ a+ v" G4 v - pthread_mutex_init(&pmt , NULL);
0 K( m3 L2 o* i! r - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);
3 w1 S1 N8 Q! i7 A/ s6 a - pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);' K# m ~, r1 y4 I( B
- ...
" b# B7 ` {7 z% W( q4 u [ - while(1). F* x( n3 ? o5 Q
- {
7 ^! t$ @* V; h9 }; D/ D/ q, r - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);' J. \+ T0 g: {2 e8 d! {
- ...9 p, I. q: m. h2 G5 W
- }
% r1 K N! U$ q& h- `' g - ...
8 \5 ^, R+ e1 M/ Y - }
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;">
3 A- P/ `& _. N8 G - </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" \
$ {; A- Y- b v2 f2 f - "Server: MJPG-Streamer/0.2\r\n" \. b3 S, C0 \) {! o% d& p
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \5 A% F/ }4 X* A1 o: M- g" w
- "Pragma: no-cache\r\n" \
6 C" j4 p- B5 s. m9 Z - "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"0 q- [' f% M8 _- {" ~
- #define BOUNDARY "boundarydonotcross"
0 ~5 X& v1 g2 d) U0 N2 U( O - printf("preparing header\n");5 ? F7 ~6 ~) F: A8 z' i
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \3 e: b1 ^ o& I
- "Access-Control-Allow-Origin: *\r\n" \% w2 f$ Z9 k3 a! r$ {4 S
- STD_HEADER \
4 d k& d! T" l - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \) j1 I/ ~* D8 M0 h
- "\r\n" \
u5 }: v: p4 `) u- P2 t# ^, x - "--" BOUNDARY "\r\n");3 U- ? \/ S! v9 |. x( }
- if(write(fd, buffer, strlen(buffer)) < 0)
% h: k; }" t0 L( N% c# e - {3 L. L! l8 Q7 d* d' N
- free(frame);) i- G# |/ U1 ?1 Q) D1 t2 ` [
- return;
2 D6 v7 T8 j Y: u# `& U - }
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 w/ r; l: ]! }5 p- \; U! T _# x; g
- "Content-Length: %d\r\n" \
/ `5 I9 n+ ]0 L* ^+ M9 Y4 W" G+ x' Y2 n - "X-Timestamp: %d.%06d\r\n" \
0 O% j2 w/ P. v9 W1 r - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);& a3 o1 y! `9 X- i
- printf("sending intemdiate header\n");
( r ^! C4 P8 {7 i, Z1 p+ }( I - if(write(fd, buffer, strlen(buffer)) < 0)1 g3 _" n1 A8 h; L
- break;& f( d4 C9 r, W1 E+ j& y& B
- printf("sending frame\n");
+ K9 R6 _. L1 K1 I4 d* v8 | - if(write(fd, frame, frame_size) < 0)
2 [5 q4 A( m' `* ]1 u" w - break;
0 s+ [7 g: @$ \% j- |" O - printf("sending boundary\n");2 u6 }1 Z, t# n5 F- Y i7 |9 n
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");4 o& i5 h4 B, N& c
- if(write(fd, buffer, strlen(buffer)) < 0)/ Y' X! `6 r! _% a0 a
- 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。 
, J" |- Y) E9 [5 P l5 S; b
5 f0 [+ U/ c( D" Y二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:
4 G* r* U. k0 v0 D' ^4 x' g, q; o3 t1 D- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)- G& z) j5 I9 J- U5 a( \! ]
- {
$ k: K W$ h! U5 P - *socket_found = socket(AF_INET, SOCK_DGRAM, 0); `5 @: s' I" X( ~
- if(*socket_found == (~0))2 w# l; o" y8 B( b0 j3 ~
- {0 h" U4 K7 C$ a' u! j; i& L- U1 i) J
- printf("Create udp send socket failed!\n");+ g7 }. g S6 l, E
- return -1;: g' c4 I9 x6 r R
- }' b* G! r6 S% t; q1 X3 ^0 r# p' W
- addr->sin_family = AF_INET;0 W2 ~4 {# Y. R9 b% J a
- addr->sin_addr.s_addr = inet_addr(ip);3 l! C. M9 Q- I% h5 k1 ^+ y
- addr->sin_port = htons(port);
4 M( e; Z+ B( v/ ]! L0 r - memset(addr->sin_zero, 0, 8);0 t3 ~; c& d/ j
- return 0;
6 S5 ]. w& u4 H" [: o" I6 z - }
复制代码 3 [" n) o2 W5 `, G) I ~2 o
' S' m Y( R% o/ y2 U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:: L- K) z! X, t- G) Z) g
8 s2 x8 F/ A9 O. R( j/ k6 f( w% T
- while(fend > 0)) R/ R% F, |6 \$ W& N$ x1 v0 \
- {
4 n6 S J2 |% o" a9 g Y - memset(picture.data , 0 , sizeof(picture.data));+ @# M' p* h* V6 ^3 A2 H' U, \# ^
- fread(picture.data , UDP_FRAME_LEN , 1, fp);
: } y; O9 ]) d" T k/ k$ H/ h - if(fend >= UDP_FRAME_LEN)9 d; d/ i( M8 f# I4 ?
- {$ P0 N% m: [9 a4 m" K& @
- picture.length = UDP_FRAME_LEN;
; ~% {7 L# Y+ ^ - picture.fin = 0;
- u9 p# Q& T' G - } ^+ x/ {$ _# G' |3 T/ |% X
- else- r/ B, @" V: _3 C9 [+ \
- {1 x3 {* V3 W' v0 }: i
- picture.length = fend;: r9 n! ]# c2 G, z% M
- picture.fin = 1;% M6 }) ?# P) x& y- _# n0 e
- }0 k0 G) u8 p# S# W. R
- //printf("sendbytes = %d \n",sendbytes);
% M3 E2 M: b) R- {% } - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);' v2 C& `$ i- B3 f8 w1 M O2 K
- if(sendbytes == -1)
# T" \' W! @* d9 l1 ]) I - {) r/ x* S+ _/ A# I% {8 K% I
- printf("Send Picture Failed!d\n");; @" Z+ M" o' S8 X! z/ L7 B2 G0 H
- return -1;
/ y% C' t' w8 X0 I - }
7 M1 g7 c% }: a* t, f0 ^ ?6 Y - else
0 e6 V5 F9 s# L: X8 _& D! ^' V4 F/ d - {
& w$ }$ p, D0 K) m3 Y4 Y4 x% t - fend -= UDP_FRAME_LEN;
, G: p' u/ [$ P# [ - }" P" O! H/ I0 l* T3 S
- }
复制代码
) P" C0 y- q1 B2 |/ t7 }
1 p8 x' _* y: G3 F; n: f2 }
9 J7 @6 r3 U, |! b7 L" V' t* G9 z7 e' Y5 V* \
iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |