Patent Publication Number: US-2019188930-A1

Title: Drive recorder

Description:
TECHNICAL FIELD 
     The present invention relates to a drive recorder, a processing method, and a program. 
     BACKGROUND 
     For analysis of causes of an accident of a vehicle such as an automobile, monitoring of the driving condition, or a safe driving guidance, various devices and systems for recording the driving condition of a vehicle have been proposed or commercialized. 
     For example, Patent Literature 1 describes a device for recording the driving condition of a vehicle that travels through operation by a driver, such as a railway train. The device described in Patent Literature 1 includes a device installed in the vehicle (drive recorder), and a driving condition recording device and a display device installed inside or outside the vehicle. The drive recorder includes a camera unit, a microphone unit, an operation unit, a driver&#39;s condition acquiring unit, a control unit, a recording unit, and a time-of-day generation unit that are provided to the vehicle. The camera unit captures a video of the front side in the vehicle traveling direction. The microphone unit collects sounds in the cab. The operation unit includes an operation member for driving the vehicle. The control unit acquires an amount of operation from the operation member and controls service operation of the train. The driver&#39;s condition acquiring unit measures biological information such as brain waves, pulse, blood pressure, and body temperature of the driver. The time-of-day generation unit generates the current time of day. The recording unit records information (video, sound, operation, biological information of the driver) measured by the aforementioned various devices as time-series information. Meanwhile, the driving condition recording device acquires various types of information recorded by the recording unit via a communication means, combines a plurality of types of information by using the time of day included in the respective pieces of information as a key, summarizes the video information, the operation condition of the vehicle, and the like in one screen, and displays it on a display device. 
     Patent Literature 2 describes a drive recorder that records an image captured by a camera mounted on a vehicle. The drive recorder described in Patent Literature 2 includes an acceleration detection unit, an accident determination unit, an identification unit, and a transmission unit. The acceleration detection unit detects acceleration of the vehicle, and senses an impact applied to the vehicle. The accident determination unit determines that an accident occurred when the magnitude of the detected acceleration exceeds a threshold. The identification unit identifies a time point at which the magnitude of the acceleration detected by the acceleration detection unit is maximized after it is determined that the accident occurred. The transmission unit transmits, to an external device, an image within a predetermined time width including the time point at which the maximum value is identified, among the recorded images. The transmission unit determines the predetermined time width based on the vehicle speed. 
     Patent Literature 3 describes a drive recorder capable of preventing images captured by a camera mounted on the vehicle from being lost even when the vehicle is burned out by an accident. The drive recorder described in Patent Literature 3 includes an imaging means, a measuring means, a recording means, an accident sensing means, a control means, and a transmission means. The imaging means captures the vehicle condition at the time of traveling. The measuring means measures the driving condition of the vehicle at the time of traveling. The accident sensing means senses that an accident has occurred in the vehicle. The control means controls, when it is sensed that an accident has occurred, to store continuous video data or/and drive data before the accident or after the accident or before and after the accident, recorded in the recording means, for a predetermined time. The transmission means transmits the video data stored in the recording means to the outside. For example, the transmission means transmits an image or the like to a mobile wireless communication device such as a mobile phone or a mobile communication device, and transmits an image or the like from the mobile wireless communications device to a server connected through a network such as the Internet. The server records an image or the like and uses it for analysis of the cause of an accident. 
     Patent Literature 1: JP 2013-47055 A 
     Patent Literature 2: JP 5926978 B 
     Patent Literature 3: JP 2006-168717 A 
     SUMMARY 
     The most part of the video recorded by the technology described in Patent Literature 1 is of a period in which no problem occurs. In other words, the most part of a video is useless for analysis of causes of an accident of the vehicle, monitoring of the driving condition, or safe driving guidance. Therefore, it takes time to find a part of the video containing a problem such as so-called near-miss or the like. Meanwhile, according to the technologies described in Patent Literature 2 and Patent Literature 3, only a video of a predetermined section including a time point when acceleration of the vehicle becomes a maximum value or a scene of an accident or the like is output to an external device. Accordingly, it is easy to find a video including a problem. Further, according to the technology of Patent Literature 2, as the vehicle speed is higher, the time width of a predetermined section is longer, for example. Therefore, it is likely to have a clue to know the scale of an accident even though the speed is high. Further, in the case of an accident in a low speed, it is possible to eliminate record of a useless video. 
     However, according to the knowledge of the present inventor, even in the case of the same speed, if another traveling condition of the vehicle differs, the length of a time period of a video useful for analysis of causes of an accident, monitoring of the driving condition, or safe driving guidance differs. Therefore, in the technology described in Patent Literature 2 that the video segments are the same in the case of the same speed, it is difficult to save a video useful for analysis of causes of an accident, monitoring of the driving condition, or safe operating guidance, without excess or deficiency. 
     An exemplary object of the present invention is to provide a drive recorder that solves the problem described above, that is, a problem that it is difficult to save necessary video information without excess or deficiency. 
     A drive recorder according to an exemplary aspect of the present invention includes 
     a video recording unit that records a video captured by a camera mounted on a vehicle, in association with a time of day; 
     an abnormal event detection unit that detects an abnormal event; 
     a time period determination unit that determines a time period, the time period including a time of day when the abnormal event is detected and having a length determined based on a traveling condition other than the speed of the vehicle; 
     a video extraction unit that extracts a video of the time period determined, from the video recording unit; and 
     a data saving unit that records or transmits to an external device a file including the video extracted, as an erasure prohibited object. 
     A processing method according to another exemplary aspect of the present invention is a processing method executed by a drive recorder. The method includes 
     recording a video captured by a camera mounted on a vehicle, in association with a time of day; 
     detecting an abnormal event; 
     determining a time period, the time period including a time of day when the abnormal event is detected and having a length determined based on a traveling condition other than the speed of the vehicle; 
     extracting a video of the time period determined, from the video recording unit; and 
     recording or transmitting to an external device a file including the video extracted, as an erasure prohibited object. 
     A program according to another exemplary aspect of the present invention causes a computer to function as 
     a video recording unit that records a video captured by a camera mounted on a vehicle, in association with a time of day; 
     an abnormal event detection unit that detects an abnormal event; 
     a time period determination unit that determines a time period, the time period including a time of day when the abnormal event is detected and having a length determined based on a traveling condition other than the speed of the vehicle; 
     a video extraction unit that extracts a video of the time period determined, from the video recording unit; and 
     a data saving unit that records or transmits to an external device a file including the video extracted, as an erasure prohibited object. 
     With the configuration described above, the present invention is able to save a video useful for analysis of causes of an accident, monitoring of the driving condition, or safe driving guidance, without excess or deficiency. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a drive recorder according to a first exemplary embodiment of the present invention. 
         FIG. 2  is a flowchart illustrating an exemplary operation of a drive recorder according to first and second exemplary embodiments of the present invention. 
         FIG. 3  is a block diagram illustrating an example of an abnormal event detection unit according to the first exemplary embodiment of the present invention. 
         FIG. 4  is a graph illustrating an example of a temporal change in acceleration of a vehicle detected by an acceleration sensor according to the first exemplary embodiment of the present invention. 
         FIG. 5  is a block diagram illustrating an example of a time period determination unit according to the first exemplary embodiment of the present invention. 
         FIG. 6  is a graph illustrating an example of a temporal change in acceleration of a vehicle detected by the acceleration sensor according to the first exemplary embodiment of the present invention. 
         FIG. 7  is a block diagram illustrating another example of a time period determination unit according to the first exemplary embodiment of the present invention. 
         FIG. 8  is a block diagram illustrating another example of a time period determination unit according to the first exemplary embodiment of the present invention. 
         FIG. 9  is a diagram illustrating an example of a correspondence table of place and the length of a time period according to the first exemplary embodiment of the present invention. 
         FIG. 10  is a block diagram illustrating another example of a time period determination unit according to the first exemplary embodiment of the present invention. 
         FIG. 11  is a diagram illustrating an example of a correspondence table of the time of day and the length of a time period according to the first exemplary embodiment of the present invention. 
         FIG. 12  is a block diagram illustrating another example of a time period determination unit in the first exemplary embodiment of the present invention. 
         FIG. 13  is a diagram illustrating an example of a correspondence table of illumination and the length of a time period according to the first exemplary embodiment of the present invention. 
         FIG. 14  is a block diagram illustrating another example of a time period determination unit according to the first exemplary embodiment of the present invention. 
