本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑
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7 e) l! G6 n/ O d: m' Y! h' [6 O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。 + ]1 [- `# ?6 k9 |
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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。
! t' e5 x( }- g$ N) h' T一、HTTP网页服务器& K3 }4 r: p& j' p' v' P b# O1 \- N
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)$ a% _. R% _) A; @& a
- {
/ ]4 Q# @, c( I& o( n+ { - struct sockaddr_in servaddr;
' V' y# d' q+ Y+ k - socklen_t addrsize = sizeof(struct sockaddr);
) y$ Q) H2 y2 v4 }; F6 } - bzero(&servaddr , sizeof(servaddr));
' p2 W& z/ x5 {( Z( z) y2 s - servaddr.sin_family = AF_INET;# A8 A3 a3 L2 P7 \2 \( v
- servaddr.sin_addr.s_addr = inet_addr(ip);8 [9 m' M- G+ B( _7 B- M
- servaddr.sin_port = htons(port);# F a% E7 b' a# [) p
- int ret;
. U4 l' [. }. P0 j - IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)
! L3 Y- @/ X3 U M+ A$ D" X$ Q4 J# S - {
+ v$ [! y9 _: d5 F/ h - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
/ F* F3 u5 y! O* X - return -1;
# I; h' f0 q) N' U0 a; \0 Y" J0 [* p - }
2 f3 |. C& v5 ?' R- o7 D/ Q, J - int on = 1;% k$ C/ m: W7 g/ D
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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- printf("setsockopt error\n");
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- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
) _; r% w! f- S6 e2 T - if(ret == -1)
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- printf("Tcp bind faiLED!\n");
. ?* l! C+ o- G+ D. j6 t - return -1;/ N0 O% _: D" K( o' L
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- if(listen(*socket_found , 5) == -1)
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F: j: S+ ~3 O5 n - printf("Listen failed!\n");
' z8 X7 O/ z5 {; N0 _0 P4 I' N - return -1; h! R2 \, i \6 S
- }
. ^# W3 } R1 G/ g' ^3 u/ O+ q R - return 0;9 S9 J( d7 c& s* P3 e3 R0 [# H7 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);
, h# p- V& V' F% W- z - void * Thread_TCP_Web_Recv(void *arg) w w8 Y' h$ v9 Q) [5 P
- {( h4 R# |* B, X* N3 n0 w
- 。。。. F+ J0 @3 N, r0 d' G; {
- while(1)
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8 Y2 v; C# K; u. O4 A& f* M - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);
- p. V4 u$ `) ^- [ - printf("fd_socket_conn = accept()\n");
7 A. A( N) K& \. ~. k* k - 。。。
6 i7 b; b+ m& c9 Z4 o* \' h - recv(fd_socket_conn , recvbuf , 1000 , 0);
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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);" c" R2 R% a6 J$ t
- pic_tmpbuffer = pic.tmpbuffer;
; B$ G3 {/ U* \+ X* l6 y - pic.tmpbytesused = buff.bytesused;
2 H9 O+ e% N# b, q1 @- \6 s( Q# k - pic_tmpbytesused = pic.tmpbytesused;
% X Q6 ^" u- `2 L0 Y; o' M% } - pthread_cond_broadcast(&pct);
' x3 `3 |6 y" P0 q - 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;
+ u2 C j: r/ I* S i4 r7 g - pthread_cond_t pct;
7 t+ l+ u% z! i - int main(int argc, char* argv[])9 d, v3 \4 j' Y( ?( i1 }0 g$ q
- {
4 o& l/ @" v; U3 i: |( H - ...
# u0 ~, G, x/ Z2 ^3 \5 |5 d0 d8 M - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);. S. @+ i/ h5 e* U4 F0 i3 g
- pthread_mutex_init(&pmt , NULL);9 } q" P" u/ L
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);# b' O* @1 n: y w4 \, ^, {
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
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- while(1)
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) G6 Q* m* ?0 e$ v, i' [1 l2 X9 E - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);
" v+ }% A* d& ^& U" B - ...
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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;">5 {* ?& S9 t% w2 Y2 E6 ^
- </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 _5 w! e- w* \ - "Server: MJPG-Streamer/0.2\r\n" \7 a9 R: D: Q4 h3 B9 Y
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \/ R( n9 o' _+ X" ]4 i5 c
- "Pragma: no-cache\r\n" \( v8 w+ V0 a& L% {. P, C
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
! [. ^) B. O1 x- c. f4 a( K - #define BOUNDARY "boundarydonotcross"- L7 L( m$ A( }4 g: x
- printf("preparing header\n");
4 f3 Q2 W L' f; ~8 p - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \/ s& F/ W5 E, g/ d
- "Access-Control-Allow-Origin: *\r\n" \3 u7 k7 {, J+ p( z
- STD_HEADER \0 S6 P3 K0 f. @. @
- "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \! ` k& K; K( c/ S* f
- "\r\n" \( Y0 O1 ?; h: K, S' E, R
- "--" BOUNDARY "\r\n");
5 t- v1 F7 k; D" E: U - if(write(fd, buffer, strlen(buffer)) < 0)7 p! Z$ x5 [1 v/ I1 j$ O
- {% ^4 A: L5 |7 i, c
- free(frame);
2 G! k* z7 Q8 V: ~* p - return;, P& s! @' ~- q: G3 {/ }
- }
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" \( Y! _ C7 C8 d1 A
- "Content-Length: %d\r\n" \0 V! {. g. S+ d" y( g; R) S4 c# [
- "X-Timestamp: %d.%06d\r\n" \
. z' o) ?1 K# Z' [) v( U- Q5 d - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
& B* W+ e$ @: \( c' X" B - printf("sending intemdiate header\n");- l/ h r, ~5 E0 h m" o% ?4 k
- if(write(fd, buffer, strlen(buffer)) < 0)
3 N6 n8 i0 x3 s* @9 o - break;& l8 h; m% B, W* l
- printf("sending frame\n");
m3 ~7 A- Q+ u- q, t& A - if(write(fd, frame, frame_size) < 0)1 b+ v: A/ O6 R+ b; p1 q. k
- break;
" _ P' N% B* L& S" l. | - printf("sending boundary\n");
2 B! C" Y/ s, o) M - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");6 R r+ M6 |/ W; m! y" L
- if(write(fd, buffer, strlen(buffer)) < 0)- L3 p. A0 R. S7 m$ ~5 O$ D. K
- 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:
" m6 o( D3 g7 C' U* z* ? w o- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)
V$ G0 i# l+ F - {
# z" |, r8 p$ H; u - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);& n0 m. g5 n. K6 g9 v9 Y& N! i3 R
- if(*socket_found == (~0))
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- printf("Create udp send socket failed!\n");
6 l1 O; l- A' @) y/ R$ s3 C - return -1;& ]7 X- {- r$ m B4 o5 X! q- b- `5 }
- }
: x4 \. j) @. l7 y* M - addr->sin_family = AF_INET;
( t3 A2 S1 F) ? U - addr->sin_addr.s_addr = inet_addr(ip);3 @" \9 E0 {. p: ]9 w
- addr->sin_port = htons(port);
1 x: ?* Z$ F- G+ `; s% M6 d6 G, P - memset(addr->sin_zero, 0, 8);
Q( c5 s% L/ R2 n3 \! b - return 0;
9 z2 g) U4 a2 \3 z2 n4 p - }
复制代码
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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:- f! v/ z' j1 [: O! a( e5 M
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% O3 |1 g4 m( F4 u, i. e- while(fend > 0)0 h1 W; v& c5 r h
- {7 i- K: w( }# L
- memset(picture.data , 0 , sizeof(picture.data));
9 T7 o X# I9 Z - fread(picture.data , UDP_FRAME_LEN , 1, fp);
1 a/ Z3 h9 ~ c1 z2 T9 L - if(fend >= UDP_FRAME_LEN)8 y5 p Y2 _' S' J6 j" ? W4 A
- {" s- n5 B% F) [ m1 r& m" S
- picture.length = UDP_FRAME_LEN;' g- c* ~) }) [' i+ N( p% w
- picture.fin = 0;
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( V+ B! j, d4 ]" ^& v - else" y4 S% y' i1 g- \# y/ g3 p: H
- {" ?' `0 P' m0 r V: V# j, H% c) \% n, q
- picture.length = fend;3 H: E4 p+ s/ `& |* `
- picture.fin = 1;
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- //printf("sendbytes = %d \n",sendbytes);
! A( H4 j0 w) L - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);1 W* i6 o" k6 h& |
- if(sendbytes == -1)
- O( k, h8 ^/ n7 z. k( _ N! S - {
8 W# N) L$ x+ _- ~' W - printf("Send Picture Failed!d\n");2 X7 M6 X, z$ y" k% u" Y; H
- return -1;
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- else8 D# [& E' W- D( b7 t8 L. I8 x
- {) C4 `- r+ }3 [. h
- fend -= UDP_FRAME_LEN;
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复制代码 3 P3 z/ B6 I0 M+ Y+ R' v" \/ J
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3 g- f1 g% p7 \& [) H/ IiMX8MPlus 核心板: https://www.forlinx.com/product/136.html |