Abstract:
A digital video system including one or more video cameras and a video server connected to the one or more video cameras is disclosed. In an illustrative embodiment, the video server includes a computer having a central processing unit (CPU) for executing machine instructions and a memory for storing machine instructions that are to be executed by the CPU. The machine instructions when executed by the CPU implement a number of functions including receiving one or more trigger event conditions, receiving data relating to the one or more trigger event conditions, generating a trigger event message based on a comparison of the one or more trigger event conditions and the data relating to the one or more trigger event conditions, and transmitting the trigger event message.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 12/708,394 filed Feb. 18, 2010, now U.S. Pat. No. 8,185,964, which is a continuation of U.S. application Ser. No. 11/125,795 filed May 10, 2005, now abandoned, which is a continuation of U.S. application Ser. No. 09/808,543, filed Mar. 14, 2001, now U.S. Pat. No. 6,891,566, which claims the benefit of Provisional Patent Application 60/189,162 filed Mar. 14, 2000. The entire disclosure of these applications are hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     This invention relates to systems for accessing, recording, and displaying camera images from any of a number of remotely located cameras and, more particularly, to such systems that provide access to images from one or more remote cameras over a public or private computer network. 
     BACKGROUND 
     With the continuing expansion and availability of public and private computer networks it is becoming increasingly common to use these networks for remote video and image surveillance. Historically, analog systems have been used for CCTV systems for purposes such as surveillance. They include an analog video camera, a video cable, and a monitor/TV and/or a VCR recording device. Multiple cameras can be hooked to multiple recording VCRs for complete coverage of one or more target areas. Specialized equipment known as a multiplexer or ‘MUX’ can be used to allow multiple cameras to be hooked to a single recording/view device. The multiplexer takes all video feeds in a sequential fashion, recording from one camera at a time. This allows the quantity of cameras to share a single recording tape. Besides the limitations of a serial tape system, additional limitations are introduced when the sequencing rate of the multiplexer is too slow to allow sufficient video record/view speed of a given camera view. Multiplexers are typically expensive and have limited expandability without purchasing additional complete systems. Also, the configuration of these systems usually requires a skilled technician to be available at the systems site which increases the total cost of implementing such systems. 
     Digital systems have become more prevalent with the advent of standardized digital componentry. These systems utilize the same analog cameras and cabling, but introduce a capture card based collector. This collector can be a proprietary digital device or a PC based computer, either of which has analog video inputs directly connected to it. These inputs convert the video to digital for viewing and recording and may even retransmit the signal to analog tape for recording purposes. A factor limiting these digital systems is that an autonomous computer is required relatively near the video sources, sometimes with user intervention required at regular intervals. These machines are also hardware bound. The number of capture cards is limited to the specific design of the collecting equipment. These systems are usually proprietary to a particular manufacturer and can be very expensive. Remote viewing is usually not available. Failover or redundancy function is also limited and expensive, due to the fact that the system is usually duplicated for redundancy. As with the analog systems discussed above, these systems also have configuration requirements that typically require a skilled technician. 
     There now exists commercially available networkable cameras that can be accessed over networks running TCP/IP, including both LANs and global networks such as the Internet. Ethernet-based digital video servers are now common that are small, autonomous, and usually contain a web-based configuration utility, as well as administration software. These cameras can be accessed and, in the case of pan/tilt/zoom (PTZ) cameras, controlled over the network using an assigned IP address and standard CGI-based URL syntax or other manufacturer-specified addressing protocols. This allows an authorized user to control the product from anywhere via the Internet or a dialup connection, and allows live images and image streams (video) to be accessed remotely using standard web browsers. 
     The video servers exist in two forms. One is a camera server that is a complete product containing both a camera and a web server with an Ethernet port. The other is a component based video server with inputs for one or more analog video feeds, which the user can connect to conventional camera PAL or NTSC video feeds. The inputted analog video feeds are converted to digital signals and sent from the video servers&#39; Ethernet port. Thus, the video servers (whether integrated in as part of a camera server or as a standalone unit) can be connected to the Ethernet-based networks commonly used in businesses and other computer enabled sites. These video servers can be connected to these network segments and are fully compatible with existing data on these networks. The video data can be received by standard PC computers which require no special hardware other than an Ethernet connection. The cameras can be easily configured by a novice user who has very basic experience with the Internet. 
     Ethernet video servers connect to an Ethernet connection and deliver digital video based on user requests or internal scripting agents. A user requests video images via standard CGI enhanced URL syntaxes. These syntaxes control the image metrics and other features of the requested video stream. The images are sent to the user as either static JPG snapshots, or as continuous JPG streams. Rates to 30 FPS are easily attainable. Since these images are delivered by Ethernet, the camera servers are very robust. Although a requested image may not be received completely in an expected time frame, the video server will wait for the user to complete its requests and processing. This virtually guarantees delivery of video, except where a connection to the video server is terminated. 
     When the user requests a video image or stream, the user is actually requesting a static image that appears to exist as a file in a directory structure on the video server. When the user requests a copy of this image, the video server actually updates it with a new image from the camera source, and the user receives a picture that is up to date. Subsequent requests are to the identical file name, and the server does the updating of its content. 
     Although IP-based network cameras and camera servers have now evolved to a relatively advanced state, the use of a browser-based interface to this hardware has seemingly impeded development of user interfaces that provide simplified, automated control over the acquisition of snapshot and streaming images over the network. Access to the camera images typically requires knowledge of the manufacturer&#39;s CGI-based syntax to access snapshot or streaming images. For example, to access a particular camera, the user may have to specify to the browser an address in the form of http/Xid:PW@111.111.111.111/cgi-bin/fullsizejpg?camera=1&amp;compression=. While this may be handled easily enough for a single camera by bookmarking or pulling the URL out of the browser&#39;s history buffer, the task becomes more difficult when the user desires to change the access parameters or where different cameras need to be accessed. Where the identified camera cannot be accessed, such as for example due to an improper address being specified, the user may simply receive a standard “404 not found” error message that is not helpful in diagnosing either the error or actual reason why access was not available. 
     Moreover, browser-based access is typically limited to either a snapshot mode or streaming images. In the snapshot mode, a single image is returned when the appropriate URL is entered into the browser. Subsequent images from the camera are then accessed using the browser&#39;s “reload” or “refresh” button. In the streaming mode, once the appropriate URL is specified, the remote server or camera simply begins streaming image files back to the browser. This results in relatively high network utilization that may be undesirable in a shared network environment. 
     It is therefore a general object of this invention to provide an improved user interface and approach to the network transmission of images from commercially available network cameras. 
     SUMMARY 
     A digital video system including one or more video cameras and a video server connected to the one or more video cameras is disclosed. In an illustrative embodiment, the video server includes a computer having a central processing unit (CPU) for executing machine instructions and a memory for storing machine instructions that are to be executed by the CPU. The machine instructions when executed by the CPU implement a number of functions including receiving one or more trigger event conditions, receiving data relating to the one or more trigger event conditions, generating a trigger event message based on a comparison of the one or more trigger event conditions and the data relating to the one or more trigger event conditions, and transmitting the trigger event message. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred exemplary embodiments of the invention will hereinafter be described in conjunction with the appended drawings, wherein like designations denote like elements, and wherein: 
         FIG. 1  is a block diagram showing a preferred embodiment of a digital video system of the present invention; 
         FIGS. 2 and 3  together depict the process flow of the user interface client application of  FIG. 1 ; 
         FIG. 4  shows the contents of the initialization file used by the user interface client application of  FIG. 1 ; 
         FIG. 5  is a diagram depicting the main menu structure of the user interface client application; 
         FIG. 6  is a flow chart showing the process used by the user interface client to provide hardware setup information; 
         FIG. 7  is a diagram depicting the server setup form displayed by the user interface client; 
         FIG. 8  is a diagram depicting the camera setup form displayed by the user interface client; 
         FIG. 9  is a flow chart showing the process used to display a motion form that allows the user to display and record video streams from one of the cameras; 
         FIG. 10  is a flow chart showing the process flow for the image viewer program of  FIG. 1 ; 
         FIG. 11  is a diagram depicting the menu structure of the image viewer program; 
         FIG. 12 a    is a flow chart of the autoindexing setup process used by the image viewer program; 
         FIG. 12 b    is a flow chart of the archive delete process used by the image viewer program; 
         FIG. 13  is an overview of an OCX control used by the user interface client and stream recorder client applications of  FIG. 1 ; 
         FIG. 14 a    is a flow chart of a portion of the OCX control that is used to access individual snapshot images from the cameras used in the digital video system of  FIG. 1 ; 
         FIG. 14 b    is a flow chart of a portion of the OCX control that is used to intermittently access images from a streaming image server; 
         FIG. 14 c    is a flow chart of a portion of the OCX control that is used to access full video streams from a streaming image server; 
         FIG. 15  is a flow chart of a portion of the OCX control that is used in the processing and recording of received images and image streams; 
         FIG. 16  is a flow chart showing the process flow for the stream recorder client application of  FIG. 1 ; and 
         FIGS. 17 a  and 17 b    together depict the motion detection routine used by the user interface client application of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , there is shown a network setup of a digital video system  20  of the present invention. The video system  20  includes a client computer  22 , a plurality of cameras  24 , and one or more standalone video servers  26 . The client computer is connected to the cameras  24  and video servers  26  via a network  28  which can include a private network segment  30  and a public network such as the Internet  32 . Other networked components can be used such as a networked storage device  34  and a networked file server  36 . Some of the cameras  24  comprise camera servers  38  which include both a video server and camera in a single integrated unit. The camera servers  38  can be, for example, Axis™ 200, 200+, or 2100 Ethernet cameras, available from Axis Communications Inc., Chelmsford, Mass. (www.axis.com). The video servers  26  can be Axis™ 2400, 2401, or 240 video servers, also available from Axis Communications, Inc. The cameras  24  that are connected to the video servers  26  can be industry standard PAL or NTSC video cameras. Client computer  22  can be a conventional personal computer having an Intel™ or compatible CPU running a Windows™ operating system and including a network interface card (not shown) for connecting to the 10/100 Mb Ethernet network  30  that uses the TCP/IP network protocol. 
     In accordance with the invention, client computer  22  includes a computer readable memory, such as a fixed hard drive shown at  40  containing magnetic media for digital storage of a user interface client application  42  that includes a user interface program along with a number of additional software components. The user interface program is in computer readable form (such as an .exe file). The additional software components include Microsoft™ Internet Explorer™ Internet extensions (included with Windows™ 95, 98, ME, 2000 and revisions), the Win32AP1 libraries (included with Windows™ operating systems), the WinInet dll (also included with Windows™ operating systems), and a compression library such as IJL115.dll (available from Intel™) to decode and recompress jpeg images received from the cameras  24 . 
     Although the user interface client program  42  is shown as being stored on a hard drive  40 , it will be appreciated that it can be stored on other digital storage devices as well. As used in the specification and claims, “digital storage device” includes any of a variety of different digital storage devices, including magnetic media such as a hard disk or removable disk, optical storage media such as a CDROM or DVD, or magneto-optical media. 
     In general, the user interface client program  42  is operable to access locally stored camera data that uniquely identifies the cameras  24  and then attempts access to those cameras over the network  28 . The program  24  is operable to verify access to at least those cameras  24  that are currently accessible, and to generate a user interface display  44  (on the computer&#39;s monitor) that includes a display window  46  for each of the cameras  24  accessed over the network  28 , and to display in each of the display windows  46  an image  48  received from the camera associated with that display window. As used in the specification and claims in reference to the program  42  or other executable program code, the phrase “operable to” [carry out some action] means that, when executed by a microprocessor or other processing device of the computer, the program directs the microprocessor to carry out or otherwise cause execution of the specified action. 
     In addition to the user interface client application  42 , the hard drive  40  also contains a stream recorder client application  50  and an image viewer  52 . Stream recorder client  50  permits high speed recording of streamed images (video) in a manner that minimizes network bandwidth utilization. Image viewer  52  permits browsing and viewing of archived images and video using a playback screen display  54 . These two programs  50 ,  52  are discussed farther below in connection with  FIGS. 10-12  (for viewer program  52 ) and  FIG. 16  (for stream recorder client  50 ). All three programs  42 ,  50 , and  52  can be developed under Visual Basic 6.0 and Visual C++ 6.0 and designed to run under Windows™ 95, 98, ME, NT, and 2000. User interface client  42  stores all camera, server and image settings to a Microsoft Access™ 7.0 database  56  and camera and user configuration data is stored in an .ini file  58 . Digitized recorded video is stored directly on hard disk  40 . 
     The user interface client application  42  is depicted in various levels of detail by  FIGS. 2-9 and 13-15, and 17   a - 17   b , with  FIGS. 2 and 3  together representing the complete process flow through the application starting from program launch. As shown in  FIG. 2 , once the user has consented to the licensing terms for use of the program, various initialization steps are performed, including:
         1. getting camera and user configuration data from the .ini file  58 ;   2. initializing the database tables  56 ;   3. configuring the layout of the display form  44  on the client computer  22 ;   4. reading the camera setups from the database table  56 ;   5. validating or creating the base path (directories) for recording of images and image streams;   6. formatting user-selectable buttons for the client user interface  44 ; and   7. retrieving embedded MAC addresses for purposes of validating access to the cameras  24  identified in the database  56 .       

     Thereafter, program  42  generates the user interface display  44  and the user can start accessing images or video or can access various menu options shown in  FIG. 5  for purposes of maintenance or changing of setup information. If the user has selected “start” to begin accessing images or video, then the next step is to initialize and test the cameras and/or servers by verifying the IP addresses, testing for a valid MAC addresses, and, if the IP addresses and MAC addresses are valid, assigning the user settings and enabling or disabling individual cameras or servers. As is known, the MAC addresses are unique to each camera and server and can be queried via FTP requests to protected areas of the camera or server&#39;s memory. Specific locations vary by manufacturer and require parsing and formatting to extract the required data, as will be known by those skilled in the art. This enables the software to be licensed on a per-camera or per-server basis and can be used to prevent access to any cameras or servers for which the user is not licensed. 
     For each camera in the database  56 , all control information assigned to that camera is stored in an array data type. This control information includes: Server Enabled, Server Name, Server Model, Server ID, Server IP, Server Mac, Server User ID, Server PW, Server Port, Cam ID, Cam Model, Cam Enabled, Cam Name, Cam Location, Cam Bldg, Cam Room, Cam Tel, Cam Room Contact, Cam Room Contact Tel, Cam Notes, Board Switch Port Nums, Cam Thumb Image Name, Cam Fullimage Name, Record Image Name, Cam Thumb Compression Level, Cam Full Compression Level, Cam Record Compression Level, Tool Tip Text, Last Pan, Last Tilt, Last Zoom, Cam PTZ (y/n), Server Switch Action, Switch Caption, Switch Notes, Email Notification, Email Address, Email Message, Enable Audio Alert, Play Audio File, Last Update Time, Time Lapse Interval, Tie Breaker Count, User Disabled, System Disabled, System Disabled Message, Recompression Value, Pan String, Tilt String, Zoom String, Home String. These parameters all control the camera and/or server used by the application and can be changed via a hardware setup form that is provided by the software for the user and that is described further below. 
     Once all tests are complete, the process moves to  FIG. 3  where the program ‘listens’ for digital input triggers generated by any of the cameras supporting this function. The client program  42  can listen for these trigger events and either flash or highlight the window associated with that trigger input, show a high frame rate view (motion window) or begin recording an image or series of images in the above formats. Trigger events are recorded to one of the database  56  tables by recording the date, time and image name. The user can review and access images saved during triggering. As will be known to those skilled in the art, triggering is accomplished by enabling a CRON script in the server that will send a message to the client computer  22 . Program  42  uses winsock controls to listen on a predefined port (1111 default). If a trigger message is received, the message is parsed for the server ID and port number. This information is compared to the relevant data from database  56  and the appropriate display window  46  is activated. The CRON script comprises one or more control instructions generated by program  42 . Although the CRON script can be generated directly using a web browser on the client computer, it will be appreciated that generation of the CRON script by program  42  eliminates common typographical errors encountered in manual CRON programming. Unique identifiers such as host PC and port are automatically added to the CRON script by program  42 . 
     Once the process begins listening for triggers it then finishes configuring the user interface display grid  44  on the client computer  22 . The display grid  44  shown in  FIG. 1  is a 3×3 grid for up to nine cameras and it will be appreciated that any size grid can be specified, with the program  42  permitting the user to specify the number of windows and the program then automatically scaling the images  48  to fit the resulting display window size. In configuring the view grid, the program  42  may disable some camera images  48 , showing instead a “No Video” or other message in the display box  46  associated with the camera  24 . This disabling may be due to, for example, the camera  24  being unreachable, disabled, or invalid. The software also sets the “record” indicators (if enabled), the show port numbers (if enabled), and the camera caption (camera name, if enabled). These are discussed below in connection with  FIG. 5 . 
     Once the screen display  44  has been configured, the display loop begins in which the program accesses and displays images from the cameras  24  on the user&#39;s screen, with the software periodically updating the display of each image  48 . Starting with the first camera displayed, the program sequentially accesses each camera  24  and displays the received image  48  in the box  46  associated with that camera, scaling the image to fit the user&#39;s selected view size. The process runs through the display loop once for each camera  24 , incrementing the current flame (display box) for each iteration until it has retrieved and displayed a snapshot image from each camera. It then continues looping through the display loop, starting again at the first camera, and runs through the process continuously, sequentially polling each camera and updating each window  46  with an updated image  48  received from the associated camera. As each display window is being updated, it can be highlighted using, for example, a colored border to distinguish it from the remaining display windows. This allows the user to see the sequential polling process and is especially useful where the images change little if at all from one update to the next. 
     The display loop of  FIG. 3  continues until either a trigger event is received, a doubleclick by the user is detected on one of the displayed windows  46 , a stream request is made by double-clicking the port number on the camera window, or the user cancels the monitoring, in which case the program pauses. If the user selects a window  46  by double-clicking anywhere on its image  48 , a motion form is displayed that permits viewing a setting of various camera parameters, as well as permitting the user to set recording parameters (such as number of frames to manually record) and initiate recording from the camera associated with the selected display window. The motion form and its use will be described further below in connection with  FIG. 9 . The program checks during the display loop to determine if the user has enabled recording. If so, the program checks user recording settings that can be set through the hardware setup process of  FIG. 6  using the recording camera setup tab of  FIG. 8 . These user configurable settings include selections to record all frames received, or interval recording where the user can specify that frames are only recorded once every so many seconds or minutes. The user can also specify that recording should only occur when motion is detected in the received video. A preferred routine for implementing the motion detection will be described further below in connection with  FIGS. 17 a  and 17 b   . Once these user settings are read, the program then checks scheduler settings that are also user configurable under the recording camera setup tab. These scheduler settings allow the user to specify certain hours during the day and days during the week when the recording is either to occur or be blocked. Scheduling can be done in 15 minute intervals. Every 15 minutes the user can select No recording, Standard Recording ( FIG. 15 ), or Video Motion Detection Recording  FIGS. 17 a -17 b   ). The program will compare this schedule to the current time of day and adjust the recording functions as necessary. This allows for up to 96 different recording schedules per day, far exceeding any typical user need. If recording is permitted for the current time on this particular day, then the program proceeds to the appropriate recording routine (record all frames, time interval recording, or motion detection) according to the user configurable settings previously read. 
     As a part of the display loop, program  42  requests images or video streams from one of the cameras  24 . The requests are formatted as standard CGI based URL syntax, i.e.:
         http//Uid:PW@111.111.111.111/cgi-bin/fullsizejpg?camera=1&amp;compression=1).       

     The images are downloaded from the cameras  38  and servers  26  to the client computer  22  where they are stored in a memory buffer, which can be implemented in RAM. The buffer is parsed and augmented with formatted date and time stamps, accurate to the millisecond. The image is assigned a name generated by the program based on the date and time of creation. The program  42  then saves the image to the hard drive  40  using the following directory structure:
         Mapped Drive and Root Path/Server Name/Camera Name/Year/Month/Day       

     This directory structure is generated in real-time as the recording executes. The images are saved in one of the following styles, based on user setup preferences:
         Single Images: Images are saved under the Day directory in a graphics file format such a jpegs. The file naming convention used is hh mm ss.jpg, where hh is the current client computer clock hour in 24 hour format, mm is minutes, and ss is seconds.       

     Multiple Images (video): Video images (i.e., time sequences of individual images) are saved at the Month directory level as hh 00 00.jpx, where the .jpx extension represents a jpeg concatenation file (streaming jpeg), which is a single file that is built by the program  42  and that comprises a series of jpeg images concatenated together, hh is the client computer clock hour in 24 hour format. These .jpx files can be read and played back by the image viewer  52 . 
     Before storing the jpeg image files or concatenating the jpegs onto a jpx stream, the images can be compressed using the compression .dll library noted above. In practice, it has been found that good quality recorded images consume an average of 7,500 bytes per image. Higher compression levels can yield a smaller file (down to 2,500 byes) at a reduced quality. Higher quality images can also be recorded at a file size of 70,000 bytes per image up to 250,000 bytes per image. 
     The program  42  can acquire images from the cameras in any of three modes: 
     Snapshot: Request one image from the server and close the connection. By running through the display loop rather than requesting a continuous stream from the server, the program iteratively requests snapshots from the cameras and servers thereby providing continuously-updated images in a manner that requires little bandwidth, with network utilization typically peaking at no more than six percent, regardless of network size. 
     Stream Frame Mode: Connect in stream mode to each camera and sequentially cycle through each of the cameras, obtaining one or more of the streamed images from one selected camera, pausing the streaming from that camera, and then obtaining one or more streamed images from the next camera until all of the cameras have been accessed and then paused. This cycle is repeated continuously until the user switches the program back out of this stream frame mode. In this mode, the processing is identical to that of the snapshot mode, with the display loop extracting at least one frame from an open stream, and then indexing to the next camera. The connection is periodically reset to remain robustness. This approach to image acquisition yields substantial performance gains over the snapshot mode and is more efficient that a continuous stream. This connection allows the video server to maintain an authorized connection to the client computer, providing enhanced performance and ultimately, augmented received frame rates. Running in this mode requires more bandwidth than the snapshot mode, but will utilize less than the full streaming mode described below, since each stream is paused as the remaining connected cameras are sequentially accessed for a frame of video. The video server buffers surplus video to the point of filling up its internal buffers, at which time the server stops grabbing video frames until the buffer is depleted, or the server is reset. Thus, as will be appreciated by those skilled in the art, this approach can also be used to control the frame rate of displayed and/or recorded video in a manner that minimizes the network bandwidth utilization. Thus, it can be used for only select ones of the cameras and for recording at a frame rate faster than that obtained by individual URL calls, but less than that provided by full streaming from the camera or video server. 
     Full Streaming Mode: Launch the stream recorder client  50  as a shelled process, pass the URL and various options via a command line syntax. The client computer connects in stream mode and retrieve images in an infinite loop. The connection is reset periodically to ensure robust connectivity across various network topologies. The received image stream is then parsed for SOI (ASCII 255+ASCII 216) and EOI (ASCII 255+ASCII 217) markers, which are the standard start-of-image and end-of-image markers. A buffer is built until these markers are found. When found, the image is displayed and that section is removed from the buffer. This process is then reiterated until a timer expires the session or the user manually closes the connection. 
     When recording, the stream recorder client  50  writes directly to the same directory used by program  42 , but uses a different naming convention to avoid contention. This naming convention can be implemented by appending a letter suffix to the filename of the jpx stream. For example, program  42  might record a filename as “11 00 00.jpx”, whereas program  50  might record images obtained at the same time as “11 00 00_s.jpx”. Since they are now uniquely named, there is no concern of one program overwriting the image files of the other. 
     Referring now to  FIG. 4 , the .ini configuration file used for program  42  will now be described. The WindowState=Normal (or Maximized) sets the main camera view grid as either normal, with the display being sized based on the Images_Across, Images_Down, Ref_Image_Width, and Ref_Image_Height parameters. The Ref_Image_Width specifies the image width of each display window  46  in units of twips (which is a known measurement unit defined by Microsoft™). There are approximately 1440 twips per inch. The image width is determined by the default image metrics that can be specified by the user via the defined in Setup/Software menu command. The Images_Across parameter specifies the number of cameras to be shown horizontally within the user interface display  44  and the Images_Down parameter specifies the number of cameras to be shown vertically. An exemplary 3×3 display grid (for a total of nine camera windows) is shown in  FIG. 1 . In the event that WindowState=Maximized, the entire screen is filled with the application&#39;s main window and displays the camera view grid in the center of the window based on the parameters noted above. The Display=Image (or List) sets the initial display type, with “Image” resulting in a display of the view grid  44  with camera images  48  shown in the display windows  46  and “List” providing a textual list of the cameras and servers with no images. 
     The HighliteFrameColor specifies the hex RGB value for the current update window, that is, it identifies the color used for the border placed around the camera window currently being updated at any one time during the display loop of  FIG. 3 . The default color is blue. The FlashFrameColor provides the hex RGB value for the camera window corresponding to the camera for which a trigger has been received. The default color is red. The ViewBackColor specifies the hex RGB value for inactive camera windows, with the default being grey. The TCPPort parameter specifies the IP port on which the camera server transmits images and the program  42  application listens. This information is used in the base CRON script. 
     The RecordMode setting can either be SINGLE or MULTIPLE, which respectively correspond to the single image jpeg and video stream jpx file formats discussed above. For “Single”, the received images are written to disk (or other non-volatile storage media) as a single jpeg file using the naming convention provided above. For “Multiple”, the images are written as jpx streams, with the RecordMode parameter (“24” shown in  FIG. 4 ) referring to how many jpx files are written per 24 hours. This parameter can have any of the following values: 1, 2, 3, 4, 6, 8, 12, 24. Thus, “1” means that the received stream of jpegs are written into a single jpx file over a 24-hour period, whereas “24” means that a new jpx file is started every hour, 24 per day. As mentioned above, the jpx format is a straight concatenation of jpeg files and, by storing the files with the .jpx rather than .jpg extension, the software avoids the possibility that a user opening the file will inadvertently launch a standard .jpg viewer that might hang due to the large sizes of the jpx files. 
     The RecordThumbnails=TRUE setting is used to tell the software to record the displayed thumbnails rather than recording the image at the Record Image parameter that is specified in the Camera Hardware Setup form of  FIG. 8 . This setting causes the program to record the same image that is viewed in the display grid  44 . When set to FALSE, the program accesses and displays one image (a thumbnail) from the camera and then accesses and records a second image (at a different size) without viewing. This allows for different image sizing and/or compression for viewing than for recording. 
     The RecordImageBasePath sets the base directory path for recording all images; that is, it sets the “mapped drive and root path” shown at the upper level of the directory structure shown above. The program will create all lower levels of the directory structure if they do not already exist. An error message is displayed if the drive is not available or the directories cannot be created or accessed, and no recording will occur. 
     The Camera_Database setting is a pointer to the database  56  that is used for all camera and camera server settings. Other settings that may be less often accessed are:
         DisplayWidth: Sets the default user interface display  44  size in twips.   BorderWidth: Sets the width of the black spacing between all thumbnail images in pixels.   SkipInactivePorts: TRUE—Thumbnails that are disabled will not be displayed when program  42  is running   ShowHighliteFrames: TRUE to show border around currently updated thumbnail.   ShowRecordIndicators: TRUE to show the record LED status indicator that can be included at a corner of the display window for each camera.   ShowCameraCaptions: TRUE to show the title caption at the bottom of the thumbnails.   ShowPortNumbers: TRUE to show the physical thumbnail port numbers.   PingTimeout: The number of milliseconds to attempt a ping to the video server before failure abort.   PingOnImageRequest: TRUE to allow ping tests on each received image burst.   CameraCaptionForeColor: Color of the camera caption in hex RGB   CameraCaptionBackColor: Back color of the camera caption in hex RGB   HTTPPort: Http port number to access all cameras. This is a global setting.   MaxFailOverCount: Number of failed camera requests before shutting down the camera port. The display window  46  will show “Unavailable”.   ReconnectAttemptIntervalSecs: Seconds to elapse before trying to reconnect a failed camera.   DefaultEmailRecipient: Email address to use when sending a motion alert.   EmailUserID: UserID used for email account access.   EmailUSerPW: User password for email account access.   ShowMotionBorder: TRUE to allow the video motion detection routine to highlight the target window when motion is detected.   EnableStatusLog: TRUE to allow status info to be written to a text log.   EnableErrorLog: TRUE to allow specific Error information to be written to a text log.   StreamViewMode: When launching a streamer, the mode it starts in can be:
           0=Icon   1=Small frame window with text info only.   2=Normal window with video displayed.   
           StreamintervalSeconds: Number of seconds to allow the streamer to run before closing:
           0=Run forever   1 to 84600=1 sec to 24 hrs run time before closing.   
           StreamMaxFPS: Maximum number of FPS to stream; 0=Max speed   StreamRecord: 0=no record on program launch, 1=record on launch.       

