摄像头远程监控的Vb.net实现方法(转)

ntwoofmyearlierarticlesforDevX,"TeachYourOldWebCamNewTricks:UseVideoCapturesinYour.NETApplications"and"BuildinganEnhancedSecuritySystemwithaWebCamandaServo,"Ishowedhowtoincorporateyourwebcamintoyour.NETapplicationsanduseitforsurveillancepurposes.However,usingthosesolutions,thevideoscanonlybeviewedlocallyonthecomputerrunningthewebcam.AninterestingenhancementwouldbetoextendtheapplicationssothatthevideocanbeviewedremotelyovertheInternet.
解压密码为lob.cn
Andso,inthisarticleIwillshowyouhowtousesocketcommunicationtosendalivevideoimagefromaservertoremoteclients.Thesampleapplicationsbuiltinthisarticleconsistsof:

・Aserverthatdisplaysthevideocapturedbyawebcam

・Aclientthatreceivesthelivevideoimagefromtheserver

Theserverwillallowmultipleclientstoconnecttoitatthesametime.Amongotherthings,itisausefulapplicationforthehomeenvironmentwhereyoucanuseitinyourofficetomonitoryourhomeorkids.

CreatingtheServer
I'llfirstcreatetheserver.UsingVisualStudio2005,createanewWindowsapplicationandnameitRemoteMonitoring.InthedefaultForm1,addaPictureBoxcontrol(seeFigure1)andsetitspropertiesasfollows:

・Size―449,253

・SizeMode―StretchImage

Figure1.AddaPictureBoxcontroltoForm1.
Figure2.Youcannowpreviewthevideofromthewebcamintheapplication.

Switchtothecode-behindofForm1andimportthefollowingnamespace:ImportsSystem.Runtime.InteropServicesDeclaretheconstantsandvariableusedfordisplayingthewebcamimage:PublicClassForm1'---constantsforcapturingthevideofromwebcam---ConstWM_CAP_START=&H400SConstWS_CHILD=&H40000000ConstWS_VISIBLE=&H10000000ConstWM_CAP_DRIVER_CONNECT=WM_CAP_START+10ConstWM_CAP_DRIVER_DISCONNECT=WM_CAP_START+11ConstWM_CAP_EDIT_COPY=WM_CAP_START+30ConstWM_CAP_SEQUENCE=WM_CAP_START+62ConstWM_CAP_FILE_SAVEAS=WM_CAP_START+23ConstWM_CAP_SET_SCALE=WM_CAP_START+53ConstWM_CAP_SET_PREVIEWRATE=WM_CAP_START+52ConstWM_CAP_SET_PREVIEW=WM_CAP_START+50ConstSWP_NOMOVE=&H2SConstSWP_NOSIZE=1ConstSWP_NOZORDER=&H4SConstHWND_BOTTOM=1'---usedasawindowhandle---DimhWndAsIntegerAfterdeclaringtheconstants,youneedtodeclarethefunctionsforvideocapture.Thefirsttwofunctionsareneededforvideocapturingpurposesandcanbefoundintheavicap32.dlllibrary,whilethenextthreefunctions(foundinuser32.dll)areusedformanipulatingthevarIoUswindows.'--ThecapGetDriverDescriptionfunctionretrievestheversion'descriptionofthecapturedriver--DeclareFunctioncapGetDriverDescriptionALib"avicap32.dll"_(ByValwDriverIndexAsShort,_ByVallpszNameAsString,ByValcbNameAsInteger,_ByVallpszVerAsString,_ByValcbVerAsInteger)AsBoolean'--ThecapCreateCaptureWindowfunctioncreatesacapturewindow--DeclareFunctioncapCreateCaptureWindowALib"avicap32.dll"_(ByVallpszWindowNameAsString,ByValdwStyleAsInteger,_ByValxAsInteger,ByValyAsInteger,_ByValnWidthAsInteger,_ByValnHeightAsShort,ByValhWndAsInteger,_ByValnIDAsInteger)AsInteger'--Thisfunctionsendsthespecifiedmessagetoawindowor'windows--DeclareFunctionSendMessageLib"user32"Alias"SendMessageA"_(ByValhwndAsInteger,ByValMsgAsInteger,_ByValwParamAsInteger,_<MarshalAs(UnmanagedType.AsAny)>ByVallParamAsObject)_AsInteger'--Setsthepositionofthewindowrelativetothescreenbuffer--DeclareFunctionSetWindowPosLib"user32"Alias"SetWindowPos"_(ByValhwndAsInteger,_ByValhWndInsertAfterAsInteger,ByValxAsInteger,_ByValyAsInteger,_ByValcxAsInteger,ByValcyAsInteger,_ByValwFlagsAsInteger)AsInteger'--Thisfunctiondestroysthespecifiedwindow--DeclareFunctionDestroyWindowLib"user32"_(ByValhndwAsInteger)AsBooleanDefinethePreviewVideo()subroutinesothatyoucandisplaytheimagecapturedbythewebcaminaPictureBoxcontrol:'---previewtheselectedvideosource---PrivateSubPreviewVideo(ByValpbCtrlAsPictureBox)hWnd=capCreateCaptureWindowA(0,_WS_VISIBLEOrWS_CHILD,_0,pbCtrl.Handle.ToInt32,0)IfSendMessage(_hWnd,WM_CAP_DRIVER_CONNECT,0)Then'---setthepreviewscale---SendMessage(hWnd,WM_CAP_SET_SCALE,True,0)'---setthepreviewrate(ms)---SendMessage(hWnd,WM_CAP_SET_PREVIEWRATE,30,0)'---startpreviewingtheimage---SendMessage(hWnd,WM_CAP_SET_PREVIEW,0)'---resizewindowtofitinPictureBoxcontrol---SetWindowPos(hWnd,HWND_BOTTOM,_pbCtrl.Width,pbCtrl.Height,_SWP_NOMOVEOrSWP_NOZORDER)Else'--errorconnectingtovideosource---DestroyWindow(hWnd)EndIfEndSubYoucannowtestifyouareabletopreviewthevideobycallingthePreviewVideo()subroutineintheForm1_Loadevent:PrivateSubForm1_Load(_ByValsenderAsSystem.Object,_ByValeAsSystem.EventArgs)HandlesMyBase.LoadPreviewVideo(PictureBox1)EndSub

PressF5totesttheapplication(besuretoconnectyourwebcamtoyourcomputernow).Figure2showsthewebcamvideodisplayedinthePictureBoxcontrol.

SavingtheVideoasImages
Youwillnowmodifytheserversothatitcanactasavideoserver,acceptingconnectionsfromclientsandsendingthemimagescapturedbythewebcam.

Thefirststepistorecognizethatthevideocapturedbythewebcamcanbesavedasindividualimages.Bydisplayingaseriesofcontinuousimagesontheclient,itissimilartowatchingavideostream.Tocaptureanimage,Ihavedefinedthefollowingsubroutine:

'---savethevideodataintotheImageglobalvariable---PublicSubCaptureImage()DimdataAsIDataObjectDimbmapAsImageDimmsAsNewIO.MemoryStream()'---copytheimagetotheclipboard---SendMessage(hWnd,WM_CAP_EDIT_COPY,0)'---retrievetheimagefromclipboardandconvertit'tothebitmapformatdata=Clipboard.GetDataObject()IfdataIsNothingThenExitSubIfdata.GetDataPresent(GetType(System.Drawing.Bitmap))Then'---convertthedataintoaBitmap---bmap=CType(data.GetData(GetType(_System.Drawing.Bitmap)),Image)'---savetheBitmapintoamemorystream---bmap.Save(ms,System.Drawing.Imaging.ImageFormat.Bmp)'---writetheBitmapfromstreamintoabytearray---Image=ms.GetBufferEndIfEndSubHere,IfirstcopytheimagedisplayedinthePictureBoxcontroltotheclipboard.IthenconvertittoanImageobjectandsaveittoamemorystream.Finally,Iusethememorystreamtowriteouttheimageasanarrayofbytes.Thearrayofbytesissavedintoaglobalvariable,Image,whichisdefinedinModule1.vb(right-clickonprojectnameinSolutionExplorerandselectAdd|NewItem….ThenselectModule):ModuleModule1PublicImageAsByte()EndModuleSavingtheimageasabytearrayallowsmetoeasilytransmittheimageoverasocketconnection.

ToensurethattheImagevariableisalwayscontainingthelatestimage,addaTimercontroltoForm1andsetitspropertiesasfollows:

・Enabled―True

・Interval―100

Double-clickontheTimercontrol(locatedunderneathForm1)torevealitsTickeventhandler.CodetheTickeventhandlerasfollows:

'---savethevideoimageatregularintervals---PrivateSubTimer1_Tick(_ByValsenderAsSystem.Object,_ByValeAsSystem.EventArgs)HandlesTimer1.TickCaptureImage()EndSubEssentially,youareinvokingtheCaptureImage()subroutineevery100milliseconds(10timespersecond)sothattheImagevariableisalwayscontainingthelatestvideoimage.

CommunicationbetweentheClientsandServer
Thefinalstepistowritethecodeforcommunicatingwithclientsoverasocketconnection.BeforeIshowyouthecodetodoso,youshouldunderstandhowtheclientwillcommunicatewiththeserver.

Figure3.CommunicationbetweenaclientandtheserverinvolvesaSendmessagethatreceivesavideocaptureasareply.AsshowninFigure3,uponconnectingtotheserver,theclientfirstsendsa"Send"messagetotheserver.Whentheserverreceivesa"Send"message,itsendsbacktotheclientanimagecapturedbythewebcam(specifically,thedatacontainedwithintheImageglobalvariable).Thetransfertakesplacesynchronouslyandtheclientwillonlysendbackanother"Send"messagewhenitisreadytoacceptanotherimagefromtheserver.Thistechniquepreventstheserverfromoverwhelmingtheclient,especiallyiftheclientisconnectedtotheserveroveraslowconnection.

Now,toenablethiscommunication,addanewclasstotheprojectandnameitWebCamClient.vb.Importthefollowingnamespace:

ImportsSystem.Net.SocketsDeclarethefollowingconstantandvariables:'---classtocontaininformationofeachclient---PublicClassWebCamClient'--constantforLine@R_301_349@character---PrivateConstLFAsInteger=10'---containsalistofalltheclients---PublicSharedAllClientsAsNewHashtable'---informationabouttheclient---Private_clientAsTcpClientPrivate_clientIPAsString'---usedforsending/receivingdata---Privatedata()AsByte'---usedtostorepartiallyreceiveddata---PrivatepartialStrAsStringDefinetheconstructorfortheWebCamClientclassasfollows:'---whenaclientisconnected---PublicSubNew(ByValclientAsTcpClient)_client=client'---gettheclientIPaddress---_clientIP=client.Client.RemoteEndPoint.ToString'---addthecurrentclienttothehashtable---AllClients.Add(_clientIP,Me)'---startreadingdatafromtheclientinaseparatethread---ReDimdata(_client.ReceiveBufferSize-1)_client.GetStream.BeginRead(data,_CInt(_client.ReceiveBufferSize),_AddressOfReceiveMessage,Nothing)EndSubTheReceiveMessage()subroutinereadsthedatasentfromtheclient.AllmessagessentfromtheclientwillendwithaLine@R_301_349@(LF)character.Becauseasinglemessagemaybebrokenupintoafewblocksduringtransmission,itisthusimportantthatyoudetectforaLFcharactertoensurethatyouhavereceivedtheentiremessage.Onceamessageisreceivedanditcontainstheword"Send,"thewebcamimageissenttotheclientusingtheSendData()subroutine(definednext):'---receivingamessagefromtheclient---PublicSubReceiveMessage(ByValarAsIAsyncResult)'---readfromclient---DimbytesReadAsIntegerTrySyncLock_client.GetStreambytesRead=_client.GetStream.EndRead(ar)EndSyncLock'---clienthasdisconnected---IfbytesRead<1ThenAllClients.Remove(_clientIP)ExitSubElseDimmessageReceivedAsStringDimiAsInteger=0DimstartAsInteger=0'---loopuntilnomorechars---Whiledata(i)<>0'---donotscanmorethanwhatisread---Ifi+1>bytesReadThenExitWhile'---ifLFisdetected---Ifdata(i)=LFThenmessageReceived=partialStr&_System.Text.Encoding.ASCII.GetString(_data,start,i-start)IfmessageReceived.StartsWith("Send")ThenSendData(Image)EndIfstart=i+1EndIfi+=1EndWhile'---partialstring---Ifstart<>iThenpartialStr=_System.Text.Encoding.ASCII.GetString(_data,i-start)EndIfEndIf'---continuereadingfromclient---SyncLock_client.GetStream_client.GetStream.BeginRead(data,Nothing)EndSyncLockCatchexAsException'---removetheclientfromtheHashTable---AllClients.Remove(_clientIP)Console.WriteLine(ex.ToString)EndTryEndSubTheSendData()subroutinesendsthedatacontainedintheImageglobalvariableovertotheclient:'---sendthedatatotheclient---PublicSubSendData(ByValdataAsByte())TryDimnsAsSystem.Net.Sockets.NetworkStreamSyncLock_client.GetStreamns=_client.GetStreamns.Write(data,data.Length)EndSyncLockCatchexAsExceptionConsole.WriteLine(ex.ToString)EndTryEndSubBackinForm1,youcannowwireuptherestofthecodetomaketheserverfunctional.Addthefollowingconstantsandvariable:PublicClassForm1'---portnoforlisteningandsendingdata---ConstIP_AddressAsString="127.0.0.1"ConstportNoAsInteger=500'---usetospinoffathreadtolistenforincomingconnections---DimtAsSystem.Threading.ThreadDefinetheListen()subroutinetolistenforincomingsocketconnections:'---listenforincomingconnections---PrivateSubListen()DimlocalAddAsSystem.Net.IPAddress=_System.Net.IPAddress.Parse(IP_Address)DimlistenerAsNewSystem.Net.Sockets.TcpListener(_localAdd,portNo)listener.Start()WhileTrueDimuserAsNewWebCamClient(listener.AcceptTcpClient)EndWhileEndSubIntheForm1_Loadevent,previewthevideobycallingthePreviewVideo()subroutineandthenspinoffaseparatethreadtolistenforincomingconnectionsfromclients:PrivateSubForm1_Load(_ByValsenderAsSystem.Object,_ByValeAsSystem.EventArgs)_HandlesMyBase.Load'---previewtheselectedvideosourcePreviewVideo(PictureBox1)'---listenforincomingconnectionsfromclients---t=NewSystem.Threading.Thread(AddressOfListen)t.Start()EndSubFinally,ifForm1isclosed,abortthethread(forlisteningforconnections)andendtheapplication:PrivateSubForm1_FormClosing(_ByValsenderAsObject,_ByValeAsSystem.Windows.Forms.FormClosingEventArgs)_HandlesMe.FormClosingt.Abort()EndEndSubCreatingtheClient
UsingVisualStudio2005,createanewWindowsapplicationandnameitRemoteMonitoringClient.InthedefaultForm1,populatethecontrolsasshowninFigure4.SetthepropertiesofPictureBox1asfollows:

・Size―449,253

・SizeMode―StretchImage

PictureBox2issettodisplaytheimageofanLCDmonitor(youcandosoviaitsImageproperty).BesuretobringPictureBox1tothefront(right-clickonPictureBox1andselectBringtoFront).Switchingtothecode-behindofForm1,importthefollowingnamespace:ImportsSystem.Net.SocketsImportsSystem.IODeclarethefollowingconstantandmembervariables:PublicClassForm1'---getownIPaddress---PrivateipsAsNet.IPHostEntry=_Net.Dns.GetHostEntry(Net.Dns.GetHostName())'---portnosandserverIPaddress---ConstPORTNOAsInteger=500Privateserver_IPAsString="127.0.0.1"'---sizeofthevideoimage---ConstSIZEOFIMAGEAsInteger=341504'---useforconnectingtotheserver---PrivateclientAsTcpClient'--usedforsendingandreceivingdata---Privatedata()AsByte'---usedforreceivingimagesfromtheserver---PrivatetAsSystem.Threading.ThreadCodetheClickeventhandleroftheStartbuttoncontrolasfollows:PrivateSubbtnStartStop_Click(_ByValsenderAsSystem.Object,_ByValeAsSystem.EventArgs)_HandlesbtnStartStop.ClickIfCType(sender,Button).Text="Start"ThenTry'---settheserverIPaddress---server_IP=txtServerIP.Text'---connecttotheserver---client=NewTcpClientclient.Connect(server_IP,PORTNO)ReDimdata(client.ReceiveBufferSize-1)'---sendmessage---SendMessage("Send")'---beginreadingdataasynchronouslyfromthe'server---t=NewSystem.Threading.Thread(_AddressOfReceiveImageLoop)t.Start()'---changethetextontheButton---CType(sender,Button).Text="Stop"CatchexAsExceptionConsole.WriteLine(ex.ToString)EndTryElse'---sendmessage---SendMessage("Stop")t.Abort()'---changethetextontheButton---CType(sender,Button).Text="Start"EndIfEndSubYoufirstconnecttotheserverusingitsIPaddressandportnumber.Youthensenda"Send"messagetotheservertoindicatethatyouarereadytoreceivetheimage.Youspinoffathreadsothatyoucanreceiveimages(viatheReceiveImageLoop()subroutine)asynchronously.TheReceiveImageLoop()subroutinecallstheReceiveImage()functionindefinitely,untilanerroroccurs:PrivateSubReceiveImageLoop()'---keeponreceivingimageuntilanerroroccurs---WhileReceiveImage()EndWhile'---displayerrormessage---MsgBox("Serverhasstoppedresponding.Pleasetry"&_&"restartingthevideo.")EndSubTheReceiveImage()functionreadstheincomingimagedata(inblocksof8192bytes,asdefinedbytheReceiveBufferSizepropertyoftheTcpClientclass)sentfromtheserver.Aseachimagesentis341504bytes(definedbytheSIZEOFIMAGEconstant;thisvalueisdependentonthewebcamused),youwillthereforereadthenumberofbytesasexpected.Oncetheimageisreceived,displayitinthePictureBoxcontrol.Toreceivethenextimagefromtheserver,sendanother"Send"message:'---receivevideoimagefromserver---PublicFunctionReceiveImage()AsBooleanDimsAsNewMemoryStreamTryDimnwsAsNetworkStream=client.GetStreamDimcounterAsInteger=0DimtotalBytesAsInteger=0Do'---readtheincomingdata---DimbytesReadAsInteger=_nws.Read(data,client.ReceiveBufferSize)totalBytes+=bytesRead'---writethebyte()arrayintothememorystream---s.Write(data,bytesRead)counter+=1LoopUntiltotalBytes>=SIZEOFIMAGE'---displaytheimageinthePictureBoxcontrol---PictureBox1.Image=Image.FromStream(s)CatchexAsInvalidOperationException'---ignorethiserror---Console.WriteLine(ex.ToString)CatchexAsExceptionConsole.WriteLine(ex.ToString)ReturnFalseEndTry'---asktheservertosendthenextimage---SendMessage("Send")ReturnTrueEndFunctionTheSendMessage()subroutinesendsamessagetotheserver:'---Sendsamessagetotheserver---PrivateSubSendMessage(ByValmessageAsString)'---addsacarriagereturnchar---message+=vbLfTry'---sendthetext---DimnsAsSystem.Net.Sockets.NetworkStreamSyncLockclient.GetStreamns=client.GetStreamDimbytesToSendAsByte()=_System.Text.Encoding.ASCII.GetBytes(message)'---sendsthetext---ns.Write(bytesToSend,bytesToSend.Length)EndSyncLockCatchexAsExceptionConsole.WriteLine(ex.ToString)EndTryEndSubWhenForm1isclosed,killthethreadthatlistensasynchronouslyforincomingimagedata:PrivateSubForm1_FormClosing(_ByValsenderAsObject,_ByValeAsSystem.Windows.Forms.FormClosingEventArgs)_HandlesMe.FormClosingt.Abort()EndSubTestingtheApplications
Youcantestboththeserverandtheclientononesinglemachine.SimplysettheIP_Addressvariable(ontheserver)to"127.0.0.1"andthenpressF5inVisualStudio2005totesttheapplication.Fortheclient,typetheserverIPaddress(whichis127.0.0.1)andclicktheStartbutton.Youshouldseethesameimageonboththeclientandtheserver(seeFigure5).Youcanalsotrytheclientandserverontwoseparatemachines.JustremembertosettheserverIPaddressaccordingly.Bestofall,youcanconnectmultipleclientstotheserver!SomePointstoNote
Pleasenotethefollowingpointswhentestingtheclientandtheserver:

・Theserverapplicationneedstobevisibleonscreen.Ifitisminimized,theclientwillnotbeabletoreceivetheimagecapturedbythewebcam.Thisisduetothefactthattheapplicationiscapturingwhateverimagesareshownonthescreen.

・ForsimplicityIhavenotaddedanysecurityfeaturesintotheserver.Inreality,youcanaddcredentialsinformationtothemessagesenttotheserverbeforetheserversendsthevideoimageovertotheclient.

・

Figure5.Youcantesttheclientandtheserveronthesamemachine