本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑 7 \* y0 t' W" a! G* r8 v: G1 m9 M
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; X0 h- w6 }) p, N9 N8 t3 O" d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.html3 ], f; f3 n+ q" i
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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 L) F8 V8 c' A& t2 K* d

5 f! d( W7 M5 _) g- b+ c+ D! N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。
5 k @6 P% X, g' {一、HTTP网页服务器
7 b+ O$ k4 [+ `+ Z! N5 O6 ^% i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)" P! W6 `. j/ i& J! J) X
- {5 H+ Z( _ K! M, a
- struct sockaddr_in servaddr;/ z2 }3 E9 j( o5 s9 S
- socklen_t addrsize = sizeof(struct sockaddr);
' g- i! ~0 z0 O* V" u" L0 x - bzero(&servaddr , sizeof(servaddr));
G: T4 Z$ \) t* l. ~3 c - servaddr.sin_family = AF_INET;3 t- V; r! @; ~) R' l# Z
- servaddr.sin_addr.s_addr = inet_addr(ip);
: f7 [/ C( a6 A; i7 N$ r, x' } - servaddr.sin_port = htons(port);" \ A* R7 k, [& G: X
- int ret;( c$ O1 h8 v' X- A- e9 O2 X1 D
- IF( (*socket_found = socket(AF_INET , SOCK_STREAM , 0)) == -1), |% J( n2 [' U7 h: w
- {! z" Z8 o$ j, T4 ?! a. V! C1 i: R8 w0 e% B
- printf("Create socket error: %s (errno :%d)\n",strerror(errno),errno); q; Z# G! z& ^$ p- u# \" \
- return -1;% f& q; K' [, O7 z7 X
- }0 `8 Y" Z/ r- h" l
- int on = 1;) |, n/ i) a$ L, K0 p
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)( X3 U4 u) K9 S7 O. ]4 g4 I
- {
9 a7 Y$ S; e+ b, l( _$ J3 i - printf("setsockopt error\n");
2 \% O- [- U, r! W: C6 K - }1 y+ c: R# x ]3 R" \1 @
- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize); P' }! u m6 i# H% H% S; Q
- if(ret == -1)
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- printf("Tcp bind faiLED!\n");7 a& r l7 Q; ~8 p0 U9 x
- return -1;
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- if(listen(*socket_found , 5) == -1)) d6 [* |! @* M4 M8 J
- {
$ |, p A, `5 |3 m5 O - printf("Listen failed!\n");
, K4 y p6 B3 _1 k, s% N$ ]8 ?1 q - return -1;
+ w) M2 i" ]8 b6 B9 |5 {. z" _ - }
6 d9 J2 e5 {4 J$ E6 o - return 0;
$ M5 p* q* B$ N: L9 ? - }
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);; v9 `$ C* S4 V! h" G. ?) a
- void * Thread_TCP_Web_Recv(void *arg)
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- 。。。4 H4 _ ^! x6 N
- while(1)
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% s, Y2 | A6 H5 ~: q5 G& k! x. @ - fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);. c: u3 g+ v# K/ g. _3 n
- printf("fd_socket_conn = accept()\n");/ O4 W5 E) c7 \
- 。。。
& x! U( b) _2 h8 g% ~ - recv(fd_socket_conn , recvbuf , 1000 , 0); N C7 i) t3 N6 V* F" G4 P
- }
! n; w0 ~+ H0 _% [' V' E - 。。。
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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);! ~" m" c+ D. k! o/ G
- pic_tmpbuffer = pic.tmpbuffer;
3 f) b+ b' w# K+ W2 J, _5 R- w - pic.tmpbytesused = buff.bytesused;9 k. W( W4 M! O. k5 T
- pic_tmpbytesused = pic.tmpbytesused;( Q( d+ L) ~7 f# N% R s6 E% v0 p
- pthread_cond_broadcast(&pct);
0 X5 Z3 a. c* P. S - 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;
b6 f2 y2 G8 p - pthread_cond_t pct;
; \& |3 K: K D' t( i; n$ ] - int main(int argc, char* argv[])
/ Z' `' L9 Q( t2 X7 c - {
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- TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP);0 G9 V; `' y, G3 x
- pthread_mutex_init(&pmt , NULL);
6 K e2 [4 J4 o9 | - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);# F. R0 i% ?" n4 D0 X+ l' v
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
s/ [- t4 M6 a$ { - ...
% S" N8 b) D; X* I8 g* X1 `0 ~ - while(1)
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- V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);5 k' T( B F! T6 r1 i- J _
- ... e& K9 M5 T: y' O$ }
- }
9 \; p ^: a$ y9 u - ...
, [0 H& g4 j' S0 F4 T" G/ _1 ] - }
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;">* N* G, V% o8 J' [# I j) M% O: G) l
- </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" \
) G. @+ p4 O, o- |) B, z - "Server: MJPG-Streamer/0.2\r\n" \7 n4 s6 Y0 Q4 Y E* v
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \* \4 s% H) i& w
- "Pragma: no-cache\r\n" \
0 X: c6 }3 s8 r+ O - "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
8 ?; J7 J6 z! g5 B4 v8 S2 } - #define BOUNDARY "boundarydonotcross"8 ^, o4 m$ h1 y v1 \! V
- printf("preparing header\n");
% y( x( a/ L$ h7 P; X7 V7 r. L6 h3 V - sprintf(buffer, "HTTP/1.0 200 OK\r\n" \. M" m- x- ]$ U( m* W- e8 S
- "Access-Control-Allow-Origin: *\r\n" \5 c2 l2 T% p+ P# S$ j( ?
