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.html7 L& b0 e( F# H" Y7 Z. `# T
; J7 }) d! s" i$ A3 Y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。 & A) g, F8 }; \& Q! t! b/ B* t# x
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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。
: `9 i$ A/ m9 i6 D W6 }& k一、HTTP网页服务器5 b: a) W- K9 I0 I; r$ U5 X' ?# x: f
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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- struct sockaddr_in servaddr;7 ?. r# p1 g8 m! `# o0 A
- socklen_t addrsize = sizeof(struct sockaddr);$ w: c3 O# @8 k
- bzero(&servaddr , sizeof(servaddr));
. L' g2 ?; h( @3 S, P C - servaddr.sin_family = AF_INET;0 f' w d+ L, [$ G1 T
- servaddr.sin_addr.s_addr = inet_addr(ip);
# i5 R I) c" ?4 [ - servaddr.sin_port = htons(port);( x; Z9 Y5 A1 j2 F5 {- [
- int ret;
0 u1 g" l+ B9 e3 ]. \* j - IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1)- K# d$ k1 M6 `, y( }/ G/ d. [
- {
7 r ]' t" b% C2 k. z9 ^8 Q - printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno);3 J }/ A9 P" S
- return -1;1 L) `. B. |- i! Z: y
- }
L+ ~0 C/ E4 O - int on = 1;2 I' j3 w4 R; F; c& ^3 h/ P8 a" ?
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)$ u' q C$ H; N
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- printf("setsockopt error\n");
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# }! `4 y9 D) a; @7 N2 J( C - ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);
+ `0 t& m, s) h' E7 f1 v6 o - if(ret == -1)& Q6 T: ~! M9 c
- {
( m/ Q3 `! K3 I: V+ Q - printf("Tcp bind faiLED!\n");! e: m+ Z$ R% i7 w. k0 n8 E9 q& O
- return -1;
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9 a3 y2 u, Q% v - if(listen(*socket_found , 5) == -1)
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- printf("Listen failed!\n");
+ @7 P$ s' [! U1 q' Y8 | - return -1;6 d1 m0 k0 h" [1 K" P
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- 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);5 H8 L% H/ b- k7 V
- void * Thread_TCP_Web_Recv(void *arg)
( ~+ O G# l- Z) z - {
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- while(1)4 B7 e" n% W s1 ?
- {
9 O2 [# [& p; P# z - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);* O5 K% D! E. J2 u: i
- printf("fd_socket_conn = accept()\n");5 ]% A' f6 K- G0 z9 h" @$ z
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- recv(fd_socket_conn , recvbuf , 1000 , 0);4 U1 w, _/ Z" l/ P* u0 ^4 K# _
- }
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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);4 b: r+ {& G- R1 b9 a* f, l7 I
- pic_tmpbuffer = pic.tmpbuffer;
0 [; O: _- S/ Z) V t+ R6 n& y7 }# F - pic.tmpbytesused = buff.bytesused;( z7 q3 q# T, H8 u7 \- d
- pic_tmpbytesused = pic.tmpbytesused;' ]* N& S y/ m) W( m
- pthread_cond_broadcast(&pct);$ |' N* x4 [3 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;
4 p+ P- R8 B$ V% [4 F& u - pthread_cond_t pct;
. ^$ v, o |) K* r+ _ - int main(int argc, char* argv[])
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- ...
% F8 Q) a# N H! n7 G - TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);1 S& C c4 s( y% c$ d |
- pthread_mutex_init(&pmt , NULL);
# \- G: R* {" ?& S- J* Z6 @5 S - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL); N0 Q2 S% Q) i, c9 P# e3 R
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
2 \/ e3 j4 J$ K- `- y - ...
% R$ N6 }8 Y" c c+ w1 m2 N8 g - while(1)1 x* J/ N4 G! V4 {
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- V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);2 I( Q8 X& I+ x; I. s
- ... q4 |7 [! E# A3 u8 a& U
- }
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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;">/ |7 @- s' }8 @) z; b' q' Y5 X
- </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" \4 W1 @- O6 i* m) v* p, P, B
- "Server: MJPG-Streamer/0.2\r\n" \
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- "Pragma: no-cache\r\n" \0 u. \- u8 B/ L* S* y! w& K* h
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"' c! H/ q% ?1 g. J( d! M: d
- #define BOUNDARY "boundarydonotcross"# ~( a, i0 a4 i' _5 ~+ B6 H" c
- printf("preparing header\n");3 p$ v; Q) v2 Y/ V
- sprintf(buffer, "HTTP/1.0 200 OK\r\n" \
7 K7 M4 W' ?% V) @" h+ c, v j) B - "Access-Control-Allow-Origin: *\r\n" \
+ s8 m' L9 }0 [ - STD_HEADER \9 |( B; E; e# J! u: I
- "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
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; l; T2 i; b p [! e& j- c; f - "--" BOUNDARY "\r\n");
0 ~6 i6 k/ t! G2 u% j - if(write(fd, buffer, strlen(buffer)) < 0)
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- free(frame);- v) B1 w1 c4 K0 m
- 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" \
. e- y5 e. A5 y7 j2 z+ ] - "Content-Length: %d\r\n" \- |! f7 ]" |! V5 S5 C/ c" ?0 R5 ]- Z
- "X-Timestamp: %d.%06d\r\n" \
+ c; Y4 s+ ] @! r7 M) b* P - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
" `% {9 W" [# e6 }$ v - printf("sending intemdiate header\n");$ G1 n4 k1 ~* b3 I# h$ g A
- if(write(fd, buffer, strlen(buffer)) < 0)
$ P: i$ Q K$ S8 k - break; C4 l" j$ y. L; E
- printf("sending frame\n");
" U& n0 ?8 b8 g - if(write(fd, frame, frame_size) < 0)
. V" Q% j) r6 T9 ?+ ` - break;
, g9 c2 m* E% s0 S# A - printf("sending boundary\n");: C2 V3 h. B. U& p% \' m
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");& x& r1 o9 k" b( O2 H& v# g
- if(write(fd, buffer, strlen(buffer)) < 0)
, O1 N$ }9 G5 U- B3 ?4 I' F$ M) w. [ - 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:, Q1 [( I5 z- H7 T5 r1 @) m$ N( m
- 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);2 L+ Q3 e1 ?+ C, R" b8 v( E5 K) ^6 M4 j; G
- if(*socket_found == (~0))
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- printf("Create udp send socket failed!\n");
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- addr->sin_family = AF_INET;0 K$ W7 w2 b, X0 [9 H' `; x% w' k- K
- addr->sin_addr.s_addr = inet_addr(ip);( z6 {" d ]- C8 W: n" L
- addr->sin_port = htons(port);
7 A7 d/ K8 U9 u l% l- i$ e - memset(addr->sin_zero, 0, 8);$ F6 O5 E1 ]4 J
- return 0;3 N7 Q5 L5 s- T Y
- }
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:
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- while(fend > 0)
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! I% Z0 X6 G( b* B4 l - memset(picture.data , 0 , sizeof(picture.data));! v+ y- U/ X9 }% a
- fread(picture.data , UDP_FRAME_LEN , 1, fp); [! J* ]9 f6 _% U. G
- if(fend >= UDP_FRAME_LEN)
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- picture.length = UDP_FRAME_LEN;
. X' ^1 O' f, S% f) g* A - picture.fin = 0;
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- { @; T# b; P$ m: ~, q5 @/ v
- picture.length = fend;5 ~# {" B$ ^; g) w5 Q
- picture.fin = 1;
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! J. W, n U+ B/ j" _ - //printf("sendbytes = %d \n",sendbytes);: W o6 J9 m+ l, b; R# O
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);+ c. n7 {4 y+ J( L
- if(sendbytes == -1)3 L3 k% A+ A$ b7 t5 c( i; f
- {
M2 T& g. n( e3 i- j0 Q: J+ P - printf("Send Picture Failed!d\n");* E9 t* h( ]( k* r1 h1 c' |
- return -1;
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- else
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& q# \+ k# X' B- R0 m' Z0 y$ t - fend -= UDP_FRAME_LEN;1 F/ _ o- z9 u; I* C/ i1 q* Z
- }. }% D8 E. A9 J1 B8 U
- }
复制代码 7 ?6 c1 X7 S, V/ I0 _5 f8 D
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! X# o |2 x2 h0 ]" LiMX8MPlus 核心板: https://www.forlinx.com/product/136.html |