本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑 7 S2 i. n8 F) I# [4 M
% K3 O- Q5 E @% a" o$ U; `# a- {

. G2 I( ?7 |( b) I7 x. I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- O. y( {; e# a, |7 J1 C" c
/ m6 l; H% f2 d4 H: N" @" f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。
s s& [2 [; r
2 x' @1 o4 R# T' @3 K7 h7 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。
( h4 Y5 K6 |# c一、HTTP网页服务器( M- q; ~# F- L
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)) C% F6 `. P& y8 s+ u- U
- {4 t, c+ x+ C: K, ^
- struct sockaddr_in servaddr;3 O/ h7 [& G- e
- socklen_t addrsize = sizeof(struct sockaddr);
% w9 O# N! ^8 H6 L - bzero(&servaddr , sizeof(servaddr));
+ h# M. T) k7 o z2 Q - servaddr.sin_family = AF_INET;$ r# G9 n1 y( H: I w
- servaddr.sin_addr.s_addr = inet_addr(ip);6 M0 H) f; R* K( g
- servaddr.sin_port = htons(port);
% ? t0 O; G# s. `( _1 v" s - int ret;/ ^3 E5 ?& Y3 w6 y5 y/ y' g" E
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)4 }0 v3 I+ g- U) s
- {, i& A9 ]5 V& B- _# D- S+ e+ y/ \
- printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);( ]0 l0 M: m* _9 a( T
- return -1;
8 @2 _+ d# q7 a. B# h - }
+ T) {/ k0 X7 S - int on = 1;
/ p9 M' A% q2 p& p" Y - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)- |4 r: L' Q9 r [3 O
- {
+ |! k! R% X/ n* I - printf("setsockopt error\n");' F# A3 _& l; s& { y) C2 R0 |
- }
1 u) J! \! O* y3 A- a3 z - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);3 Y& k- K1 n' z. A- _
- if(ret == -1): p( {1 F$ n: a. B
- {. m" l% K% Q3 H) B1 o
- printf("Tcp bind faiLED!\n");
3 N3 i B0 M% K X! V3 j - return -1;
3 I; h) f# L( e g - }
) y) j3 H% {& w2 [) o$ H. M: n! F% v5 O - if(listen(*socket_found , 5) == -1)
4 r, I% T; T" c& g/ z - {+ G- t& B9 v3 W4 V2 j @
- printf("Listen failed!\n");
5 }' h' N. i! Q, p1 _, ?1 ~ - return -1;
) J. Q9 t3 J: ]2 i+ A - }/ g6 [" [6 e8 e5 i* R' C7 {
- return 0;
1 u/ p3 y0 R+ ?4 t9 g - }
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);
0 p, b$ J) P+ ~) F2 s - void * Thread_TCP_Web_Recv(void *arg)
# G0 ?, a; o8 k' e - {7 w3 z* ?5 N. D9 i: W2 e
- 。。。) Q) F1 E- F$ m' O0 `+ k5 p H) @
- while(1)/ ^ }- s. ]5 a/ ~
- {- g: m( L5 R3 K0 z9 x
- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);9 u; F# j3 j# h; R5 K
- printf("fd_socket_conn = accept()\n");
" w+ L( B# ?' | - 。。。& C1 x P6 U7 X. J
- recv(fd_socket_conn , recvbuf , 1000 , 0);
5 } b& Q1 X* Y/ y, v( J - }8 w4 M* u8 J. ]# }0 D% |. n( v
- 。。。( X, S' Y! Y1 U* C) K
- }
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);
$ q1 ^7 {" S& X - pic_tmpbuffer = pic.tmpbuffer;; X9 T. W. q5 R9 C& n! R
- pic.tmpbytesused = buff.bytesused;! ^ ]* F9 ~ v) v
- pic_tmpbytesused = pic.tmpbytesused;
# B( i @( ^: l2 ^- V2 s - pthread_cond_broadcast(&pct);- X4 p6 j. }" h% y2 Q! W
- 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;
+ W4 H- |# p0 }% e! J - pthread_cond_t pct;
: B" K; T' _5 O2 f, @6 N - int main(int argc, char* argv[])
; m7 \6 n2 f3 v: p5 o. m - {
. h; y9 ^2 { y8 b1 g; D l - .... P6 G5 @- p% j; G
- TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
" x% T6 m3 X; c' d - pthread_mutex_init(&pmt , NULL);
; I. u' F" {' s - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);6 ~. {$ l+ B- C+ i" @* s
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
( N( l# [; G+ X: e - ...! }8 v. M2 w, p. A% O
- while(1)
. v0 g) q( F+ L8 n2 T0 H+ O, L - {, j6 ? c2 L) L" I
- V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);
5 R4 D; P( b: q2 ^8 ~$ x1 E - ...* J) J- i4 I' m# w, K" r
- }
( \4 |" X% @, i6 H$ u - ...6 u2 ~- |$ y7 @( E* r( O. Q
- }
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;">$ ~) Y, M" t! ]9 O+ y7 e( M6 D1 R3 Z2 b4 v
- </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" \
) D; g" m2 g8 m B# j- q' x - "Server: MJPG-Streamer/0.2\r\n" \
2 W* V& @- c" ]! J - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \- v" M2 |! S, {. o# L& S; `
