本帖最后由 飞凌-marketing 于 2022-1-27 11:00 编辑 : ^) y( b5 L! Z9 H2 X3 s: D
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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。 , u o; h$ g' g T9 K4 r6 d
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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。
# a" X: O! M% ]2 Z" \一、HTTP网页服务器" k! J% ~$ i8 ~2 E0 r/ h
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 X& z6 a4 D7 L9 U, b* D) }: C - socklen_t addrsize = sizeof(struct sockaddr);: G! A8 d0 {: @& ^1 m% b1 {/ C
- bzero(&servaddr , sizeof(servaddr));
8 m. \, c/ O3 _ - servaddr.sin_family = AF_INET;1 Q& O. `* {( ]& I2 L+ i
- servaddr.sin_addr.s_addr = inet_addr(ip);
' u' ~5 b1 x8 o, | - servaddr.sin_port = htons(port);5 T' S+ _2 L0 i( W* ?/ F! E
- int ret;" G' p7 L& h" O5 N) o) `
- 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);4 a1 M0 u9 f/ z0 q4 ]
- return -1;& V `$ W, q- N- G+ g
- }
y. g. l1 X4 r - int on = 1;& W$ Z2 X4 V. Y* ?, g$ b9 V0 v* s
- if(setsockopt(*socket_found , SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)8 c. D9 B Z4 K$ Y
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- printf("setsockopt error\n");
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- ret = bind(*socket_found , (struct sockaddr *)&servaddr , addrsize);( L! [, ~: ~6 G+ M
- if(ret == -1)
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- printf("Tcp bind faiLED!\n");
: V4 B% H! s. k7 i1 x - return -1;3 x1 h0 n$ C# R$ a1 l% D1 c
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- if(listen(*socket_found , 5) == -1)# \- ^: b6 t* } F' S; e6 [
- {
9 M! |5 R3 L: `9 f0 L# ?" w* O* U - printf("Listen failed!\n");
: e6 R6 i( {& `. Z, l) n - return -1;* M( [6 c: ~$ R. t
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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);
+ ~! ^! P1 v( t - void * Thread_TCP_Web_Recv(void *arg)
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- while(1)
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- fd_socket_conn = accept(socket_web_server , (struct sockaddr *)&sockaddr_in_conn , &addrsize);- ^, L8 E* T& q" P* O
- printf("fd_socket_conn = accept()\n");
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9 w6 o& d# ^2 z% @0 ` - recv(fd_socket_conn , recvbuf , 1000 , 0);
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- 。。。" |7 k' R4 x( [; `" m
- }
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);# O7 ~9 e2 W) N; C% l6 l
- pic_tmpbuffer = pic.tmpbuffer;( M$ S, \# q8 @# a; [) ?
- pic.tmpbytesused = buff.bytesused;
3 T- k3 W/ m' x9 E' a - pic_tmpbytesused = pic.tmpbytesused;
3 I5 a2 g- ]2 Q! _+ @- } - pthread_cond_broadcast(&pct);1 {& k& F! w( ^, I
- 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;
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8 B' @8 t: z4 l r5 i - int main(int argc, char* argv[])6 z( a. ?' s$ g0 x# ]: d
- {
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- TCP_Server_Found(&socket_web_server , (char*)argv[2] , PORT_TCP); w- Y: m9 b$ d. }5 F8 i- {6 d5 g) o
- pthread_mutex_init(&pmt , NULL);
- y# n) ?, B! z$ Z- O - pthread_create(&tid_tcp_web_recv , NULL , Thread_TCP_Web_Recv , NULL);' a0 V6 A& G% t: k+ f C7 |
- pthread_create(&tid_tcp_web_send , NULL , Thread_TCP_Web_Send , NULL);
! F4 k6 W9 D5 ~" \ - ...
3 I# _7 s4 o9 R. e3 ?; ` - while(1)
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' |! P o, N2 e! d; n% E+ E' T0 Y - V4l2_Grab_Mjpeg(false , MJPEG_FILE_NAME);
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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;">
+ S( K( { T* O) Q& j/ ]; d7 w - </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" \/ w* @: @4 n# i( j
- "Server: MJPG-Streamer/0.2\r\n" \/ \! O- K9 R6 v1 ^% ]2 W
- "Cache-Control: no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0\r\n" \
$ t5 m* X+ }; u+ j9 V% L2 z4 I - "Pragma: no-cache\r\n" \$ D/ F& P S+ S! L" u8 x
- "Expires: Mon, 3 Jan 2000 12:34:56 GMT\r\n"
4 Y7 v' H5 N, X; \4 X, { - #define BOUNDARY "boundarydonotcross"1 Z ~! M- m0 F6 U3 O4 h
- printf("preparing header\n");
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- "Access-Control-Allow-Origin: *\r\n" \) g4 f/ a' n5 A9 T& Y2 u7 E
- STD_HEADER \
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# \% O8 J3 W- \; S# P2 Y, |- v - "--" BOUNDARY "\r\n");9 o" O* S7 [* x0 v0 [9 T, T9 h
- if(write(fd, buffer, strlen(buffer)) < 0) h& n$ ?1 U, Y8 m
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- free(frame);" P, V" \. A6 ^' i6 a( s
- 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" \
# ?4 d" ~5 w" v - "Content-Length: %d\r\n" \
$ B+ L: I, |' ~& o8 R - "X-Timestamp: %d.%06d\r\n" \
& O; w! e% o* j* N - "\r\n", frame_size, (int)timestamp.tv_sec, (int)timestamp.tv_usec);7 D# S0 p& b" d6 _1 I2 o( j
- printf("sending intemdiate header\n");9 ^6 I/ i# R8 ]: ?4 j& ^4 B: h
- if(write(fd, buffer, strlen(buffer)) < 0)
1 v# X/ ^$ _, z g% T - break;
* p; x7 n4 h7 k9 s) s+ H2 C - printf("sending frame\n");
0 j- q4 V5 a4 V' I5 a - if(write(fd, frame, frame_size) < 0)5 a5 @/ C) m: ~/ F/ y" }$ Q( U
- break;1 T3 ]6 X$ u! p! v; d
- printf("sending boundary\n");% K6 D! Y, |4 K% ^2 B
- sprintf(buffer, "\r\n--" BOUNDARY "\r\n");
# ~) P8 Q7 t4 I' D - if(write(fd, buffer, strlen(buffer)) < 0), t) N4 ?. H9 a
- 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:3 ]# r* F) T; r& h' E$ y
- int UDP_Send_Found(socklen_t* socket_found , struct sockaddr_in *addr , char* ip , int port)
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2 i, S6 T) ]& P' h - *socket_found = socket(AF_INET, SOCK_DGRAM, 0);1 Q7 `) T1 z, e ~: x L. W
- if(*socket_found == (~0))! p+ |5 x8 _. K& ]* f! `
- {
! V- e' y8 L' p+ M - printf("Create udp send socket failed!\n");
& j2 ~7 C8 T) h" Y5 w - return -1;
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; r! ~/ Z1 u5 t: i - addr->sin_family = AF_INET;( j C% n: @4 @, n# H
- addr->sin_addr.s_addr = inet_addr(ip);
# v: |1 h& u. r8 O0 C2 P - addr->sin_port = htons(port);4 m) B2 G4 H* ^3 N7 v
- memset(addr->sin_zero, 0, 8);" [+ n, j% _) U( J
- return 0; z& A- m2 @# |. L& G" A
- }
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)0 v0 E( R7 q/ a# S
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- memset(picture.data , 0 , sizeof(picture.data));
/ _: k, b/ o. n# p2 C; V& R/ K) C - fread(picture.data , UDP_FRAME_LEN , 1, fp);
3 j7 n$ M* i5 E, w1 P3 U# e$ Q$ y - if(fend >= UDP_FRAME_LEN); [' X4 w. s" |
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- picture.length = UDP_FRAME_LEN;
U, v0 J: g$ |- q; D; W6 R - picture.fin = 0;! H' n' o/ q! O5 `* k
- }
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- picture.length = fend;
# T, h' x& C6 [. a - picture.fin = 1;
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& q0 k" I, t4 P; W- |) D. Y# T - //printf("sendbytes = %d \n",sendbytes);
7 E0 |$ y6 h) k$ N# W+ R" a) f p - sendbytes = sendto(socket_send, (char *)&picture, sizeof(struct Package), 0, (struct sockaddr*)&addr,addr_len);/ P7 c1 Q P' D0 s
- if(sendbytes == -1)8 Z- H; T3 D6 |1 q8 _7 Z
- {
/ m# H$ W$ r9 K2 \ - printf("Send Picture Failed!d\n");3 a: z, L( a' m9 Y) A
- return -1;
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- {
# g/ `- q* |% D" i - fend -= UDP_FRAME_LEN;; S7 v7 F, x- P& O( m0 v) {4 ?
- }
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复制代码
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iMX8MPlus 核心板: https://www.forlinx.com/product/136.html |