本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑 " ~# e" U+ o8 D6 C2 c
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& T u4 |7 |* D( X% ~6 e* 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
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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。 ( u" S/ h7 x$ n' ~
一、HTTP网页服务器2 Q3 r: C. Q) S/ o" v5 h9 l6 t) g
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)
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* K# P: P) r* o; a - struct sockaddr_in servaddr;) L# F, V' D7 O
- socklen_t addrsize = sizeof(struct sockaddr);
/ ]( h) @3 [+ A! r - bzero(&servaddr , sizeof(servaddr));
0 }9 ?6 \6 f- G$ g% S" V! t - servaddr.sin_family = AF_INET;' R6 _! _% g* a$ @% T
- servaddr.sin_addr.s_addr = inet_addr(ip);
& a K) V* t& s - servaddr.sin_port = htons(port);& p; j% m! h( \. t" d
- int ret;, c$ e6 j/ y# Y8 _: n7 I
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)) o+ m+ E/ g" r: q5 K" ]( [
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- printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);4 J3 H1 {* d0 k
- return -1;1 o- r7 R7 ^; a$ g
- }
r' w( B/ L: ~* l! A- S: r0 \5 C - int on = 1;
( ?% v1 o T; e! d3 { - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)# f" P. d2 M% C3 j/ }
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- printf("setsockopt error\n");
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8 w7 l5 I. _6 z6 q. O; X# | - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);! X: g; Q# Q" v1 M+ Q* N/ A+ x- W
- if(ret == -1)
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! Q7 Z" N& `% M, M4 V - printf("Tcp bind faiLED!\n");( B5 ^. L, ]( o$ L! C6 Y
- return -1;( Z* J1 U3 q. j$ l( J% \
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- if(listen(*socket_found , 5) == -1)
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- printf("Listen failed!\n"); B0 Q4 J0 ^8 x. C& a. V- F
- return -1;
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- return 0;9 M' {% \/ @9 F( p' i0 V
- }
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);
) k" W. J& X% v - void * Thread_TCP_Web_Recv(void *arg)
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- while(1)
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- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);. ]) H3 @% k) Y5 b+ l& M" F" p
- printf("fd_socket_conn = accept()\n");
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- recv(fd_socket_conn , recvbuf , 1000 , 0);! w- O, ~+ z- M# z
- }
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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);
w6 h' i) c6 v4 W' ?* O! ~ - pic_tmpbuffer = pic.tmpbuffer;
/ k1 n- |1 a3 o& m. s5 O - pic.tmpbytesused = buff.bytesused;) j+ S8 k" C# \" W
- pic_tmpbytesused = pic.tmpbytesused;
* Q: W* x# a+ W/ I9 y Q& f - pthread_cond_broadcast(&pct);
+ T5 v( M/ w7 s+ z5 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;8 Z2 x( k$ A. u/ l T6 v
- pthread_cond_t pct;
9 E/ c! M+ \2 k - int main(int argc, char* argv[])& | [7 Q* e1 C) l% S9 c
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- ...
! k5 x6 p& r2 b3 n |+ X - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
& s/ l8 w, d# E3 s9 n' K# U i - pthread_mutex_init(&pmt , NULL);
. a6 Q8 R/ h( y* c/ R) h! s - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);
+ u5 y( r2 L+ r1 S" Z+ Z - pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);& ?$ V( j, P* i& F; \) n
- ...
& F! _5 `9 W- N/ X# g - while(1)5 Q% r4 |5 [$ i' J/ j
- {( ]0 j) u$ o) _; p% W
- V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);
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- }
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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;">. x) G* J* v5 {, i: Y5 N
- </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" \
9 @ z0 ~& @8 [( e - "Server: MJPG-Streamer/0.2\r\n" \
! J+ |8 o, ~* k' j - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
+ a0 c8 A, f" n% F# E - "Pragma: no-cache\r\n" \2 Q! {2 h4 ~$ |# ?6 \" W- ~& R
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"" ^0 m* p( R7 z/ ?! A
- #define BOUNDARY "boundarydonotcross" o& G7 t3 f! W2 J8 R9 t
- printf("preparing header\n");5 u8 Y$ T7 L4 n' X. `& t
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \1 P9 L$ z' B5 `0 |: q
- "Access-Control-Allow-Origin: *\r\n" \
9 i$ _4 W8 K2 Q) S$ {) } - STD_HEADER \7 L0 `9 i2 ~) W; ^+ J4 K, `; _
- "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
1 ~; P+ E0 `3 f! J) c - "\r\n" \
: C+ o0 E6 f r' C- D - "--" BOUNDARY "\r\n");3 Y) d0 M; _* ?0 T4 e' Z1 K
- if(write(fd, buffer, strlen(buffer)) < 0)
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0 w: M* i3 R' T4 J" P3 V& R, d# c7 N4 P - free(frame);
* ]1 @ F: Q d- ~) C - return;5 V1 @4 w2 I0 F3 g; _* c
- }
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" \6 ~* z7 f/ `2 K/ X
- "Content-Length: %d\r\n" \* m+ {/ q8 S* p! y
- "X-Timestamp: %d.%06d\r\n" \
+ w: [, t" j1 z O - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);: n4 a! U$ i- A" b+ t
- printf("sending intemdiate header\n");7 N: I, i9 h* a- { |
- if(write(fd, buffer, strlen(buffer)) < 0)( t u9 D! H4 {. i7 X
- break;+ ~* B6 r6 [ T9 g$ i& R9 z* F3 X
- printf("sending frame\n");
, R1 N; j4 ^& J. D* M8 L+ t - if(write(fd, frame, frame_size) < 0)
: n3 D, J/ A2 `* j S - break;- q `$ h/ T# o8 B
- printf("sending boundary\n");' {7 ~( Z" }3 u {/ v- K$ C6 x; t- z
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");3 D' e6 r" Y) i1 O+ c! }0 v
- if(write(fd, buffer, strlen(buffer)) < 0)
[& ^( E5 F' L# M0 o! R0 r0 L - 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:' H# V9 c3 M! ]) F: |4 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);
7 y z8 A' _& M2 d& U) o - if(*socket_found == (~0))
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- printf("Create udp send socket failed!\n"); u9 Q! v+ R" l9 g! h, t4 Y
- return -1;% S6 k3 z0 F/ H7 Z
- }
! { q; i9 ?- L! ]' u - addr->sin_family = AF_INET;
; T8 h! f# b" z: Z) O1 Q - addr->sin_addr.s_addr = inet_addr(ip);; ?7 z$ [/ |9 h2 \. F: h
- addr->sin_port = htons(port);" U/ |0 s- \6 m- w/ u4 i1 w2 c
- memset(addr->sin_zero, 0, 8);
' X: y' c6 d4 j: m, b - return 0;
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复制代码
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) ]' t4 G! N5 \( x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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- while(fend > 0)# n# v8 X: [( t. d. ~
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- memset(picture.data , 0 , sizeof(picture.data));5 N1 b# u: F/ G' P
- fread(picture.data , UDP_FRAME_LEN , 1, fp);
! s/ g' B& N+ t0 L$ ` - if(fend >= UDP_FRAME_LEN)
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- picture.length = UDP_FRAME_LEN;
/ t0 Q6 V8 U' A5 @ - picture.fin = 0;
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- else
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- picture.length = fend; L7 L) G9 J/ \% F
- picture.fin = 1;4 N, |$ R) O: ^9 A/ P/ j
- }
# O# r! E& ~0 Y - //printf("sendbytes = %d \n",sendbytes);; Y7 C4 x- F) x) T; _
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);3 B4 n9 j6 E+ b% _
- if(sendbytes == -1)+ O. C H9 F5 i
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- printf("Send Picture Failed!d\n");0 d# {+ K) l7 {
- return -1;
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- else+ A% N( f9 Z5 j7 W3 ~! }
- {( S; \7 }- F/ _$ |8 w; |% e2 D1 E
- fend -= UDP_FRAME_LEN;
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- }
复制代码
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! j# Y/ q& M' O+ t+ z, YiMX8MPlus 核心板: https://www.forlinx.com/product/136.html |