- "Pragma: no-cache\r\n" \5 ~% s$ Z1 e( S$ U; C0 @7 S( ^
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"+ }+ K1 r' y, j3 t$ A
- #define BOUNDARY "boundarydonotcross"
% E+ d; E& z8 u - printf("preparing header\n");
6 V+ I0 h9 c% t& ? P$ d - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \( X% J* |4 ~& ?. c: V$ v
- "Access-Control-Allow-Origin: *\r\n" \4 m: \. u7 H: \* R
- STD_HEADER \
9 @& R4 |" K. w$ Y8 s1 O$ e" L - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
i6 X3 K) s% `; j; m: f - "\r\n" \. e4 s8 C4 y/ ~* `+ V$ P
- "--" BOUNDARY "\r\n");
8 s" W4 z6 ^& m# I5 P - if(write(fd, buffer, strlen(buffer)) < 0)
. g" q2 u; x- @3 s - {
0 a5 V6 x# p: b. @ - free(frame);
& }. U9 m) c" ~- x7 A - return;
. L+ q8 f0 Q" r$ e8 M - }
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" \$ T* c/ D- }" M: L1 u
- "Content-Length: %d\r\n" \( _: u0 I. ?' A. S! P' E: K
- "X-Timestamp: %d.%06d\r\n" \
6 C1 M$ ~; e5 \ - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
& e+ G2 d" C' ?* i - printf("sending intemdiate header\n");
S: q: z4 r8 x - if(write(fd, buffer, strlen(buffer)) < 0)
" v3 L+ O& r! J! w/ ] - break;
) ?9 ^6 y' k4 y( l% p6 t% \ - printf("sending frame\n");
v3 Y' N$ L% G' F g - if(write(fd, frame, frame_size) < 0)
?; b7 b9 H5 `/ [% T$ B, Z - break; F" C; a: F w& u" D# Q8 ~
- printf("sending boundary\n");
( c1 |4 h: C8 D) h/ n1 H- F1 j - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
# V* H) |$ ~0 g# R" Z5 ]" Y- | - if(write(fd, buffer, strlen(buffer)) < 0)
, [! z. L+ x2 f3 T" ^( v - 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。 
! Q, X: ~5 ^% }7 R8 J7 }0 _& Q2 M- Q D; V
' [# B3 W0 W/ y二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:( V6 D1 [& E; A# `2 I+ y) I
- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)
L6 n+ @$ P1 ]: c - {' y4 e/ ^- K' y* J |, l/ l
- *socket_found = socket(AF_INET, SOCK_DGRAM, 0);
# M" G4 n$ ~4 L9 c; \ - if(*socket_found == (~0)); P* P% S' F) q; M9 d
- {/ g! V, V. ~) i1 T) q
- printf("Create udp send socket failed!\n");) _+ r N& \% I4 X6 V& Q
- return -1;* m4 W. J2 x; d5 n" S! t$ u
- }" z4 z- I' m& f+ k
- addr->sin_family = AF_INET;
% O; r# Y* D$ f1 B2 j/ M - addr->sin_addr.s_addr = inet_addr(ip);
( l" Z% n4 ]& x+ @ - addr->sin_port = htons(port);
6 U& a) x v% M5 F+ K3 r - memset(addr->sin_zero, 0, 8);
' l, p. ^/ h, t$ ?: @- v - return 0;
5 @* [% g: i8 L! q - }
复制代码
Z3 a# Z! D$ l5 r1 K1 g' M9 _" O( i7 a& A" B8 `6 b
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. b. w+ R4 ?) O! Q4 r7 V) d( N% ?; g! s/ [2 o9 B
5 R- X" Z5 s/ m0 J) u7 [
- while(fend > 0)
6 K3 z4 q: x# [2 _ - {6 ` D2 `2 @4 j
- memset(picture.data , 0 , sizeof(picture.data));
9 \" ~+ g6 y+ u! \ - fread(picture.data , UDP_FRAME_LEN , 1, fp);
; B8 y' D6 U5 I3 C$ q- [ - if(fend >= UDP_FRAME_LEN)
9 I- o# P# f) R4 y' D; [4 B; F3 @" } - {
0 M1 U5 ~& K( p& u5 Q+ h4 m7 Y9 O - picture.length = UDP_FRAME_LEN; [- P" ?. L* p3 @2 K5 e3 d
- picture.fin = 0;* ~" @' \- L* _! Q7 q3 n0 v
- }
# [. @6 i) e* P6 x5 L$ I - else& m5 w* T, D9 O; l' s k5 e7 k
- {
! G1 C7 r0 B" }: f1 U- S" ]# S: k - picture.length = fend;
9 p1 l& e i9 C8 m7 E8 u - picture.fin = 1;) P* c4 N. {6 v9 E& a0 O9 U
- }
! U2 b9 G- ~* C; L - //printf("sendbytes = %d \n",sendbytes);( U# a4 {# w# ?: r
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);. G$ T4 W' ~$ h
- if(sendbytes == -1)
/ A1 I) y& q, X6 o$ v - {
1 }. ^+ M6 `# b* t0 h - printf("Send Picture Failed!d\n");
( l5 j7 v) b6 {: G( F r - return -1;) K5 q( v9 E3 J
- }
" j5 f$ V) W( D7 @2 ~6 D, f1 a, p) H5 x - else; S j3 [7 p8 N+ [- K' F
- {
/ M3 V5 T! Y1 `- g4 N* }( R) S - fend -= UDP_FRAME_LEN;1 F, S: i, B& B8 b: h
- }! d3 P3 T$ j7 k) ~- _0 g$ o
- }
复制代码
) V( S3 k4 _' I, x4 z$ K! U/ e- y4 O, f$ {

% k" B+ S/ z5 D/ a5 W9 s% R3 `! Q2 r7 t7 H) F! R' W2 Y n
iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |