本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑 8 _2 h% w* z* y" H( s$ B$ _5 m
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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. f, t# v1 {% A m6 I6 E4 j
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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。 4 J. p1 w# P5 ^; W$ `+ W4 v; h
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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。
1 h7 r: s1 K6 _一、HTTP网页服务器! ^7 O. @# ?. M0 s! K
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)
% W; O6 u2 O% s8 Z8 q# z" S5 w6 v - {
# P+ R- _3 r) U2 m) b - struct sockaddr_in servaddr;6 ?) i4 g1 v0 I" B
- socklen_t addrsize = sizeof(struct sockaddr);
# @8 ]7 X) Y4 B" N - bzero(&servaddr , sizeof(servaddr));
# ^" `% h, g! N# a$ s1 ~ - servaddr.sin_family = AF_INET;
) t. [! I2 r! }' {( r2 C: h6 G9 u2 G - servaddr.sin_addr.s_addr = inet_addr(ip);
- S9 i" H: F6 t7 D, ~/ h - servaddr.sin_port = htons(port);% z6 O0 |6 F' [ {, [
- int ret;
+ f: H& C8 \0 E - IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)
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- printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
, {, \+ `( B! I; ?! s6 t0 R - return -1;0 F/ v) k8 P5 A) U- j: y3 A- I* I5 `
- }
8 ~3 {7 j! z6 ~4 r9 G0 Z - int on = 1;
* n/ L5 j# q4 _& L7 A0 i- t. M3 s - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)& q+ i& |' \7 Z/ z2 d, X# l' z
- {+ `1 c" h% z) B' S5 p
- printf("setsockopt error\n");& Z6 _+ w" @- q1 s, V$ M8 x' Q
- }
& u' p# |3 Y/ O9 o - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
) X# f% {$ R: C9 y% z$ n. C - if(ret == -1)# S1 h4 u" t$ w4 G% L
- {
5 d5 N6 L6 V4 L6 a6 Z - printf("Tcp bind faiLED!\n");
* A+ y4 y4 G. O4 Z% | - return -1;
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- if(listen(*socket_found , 5) == -1), t q3 H7 |+ g, @3 `+ y! S
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- printf("Listen failed!\n");
% {3 T( [4 x" b2 ^; u - return -1;
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- return 0;; ^6 J" N& t, z0 y, N% N- [
- }
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);9 } }: J$ @$ Z' A3 p0 q0 s
- void * Thread_TCP_Web_Recv(void *arg), O x0 ~0 B: m) S4 i- V, X* o0 r
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- 。。。2 G0 }7 |3 i/ O) u- B
- while(1)2 N3 l0 {; S1 y
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- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);8 H5 j( e, c0 j4 `( v
- printf("fd_socket_conn = accept()\n");* {* [4 w: ~" q+ ]
- 。。。
; _6 \; ~/ z# ~& U - recv(fd_socket_conn , recvbuf , 1000 , 0);
% P8 w* @# K0 x1 Z7 r - }
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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); o8 D& D$ y1 V: I ]7 x
- pic_tmpbuffer = pic.tmpbuffer;0 i& m# Z6 Q" t0 t' B, H
- pic.tmpbytesused = buff.bytesused;, {/ F* x& w5 U" M
- pic_tmpbytesused = pic.tmpbytesused;, Y7 {! s! c7 _( H1 J5 [! Q4 J
- pthread_cond_broadcast(&pct);9 W; R' u9 A. A: a% N p7 F
- 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;: ]9 a( N4 E! U& I& ^
- pthread_cond_t pct;
5 h( Z/ n( p& v3 f - int main(int argc, char* argv[])
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- ...+ l i4 x4 Y9 n# A. b; s- }* t
- TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
7 U4 ~$ H/ h- d( ?% x/ e& @ - pthread_mutex_init(&pmt , NULL);
]1 @# A, `; I1 h' G& |% ~6 X/ ] - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);0 S; x L7 U4 x) x
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);2 {* j+ ?. m8 Z5 R3 t6 S
- ...$ c" c7 o) q3 ^# G8 S
- while(1); Z% g+ V7 P1 |: |
- {
6 _4 J& v7 c# W - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);' g. A9 R$ O+ M1 N. V$ p4 z( N
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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;">: }0 a& @- i' n& V
- </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" \
; z1 R4 A$ c2 I- l' ?5 \ - "Server: MJPG-Streamer/0.2\r\n" \
* J, M1 ~8 A8 J- X, ]7 h - "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
0 ?1 M& ]2 K3 N b) c* K" R s/ }6 P; t" k - "Pragma: no-cache\r\n" \7 ^9 l0 z4 w9 g @6 r1 T
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"# S8 ^' q$ L% P* T7 y: b
- #define BOUNDARY "boundarydonotcross"
' T3 x* v* x; d6 {# l - printf("preparing header\n");
, h, C% \/ u& s# D$ J1 o. @2 | - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \0 u, C) V% g7 [" ]" M: ?
- "Access-Control-Allow-Origin: *\r\n" \( i; i6 y# L# U
- STD_HEADER \8 L* G' o/ y7 M$ `6 l ^8 x
- "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \; S2 u* ]* [: Q
- "\r\n" \
4 o4 u3 ?% }- P - "--" BOUNDARY "\r\n");
- }! o8 @' Z+ [ - if(write(fd, buffer, strlen(buffer)) < 0)
7 z$ b6 S7 G0 _2 z, } - {
; h% d6 i \- X, w U# W - free(frame);; F* @1 w `8 P! L. B2 d: c
- return;" N2 Q; n7 {5 N6 M% i
- }
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" \% U/ M9 o4 s3 h+ V$ c3 m
- "Content-Length: %d\r\n" \& @: [+ W3 D" i2 B# z0 N6 K9 ?
- "X-Timestamp: %d.%06d\r\n" \. b! c+ g& B F2 w$ w c- Q
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);* W' P, T, |/ ?4 @) {4 U
- printf("sending intemdiate header\n");
# r3 t( D8 _& B - if(write(fd, buffer, strlen(buffer)) < 0) \8 M* ^% Z5 b0 G7 w
- break;. [2 y; Y) m/ L) n
- printf("sending frame\n");$ i% J6 t1 ~7 J( d& t- Y& D1 D
- if(write(fd, frame, frame_size) < 0)
6 b4 ?0 d& P5 e- j/ ~7 z) n6 C- q - break;
8 ^4 R) u) k* R - printf("sending boundary\n");
0 Q! m2 G( {5 s9 h5 l8 M - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
L* `- H4 c R8 L ?8 ? - if(write(fd, buffer, strlen(buffer)) < 0)
& z; }; ^9 G" j% S% C. d - 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。  7 o) B0 a8 _$ ^5 ]

: u1 s* G' P& Z二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:! w* \4 B% a" T" e p
- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)8 d1 S: J. `2 o, Z; q7 R. W
- {
0 F! [- L9 u3 B' D& |/ R! A - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);
/ }4 z7 K* c$ y' Q( w$ O/ c - if(*socket_found == (~0)): B0 a. o t2 j- s+ i
- {8 R5 n: l4 V2 O( `1 P$ w
- printf("Create udp send socket failed!\n");
; A5 q" z {, a3 } - return -1;
% T1 U7 p: q$ R" R& F - }
1 Q" u$ `% g. F$ Y - addr->sin_family = AF_INET; M. e8 M7 v' C
- addr->sin_addr.s_addr = inet_addr(ip);( [. O' Z6 ~5 D; M4 Y1 G/ f
- addr->sin_port = htons(port);2 P! j+ B& p B s
- memset(addr->sin_zero, 0, 8);4 B4 ^$ m) Z7 G. P, S
- return 0;
: m; x+ E3 i8 r8 h9 V- f- f& [+ a% ` - }
复制代码 4 H* V4 ]* S. U# x; ]9 q
" ~( N* U. S8 g, f. z% t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:( Z" e& s+ a5 {$ G0 I s
+ e# ^. G& N+ j, p9 z/ o6 K; k8 h* W/ ], {! U
- while(fend > 0) H3 F& R; Z( e& a
- {
5 j7 d1 g3 \2 p% l - memset(picture.data , 0 , sizeof(picture.data));
' w% _3 s% b# T0 A - fread(picture.data , UDP_FRAME_LEN , 1, fp);; ?* b3 m Y' u! f' x/ T
- if(fend >= UDP_FRAME_LEN)
" L% t3 x9 X! ^7 W' ` - {
" Z6 a" o; P$ h; w - picture.length = UDP_FRAME_LEN;- c' Y% l! f3 T. z* m' t
- picture.fin = 0;
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- else
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- picture.length = fend;
9 l9 K I- C9 ?( C$ r) q( a3 n' @ - picture.fin = 1;6 B( ^2 ~0 E+ @7 i5 l; g
- }
3 k) X+ i+ u2 F+ X# }* t, A* [ - //printf("sendbytes = %d \n",sendbytes);
. \, \' w v) B6 H; s% q - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);# s: n$ N7 o; v; {. `3 k% {, e4 R, o
- if(sendbytes == -1)- N/ @( V$ c0 F+ L. Z: V6 j* ~& @
- {
* { e' A' N* D - printf("Send Picture Failed!d\n");. B/ R" q) `. Z) u& s' U) [
- return -1;
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- else
5 C/ o8 x8 p/ A8 _: F - {
- B b, ?& @8 G8 u. A) T% b& W - fend -= UDP_FRAME_LEN;' x$ t, p3 |/ o$ o# Q" B6 H
- }+ i- G* Q T4 N! o$ g$ @
- }
复制代码
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iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |