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
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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。 6 _$ y' H. @* R3 I r

; h2 u7 }" i# ~0 a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。
( k8 j; v1 Q( H4 O4 \一、HTTP网页服务器) E5 t+ k1 ~4 D. Y
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); N+ R9 D5 Y5 |+ ^
- {5 F. R) P1 l1 ~8 b# l
- struct sockaddr_in servaddr;
4 p8 E7 `' m& J3 i - socklen_t addrsize = sizeof(struct sockaddr);- O5 f+ V- s' ^
- bzero(&servaddr , sizeof(servaddr));2 p' P4 [3 ]$ H
- servaddr.sin_family = AF_INET;
1 e+ J- K& T" M4 M8 K9 J5 D, r! g - servaddr.sin_addr.s_addr = inet_addr(ip);- f7 h( g- X; a s1 k) [
- servaddr.sin_port = htons(port);
1 ?2 s1 u7 v: _( ~. d* V: P; t - int ret;, N. n" g( X9 _' }& Q4 O$ X4 e
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)6 M/ B9 m L% m7 A
- {
8 Z# N" B% c* U; m - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);
" `9 c7 k; ]; t% _ N - return -1;1 j& b2 ?+ h9 @/ y1 i G G
- }
1 i/ y; U. G" Q A9 K9 s - int on = 1;
1 i$ @$ X9 T5 G+ a - if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
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4 L3 R+ y$ D% p; u - printf("setsockopt error\n");# m) M ]) R! h4 @' F
- }
: Z: `$ b: J. Y: ]6 C - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
$ h5 ?& v% l$ q - if(ret == -1)$ e4 X1 I) I/ p3 f$ [
- {
N+ ]7 O5 D: P0 d" ] - printf("Tcp bind faiLED!\n");
% I& k) G: ^6 a- r" F0 n - return -1;
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- if(listen(*socket_found , 5) == -1)0 Y w! r! X4 R. n4 l& E
- {
7 }2 |$ j/ Y6 S t - printf("Listen failed!\n");
; e4 C: W) \4 X2 _ R - return -1;
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2 _; l) d5 Q& M$ X2 j! T) h - return 0;
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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);- ]# g6 w4 \8 f% z9 a7 a7 S9 d2 I, S. {
- void * Thread_TCP_Web_Recv(void *arg)
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- while(1)2 P# c) W8 w6 D2 e: Z; l
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- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);! l2 |, ]6 l: o5 j$ W
- printf("fd_socket_conn = accept()\n");4 M5 Z( N; X$ U/ Y0 a
- 。。。! _. m+ j! U8 i! [% t2 {
- 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);: j. s* z9 v( M
- pic_tmpbuffer = pic.tmpbuffer;
. S" f' Z- I: W% I - pic.tmpbytesused = buff.bytesused;
/ r4 m g: e7 k6 H6 e! R - pic_tmpbytesused = pic.tmpbytesused;
& U4 ^- U3 k! w' D+ u3 d - pthread_cond_broadcast(&pct);
* H) F! W& u: ~ 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;- N' w7 [& v& U$ i
- pthread_cond_t pct;
, M/ @% K9 S+ I2 W2 L - int main(int argc, char* argv[])
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- ...: d4 Q c7 w5 k) P0 D
- TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);
- o" ]( @+ Z" y5 w$ w2 ` - pthread_mutex_init(&pmt , NULL);, Z) R* F7 Q4 }0 ?8 m4 s8 _
- pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);3 P. x& @; |" F' ~: c* i
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
; N1 H3 \4 P2 |$ e - ...
: H6 i& P) E5 X - while(1)
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- V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);* f: L0 @2 M1 ]1 A+ c7 E
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- ...5 \/ v4 o( q+ R: x: }- D
- }
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;">
) M A5 K8 {9 k3 o" e - </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" \ C$ A, w' q0 ]
- "Server: MJPG-Streamer/0.2\r\n" \; p! N* j3 I, \. _' z5 K
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
: z. P) Y& f2 e8 c - "Pragma: no-cache\r\n" \9 w: H- E2 b; r" |; i! O& P
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"4 \+ L: e% ?% z* h2 m
- #define BOUNDARY "boundarydonotcross"" @8 C2 @ H. |
- printf("preparing header\n");& Z) \& _3 s' f& t
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
) N' f. k+ M. a$ _: Z% j - "Access-Control-Allow-Origin: *\r\n" \( e, I* o' ] e1 e5 V4 F) Y) E0 x1 Q
- STD_HEADER \7 u7 k9 X* v" T& S# g
- "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
$ w8 a6 ?& x2 f/ }6 n: X7 E* I* m - "\r\n" \6 A* w9 S% r2 X# F3 X
- "--" BOUNDARY "\r\n");) g* ?1 z$ W$ ~2 o3 t
- if(write(fd, buffer, strlen(buffer)) < 0)
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- free(frame);5 W# v7 \7 I# g$ j/ J
- 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" \
' i1 U2 `5 `3 J) I - "Content-Length: %d\r\n" \$ F: M2 D5 k9 e9 k9 A: W% c! M
- "X-Timestamp: %d.%06d\r\n" \
7 b8 x8 q- J0 G6 }$ K - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);* ?# ~7 t% s7 v7 @' W! F9 j
- printf("sending intemdiate header\n");% X3 v! X4 j0 I7 a" K) z
- if(write(fd, buffer, strlen(buffer)) < 0), Y: `$ d2 o7 P: b" Z# r
- break;
7 H% S; S5 c2 S3 t - printf("sending frame\n");
' w8 E. {3 ~5 ?5 F, W# v/ x - if(write(fd, frame, frame_size) < 0)$ O3 f% ~# A6 w( @
- break;
0 e$ Y8 o7 |0 |: t, @6 Q! ^1 [" v - printf("sending boundary\n");) Z9 Q* W P( r1 Q, R4 W
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");$ C" _3 m5 V7 r, g
- if(write(fd, buffer, strlen(buffer)) < 0)
- m$ Z3 p+ Q0 B6 |$ T4 w5 v7 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:
S# E. R3 t+ Z( u* F4 G- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)$ t( f) ?8 F6 ~4 z: j
- {, A8 T8 Y5 z q3 w2 k
- *socket_found = socket(AF_INET, SOCK_DGRAM, 0);* B& z; r, q6 e) M- J$ K9 s& N
- if(*socket_found == (~0))9 X# h6 w2 @. s8 Z0 b
- {
3 P: @1 l3 X3 Q/ M/ \8 v: I' u# y5 l - printf("Create udp send socket failed!\n");. e1 ^1 R# O" i: L% f
- return -1;
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j! p" i" i/ N \ - addr->sin_family = AF_INET;; p0 X" n# v" i) X
- addr->sin_addr.s_addr = inet_addr(ip);7 v1 v* _0 M6 W
- addr->sin_port = htons(port);
8 H1 A9 M* V8 `, R! m2 G6 ^+ x) v - memset(addr->sin_zero, 0, 8);/ H# z) C" |+ r/ ]$ p
- return 0;
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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:/ g! M, W v$ L% \6 W& h
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0 s; Q R) b6 I5 F/ E7 R ?5 C- while(fend > 0)1 L; B* J; f3 I
- {! G9 I& D7 I: r3 Y! g; Y+ Z _9 a, ?
- memset(picture.data , 0 , sizeof(picture.data));* q8 Z; N7 k1 i/ F
- fread(picture.data , UDP_FRAME_LEN , 1, fp);$ c9 w7 P5 d6 S0 Q3 e
- if(fend >= UDP_FRAME_LEN)
# H; T& [6 U7 n t - {
3 a3 y2 t* h2 Q7 r6 ^1 `6 y - picture.length = UDP_FRAME_LEN;; e) [" c: T5 q( ^* q) v" C
- picture.fin = 0;- }% x7 B1 g& g) h2 ^! V: ^- b& ]
- }
: |4 W3 b4 ?+ d' K4 y" u" H) i - else" P" d2 I' V: r& I% F, f7 Q
- {) P" ^+ Z) D# O
- picture.length = fend;( e* _% y2 Y. m
- picture.fin = 1;
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- //printf("sendbytes = %d \n",sendbytes);/ ^) U+ k) C) Z4 {0 Q% S
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
$ T9 V" X4 b; w7 H7 p2 t4 l! \7 W - if(sendbytes == -1) u& t6 G9 ^6 g. G5 j$ F" R
- {
2 d0 u& a2 }+ f - printf("Send Picture Failed!d\n");3 B7 c+ T1 }5 t0 y+ t0 `2 n
- return -1;/ {8 D9 h9 b6 _5 O- R* n
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- else$ h) G1 }4 q `, n6 d5 h
- {3 t# }# p% a# J2 {
- fend -= UDP_FRAME_LEN;
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- }
复制代码
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iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |