本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑
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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( [+ ?+ }6 R' m% [
! ~ z. U6 V. Y7 [6 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。
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A& ]( \8 \, }3 l* Y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。
6 i! E6 D) [0 X一、HTTP网页服务器
; H1 U/ k/ N4 L# 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)7 x1 {) }. F& U& u( O3 q0 M5 I
- {
: x% m: { l- L/ O2 @/ u( W - struct sockaddr_in servaddr;& I I9 M5 X1 ]
- socklen_t addrsize = sizeof(struct sockaddr);+ e2 @: Y9 \7 t& C/ K) D- I
- bzero(&servaddr , sizeof(servaddr));
! @) Q" c, i: I7 N ~& M - servaddr.sin_family = AF_INET;, b" N. }" K; p; }- ?
- servaddr.sin_addr.s_addr = inet_addr(ip); X/ s z" Y% ]; S
- servaddr.sin_port = htons(port);7 A* x. L' F! z" T* R/ x# i- Y
- int ret;) x8 _" E% u! Y/ _
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)
& ~- H: I1 o/ Y; C - {
7 E2 J N6 B& f/ K - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
7 K1 W; D/ {4 [$ b/ m J W8 E - return -1;
" Z- m9 r" L; C( _5 n3 s - }
# M+ `- @ F d' M# e- e - int on = 1;9 H5 f+ f3 n( U) j" }
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
5 e4 }8 A. |- I ] - {
1 M, j) C0 x* p7 d6 t5 }+ o/ ?( n. t - printf("setsockopt error\n");
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- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
( I) }+ p- N6 t; ?' Z: t# ]) M2 h! d# V - if(ret == -1)
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- printf("Tcp bind faiLED!\n");
5 V4 M0 @3 b. V. _9 X- H; ` - return -1;4 A2 p- n6 a6 P% b
- }
3 T" N# G/ |# \8 A8 E% D - if(listen(*socket_found , 5) == -1)) W# A7 Z. V- M: y9 }' y3 X! j' {
- {
' \5 c; e& L) M - printf("Listen failed!\n");8 H! R! A+ X" T+ p
- return -1;% G: [0 S" o6 d( I/ S
- }
% D$ f( U# q! D - return 0;+ H5 | z1 Q3 |/ J
- }
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 _. A5 m8 U- y! o( `+ |/ W
- void * Thread_TCP_Web_Recv(void *arg)) `) B! Z, z3 k- C% J# z" t2 A
- {
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+ U+ z4 Z9 K& b9 Y' G* j0 Z3 } - while(1)
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. l, z- H7 c+ l6 q/ q6 \ - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
4 b" Q* h) T! @/ S c6 V - printf("fd_socket_conn = accept()\n");
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2 M* h. |8 G2 G' b" B/ ? - recv(fd_socket_conn , recvbuf , 1000 , 0);' t& ^" K, e2 n9 K
- }! n& ]7 N) P1 I+ l1 ]0 s$ o
- 。。。
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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);
* A9 `9 I$ {" f6 V0 U - pic_tmpbuffer = pic.tmpbuffer;
2 q8 C, Z, n N2 T( J; J Y" P - pic.tmpbytesused = buff.bytesused;
9 p4 t) {1 \) v, i& ]0 ~+ F - pic_tmpbytesused = pic.tmpbytesused;4 L& ?6 k$ C5 D% B3 @+ z/ Q
- pthread_cond_broadcast(&pct);
6 `2 B0 B5 o s; z7 U: D& x$ \ - 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;
% |" Q( Y4 J1 p) B - pthread_cond_t pct;
& K# Z) u0 C) \ - int main(int argc, char* argv[])
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- ...3 e7 d9 @" e$ \& L/ w' Z- a0 v5 I
- TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);$ o) p' b/ n# h! A$ |) B, y' X9 W
- pthread_mutex_init(&pmt , NULL);
! f& j8 ~( O2 O0 p% D% E& P - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);
8 k0 w! f( K2 f' W9 u - pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);# L8 o* {9 R9 c8 P+ M
- ...
7 J" I5 d9 g8 b6 F - while(1)/ ]% ]- G) V1 h5 U D5 J, @
- {1 D4 @& H/ U' Y- N) p0 R* l
- V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);. F7 B6 [0 K+ J- q
- .... [7 l3 a' L* }8 B) \0 Y
- }
+ f! M8 e+ [4 z3 a0 N - ...
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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;">" F6 C: @1 ]4 j5 M# o
- </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" \1 n0 p+ m- p" a: }8 C7 |
- "Server: MJPG-Streamer/0.2\r\n" \( P3 j9 W* [1 l) u; i
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
. u4 ]/ }" g; G9 i9 W. F' I - "Pragma: no-cache\r\n" \
( [- D5 m- \ Y4 f8 u3 R; D - "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n") T, T2 k$ \# d; d* h
- #define BOUNDARY "boundarydonotcross"; d" n7 B. J- t# z. d
- printf("preparing header\n");
6 L- Y: P* ^' G* j! D, p2 B - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \. L$ m4 x; X; V8 q& N. J1 _
- "Access-Control-Allow-Origin: *\r\n" \! o( K8 k- _% o
- STD_HEADER \
) M% v$ u9 n4 Q; Q- d - "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
8 ^& f6 c- [6 a x: J: n - "\r\n" \! I# X' m! M4 C7 _, H H: N* N
- "--" BOUNDARY "\r\n");0 D. I4 O1 Z( [9 A1 d
- if(write(fd, buffer, strlen(buffer)) < 0)# z( F8 W. A, y3 y+ J/ j
- {
4 H7 J! D5 I5 [& V: |, ~# o0 S" Y - free(frame);5 c& @7 u: L4 ? g! Q" K9 ~
- return;
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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" \
0 U9 k7 n4 j. B* d - "Content-Length: %d\r\n" \/ c' p: O2 c$ I
- "X-Timestamp: %d.%06d\r\n" \9 ^ G9 ~! h1 c# `
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);# y$ U/ R' t0 f" n6 M+ w9 e
- printf("sending intemdiate header\n");8 e! B% B) z( U0 v4 g7 w
- if(write(fd, buffer, strlen(buffer)) < 0)
; M3 I: @4 u9 P6 M - break;; }9 l# o% [) K" ^* W
- printf("sending frame\n");! P- V; c; g7 v4 c- m6 h4 ?. v
- if(write(fd, frame, frame_size) < 0)
! N& u( C8 [0 _! ~+ Y( a - break;2 b; U# ?, t5 i
- printf("sending boundary\n");: S& d# ?" V2 M$ p* f
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
7 q+ `! G6 N$ I ?. A7 T - if(write(fd, buffer, strlen(buffer)) < 0)
# O( ~2 ?/ f- c6 T$ f+ H& y - 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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二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:! i8 O5 n3 C* `, f9 G- W
- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)" {0 u- @# h7 f% q: `, L5 x" h# l' \( j# b
- {
" P7 H% W' [& b, M - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);
2 m4 O( D- L& n% m, Y! R - if(*socket_found == (~0))
2 E! C3 W! L5 n3 E5 x5 r - {
+ K6 z2 Z3 }+ K4 E9 T; ? - printf("Create udp send socket failed!\n");! D: C7 x% D" r* i* T) ]9 `6 U. K
- return -1;
9 I& ^8 K$ Q4 U# q' U- Z* E - }& G( I8 K s0 V9 K1 T8 ]
- addr->sin_family = AF_INET;
0 g+ J, t& V4 ~4 A B- p - addr->sin_addr.s_addr = inet_addr(ip);5 @$ b# q+ C. t
- addr->sin_port = htons(port);
9 T4 o: b G5 Z4 F! n* S9 H6 d - memset(addr->sin_zero, 0, 8);
# j+ V7 E$ I" O9 z3 _6 Z/ P - return 0;
, P2 k) V0 \9 o/ y1 h* G: d - }
复制代码
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' f! [7 Y4 E: D+ t6 i' q% 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:
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' N/ m; q+ S/ a# ^* x0 P' {
- while(fend > 0), i V' s, ?# e- e0 o- X( N
- {
! q$ n9 {9 }- X9 a _ - memset(picture.data , 0 , sizeof(picture.data));" s3 u9 a O& m, }# G8 a7 v
- fread(picture.data , UDP_FRAME_LEN , 1, fp);
+ I5 G2 s+ @$ ^# ~+ ?. |; n" G - if(fend >= UDP_FRAME_LEN)
5 u. n& Z% a" h' r+ R/ T - { B$ u+ T( a; B, ]1 Q! ?* j
- picture.length = UDP_FRAME_LEN;
5 y$ ?6 F/ ?6 L+ M1 \1 ? - picture.fin = 0;
: D3 r1 a: }5 z) Q) V - }
, i2 E' o* d$ I* y* C& l/ A( a& k - else
) u/ m" ^2 @+ [ - {
! S: r: g8 D7 W5 o' P - picture.length = fend;5 H* a* |+ s! F. w
- picture.fin = 1;
# r& m3 r6 E' U - }
: R; ?$ V/ o$ s- K - //printf("sendbytes = %d \n",sendbytes);
) c- h p" }! N& i0 t - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);4 C, k' G8 w0 Y& |& ]6 ^+ I+ ^
- if(sendbytes == -1)
9 d4 P6 H% q' B, V. T, | - {
. M2 g& T; C7 P) F6 p( s - printf("Send Picture Failed!d\n");
8 S6 p, _9 N4 s, H - return -1;: h2 d7 |, n# l
- }1 a {- P& i2 \. v7 s
- else
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- fend -= UDP_FRAME_LEN;
, f% g* j5 p0 C/ T* m4 e! y6 ~2 U0 | - }
& D4 P7 t' V7 @# t' V - }
复制代码
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iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |