AU2006252142A1 - Video rate determination - Google Patents

Description

S&F Ref: 790615

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT Name and Address of Applicant Actual Inventor(s): Address for Service: Invention Title: Canon Kabushiki Kaisha, of 30-2, Shimomaruko 3-chome, Ohta-ku, Tokyo, 146, Japan William Simpson-Young Rajanish Calisa Spruson Ferguson St Martins Tower Level 31 Market Street Sydney NSW 2000 (CCN 3710000177) Video rate determination The following statement is a full description of this invention, including the best method of performing it known to me/us:- 5845c(616517_1) \O I VIDEO RATE DETERMINATION

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Field of the Invention C1 The present invention relates generally to digital video recording and, in particular, to a method and apparatus for displaying video data. The present invention also relates to a computer program product including a computer readable medium having recorded ri thereon a computer program for displaying video data.

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Background Video recording systems that allow a user to record the signal of a broadcast television program to a storage medium, such as a computer hard disk drive, and that allow the recording to be displayed (or played back) at a later date, are known. In some video recording systems, the display (or play back) of the recording can occur at the same time as the television program continues to be recorded. For example, the user may begin watching from the beginning of a recording of a television program while the program is still being broadcast.

In some of the video recording systems described above, video data can be displayed (or played) at an accelerated rate or unwanted content, such as advertisements, can be skipped. Using such methods a user can complete displaying all of the recorded video data for a program leading to the point where the user can seamlessly continue to watch the program live as the program is broadcast. Such a feature is known as "catch-up play" since the user may watch a recorded program and catch up to a live broadcast of the program. In a variation, some video recording systems vary a rate of acceleration used for the display (or playback). The rate of acceleration is typically determined from a calculation based on an amount of program time to be caught up and an amount of recorded time that equates to unwanted content such as advertisements.

790615.doc Final C:\NrPortbl\SAF\PDM\6 13338_ I.DOC \O L One known video recording system comprises a television display including a feature Sfor recording broadcast video data and a video phone feature. Both the recording feature C and the video phone feature use the same television display. In such a system, when the user is watching a live broadcast television program they may be interrupted by a video phone call. The system responds to the interruption by initiating recording of the broadcast (Ni r television program. When the video phone call is finished, the system will allow the user to resume watching the television program from the point that the interruption occurred and will use catch-up play so that eventually the user may be watching their program live again.

There are known video based monitoring systems that gather alarm data and present this alarm data as a log of alarm events. An example of an alarm event could be a 'motion ON' when motion is detected in video data or 'sensor ON' when a door is opened causing a door sensor of the system to activated. Another example of an alarm event may be an 'object ON' when an object is detected in the video data. Such an object may be detected using known object detection techniques.

When a user activates the log the user is shown live video data from a camera that has been associated with alarm events from the area in which the alarm occurred.

However, in viewing the live video data, the user may not see the situation that caused the alarm to occur. For example, a person that triggered the alarm may have passed out of view and will no longer be visible.

There are known video based recording and monitoring systems that record video data continuously. In such systems when an alarm condition occurs an alarm "ON event" appears in a notification log. In a variation of such a system, recording is only performed during the period that there is an alarm condition, which is between an alarm ON event and 790615.doc Final C:\NrPortb]\SAF\PDM\613338_I .DOC \O an alarm "OFF event". Further, some systems extend the recording time by a fixed amount

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after the alarm OFF event. This is known as "post-event record time".

r Still other video recording systems can record for a limited time prior to an event Soccurring by using a circular buffer as a temporary store of the received video data. Video data is copied from the circular buffer to a final destination when an alarm ON event Soccurs. In such systems, the duration of the video data that is buffered and recorded prior to the event is known as the pre-event record time.

Some video recording systems are used for security monitoring. Operators of such systems may be monitoring a large number of video data streams, possibly from a number of distributed sites and these video data streams may generate a high number of alarm events that must be monitored. Often the operator is required to perform a number of manual steps to monitor alarm events. If a user activates an alarm ON event item in the notification log of the system described above, then recorded video data of the event, from an associated camera is displayed to the user. In such a system the operator can see immediately what happened previously when the alarm condition was triggered. However, the user is unable to quickly and efficiently determine how the situation progressed from the time that the alarm event was triggered to the current time.

Thus a need clearly exists for an improved method of displaying video data.

Summary According to one aspect of the present invention there is provided a method of displaying video data using a video recording system, said method comprising the steps: recording video data, captured by a camera of said video recording system in response to notification of a detected event, for a period of said event and for a predetermined period after said event; 790615.doc Final C:\NrPortbl\SA FPDM\6133381 .DOC NO -4receiving a request, during the period of said event or during said predetermined Speriod, to display the recorded video data associated with said event; determining a play rate based at least on said predetermined period, in response to said request; and 5 displaying said video data associated with said event at said play rate.

(Ni i According to another aspect of the present invention there is provided an apparatus

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for displaying video data using a video recording system, said apparatus comprising: recording means for recording video data, captured by a camera of said video recording system in response to notification of a detected event, for a period of said event and for a predetermined period after said event; receiving means for receiving a request, during the period of said event or during said predetermined period, to display the recorded video data associated with said event; determining means for determining a play rate based at least on said predetermined period, in response to said request; and display means for displaying said video data associated with said event at said play rate.

According to still another aspect of the present invention there is provided a computer readable medium, having a program recorded thereon, where the program is configured to make a computer execute a procedure to display video data using a video recording system, said program comprising: code for recording video data, captured by a camera of said video recording system in response to notification of a detected event, for a period of said event and for a predetermined period after said event; 790615.doc Final C:\NrPortbl\SAF\PDM\613338 I.DOC code for receiving a request, during the period of said event or during said Spredetermined period, to display the recorded video data associated with said event; ri code for determining a play rate based at least on said predetermined period, in response to said request; and code for displaying said video data associated with said event at said play rate.

(N Other aspects of the invention are also disclosed.

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Brief Description of the Drawings Some aspects of the prior art and one or more embodiments of the present invention will now be described with reference to the drawings and appendices, in which: Fig. 1 is schematic diagram of a digital video recording system upon which embodiments described may be practiced; Fig. 2 is a schematic block diagram of a general-purpose computer upon which a viewer described herein may be practiced; Fig. 3 is a schematic block diagram of a general-purpose computer upon which a storage server described herein may be practiced; Fig. 4 is a flow diagram showing a method of generating an event notification; Fig. 5 is a flow diagram showing a method of recording video data; Fig. 6 is a flow diagram showing a method of sending event data; Fig. 7 is a flow diagram showing a method of streaming video data; Fig. 8 is a flow diagram showing a method of displaying video data; Figs. 9(b) and 9(c) show three examples in terms of time, the relative timing of events and user actions; and Fig 10 shows an example of a user interface that may be used with the system of Fig.

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SDetailed Description including Best Mode Where reference is made in any one or more of the accompanying drawings to steps r and/or features, which have the same reference numerals, those steps and/or features have for the purposes of this description the same function(s) or operation(s), unless the contrary intention appears.

(Ni r It is to be noted that the discussions contained in the "Background" section and that above relating to prior art arrangements relate to discussions of documents or devices which form public knowledge through their respective publication and/or use. Such should not be interpreted as a representation by the present inventor(s) or patent applicant that such documents or devices in any way form part of the common general knowledge in the art.

Methods of displaying video data are described below with reference to Figs. 1 to In the exemplary embodiment, the described methods are implemented within a digital video recording system 100 as shown in Fig 1. The system 100 comprises a storage server 300, a viewer 200 and a network video camera 120 connected to a network 220, such as the Internet or an Intranet. The network 220 may also be a local area network (LAN).

Typically the network 160 is an Internet Protocol (IP) based network and the storage server 300 viewer 200 and camera 120 all have the ability to communicate with each other over the network 220 using IP. Some examples of proprietary cameras 120 are the Canon T M VB-C50i video camera.

In another embodiment, the system 100 may comprise a plurality of video cameras, similar to the camera 120. Further, the system 100 may comprise a plurality of storage servers similar to the storage server 300. Still further, the system 100 may comprise a plurality of viewers similar to the viewer 200.

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The camera 120 is responsible for the capture of video data representing images.

SThe video data is output by the camera 120 as a stream of video data. The camera 120 may optionally comprise sensor inputs to which sensors may be connected. If a sensor connected to the camera 120 is activated, then the system 100 may be configured to generate an event notification.

C The storage server 300 may be used for monitoring the output of video data from the

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camera 120 and for recording requesting and storing) the video data. The storage server 300 may also be used for accessing video data, for event handling and for control of the system 100.

The video data captured by the camera 120 may be uploaded, via the computer network 220, to the storage server 300. The video data may be processed by the storage server 300 and/or stored on a hard disk drive 310 of the storage server (see Fig. so that the video data may be viewed by a user using a display 314 (see Fig. 3) of the storage server 300.

Alternatively, the video data may be exported, via the computer network 220, from the storage server 300 to the viewer 200, as seen in Fig. 1. The viewer 200 may be used for processing and displaying one or more frames of the exported video data. The viewer 200 may be configured to receive video data directly from the camera 120 and to present the video data to a user using a display device 214 (see Fig. 2).

As seen in Fig. 2, the viewer 200 is preferably formed by a computer module 201, input devices such as a keyboard 202, mouse 203 and remote control 251, output devices including a printer 215, a display device 214 and loudspeakers 217. A network interface 208 configured within the computer module 201 may be used for communicating to and from the computer network 220, for example connectable via a network link 221 (such as a 790615.doc Final C:\NrPortbl\SAF\PDM\613338_ .DOC coaxial cable, a twisted pair cable, a fibre optic cable, a wireless connection using 802.1 lb Sor BluetoothTM or other connection type). A Modulator-Demodulator (Modem) transceiver N device (not shown) incorporated within the network interface 208 or otherwise, may also be used to obtain access to the computer network 220, via a telephone line for example.

The computer module 201 typically includes at least one processor unit 205, and a r, memory unit 206, for example, formed from semiconductor random access memory (RAM) and read only memory (ROM). The module 201 also includes a number of input/output interfaces including an audio-video interface 207 that couples to the video display214 and loudspeakers217, an I/O interface213 for the keyboard202 mouse203, printer 215 and optionally a joystick (not illustrated) or trackball (not illustrated). The module 201 also includes a radio frequency (RF) receiver 250 for receiving RF input signals from the remote control 251.

Optionally the module 201 may include a touch-screen (not shown) formed by an overlaid touch-sensitive surface on the video display 214, allowing user input by touching or moving a finger along the video display 214. A storage device 209 is provided and typically includes a hard disk drive 210 and a floppy disk drive 211. A magnetic tape drive (not illustrated) may also be used. A CD-ROM drive 212 is typically provided as a nonvolatile source of data. The components 205 to 213 and 250 of the computer module 201, typically communicate via an interconnected bus 204 and in a manner, which results in a conventional mode of operation of a computer system as known to those in the relevant art.

Examples of computers on which the described arrangements may be practiced include IBM-PC's and compatibles, Sun Sparcstations or alike computer systems evolved therefrom.

790615.doc Final C:\NrPortbl\SA 17PDM\613338 I.DOC \O r

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The storage server 300 is also shown in detail in Fig. 3. The storage server 300 is Spreferably formed by a computer module 301, input devices such as a keyboard 302 and mouse 303, output devices including a printer315, a display device314 and loudspeakers 2317. A network interface 308 is also configured within the computer module 301 and may be used for communicating to and from the computer network 220, r for example connectable via network link 321 (such as a coaxial cable, a twisted pair cable, a fibre optic cable, a wireless connection using 802.1 lb or BluetoothTM or other connection type). A Modulator-Demodulator (Modem) transceiver device (not shown) incorporated within the network interface 308 or otherwise, may also be used to obtain access to the computer network 220, via a telephone line for example.

Similar to the computer module 201, the computer module 301 typically includes at least one processor unit 305, and a memory unit306, for example formed from semiconductor random access memory (RAM) and read only memory (ROM). The module 301 also includes a number of input/output interfaces including an audiovideo interface 307 that couples to the video display 314 and loudspeakers 317, an I/O interface 313 for the keyboard 302, printer 315 and mouse 303 and optionally a joystick (not illustrated) or trackball (not illustrated). Optionally the module 301 may include a touch-screen (not shown) formed by an overlaid touch-sensitive surface on the video display 314, allowing user input by touching or moving a finger along the video display 314. A storage device 309 is provided and typically includes a hard disk drive 310 and a floppy disk drive 311. A magnetic tape drive (not illustrated) may also be used. Peripheral storage devices (not shown) connected to the computer module 301 may be used. In addition, network accessible storage devices or collections of such devices (not shown), including Network Attached Storage (NAS) and Storage Area Networks (SAN), may be 790615.doc Final C:\NrPortbl\SAF\PDM\613338_ I.DOC

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connected to the network 220 and may be accessed through the network interface 308. A CD-ROM drive312 is typically provided as a non-volatile source of data. The r components305 to313 of the computer module301, typically communicate via an interconnected bus 304 and in a manner, which results in a conventional mode of operation of such a computer system as known to those in the relevant art.

r The camera 120 has a similar configuration to the computer modules 201 and 301.

The camera 120 includes a memory memory 306) and a processor a processor 305). However, the hardware configuration of the camera 120 will not be explained in further detail herein.

The methods described herein may be implemented as software, such as one or more application programs executable within the viewer 200, the storage server 300 and/or the camera 120. In particular, the steps of the described methods are effected by instructions in the software that are carried out within the viewer 200, the storage server 300 and/or the camera 120. The instructions may be formed as one or more code modules, each for performing one or more particular tasks. The software may also be divided into two separate parts, in which a first part and the corresponding code modules performs the described methods and a second part and the corresponding code modules manage a user interface between the first part and the user. The software may be stored in a computer readable medium, including the storage devices described below, for example. The software may be loaded into the viewer 200, the storage server 300 and/or the camera 120, from the computer readable medium, and then be executed by the corresponding computer module 201 and/or 301. A computer readable medium having such software or computer program recorded on it is a computer program product. The use of the computer program 790615.doc Final C:\NrPortbl\SAF\PDM\613338_ I.DOC S-11-

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o product in the system 100 preferably effects an advantageous apparatus for implementing Sthe described methods.

C, In the example of Fig. 1, the camera 120 is directed at a scene 132 consisting of a house 116. A man 112 is seen approaching the house 116. A previous location of the man is indicated in Fig. 1 by a dotted representation 114. The viewer 200 utilises a user r, interface. Input from a user 140 is typically given via the remote control 251.

In the example of Fig. 1, an image 133 of the scene 132 captured by the camera 120 and recorded by the storage server 300 is being displayed on the display device 214 of the viewer 200. In the example, video data representing the image 133 was previously recorded and the man 100 appears on the display 214 at his previous location.

A method 400 of generating an event notification will now be described with reference to Fig. 4. The method 400 may be implemented as software resident in the memory of the camera 120 and being controlled in its execution by the processor of the camera 120.

The method 400 begins at step 402, where the processor of the camera captures video data representing an image. In step 410, the captured video data representing the image is sent by the camera 120 in an open HTTP connection to the storage server 300. At the next step 404 the camera 120 analyses the captured video data using known motion detection techniques. Also at step 404, the camera 120 determines the motion detection status of the image represented by the captured video data. The motion detection status may be "ON" motion is detected in a scene represented by the captured video data) or "OFF" (i.e.

no motion is detected in the scene represented by the captured video data). At step 406, the camera 120 determines whether the motion detection status has changed for the scene 132) represented by the video data. At the next step 408, if the camera 120 790615.doc Final C:\NrPortbl\SA PDM\613338_ I.DOC ID -12determines that motion detection status has changed, then the method 400 proceeds to step

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S410. Otherwise, the method 400 returns to step 402. At step 208, an event notification is C sent to the storage server 300 over an open HTTP connection. The event notification is a message that includes the essential information concerning the event including: Type of the event motion detection); C1 State of the event ON or OFF).

As described above, at the step 404, the camera 120 analyses the captured video data using known motion detection techniques in order to detect motion in the video data.

In another embodiment, the camera 120 may analyse the captured video data using known object detection techniques in order to detect an object in the video data. In still another embodiment, the event notification may be generated in response to the activation of a sensor connected to the camera 120.

A method 500 of recording video data will now be described with reference to Fig.

The method 500 may be implemented as software resident on the hard disk drive 310 of the storage server 300 and being controlled in its execution by the processor 305.

The method 500 performs the step of recording video data, captured by the camera 120 of the video recording system 100 in response to the processor 305 receiving notification of a detected event an event notification message) from the camera 120.

In response to receiving such an event notification message, the processor 305 records some video data from before the event, for the period of the event and for a predetermined period after the event. The duration of video data recorded from before the event is based on a pre-determined pre-event record period. The duration of video data recorded during the event corresponds to the period of the event. For example, if the event corresponds to the presence of a person in view of the camera 120, the duration of video data recorded 790615.doc Final C:\NrPortbl\SAF\PDM\613338_1 .DOC IO -13-

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corresponds to the period of time during which the person was in view of the camera 120.

The duration of video data recorded after the event is based on a pre-determined post-event N record period.

As will be described in detail below, the recorded video data associated with the event may be displayed at a play rate determined based at least on the predetermined postr event record period. The play rate is preferably determined in response to receiving a

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request to display the recorded video data associated with the event. The play rate is preferably determined such that display of recorded video data associated with the event is completed by the end of the predetermined post-event record period.

The request to display the recorded video data may be received during the period of the event or during the predetermined post-event period. The event may be motion detected in the captured video data or an object detected in the captured video data.

Alternatively, the event may be the activation of a sensor connected to the camera 120.

The pre-event record period and post-event record period are typically configured by a person who is an administrator of the video recording system 100. In one embodiment, the pre-event record period and the post-event record period are configured to be common values for all cameras 120) connected to the network 120. In another embodiment, the pre-event record period and the post-event record period are configured to be specific values for each camera. In such an embodiment, an administrator can set an important camera 120), for example, to have a long pre-event period.

The method 500 begins at step 502, where video data representing an image is received over an open HTTP connection from the camera 120. For example, the storage server 300 may receive the video data sent by the camera 120 at step 410 of the method 400. At the next step 504, the processor 305 adds the received video data to a circular 790615.doc Final C:\NrPortbl\SA F\PDM\613338 I.DOC I-14-

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buffer configured within the memory 306. Typically, the circular buffer resides in RAM Sconfigured within the memory 306. Alternatively, the received video data may be stored C on a storage device such as the hard disk drive 310. The capacity of the circular buffer is selected to store the number of frames of video data required for the duration of the preevent recording period at an expected frame rate.

C Then at the next step 506, the processor 305 determines if any new event data has been received from the camera 120. At the next step 508, if the processor 305 determines that new event data has been received, then the method 500 proceeds to step 522.

Otherwise, the method 500 proceeds to step 528. At step 522, a 'Previous event state' variable configured within memory 306 is set with the value of a 'Current event state' variable configured within the memory 306. Then at the next step 524, the 'Current event state' variable is set with the value of the newly received event data which may be "ON" or "OFF". At the next step 526, the new event data is written to an event log configured within the hard disk drive 410. Typically each event is recorded in the event log as a single line of text data and the event log is stored in a file on the hard disk drive 310 of the storage server 300. The event log may record the following information for each event logged: Time that the event is received; Type of the event motion detection, object detection, sensor activation); State of the event ON or OFF); Name or IP address of the associated network camera 120.

Typically, the pre-event record period is also included in the event data if the event log marks a change to the "ON" state and the post event recording period is included in the event data logged if the event is marking change to the OFF state.

790615.doc Final C:\NrPortbl\SAF\PDM\61 33381 .DOC IND Following step 526, the method 500 proceeds to step 528. Further, as described

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above, if, at step 508, the processor 305 determine that there was no new event data then N the method 500 proceeds directly to step 528.

At step 528, if the processor 305 determines that the 'Current event state' is 'ON', then the method 500 proceeds to step 530. In step 530 all the video data representing K1 a set of one or more images) stored in the circular buffer is flushed to a file where the video data is recorded for long term storage. Following step 530, the method 500 returns to step 502. If the 'Current event state' has just become the video data representing the set of copied video images corresponds to the pre-event recorded video data and the duration of the video data representing the video images is the pre-event record period. If the event was already the video data representing the video images is typically only the most recently received frame of video data. After step 530, the circular buffer is empty.

If at step 528, the 'Current event state' is OFF then the method 500 proceeds to step 532. At step 532, if the processor 305 determines that the 'Previous event state' is OFF, then the method 500 proceeds to step 534. Otherwise, the method 500 proceeds directly to step 536. At step 534, a 'Record stop time' value is determined as follows: Record stop time current time post event record period Following step 534, the method 500 proceeds to step 536.

At step 536, the processor 305 determines if the 'Record stop time' value has been exceeded. If the current time is less than the 'Record stop time' value, at step 536, then the method 500 proceeds to step 530. Otherwise, the recording for the recent event is completed and the method 500 returns to step 502.

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A method 600 of sending event data will now be described with reference to Fig. 6.

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The method 600 may be implemented as software resident on the hard disk drive 310 and being controlled in its execution by the processor 305. The method 600 allows clients the viewer 200) on the network 220 to receive event data.

The method 600 begins at step 610, where the processor 305 receives a request from CI the viewer 200 to serve event data to the viewer 200. At the next step 612, the processor 305 waits until new event data is written into the event log configured within the hard disk drive 310. When new event data is detected then the new event data is read from the event log by the processor 305. At the next step 614, the event data is formatted and sent to the viewer 200. Following step 614, the method 600 returns to step 610 and the method 600 is repeated.

A method 700 of streaming video data will now be described with reference to Fig.

7. The method 700 may be implemented as software resident on the hard disk drive 310 of the storage server 300 and being controlled in its execution by the processor 305.

The method 700 begins at step 702, where the processor 505 waits for a request from the viewer 200 to show video data for an event. In the present example, the processor 205 performs the step of receiving a request to display the recorded video data associated with the event. The request may be received during the period of the event or during the predetermined post-event period. In step 702, the request is parsed to recover information about the identity of the camera 120 associated with the event and the time of the event.

At the next step 703, if the processor 305 determines recording associated with the event is finished, then the method 700 continues to step 709. Otherwise, the method 700 proceeds to step 704.

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At step 704, the processor 205 performs the step of determining a play rate based at

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least on the post event record predetermined period, in response to the request. The details of the determination of the play rate are described later in this document. At the next step S705, if the processor 305 determines that the play rate is greater than a predetermined play rate threshold, then the method 700 continues at step 711. Otherwise, the method 700 N proceeds to step 706. At step 711, the play rate is set to a normal play rate 1.0) and

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then the method 700 proceeds to 709. In another embodiment, at step 711, the play rate may be set to a maximum acceptable play rate ten (10) times normal play rate) that has been configured for the video recording system 100.

At step 706, the recorded video data is streamed to the viewer 200 over a previously established HTTP connection. The video data is cued to start from the beginning of the pre-event record period and displays at the play rate determined in step 704. When display (or playback) of the recorded video data is completed, the method 700 proceeds to step 708. In step 708, live video data received from the camera 120 is streamed to the viewer 200 over the HTTP connection. The viewer 200 uses the streamed video data to perform the step of displaying the video data associated with the event at the play rate.

At step 709, the processor 305 sends a message to the viewer 200 indicating that if the event is played, some live video data will be missed. Accordingly, the display of the video data is dependent on the play rate meeting a predetermined condition the play rate being below the predetermined play rate threshold). Typically the message sent by the processor 305 is received by the viewer 200 and a warning is displayed to a user together with a request for confirmation that this is OK. In step 710, if the processor 305 receives a notification indicating that it is OK for the user to miss live video, then the method 700 proceeds to step 706. Otherwise, the method 700 proceeds to step 708.

790615.doc Final C:\NrPortbl\SAF\PDM\6133381 .DOC ID-18- A method 800 of displaying video data will now be described with reference to Fig.

8. The method 800 may be implemented as software resident on the hard disk drive 210 of C the viewer 200 and being controlled in its execution by the processor 205.

The method 800 begins at the first step 802, where the processor 205 displays a list of recent ON events retrieved from the storage server 200 executing the method 600 ,I described above. At the next step 804, the processor 205 detects selection of an event from the displayed list of recent events. For example, the user 140 may select an event on the display 214 using the remote control 251.

The method 800 continues at the next step 808, where the processor 205 sends a request to the storage server 300 to display video data for the event selected at step 802.

As part of step 808 the processor 205 establishes an HTTP connection with the storage server 300 that can be used to receive a stream of video data. The request to show video data for an event as sent at step 808 includes the following information: the identity of the associated camera 120; 0 the time of the event; and the pre-event record period.

The method 800 concludes at step 808, where the processor 205 receives video data from the storage server 300. In particular, the processor 205 receives the stream of video data sent by the processor 305 of the storage server 300 at steps 706 and/or 708. Also at step 808, the video data received is decoded and displayed on the display 214 at the play rate. In the case when the processor 205 receives the stream of recorded video data associated with the event at step 706 and the stream of live video data at step 708, the processor 205 performs the step of switching back to displaying live video data after displaying the recorded video data.

790615.doc Final C:\NrPortbl\SAF\PDM\61 3338_1 .DOC I-19- In the use of video surveillance systems, typically a user, such as a security guard,

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Snotices an alarm associated with an event at some time after the event has occurred but C1 before the completion of the event or before the completion of post-event recording associated with the event. As described above, at step 704 a play rate is determined. The play rate represents the speed of display (or playback) of the recorded video data from the Stime that the user selects an event to the time that the recorded video data is displayed.

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When the user selects an event to view, the video data that is displayed typically includes the pre-event recorded video data, the video data of the event, and the post-event recorded video data. The play rate is preferably determined in such a way as to ensure that the full recorded duration of captured video data is displayed to the user but also to ensure that the user does not miss seeing any video data from the camera 120 whether the video data is recorded or live. As described above, the play rate is determined based on the predetermined post-event period. The play rate is preferably determined such that display of recorded video data associated with the event is completed by the end of the predetermined post-event period. As also described above, the play rate may be further based on the period of the event (or ON period). Still further, the play rate may be based on a period prior to the event pre-event record period).

Figs. 9(b) and 9(c) shows the timing of three example scenarios in terms of time represented by the horizontal arrows 910, 930, 950, the relative timing of events 911,912, 931, 951, 953 and user actions 913, 932 and 952.

Considering Fig the user selects an event at 913 after the event has returned to the OFF state at 912 but before the end at 919 of the post event record period 916. In this case the play rate is determined as follows: Play rate P A (1) 790615.doc Final C:\NrPortbl\SA F\PDM\613338_1 .DOC NO where P represents the total duration of the video data that needs to be displayed.

SP pre-event record period 914 ON period 915 post event period 916 r A represents the time available before the recording stops; and A recording stop time 919 user action time 913.

If the determination of the play rate at step 704 is equal to two then the video r data will be displayed (or played) at double normal display speed for the video data. If the

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user action time is very close to the recording stop time then the determined play rate will be very high and not acceptable for displaying (or playing) to a user. To avoid such a situation, there is a threshold play rate value configured for the system 100. If the determined play rate is greater than the threshold play rate value, then the normal play rate is used. The play rate determined at step 704 is compared to the threshold play rate at step 705. Accordingly, the display of the video data is dependent on the play rate meeting a predetermined condition the play rate being below the predetermined play rate threshold).

Considering the example of Fig. a user action occurs at 932 while the event is still in the ON state the event moved to the ON state at 931). In the example of Fig.

a modified play rate is determined as follows: Play rate P1 Al (2) where P1 pre-event record period 934 ON period 735 post event period 936; and Al post event period 936). In the example of Fig. the eventual value for finishing of recording may be greater than the assumed value of the end of the post event period which occurs at 939. The value of the post event period 939 is the earliest possible completion for recording given that the event is still in the ON state.

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Finally, considering the example of Fig a user action occurs at 952 after Srecording has finished at 959. Accordingly, it will not be possible for the user to view all C1 recorded video data without missing some live video data. In this case, at step 703 of the method 700, the processor 305 of the storage server 300 and the method 700 will proceed to step 709.

ri Fig 10 shows an example of a user interface 1020 that may be used with the system

NO

100. For example, the user interface 1020 may be displayed on the display 214 of the viewer 200. The user interface 1020 comprises a network camera icon 1022 in the top left part of the user interface 1020. The camera icon 1022 is associated with the actual network camera 120 in the system 100. When an alarm event occurs associated with the camera 120 then, at step 802 of the method 800, the network camera icon 1022 is highlighted as represented by a dashed line 1024 in order to display the event notification.

The network camera icon 1022 remains highlighted until the user selects the icon 1022.

When the user selects the event as described in step 804, the video data stream received by the viewer 200 from the storage server 300 at step 808 is displayed in a window 1026 of the user interface 1020. If the user presses button 1028 using the mouse 203 in a conventional manner), the video data is displayed (or replayed) from the start of the pre-event recorded video data associated with the event. If the user presses button 1030, then the method 800 concludes.

Industrial Applicability It is apparent from the above that the arrangements described are applicable to the computer and data processing industries).

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The foregoing describes only some embodiments of the present invention, and Smodifications and/or changes can be made thereto without departing from the scope and 0 C1 spirit of the invention, the embodiments being illustrative and not restrictive.

In the context of this specification, the word "comprising" means "including principally but not necessarily solely" or "having" or "including", and not "consisting only C of". Variations of the word "comprising", such as "comprise" and "comprises" have Scorrespondingly varied meanings.

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Claims (4)

1. 2. The method according to claim 1, wherein said event is motion detected in the captured video data.
2. 3. The method according to claim 1, wherein said event is an activation of a sensor.
3. 4. The method according to claim 1, wherein said event is an object detected in the captured video data. The method according to claim 1, wherein said play rate is further based on the period of the event.
4. 790615.doe Final C:\NrPortbl\SAF\PDM\613338_ I.DOC IN -24- O 6. The method of claim 1, wherein said play rate is further based on a period prior r, to the event. 7. The method of claim 1, wherein said play rate is further based on the period of the event and the period prior to the event. 8. The method of claim 1, further comprising the step of switching back to displaying live video data after displaying the recorded video data. 9. The method of claim 1, wherein the display of said video data is dependent on said play rate meeting a predetermined condition. The method of claim 1, wherein said play rate is determined such that display of recorded video data associated with said event is completed by the end of said predetermined period. 11. An apparatus for displaying video data using a video recording system, said apparatus comprising: recording means for recording video data, captured by a camera of said video recording system in response to notification of a detected event, for a period of said event and for a predetermined period after said event; receiving means for receiving a request, during the period of said event or during said predetermined period, to display the recorded video data associated with said event; 790615.doc Final C:\NrPortbl\SAF\PDM\613338_ I.DOC I \O determining means for determining a play rate based at least on said predetermined Speriod, in response to said request; and Ni display means for displaying said video data associated with said event at said play rate. 12. A computer readable medium, having a program recorded thereon, where the program is configured to make a computer execute a procedure to display video data using a video recording system, said program comprising: code for recording video data, captured by a camera of said video recording system in response to notification of a detected event, for a period of said event and for a predetermined period after said event; code for receiving a request, during the period of said event or during said predetermined period, to display the recorded video data associated with said event; code for determining a play rate based at least on said predetermined period, in response to said request; and code for displaying said video data associated with said event at said play rate. 13. A method of displaying video data using a video recording system, said method being substantially as herein before described with reference to any one of the embodiments as that embodiment is shown in the accompanying drawings. 790615.doc Final C:ANrPortbl\SA F\PDM\6133381 .DOC IND -26- DATED this Nineteenth Day of December 2006 CANON KABUSHIKI KAISHA c-I Patent Attorneys for the Applicant SPRUSON&FERGUSON I 790615.doc Final 790615.oc FnalCNrPortbl\SA F\PDM\613 33 8_ 1. DOC