- STD_HEADER \, C+ f0 _2 n) {1 F1 k
- "Content-Type: multipart/x-mixed-replace;boundary=" BOUNDARY "\r\n" \
* G" s0 {2 J8 s0 M8 d; L! ] - "\r\n" \- W- \& H/ q5 P8 W
- "--" BOUNDARY "\r\n");' S0 W' v! u5 A; [7 u
- if(write(fd, buffer, strlen(buffer)) < 0)4 F5 j& A8 a# O" N
- {* t9 f4 ]# C* P
- free(frame);. A2 \' _# t' @: T9 [
- return;5 i: I, ~6 _4 b o
- }
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" \
- R! L* _# Z5 I9 `+ t6 r/ j6 r8 b! n - "Content-Length: %d\r\n" \" E7 M$ s& B5 C' n' m% o
- "X-Timestamp: %d.%06d\r\n" \, o n0 X, J* _) l3 J1 V
- "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);
) e$ _0 T# u( }7 A - printf("sending intemdiate header\n");
1 Z" a; Y0 B( D$ ^* M9 Z! n - if(write(fd, buffer, strlen(buffer)) < 0)% N" a8 F6 V- ]
- break;
4 ^. K/ k5 R# l1 L% M. z - printf("sending frame\n");, f1 p0 E9 T, ?7 ?
- if(write(fd, frame, frame_size) < 0)
2 K# U) w; t# |4 `! x - break;
4 T" N6 y& W7 ~7 f, z9 V - printf("sending boundary\n");
+ v' _" {( \2 ?! v H - sprintf(buffer, "\r\n--" BOUNDARY "\r\n");" c- o. T2 x( \4 b. }& g
- if(write(fd, buffer, strlen(buffer)) < 0)
' }" l# J; z" w. d' o5 }$ 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。  0 |7 Y/ ~/ Z2 \; y1 D q3 ^$ G. U, E

3 D: A/ y/ E. i1 W' U$ C二、UDP上位机UDP发送操作,同样需要先建立UDP Socket:
3 b' {# k* X) |3 v) M" @5 `% x- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)
! {/ q# t) Z' E6 K - {
5 T- m4 _+ N [7 Q \' L+ C5 t - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);2 k2 r' \4 g$ V0 ^
- if(*socket_found == (~0))1 D8 K5 S J' _3 C
- {7 \0 B! ~# d& {9 c S! e- t1 z M
- printf("Create udp send socket failed!\n");2 C# L8 [( V9 Y
- return -1;: S' @/ |( C, }( W' Z
- }
z0 x. z( z! o Y7 b* X" H% W - addr->sin_family = AF_INET;, A. w) }+ e6 j9 F. r
- addr->sin_addr.s_addr = inet_addr(ip);
3 W u! x1 o1 Z- z5 x. O - addr->sin_port = htons(port);
. N# X+ z1 i' d" d8 z2 n% b - memset(addr->sin_zero, 0, 8);1 u# s8 y% u% q9 }5 c+ t2 g
- return 0;# O8 ^& s J& H+ T
- }
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:0 @, x/ M" @6 j$ T" j6 Q
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- while(fend > 0): b3 M: P" E6 ]: X
- {
1 N5 |2 u. e, W$ Y U I% C - memset(picture.data , 0 , sizeof(picture.data));# I Q `& C# i+ o
- fread(picture.data , UDP_FRAME_LEN , 1, fp);
" _5 R; L+ O' ~ {" r; h0 g0 F - if(fend >= UDP_FRAME_LEN)
+ P. p K+ K, z: e" C$ H- d9 ` - {$ v( D2 y M% O0 x
- picture.length = UDP_FRAME_LEN;
/ g! \5 o. U" e6 J% c' g# d% G$ S - picture.fin = 0; j$ S' B& `2 {6 z
- }
" S) z, C: k% L( P) l o - else
. O* \1 Y4 P9 C0 e" C4 S a - {
: S0 q% p2 B5 d& H" w8 r, @ - picture.length = fend;5 i" e4 k% N+ n0 E+ C! ~0 a/ d
- picture.fin = 1;
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8 L' \8 x$ j% q) e - //printf("sendbytes = %d \n",sendbytes);7 _4 P8 |8 U1 D; X# J' N/ G
- sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);
0 X3 M5 g5 A7 w. \1 D4 N - if(sendbytes == -1)3 a0 u3 P; S9 e5 I% S& X6 Z8 X
- {
+ x4 P4 ?& ^) s$ [% h - printf("Send Picture Failed!d\n");( S- d3 `( l$ u2 q7 {
- return -1;
- p" m8 O2 ~' |3 G3 q, @6 M - }
7 S: e2 X' x! h9 |. p; ? - else
6 o, m: f8 y) K% t - {
6 n5 P; C3 q" s+ S, L% f& y, V: \ - fend -= UDP_FRAME_LEN;
* {' h6 \0 ?: |" [; m - } L$ C& L9 i2 K2 _/ G1 E
- }
复制代码 ) O" q' t0 K1 _3 \0 x0 h
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" f2 {" G6 ]5 F N( a/ x3 AiMX8MPlus 核心板: https://www.forlinx.com/product/136.html |