本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑 : V# B3 P. g2 @/ v" C& X6 n- _$ Q- A
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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. e8 s' M# l, ~9 V/ ^* k$ p
. F/ X" V0 v. |: M8 b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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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。
( X8 ~5 C! L _) }一、HTTP网页服务器
9 M5 _; I1 V( |- C: w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)$ V5 n% ]' d9 u6 Z; c6 I2 Q
- {
6 e5 u" a3 w5 Q9 i$ t& a, C - struct sockaddr_in servaddr;$ z5 ~$ l( u" g$ D [
- socklen_t addrsize = sizeof(struct sockaddr);
' [& F- m J- T3 r0 R1 b$ \ - bzero(&servaddr , sizeof(servaddr));2 P+ \7 U* E# O
- servaddr.sin_family = AF_INET;
# |/ ^) h7 m' T | - servaddr.sin_addr.s_addr = inet_addr(ip);' ?- j5 G2 a) q
- servaddr.sin_port = htons(port);. q/ x/ t; ?# Y: _
- int ret;
4 B9 b1 D" U3 l - IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)
* r0 s1 a r$ {6 x& a- E0 h - {
/ }, e4 C9 h6 J' E* E1 u - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
" u% d0 U% f6 P/ ~ - return -1;$ }% P/ @3 |( q" d
- }
0 t5 _3 N$ M) |. z$ X0 D3 f# z! \ - int on = 1;
* g" T, S8 k; o - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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4 e" }3 `& |) J - printf("setsockopt error\n");8 Z1 ]0 Y/ k0 L8 [! Q* q
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- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
- E3 z9 u0 X T0 j; r - if(ret == -1)
0 x7 w7 R( A, j o. e - {
5 f( o$ Q: r5 } - printf("Tcp bind faiLED!\n");' ]+ B) M$ t2 @8 h( X% v
- return -1;# @! U8 ]5 C1 [( k5 E: V" q8 T- p" m
- }
, V8 F* ]% x8 Z7 C1 {) j - if(listen(*socket_found , 5) == -1)5 O2 N: W; Z+ w" r% \8 I
- {
( p8 W; u" X! a5 K8 O- ~ - printf("Listen failed!\n");
0 P' L( y; m8 d - return -1;
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- return 0; l! X5 V5 u+ p# ] _/ 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);
! ^+ `( v& k* d" U) z$ V& w - void * Thread_TCP_Web_Recv(void *arg) b" u$ b: E" h+ Y
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- 。。。
8 h; F: [9 i$ D! @ - while(1). q# e- |% W; Z/ a$ s- h/ F
- {
7 _; D( ?7 A& h; I - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);" w) I+ }- Z0 A' J9 s7 t
- printf("fd_socket_conn = accept()\n");/ V i5 F9 s+ a' h' \0 Y! z; m) l
- 。。。3 X& b) Y. z3 T& F
- recv(fd_socket_conn , recvbuf , 1000 , 0);, g/ P8 s4 n) A* x5 \
- }
# D1 Y: }! J/ u - 。。。
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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);
7 A7 z+ R! E _# z; a - pic_tmpbuffer = pic.tmpbuffer;/ Z1 T) n; U$ E ]% g$ L
- pic.tmpbytesused = buff.bytesused;
2 A( d1 Q( O2 [& @- |6 v: y, y7 J; _1 M - pic_tmpbytesused = pic.tmpbytesused;/ E! i6 @# K/ J
- pthread_cond_broadcast(&pct);
8 _) @6 l! c/ d( O0 J! n - 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;
2 S7 j# N0 [- g: c# E, x - pthread_cond_t pct;+ n) w } h3 c1 K; M! Q' p
- int main(int argc, char* argv[])
* S9 p) [+ I. A" x+ J8 S( p - {
7 P. G# \! t; Y* r' Y. L: b - ...
7 R. q- `- c$ p1 C( P0 F" h - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
+ l3 f: R- o- g4 e - pthread_mutex_init(&pmt , NULL);
3 K6 o* A0 C2 D" ?. ^8 T/ G - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);1 ^& y/ h' J, |+ ]0 m3 g
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);+ W* q; J u1 A A5 {1 P/ ^$ E# Q
- ...
: h0 V; P) ^, H5 t* w# } - while(1)* l7 U# K3 C$ L! a* ?7 w
- {
_; K6 T; J2 P- G: h q) \ - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);: j' S7 j$ m* j b2 Y2 { I
- ...
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# Y' @6 y# j M& ~1 L - ...
" s) s) D: C2 e6 u- x - }
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;">" Q) A- A, ]$ T+ V# G' _" a
- </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" \
6 f5 w' `1 S$ `6 U: f$ N. H - "Server: MJPG-Streamer/0.2\r\n" \
! K0 f2 r: n' g* |3 v6 l9 m' I - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \0 e" v6 }" I" i5 j2 Q
- "Pragma: no-cache\r\n" \/ h* s c* p$ k9 H- o* ~+ _
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
6 ^6 i+ h" c. Z7 ] n3 r t - #define BOUNDARY "boundarydonotcross"
# k, i" g* Q1 n' G2 h/ a- x! P - printf("preparing header\n");
* t8 U8 h+ j9 I - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
. ~- T, H! ` P' V8 R# b - "Access-Control-Allow-Origin: *\r\n" \
m6 \/ d" T8 v& ~1 R - STD_HEADER \
- K8 a" X; ~0 |; B; ^, R8 `& Z- a( O - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \. w5 r% F: Y& u' j
- "\r\n" \
- [/ M K* w- B0 z% `3 V) |% k5 C - "--" BOUNDARY "\r\n");
, I) B: T& i( m9 \5 V4 k/ e - if(write(fd, buffer, strlen(buffer)) < 0)5 R* @- _9 V& K* c* D; v* \. P
- {
- G& L, o& V% H- b - free(frame);) O1 r3 |' o2 _' w0 z/ t3 d
- return;
5 m3 a; b' w/ s0 z8 T - }
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" \
, {' \ S% b; b' _& P6 F - "Content-Length: %d\r\n" \
1 o( V( {6 @9 i. F, h - "X-Timestamp: %d.%06d\r\n" \7 G) Z Q. [! g9 r, b% k* h
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
3 S' W1 B8 i( B& T; z: e& x - printf("sending intemdiate header\n");
, L7 F4 I6 t. ^4 `& b2 l: c& h - if(write(fd, buffer, strlen(buffer)) < 0)
/ q+ N$ q, W3 F) z6 v! y2 ^) e* V - break;) q) P" I* T" ]* m- L, R0 J, M
- printf("sending frame\n");, P6 f$ t3 \/ `
- if(write(fd, frame, frame_size) < 0)1 g9 z; W& ~6 F! P& F+ [
- break;
' G9 k8 u6 ]) [( J( J/ Z5 n - printf("sending boundary\n");) y$ Z# y" t" U! @0 ~
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
7 C* k- c; E- F( d. w; ` - if(write(fd, buffer, strlen(buffer)) < 0)
: |( m) X7 S, z' N8 p5 o6 e - 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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5 P% D8 i9 c& Y' A# z5 M二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:0 f3 O7 r8 ^% B" A( {
- 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);
) e( \0 H. A, i3 @3 k2 O - if(*socket_found == (~0))' x4 n* w( ], g# s( {/ {
- {
" d& g3 T- n" ]2 ?7 M; V0 z - printf("Create udp send socket failed!\n");
- o9 d& p# r: n6 H4 S+ [. X - return -1;. Y* N1 g; a. Z' A
- }6 k, z1 e: A- [" `& C! E0 T
- addr->sin_family = AF_INET;
* X3 K# ?$ f3 { - addr->sin_addr.s_addr = inet_addr(ip);
; N- g( b7 v2 `/ C. n- T3 q - addr->sin_port = htons(port);
+ y$ W& E' P9 A, `. C) V" O - memset(addr->sin_zero, 0, 8);; D6 B" u n7 d$ U! \
- return 0;, Z% s% V @5 L$ I* d9 T, t2 B: [
- }
复制代码 * R7 g, R4 o2 P9 }# W/ ~
/ A! Z+ G) X" v6 T. ?* v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:7 H* A l- E, W) L1 k3 @2 G
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- while(fend > 0)
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- memset(picture.data , 0 , sizeof(picture.data));
9 ^ ?, U: }" W/ ~4 U7 p - fread(picture.data , UDP_FRAME_LEN , 1, fp);1 F$ Z& ^* y- M" {3 m* o5 A4 l
- if(fend >= UDP_FRAME_LEN), e0 ~" w+ H+ X
- {
' z2 o/ B2 F- U' c - picture.length = UDP_FRAME_LEN;
& H3 g3 T9 ]7 z5 k- `) W: E( ?# @ - picture.fin = 0;% N8 o/ j. P& F$ a
- }
3 q2 d# q+ j s1 D - else. l `0 Y( K9 S% @+ g4 X
- {
}8 S- [" Y5 x$ a" F E - picture.length = fend;
& D4 }6 F( A( j5 k( U - picture.fin = 1;! @9 D& T9 V! X/ q2 ~; @
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- //printf("sendbytes = %d \n",sendbytes);
/ @! f% l+ D$ f6 u6 L - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
8 o* V* q* \/ F# s* s4 I s D& h - if(sendbytes == -1): ?5 H; a: l9 g3 O
- {2 s; [3 ?% A" ?8 \* p7 \
- printf("Send Picture Failed!d\n");, D0 `$ @7 S9 [! p
- return -1;; P( C3 n0 D" ~0 u0 n+ \3 `3 o
- }
% d' D1 |* \/ ]* E. U - else
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) h3 a/ y" I/ ^" Z - fend -= UDP_FRAME_LEN;; V- {& @" o: p* _ \* v
- }
$ Z0 T) T3 R2 E - }
复制代码
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* b; b Z! [' WiMX8MPlus 核心板: https://www.forlinx.com/product/136.html |