     Referring now to  FIG. 5 , there is shown the menu structure for the Main Menu displayed by the program  42  as a part of its user interface. In the Display menu, the “List” command displays the cameras as a text grid only—no image is displayed. The “Thumbnail” command displays the cameras as a graphical grid, displaying images  48  received from the cameras  24  using the display loop of  FIG. 3 . In the Setup menu, the “Hardware” command launches the Hardware Setup form which permits hardware configuration using the process of  FIG. 6 . The user can add/delete/edit the different server and camera settings. Also in the setup menu is the ‘Software’ command which launches a form that allows the user to graphically modify the core setting of the .ini file. The ability to manually edit the file also is available via the ‘Other’ Tab and then the first ‘Edit’ button. The ini file can also be edited with any user editor such as Microsoft™ Notepad. The Archive menu contains a single command, “Browse Archived Images” which launches the image viewer  52  executable shown in  FIG. 10 . The Help menu includes a “Dump all Server Settings” command which writes all server and camera data to a text file. This information will be located in the application&#39;s directory in a file called CameraDump.txt. This information can be useful in troubleshooting functional problems with the system. 
       FIG. 6  depicts the Hardware Setup routine that is invoked by selecting “Hardware” under the Setup menu. This process is used to add or delete cameras and servers, and to edit existing camera or server setups, if desired. The servers and cameras are shown in a tree structure on the left side of a new window on the computer screen and, where an existing server is selected, a set of server hardware setup tabs (shown in  FIG. 7 ) are displayed on the right side of the screen to permit configuration of various server parameters, including many of the control information items listed above. Where an existing camera is selected, the camera hardware setup tabs of  FIG. 8  are displayed on the right side of the screen for editing of camera parameters and control information noted above. All panels for each of the tabs of  FIGS. 7 and 8  includes an Update button to save changes made on the tab. 
     For the server hardware setup tabs of  FIG. 7 , the Connection tab provides a display that permits the user to set the fundamental server settings for the program&#39;s CGI base parameters. These options are used in the URL requests to the server. The Connection tab contains the basic server information. The fields are: 
     
       
         
               
               
             
           
               
                   
               
             
             
               
                 Server Name 
                 Name to identify the server. 
               
               
                 Server Model 
                 Name to identify then camera. 
               
               
                 Server Enabled 
                 Check to enable, uncheck to disable. 
               
               
                 Server Serial Number 
                 Authenticates the server. Numbers and Letters 
               
               
                   
                 only. 
               
               
                 Server IP Address 
                 IP address as 123.123.123.123 
               
               
                 Server Root ID 
                 Root user ID. Can also be a regular User ID. 
               
               
                 Server Root Password 
                 Root user PW. Can also be a regular User PW. 
               
               
                 Server Notes 
                 Notes for this Server, for reference only. 
               
               
                   
               
             
          
         
       
     
     If the Server Root ID and Server Root Password are not used, the Host Scripting tab will not function. The Connection panel also includes two buttons: 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Add New Server 
                 Creates a new Server. 
               
               
                   
                 Delete Server 
                 Deletes an existing Server. 
               
               
                   
                   
               
             
          
         
       
     
     The Switch Inputs tab contains the information related to the digital inputs on the server and can be used to set the program&#39;s preference settings for trigger responses from the server. This includes the Show Motion form, Flash Window, and Record Image options shown in  FIG. 3 . The ports are disabled by default. The fields are: 
     
       
         
               
               
             
           
               
                   
               
             
             
               
                 Switch Port 
                 The port being edited. 
               
               
                 Switch Action 
                 The action to be performed upon trigger. 
               
               
                 Switch Caption 
                 The name to identify the Switch Action. 
               
               
                 Enable Audio Alert 
                 Enables or Disables an Audio alert segment. 
               
               
                 Play Audio 
                 Windows .wav file to play upon a trigger event. 
               
               
                   
               
             
          
         
       
     
     The Relay Output tab provides a display that permits editing of functional settings for latching or pulsing the server relay output. As is known to those skilled in the art, this relay can be attached to a siren, autodialer, or other device compatible with the characteristics and limitations of the server&#39;s relay. The fields are:
         Enable Relay   Relay Caption   Relay Notes       

     The Host Scripting tab provides a display for programming or displaying basic CRON scripts on the server. The basic script allows the server to broadcast trigger events from the switch inputs. That is, the script enables to server to send messages to program  42  that are specific to triggering events on the server such as switch closures, infrared, microwave, magnetic, or other forms of sensors. For example, the base CRON script used in Axis™ 2400 series servers is:
         0-59 0-23 1-31 1-12 0-6/=xx:   alert-host yyy.yyy.yyy.yyy-port zzzz-message “Port Trigger”;
 
where xx is the server port 1-4, yyy.yyy.yyy.yyy is the IP address of the client computer  22 , and zzzz is the port specified in the .ini file for communication between the program  42  and the server. The fields on this tab are:
       

     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Enable Script 
                 Enable/Disable CRON script activation. 
               
               
                   
                 Script Text 
                 CRON script text. 
               
               
                   
                   
               
             
          
         
       
     
     The Host Scripting panel also contains four buttons: 
     
       
         
               
               
             
           
               
                   
               
             
             
               
                 Template 
                 Sets a basic CRON script for triggering. 
               
               
                 Clear 
                 Clears the Script window. 
               
               
                 Download from Server 
                 Retrieves existing CRON script from the Server. 
               
               
                 Upload to Server 
                 Sends the Script text to the Server. 
               
               
                   
               
             
          
         
       
     
     For the camera hardware setup tabs of  FIG. 8 , the Info tab allows the user to set the camera name, Pan/Tilt/Zoom (PTZ), and text reference fields for each camera, as well as enable or disable the camera. In particular, the Info tab includes the following fields: 
     
       
         
               
               
             
           
               
                   
               
             
             
               
                 Camera Name 
                 Name of Camera. 
               
               
                 Camera Model 
                 Camera Model; Select from list. 
               
               
                 Camera Enabled 
                 Enables/Disables the Camera Image. 
               
               
                 Enable Camera Movement 
                 Indicates whether a camera can move. 
               
               
                 Camera Location 
                 This text is for reference only. 
               
               
                 Camera Bldg 
                 This text is for reference only. 
               
               
                 Camera Room 
                 This text is for reference only. 
               
               
                 Camera Room Tel 
                 This text is for reference only. 
               
               
                 Camera Room Contact 
                 This text is for reference only. 
               
               
                 Camera Room Contact Tel 
                 This text is for reference only. 
               
               
                 Camera Notes 
                 This text is for reference only. 
               
               
                   
               
             
          
         
       
     
     The Presets tab allows the user to define any quantity of user defined presets for Pan/Tilt/Zoom. The user is shown a thumbnail of a static snapshot for any new positional requests. The fields are: 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Preset Views 
                 Enables the user to Add/Change Views 
               
               
                   
                 Preset Notes 
                 Text Notes for the selected preset. 
               
               
                   
                 Pan 
                 Pan Value 
               
               
                   
                 Tilt 
                 Tilt Value 
               
               
                   
                 Zoom 
                 Zoom Value 
               
               
                   
                   
               
             
          
         
       
     
     There is one button: 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 H 
                 Sets the Preset to HOME 
               
               
                   
                   
               
             
          
         
       
     
     There are three slider controls: 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Pan 
                 Pan Value 
               
               
                   
                 Tilt 
                 Tilt Value 
               
               
                   
                 Zoom 
                 Zoom Value 
               
               
                   
                   
               
             
          
         
       
     
     The Displayed Image tab allows the user to set the image size and compression level request for the camera server image retrieval. These parameters are mapped against CGI type parameters defined by the server. The user representations are simplified terms versus the CGI syntax. Three image styles are defined here. Each style is set for the three image request types. This value is used by the server when sending requested images to the application. The fields are: 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Thumbnail Image 
                 Main View with all cameras. 
               
               
                   
                 Full View Image 
                 Detailed View of a single camera. 
               
               
                   
                 Record Image 
                 Recorded Image style. 
               
               
                   
                   
               
             
          
         
       
     
     The Thumbnail Image is displayed on the Main form with all the other camera views. The Full View Image is displayed on the Motion form. The Record Image is used whenever a save request is made by the application. Each Image style has a related compression value. The compression values are selectable for each Image style. The following considerations should be used when selecting the Image styles: 
     Image Size
         Largest images: slowest access, largest file size   Smallest images: fastest access, smallest file size       

     Compression Value
         Lowest compression: best image quality, slowest access   Highest compression: worst image quality, fastest access       

     The Switch Inputs tab allows the user to bind any or all available digital switch ports to a display window. That is, the digital switch inputs must be bound to camera ports. This setting tells the application which cameras to record/notify when a trigger event occurs and allows the application to notify the user on screen which port trigger(s) is/are associated with a camera view. Each defined switch input is listed with a check box that can be selected to bind the camera to that switch input. 
     As mentioned above in connection with  FIG. 3 , the Recording setup tab permits the user to set automatic recording options for interval recording a camera. The interval is expressed in seconds. The camera will record an image at the specified interval if the hardware can meet these expectations. Otherwise, the image is recorded as quickly as possible after the interval has expired. The fastest interval that can be used is derived from observing the cycling rate of all cameras. On a quality system the fastest interval is about ¼ second for any camera. The fields are: 
     
       
         
               
               
             
           
               
                   
               
             
             
               
                 Interval Recording 
                 The camera will record images at a set 
               
               
                   
                 interval. 
               
               
                 Record an Image every. . . 
                 The Interval to record images automatically. 
               
               
                 Compression Index 
                 This value sets the save compression value. 
               
               
                   
               
             
          
         
       
     
     The compression value is used by the compression library to set the amount of compression for image saves. The lower the number, the higher the compression. The range is between 5 and 40. The most commonly-used value is between 30 and 35. 
     The Email tab permits the user to set an email address to which an email notification will be sent upon occurrence of a trigger event. An image from the triggered camera can be attached to the email. The Performance tab permits the user to specify a unique User ID so that the camera or video server administrator can set or limit the bandwidth of video transmission on a user-by-user basis. 
     When a user double-clicks on a camera window  46 , the program  42  brings up a Motion Form which runs the process shown in  FIG. 9 . This permits the user to bring up a detailed view of the image from a particular camera, with the image being updated at an increased rate. Complete camera and server information is displayed on this form. The user can Pan/Tilt/Zoom supported cameras, click on preset positions, record images, or display any trigger events. 
       FIG. 10  depicts the process flow provided by the image viewer program  52 , which can be, but need not be, a separate executable than program  42 . This process can be launched from within program  42  using the “Browse Archive Images” command in the Archive menu of  FIG. 5 . This program  52  can include authentication capability to provide the user with access to only those archived images that have come from servers accessible to that user. This is indicated in  FIG. 10  where the program reads the database for defined servers and parses the record path for matching servers. Then it will display a tree structure showing only those archived images and streams that came from cameras or servers defined in the database for that user. Once the user has selected an archived jpg or jpx file, the image is brought up on the screen and, for jpx streams, the user can play, pause, stop, frame advance and review using buttons that emulate a VCR panel. A refresh button can also be provided to reload the archive if additional images are being written to it in the background by the user interface client program  42 . The image viewer program  52  can include an autodelete function, in which case a five minute timer is started. The program then checks the archive age against user date settings, and deletes the archived .jpg and .jpx image files that are older than the specified date or time period. The program  52  can also include an autoindex feature which, when enabled, automatically indexes the archived jpx files every hour to build an index into the jpx file for quick access by the program into any point in the jpx file. This index feature is discussed next. If the autoindex feature is not enabled, then the index is not built until the first time the jpx file is loaded. 
     In installations where very high speed recording is being performed, the jpx file can become quite large. A typical jpx file for an hour of video is 1 to 5 MB, while high speed recording can easily exceed 20 MB and even reach 100 MB. Since the jpx is purely concatenated JPG images, aligned head to tail, the only way to view the images within the jpx file is to parse the SOI and EOI markers and display the image in between them. For incremental playback, this process is easily controlled. However, when a user wants to “rewind”, “fast forward”, or randomly jump to a portion of video, this process requires the program  52  to process from its current position and read all video frames in between. Jumping over frames does not work for these files since, in order to most efficiently store the images, the images within the jpx file are relatively unique in length. This process of reading in all of the frames can be undesirably slow when the jpx file is large. To overcome this issue, the image viewer program  52  creates an index of the SOI and EOI markers of each image in the jpx file. This index is stored as an array of pointers into the jpx file and is stored using .ndx as its filename extension. The program  52  will look for this index and use it to load the image pointers instead of reading the entire jpx. The image pointers identify the memory locations of the SOI and EOI markers, thereby allowing the program to easily locate and retrieve individual images contained within the jpx file. The ndx file can be loaded in less than a second, as compared with jpx load times of up to a minute or more, depending on jpx size. The index is created on the first user access to the jpx image file or when an autoindex event is processed, as described above. Successive requests from the user to a jpx will allow the program to read the ndx file rather than a conventional approach which would entail reading the entire jpx file. With the index file, the pointers can be read into memory and accessed quickly, even for very large jpx files. 
     The ndx index file also makes possible the use of the image viewer program  52  as a plug-in for commercially available web browsers. In conventional browser-based retrieval of video, the video files can be quite large, and the user can therefore typically only request a small number of frames. The user does not know the stream size, frame count, index of time pointers, etc. By implementing the image viewer  52  as a plug-in component for a web browser, viewer can be used to provide web page access from a web browser to stored jpx images. This alleviates the necessity of a specialized software product to view the archives. Since this image viewer plug-in utilizes the ndx index file, the user can retrieve a wealth of video specific content in a very short period of time, allowing realtime display of video (assuming the user has sufficient bandwidth) of the Internet or other network. 
     When implemented as a plug-in, the image viewer  52  can also be used to view “live” a stream that is being recorded on a network server. This can be accomplished using server software that records the jpx files in the manner described herein, with the image viewer then only parse the target jpx file on the network server for the latest video frame. By displaying this video frame, the user sees live video that originated from the camera server, but is being supplied by what can be a much higher performance network server. Thus, since the user is now viewing recorded video from a higher performance server, the number of simultaneous connections to the video feed is highly scalable by implementing standard web server components. This is advantageous since all Ethernet video servers are highly susceptible to overload from multiple user requests and performance is degraded linearly with each simultaneous connection. 
       FIG. 11  depicts the main menu for the image viewer program  52 . The “Tree” command under the Browse Mode menu item allows the user to browse all permitted archives by server, camera, date, and type. The “Date” command allows the user to search by date/time for a selected server and camera. The ‘Directory List’ command lets the user browse all attached drives manually. The Indexing command under the Maintenance menu allows the user to set the autoindexing features described above. The process used by the image viewer program  52  for setting up the autoindex feature is shown in  FIG. 12 a   . The “Delete” command under the Maintenance menu allows the user to manually delete archives or automatically delete archives older than a selected date/time stamp.  FIG. 12 b    depicts the process flow when the “Delete” command is selected. The “Format Conversion” command under the Tools menu allows the user to convert images to other standardized formats. The Display Mode menu allows the user to playback the images either as thumbnails (like images  48  displayed in the windows  46  generated by the user interface client program  46 ) or in a cinema (fullscreen) mode. 
     Rather than using the ActiveX control provided by the camera/server manufacturer, the user interface client program  42  and stream recorder program  50  utilize their own ActiveX control to interface with the cameras and servers. An overview of this OCX control is shown in  FIG. 13 . Further details of the control for obtaining and displaying an image are shown in  FIGS. 14 a -14 c   , and further details of the control for obtaining and recording an image are shown in  FIG. 15 . The implementation of a suitable OCX control using the process steps shown in these figures will be known to those skilled in the art and therefore no further elaboration of the design of this control is necessary. 
     Referring now to  FIG. 16 , there is shown the program flow of the stream recording client program  50 , which is a separate executable that permits high speed recording of image streams (video) in a manner that minimizes network utilization. The program  50  enables the streaming output from the camera servers using the OCX control described above internally within the program as direct subroutine calls. Streaming is initiated using a CGI enabled URL that is sent in the same manner as described above for the user interface client program  42 , except that the CGI syntax is set to zero to indicate streaming output from the server. As indicated in  FIG. 16 , the program  50  utilizes a timer to reset the connection to the server before it is automatically terminated by the network. More specifically, for some networks, such as the Internet, a connection cannot typically be permanently held, but rather will be terminated automatically after a period of time (e.g., 50-70 minutes). The program  50  avoids this problem and enables nearly uninterrupted streaming by automatically resetting the connection before the external termination and then continuing to append the streaming images onto the end of the jpx file. This can be done with the loss of little or no streaming data from the camera. 
     Referring now to  FIGS. 17 a  and 17 b   , the video motion detection routine of program  42  is used to allow the recording of images to be performed only when a moving subject is present. When enough motion is present, the system will begin recording video until motion has stopped. When motion is sensed according to this routine, the program will perform any or all of the following functions:
         record video up until video motion is no longer sensed and an “extra frames” count is exhausted;   send an email to a user as selected in the hardware setup panel based on settings from the .ini file;   attach an image to the email of the first frame of video that motion was detected on;   show a yellow border around the target window where motion was detected;   announce motion ON and motion OFF with two way files, hello.wav and goodbye.wav, which the user may reset to any sounds desirable.       

       FIGS. 17 a  and 17 b    detail the logic flow of this process. In general, the motion detection routine uses RGB color component filtering of the actual pixel data. By breaking down the image into these components, the values of each color component per pixel is represented as a decimal value of 0 (No color) to 255 (bright color). These values are compared to user-defined settings in the program  42  for filtering, allowing specific component or combined colors to exhibit reduced or enhanced movement sensitivity. For example, outdoor cameras are very prone to false triggering when blowing grass/leaves or shadows are present. By filtering out more green component, false triggering is reduced to a very acceptable level. This gives the program the ability to use motion detection in a much more broad range of use than other comparable systems. 
     The process begins by taking the first image (i.e., frame) of a video sequence and placing it into a buffer where it will be used as a reference image. The reference image is compared to subsequent video frames on a pixel-by-pixel basis. Preferably, the reference image is compared to subsequent images as they are being received (i.e., as soon as they are received) by the client computer so that the program is operable to provide real time motion detection. For each pixel in the current image, the program performs a comparison of the color component values for that pixel with the color component values of the corresponding pixel in the reference image. If the difference in color component values for corresponding pixels from the two images differ by more than a preselected amount, the program generates a motion detect signal which can be implemented as the Record Flag shown in  FIG. 17 b   . For each of the RGB color components, a separate counter (Count_Red, Count_Green, and Count_Blue) is used that tracks the total number of pixels within the current image for which that color component value differs from that of the reference image by more than a preselected amount. This is done using a user-selectable filter levels for each of the color components. In particular, if for a particular RGB color component, ABS(P ref −P cur )−FilterLevel&gt;0 then the Count is incremented for that color component. Separate filter levels are used for each color component and these filter levels can be set by the user. As will be appreciated, the FilterLevel is an offset that aids in removing unwanted noise inherent in video sources, as well as “pixelation” or “tiling” inherent in jpg image sources under compression. When the entire image is processed, the Count_Red, Count_Green, and Count_Blue counters are compared to a user specified minimum, which can be different for each of the color components. If all three exceed their respective minimums, motion is considered present and the Record Flag is set to tell the program to proceed with recording. 
     Once motion is detected, the system records video and continues the pixel comparisons for each subsequent frame until the routine detects that motion is no longer present. To prevent the recording from ending before a subject has completely left the camera&#39;s field of view, the program continues recording until a specified number of extra frames have been recorded. This is carried out using an Extra Frames counter that is decremented once per frame starting with the first frame received after no further motion has been detected. As with the other counters, the number used for this counter can be user specified. Periodically, a new reference frame is selected from the video stream. This is done at regular intervals as specified by a user “Refresh Interval” setting, which is an image frame count. This Refresh Interval is used in conjunction with a frame counter C_Ref such that, once the C_Ref counter exceeds the Refresh Interval number, the reference buffer is emptied and the counter reset to zero. 
     The core function of the video motion detection is based on a count of pixels for which at least one color component value differs from that of the reference image by a preselected amount. Minimum object size detection can be implemented using the routine of  FIGS. 17 a  and 17 b    with the addition of an X by Y (width by height) template that scans the X by Y pixel information. If all pixels have a color component value that differs from that of the reference image by a preselected amount within the X by Y area, motion is detected. The program highlights the object with a bounding rectangle. This process can be used to filter out objects that are too small to be considered motion. 
     Apart from minimum object size detection, the program  42  is also operable to permit the user to specify a region of the camera&#39;s field of view so that the program performs the pixel comparisons only for those pixels located within that region. This region of interest processing is implemented by providing the user with the ability to mask out specific portions of a video frame, which will then be ignored by the motion detection. This concentrates the motion detection to specific regions of the screen. Typical region of interest masks employ grids or regions based on a grid array of squares. These areas are selected to mask out the regions. This tends to be somewhat granular in use. The program  42  uses a pixel based approach to masking the images. The user first creates a region of interest by defining the mask using the computer mouse to paint a black or other colored area on the image. The painted areas represent those portions not desired for use in detecting motion. A tool palette of square or other shape may be employed to create the painted mask. The mask is converted to a black and white mask and saved as a .bmp file based on the camera name. When video motion detection is used by the program, individual pixels from the reference and current images will be compared only if the corresponding mask pixel is not black. Users may edit the mask in Microsoft™ Paint or other image editor to refine the mask to the pixel level. 
     Implementations of this type of streaming media have a common difficulty; namely, Ethernet connectivity is at best a highly reliable but not a totally reliable connection. Occasionally, power fluctuations, excessive image requests, overloaded or failing networks and a multitude of other issues can cause the connection to the camera to fail. Competing implementations often cause the application to abnormally abort or stop responding, requiring the user to close and restart the application. This condition is very serious since recorded video will not be available while the program is not responding. The user interface client program  42  and stream recorder client program  50  address this issue by identifying three modes of failure, and providing contingency functions to overcome these problems. These modes are:
         1. failure upon connect;   2. failure upon image request (read); and   3. failure during midstream read of image.       

     Failure types 1 and 2 are easily overcome by the implementation of the default timeout of failed requests by the Wininet dll and its related components. The program can count these failures on a per camera basis and optionally shut down the camera and reattempt access periodically. This maximum failure count and reattempt connections are user selectable on a global scale. 
     Type 3 failures are usually serious and can cause the program to stop responding. By executing the request asynchronously or in a worker thread, the request can be timed and if abnormally long, cancel the request and try again. This allows the application to continue to function consistently. Preferably, the program utilizes both methods to insure robust connectivity. 
     It will thus be apparent that there has been provided in accordance with the present invention a digital video system and computer program therefor which achieves the aims and advantages specified herein. It will of course be understood that the foregoing description is of preferred exemplary embodiments of the invention and that the invention is not limited to the specific embodiments shown. Various changes and modifications will become apparent to those skilled in the art. For example, although the invention has been described as it would be implemented using TCP/IP network cameras and camera servers, it will be appreciated that the invention can be used in conjunction with other image sources. For example, rather than specifying a URL to access a particular camera, the invention could be used to specify a memory location or utilize a .dll file to access images from, for example, a video capture card, USB or IEEE-1394 (Firewire) ports. All such variations and modifications are intended to come within the scope of the appended claims.