本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑
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" |+ D$ Q: _ y! V! A+ w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 S" E+ k1 p4 [8 h+ N

6 a) `8 c7 I+ ]9 q! A6 C% ~# J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。
# P, E: r8 D' o( e+ R& G* C一、HTTP网页服务器
0 R0 a! ]( ~, X: d) V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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: {+ l' D. p- x* A5 } - struct sockaddr_in servaddr;! q ~ U8 F5 V$ n) V
- socklen_t addrsize = sizeof(struct sockaddr);
+ v. n( h4 W0 v4 {% |; [/ } - bzero(&servaddr , sizeof(servaddr));
% @* v8 c2 ~7 m. }; F. K& ?" V - servaddr.sin_family = AF_INET;
4 [' M% z# {7 K; V - servaddr.sin_addr.s_addr = inet_addr(ip);
$ T7 O7 x6 g* y4 O4 F9 _* Z - servaddr.sin_port = htons(port);# h' p( q4 |3 ]5 r9 f# M" I9 a
- int ret;
& n, v: y; a: H; e/ @ - IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1): G% K K! I* t) o
- {
" a* j- K9 J& l/ M3 D - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
8 h3 O. E9 N! T4 R: w4 ]+ p: F - return -1;
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- int on = 1;! l9 }; D: x; m
- 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: i0 O; v7 J, i g/ Z2 i) U7 a' p
- if(ret == -1)+ Z! ?4 n1 ]4 q+ X+ \0 P( Z5 U
- {
7 N3 R' i6 Q6 q9 q: T3 y - printf("Tcp bind faiLED!\n");7 e& d* i0 O& E2 k3 H
- return -1;
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- if(listen(*socket_found , 5) == -1)
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- printf("Listen failed!\n");
; {- D4 o# y* s+ Z - return -1;
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- return 0;) `# N P+ X `# ^+ o
- }
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);
2 a% r2 f% g+ {/ J+ Z, V - void * Thread_TCP_Web_Recv(void *arg)
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# @5 V9 Q4 X) v - while(1)2 L2 i% x% [" [: w+ Y: d
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- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);3 J/ _) k( r+ D' T0 k) b
- printf("fd_socket_conn = accept()\n");
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- recv(fd_socket_conn , recvbuf , 1000 , 0);
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- 。。。
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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);
1 s/ k$ j \; W; d5 r - pic_tmpbuffer = pic.tmpbuffer;
* L/ x- F2 v- V; B ?* q' S - pic.tmpbytesused = buff.bytesused;6 b# r) h. A, P, Q( E" x" \
- pic_tmpbytesused = pic.tmpbytesused;. x) N8 v8 s* [/ F5 n) w! k
- pthread_cond_broadcast(&pct);
; a( D' w7 k; ~ `1 E - 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;
4 E% ~1 j& V# {4 G* x! {& M - pthread_cond_t pct;
8 |. l9 M/ K8 A5 r8 [5 s - int main(int argc, char* argv[])8 I5 R* I' U% r6 V/ V
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- ...
: Q0 H k9 q$ U' n( `5 L# V - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);6 Q3 Z3 L9 I/ _ u! u# M( C
- pthread_mutex_init(&pmt , NULL);
2 k! g/ |6 }( N G: m/ Y - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);
% K* _, G% f2 q' b+ Q# P - pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);& G' r" N9 W1 H6 Z
- ...
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- {
0 N1 k+ ?- {+ L6 ^ - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);8 G6 T) N5 z' R
- ...
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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;">0 [3 m- l1 g4 x" W o' f
- </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" \
, Y( y- A2 _. c. J& P - "Server: MJPG-Streamer/0.2\r\n" \+ t8 G& F) [* n5 S6 y) d& ^
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \; p- D: { M* h* H6 U
- "Pragma: no-cache\r\n" \
( Y% h4 r- f6 P$ B+ | - "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
V" O6 b* F. [! i, \ - #define BOUNDARY "boundarydonotcross"' c1 |1 I! q/ u* t8 f
- printf("preparing header\n");
* V- I2 f6 N; Z9 T% s - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \6 L/ v1 E% J/ a5 r+ w* ~( i
- "Access-Control-Allow-Origin: *\r\n" \
5 [& j: v- R( b4 \ - STD_HEADER \# W+ ?! g3 p. @: W# J
- "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \8 z; T% f& T7 h- Z
- "\r\n" \8 ~3 l% y2 G1 ] y2 p7 L' ~
- "--" BOUNDARY "\r\n");
" ]! e0 @6 Y) l) R8 t - if(write(fd, buffer, strlen(buffer)) < 0)
; @( @" d6 S% J - {
. R M; I! Z5 z" I! K. Y - free(frame);% g1 \2 q0 U! e
- return; ^; o* ^& y. e; c9 x+ ?/ Q4 f
- }
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" \
4 O; d5 L9 V2 [! d' Y' e% Q; c - "Content-Length: %d\r\n" \6 _ v" V/ g0 h/ U( V) y. H. p
- "X-Timestamp: %d.%06d\r\n" \
9 ]; ^5 T; u6 A7 p' k - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
! `4 u- W3 e6 y- ~# F/ z0 i' Z! v- u( R! ] - printf("sending intemdiate header\n");: W" X5 Y: N; W' |& I* o
- if(write(fd, buffer, strlen(buffer)) < 0)+ G% n( p/ @# l" } z
- break;( J3 w) `# Q, I6 M, P7 {3 F2 t
- printf("sending frame\n");! g5 a0 r) g/ H% E
- if(write(fd, frame, frame_size) < 0)& Z" W' k0 u4 D! a& j% j- a
- break;
" }4 ?: H. y8 t/ L - printf("sending boundary\n");9 \/ ?1 m z4 Y4 s( r7 i/ g( n. F
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
' u4 N; }2 T% W, @+ u, l$ f% |" N - if(write(fd, buffer, strlen(buffer)) < 0)
; F/ N5 m( I7 n' O) I' @ - 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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+ F8 k/ G/ Q- @! u1 j- l二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:
8 \4 T! t+ h/ K$ d- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port). N. w) v; e4 Y$ S5 i6 A
- {
9 R: `# B2 ^6 w# F& G( y* ^ - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);& Y5 P" |0 w( p: e' \7 j( j" u
- if(*socket_found == (~0))- M# b7 n, h8 K1 v
- {" o" q" A+ m0 \( J. e r- a
- printf("Create udp send socket failed!\n");- E# l W" g" g5 ]
- return -1;5 p3 t' V! P9 v# Y6 g4 m
- }
' _7 W. k9 }: N9 V - addr->sin_family = AF_INET;1 o; s- _) [/ i5 E
- addr->sin_addr.s_addr = inet_addr(ip);1 d8 A3 e) G" Q# b9 B" W3 e, s1 z- O
- addr->sin_port = htons(port);. z0 ?6 `+ I5 p! j, `
- memset(addr->sin_zero, 0, 8);% a Y/ s. ]" r) N- g
- return 0;9 [; ~ a+ G. P$ P, R) I
- }
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:# {! X' I# a& }# C* x& L* U
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- while(fend > 0), ?0 x8 Z9 R$ ]% V( E
- {% v- c2 W; X- E! ^& z8 y
- memset(picture.data , 0 , sizeof(picture.data));
9 e) {; M3 _' @7 E4 c5 \ - fread(picture.data , UDP_FRAME_LEN , 1, fp);
4 x, O, t0 @5 q) D$ M! x% L - if(fend >= UDP_FRAME_LEN); J7 P) S0 z5 r& I, H: o
- {6 Y: _" {4 |8 @4 f
- picture.length = UDP_FRAME_LEN;
p$ R) E7 x9 s. G - picture.fin = 0;( n& S" e4 _( z8 {0 ]7 B) \
- }% P0 F6 t# o* u1 {
- else
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( l: X6 Y( l g/ @4 y - picture.length = fend;
: s" g% Y6 C6 R - picture.fin = 1;
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( E4 v& t, R7 h4 @+ Y) f/ ]3 h' B - //printf("sendbytes = %d \n",sendbytes);* j# l. X9 z( @; g0 V6 v" J
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);: {4 C! s' p% x) }# ^/ d
- if(sendbytes == -1)) W0 X7 Q1 g; f/ ^% v7 \# }0 O
- {* z) ~2 Z# S, r
- printf("Send Picture Failed!d\n");
0 T! [; I: W, |& |0 b" T - return -1;
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- {
$ S5 I* d0 ]' J' M9 f; i% N" A, i - fend -= UDP_FRAME_LEN;( M% x" b1 ]! {; }- I
- }
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复制代码
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9 T) c5 M) j W( B& ziMX8MPlus 核心板: https://www.forlinx.com/product/136.html |