         FIG. 15  is a diagram illustrating an example of a correspondence table of weather conditions and the length of a time period according to the first exemplary embodiment of the present invention. 
         FIG. 16  is a block diagram illustrating another example of a time period determination unit according to the first exemplary embodiment of the present invention. 
         FIG. 17  is a diagram illustrating an example of a correspondence table of biological information and the length of a time period according to the first exemplary embodiment of the present invention. 
         FIG. 18  is a diagram illustrating an exemplary format of a file created by a data saving unit according to the first exemplary embodiment of the present invention. 
         FIG. 19  is a diagram illustrating another exemplary format of a file created by the data saving unit according to the first exemplary embodiment of the present invention. 
         FIG. 20  is a block diagram of a drive recorder according to a second exemplary embodiment of the present invention. 
         FIG. 21  is a block diagram of a driving condition recording device according to a third exemplary embodiment of the present invention. 
         FIG. 22  is a block diagram illustrating an example of an information terminal device according to the third exemplary embodiment of the present invention. 
         FIG. 23  is a flowchart illustrating an exemplary operation of the information terminal device according to the third exemplary embodiment of the present invention. 
         FIG. 24  is a diagram illustrating an exemplary format of a file recorded in a data saving unit according to the third exemplary embodiment of the present invention. 
         FIG. 25  is a flowchart illustrating an exemplary operation of an information terminal device according to a fourth exemplary embodiment of the present invention. 
     
    
    
     EXEMPLARY EMBODIMENTS 
     Next, exemplary embodiments of the present invention will be described in detail with reference to the drawings. 
     First Exemplary Embodiment 
       FIG. 1  is a block diagram of a drive recorder according to a first exemplary embodiment of the present invention. Referring to  FIG. 1 , a drive recorder  100  according to the present exemplary embodiment is mounted on a vehicle such as an automobile, and has a function of recording the driving condition of the vehicle. The drive recorder  100  includes a camera  110 , a video recording unit  120 , an abnormal event detection unit  130 , a time period determination unit  140 , a video extraction unit  150 , and a data saving unit  160 . 
     The camera  110  captures a video of a front side in a traveling direction of the vehicle at a predetermined frame rate. As the camera  110 , a charge-coupled device (CCD) camera or a complementary MOS (CMOS) camera may be used, for example. 
     The video recording unit  120  has a function of recording, on a recording medium, a video captured by the camera  110  while adding capturing time-of-day information thereto. As the recording medium, a readable/writable memory card (e.g., SD card), a magnetic disk, or the like may be used, for example. The video recording unit  120  performs writing of a video from the head of a buffer area set in the recording medium, and when writing is completed up to the end of the buffer area, returns to the head and performs writing again. A maximum video time that can be recorded in the buffer area is determined depending on the image quality, frame rate, and the capacity of the buffer area. The video recording unit  120  can be implemented by a dedicated hardware, or by a general-purpose processor, a memory, and a program, for example. 
     The abnormal event detection unit  130  has a function of detecting an abnormal event. When the abnormal event detection unit  130  detects an abnormal event, the abnormal event detection unit  130  notifies the time period determination unit  140  of abnormal event detection information including the detection time of day thereof. The abnormal event detection unit  130  may be implemented by a dedicated hardware, or by a general-purpose processor, a memory, and a program, for example. 
     The time period determination unit  140  has a function of determining a time period of the video to be saved. When the time period determination unit  140  is notified of the abnormal event detection information from the abnormal event detection unit  130 , the time period determination unit  140  determines a time period that includes the time of day when the abnormal event is detected and that has a predetermined time length. The time period determination unit  140  determines a predetermined time length based on the traveling condition other than the speed of the vehicle. The time period determination unit  140  notifies the video extraction unit  150  of the determined time period. The time period determination unit  140  can be implemented by a dedicated hardware, or by a general-purpose processor, a memory, and a program, for example. 
     The video extraction unit  150  has a function of extracting a video of the time period notified from the time period determination unit  140 , from the video recording unit  120 . The video extraction unit  150  notifies the data saving unit  160  of the extracted video and the information of the time period. The video extraction unit  150  can be implemented by a dedicated hardware, or by a general-purpose processor, a memory, and a program, for example. 
     The data saving unit  160  creates a file that includes the video extracted by the video extraction unit  150  and information of the time period, and records it on a recording medium as an erasure prohibited object. The data saving unit  160  also transmits the created file to an external device by using a communication device, not illustrated, provided to the drive recorder  100 . The data saving unit  160  can be implemented by a dedicated hardware, or by a general-purpose processor, a memory, and a program, for example. The data saving unit  160  can also be implemented by an SD card having a wireless communication function such as Wi-Fi or Bluetooth (registered trademark). 
       FIG. 2  is a flowchart illustrating an exemplary operation of the drive recorder  100  according to the present exemplary embodiment. Hereinafter, operation of the drive recorder  100  will be described with reference to  FIG. 2 . 
     When the ignition switch of the vehicle is turned on, the drive recorder  100  starts operation illustrated in  FIG. 2 . 
     First, the camera  110  of the drive recorder  100  starts operation to capture a video of the front side in the traveling direction of the vehicle at a predetermined frame rate (step S 101 ). Then, the video recording unit  120  starts operation to record the video captured by the camera  110  in the buffer area of the recording medium, in association with capturing time-of-day information (step S 102 ). The capturing of the video by the camera  110  and the recording of the video by the video recording unit  120  are continued until the ignition switch of the vehicle is turned off. 
     On the other hand, in parallel with the operation described above, the operation described below is performed. First, the abnormal event detection unit  130  detects presence or absence of an abnormal event (step S 103 ). When the abnormal event detection unit  130  detects an abnormal event, the abnormal event detection unit  130  notifies the time period determination unit  140  of abnormal event detection information including the time of day when it is detected. When the time period determination unit  140  is notified of the abnormal event detection information, the time period determination unit  140  determines a time period having a predetermined time length and including the time of day when the abnormal event is detected, based on the traveling condition other than the speed of the vehicle (step S 104 ). Then, the time period determination unit  140  notifies the video extraction unit  150  of the determined time period. The video extraction unit  150  extracts a video of the notified time period from the video recording unit  120  (step S 105 ). Then, the video extraction unit  150  notifies the data saving unit  160  of the extracted video and the information of the time period. The data saving unit  160  creates a file including the video extracted by the video extraction unit  150  and the information of the time period, and records it on the recording medium as an erasure prohibited object (S 106 ), and transmits the file to an external device (S 107 ). 
     As described above, according to the present embodiment, it is possible to save necessary video information without excess and deficiency. This is because the time period of the video to be saved is determined based on the traveling condition other than the speed of the vehicle. 
     Next, the abnormal event detection unit  130  will be described in more detail. 
     &lt;Example 1 of Abnormal Event Detection Unit  130 &gt; 
       FIG. 3  is a block diagram illustrating an example of the abnormal event detection unit  130 . The abnormal event detection unit  130  of this example includes an acceleration sensor  131  and a comparator  132 . The acceleration sensor  131  detects acceleration G of the vehicle, and outputs the detected result to the comparator  132 . The acceleration sensor  131  is preferably capable of detecting acceleration of at least two axes namely the front and rear left and right axes. The comparator  132  compares the acceleration G of the vehicle detected by the acceleration sensor  131  with a reference value G th , and outputs abnormal event detection information including the current time of day when the acceleration G exceeds the reference value G th . 
       FIG. 4  is a graph illustrating an example of a temporal change in the acceleration G of the vehicle detected by the acceleration sensor  131 . A curve indicated by a solid line represents the detected acceleration G, and a straight line indicated by a broken line represents the reference value G th . The comparator  132  compares the acceleration G with the reference value G±, and outputs the abnormal event detection information including a time-of-day t 1  when the acceleration G exceeds the reference value G th . 
     &lt;Another Example of Abnormal Event Detection Unit  130 &gt; 
     In the example described above, the abnormal event detection unit  130  detects an abnormal event based on the acceleration of the vehicle. However, the abnormal event detection unit  130  may detect an abnormal event based on another type of information such as speed of the vehicle, for example. For example, the abnormal event detection unit  130  compares the speed of the vehicle detected by the vehicle speed sensor with the legal speed limit of the place, and when the vehicle speed exceeds the legal speed limit by a predetermined value or more, the abnormal event detection unit  130  outputs abnormal event detection information including the current time of day of that time point. The legal speed limit of the traveling place can be obtained by means of a method of recognizing an image of a road sign captured by the camera  110 , a method of acquiring it from car navigation, or the like. Furthermore, the abnormal event detection unit  130  may detect an abnormal event based on biological information of the driver. For example, the abnormal event detection unit  130  compares biological information (one or a combination of body temperature, blood pressure, heart rate, blood glucose, used calories, brain waves, oxygen concentration, expiration, posture, and the like, for example) of the driver detected by a biological sensor, with normal values, and when the biological information is out of the normal values, the abnormal event detection unit  130  outputs abnormal event detection information including the current time of day of that time point. 
     Next, the time period determination unit  140  will be described in more detail. 
     &lt;Example 1 of Time Period Determination Unit  140 &gt; 
       FIG. 5  is a block diagram illustrating an example of the time period determination unit  140 . The time period determination unit  140  of this example includes an acceleration sensor  1411 , a maximum value detector  1412 , and a comparator  1413 . The acceleration sensor  1411  detects the acceleration G of the vehicle, and outputs the detected result to the maximum value detector  1412 . It is preferable that the acceleration sensor  1411  is capable of detecting acceleration of at least two axes namely the front and rear left and right axes. The maximum value detector  1412  detects a maximum value G max  in a period from the occurrence time of day of an abnormal event indicated by abnormal event detection information until the magnitude of the acceleration detected by the acceleration sensor  1411  reaches near a value 0, or in a period from the occurrence time of day of an abnormal event until a predetermined time elapses, and outputs the detection result to the comparator  1413 . The comparator  1413  compares the maximum value G max  with preset reference values G 1  and G 2  (G 1 &lt;G 2 ), and outputs information of the time period corresponding to the comparison result. Specifically, the comparator  143  determines that when G max &lt;G 1 , a time period T 1  is set, when G 1 ≤G max &lt;G 2 , a time period T 2  is set, and when G 2 ≤G max , a time period T 3  is set. Here, the time period T 1  represents a time period from a time-of-day t 1 - a  to a time-of-day t 1 + b . The time period T 2  represents a time period from a time-of-day t 1 - c  to a time-of-day t 1 + d . The time period T 3  represents a time period from a time-of-day t 1 - e  to time-of-day t 1 + f . The time-of-day t 1  represents the time of day when an abnormal event is detected. Further, a, b, c, d, e, and f are constants, and (a+b)&lt;(c+d)&lt;(e+f). Further, a=b, c=d, and e=f may be satisfied, a&lt;b, c&lt;d, and e&lt;f may be satisfied, or a&gt;b, c&gt;d, and e&gt;f may be satisfied. 
       FIG. 6  is a graph illustrating an example of a temporal change in the acceleration G of the vehicle detected by the acceleration sensor  1411 . A curve indicated by a solid line represents the detected acceleration G. G th  is a reference value used for detecting an abnormal event by the abnormal event detection unit  130 . G max  is a maximum value of acceleration detected by the maximum value detector  1412 . G 1  and G 2  are reference values given to the comparator  1413 . In the case of  FIG. 6 , as G 1 &lt;Gmax&lt;G 2 , the comparator  1413  outputs the time period T 2  from the time-of-day t 1 - c  to the time-of-day t 1 + d.    
     The time period determination unit  140  illustrated in  FIG. 5  determines the length of a time period based on the magnitude of the acceleration of the vehicle. Therefore, it is possible to save a video of a longer time period for an accident having larger acceleration, that is, a larger-scale accident, even though the speed immediately before the collision is the same. This makes it possible to analyze the cause of an accident for a critical accident more reliably. In addition, it is possible to grasp the effect of a large-scale accident over a relatively long time. 
     &lt;Example 2 of Time Period Determining Section  140 &gt; 
       FIG. 7  is a block diagram illustrating another example of the time period determination unit  140 . The time period determination unit  140  of this example includes an acceleration sensor  1414  and a pattern determination unit  1415 . The acceleration sensor  1414  detects the acceleration G of the vehicle, and outputs the detected result to the pattern determination unit  1415 . It is preferable that the acceleration sensor  1411  is capable of detecting acceleration of at least two axes namely the front and rear left and right axes. The pattern determination unit  1415  determines a change pattern of acceleration detected by the acceleration sensor  1414 . The pattern determination unit  1415  also determines and outputs a time period including the occurrence time of day of the abnormal event indicated by the abnormal event detection information and having a length determined based on the determination result. 
     The pattern determination unit  1415  determines a change pattern of the acceleration based on the detection result of the acceleration G output from the acceleration sensor  1414  during a predetermined period. As the predetermined period, the pattern determination unit  1415  may use a predetermined period around the occurrence time of day of the abnormal event indicated by the abnormal event detection information, for example. Thereby, the length of the time period can be determined based on a short-term change pattern of the acceleration at the time point when the abnormal event is detected. For example, it is possible to measure a time from the occurrence time of day of an abnormal event until the value of the acceleration becomes almost 0, and determine a longer time period as the time becomes longer. 
     As the predetermined period, the pattern determination unit  1415  may also use a period from when the ignition switch is turned on immediately before until the occurrence time of day of the abnormal event indicated by the abnormal event detection information, for example. Thereby, it is possible to determine the length of a time period based on a long-term change pattern of acceleration up to the time point when the abnormal event is detected. For example, the driving tendency of the driver may be determined based on the number of times that sudden acceleration and sudden deceleration are made, and in the case of a so-called rough driver, a time period may be set to be longer as compared with the other drivers. 
     &lt;Example 3 of Time Period Determination Unit  140 &gt; 
       FIG. 8  is a block diagram illustrating another example of the time period determination unit  140 . The time period determination unit  140  of this example includes a global positioning system (GPS) sensor  1416 , and a correspondence table  1417  of the place and the length of a time period, and an arithmetic unit  1418 . The GPS sensor  1416  detects the longitude and the latitude representing the current position of the vehicle based on signals received from GPS satellites, and outputs the detection result to the arithmetic unit  1418 . The correspondence table  1417  of the place and the length of a time period contains one or more sets of place information defined by the longitude and the latitude and information of the length of a time period of that place. The arithmetic unit  1418  searches the correspondence table  1417  of the place and the length of a time period by using, as a key, the longitude and the latitude representing the current position of the vehicle detected by the GPS sensor  1416 , and based on the search result, determines and output a time period including the occurrence time of day of the abnormal event indicated by the abnormal event detection information and having a length corresponding to the current position of the vehicle. 
       FIG. 9  is a diagram illustrating an example of the correspondence table  1417  of the place and the length of a time period. The correspondence table  1417  of this example contains sets of place information defined by two points (e.g., end points of upper left and lower right of a rectangular area) and the length of a time period to be used at that place. For example, on the second line, it is stored that at a place in a rectangular area in which a point represented by longitude x 11  and latitude y 11  and a point represented by longitude x 12  and latitude y 12  are the end points of upper left and lower right, the length of a time period is T 1 . 
     The arithmetic unit  1418  searches the correspondence table  1417  for position information in which the position of the vehicle defined by the latitude and the longitude detected by the GPS sensor  1416  is included in the rectangular area. Then, when the search succeeded, the arithmetic unit  1418  outputs a time period including the occurrence time of day of the abnormal event indicated by the abnormal event detection information and and having a length stored in the correspondence table  1417  corresponding to the searched place information. Meanwhile, when the search failed, the arithmetic unit  1418  outputs a time period that includes the occurrence time of day of the abnormal event indicated by the abnormal event detection information and that has a preset standard length. 
     The place information recorded on the correspondence table  1417  may be a place where accidents occur frequently, and the length of a time period corresponding thereto may be a value longer than the standard. Thereby, it is possible to save a video of a longer time at the point of place where accidents occur frequently, compared with other points of place. Further, the place information recorded on the correspondence table  1417  may be a place where saving of a video is not needed, for example, and the length of a time period corresponding thereto may be a value 0. The place where saving of a video is not needed may include, in the case where a vehicle is a transportation track of a certain company, for example, a place within the premises of the company. In the case where there are many uneven portions in the company&#39;s premises, it is possible to prevent a large amount of video from being saved wastefully each time a transportation track passes through the uneven road. 
     &lt;Example 4 of Time Period Determination Unit  140 &gt; 
       FIG. 10  is a block diagram illustrating another example of the time period determination unit  140 . The time period determination unit  140  of this example include a clock  1419 , a correspondence table  1420  of the time of day and the length of a time period, and an arithmetic unit  1421 . The clock  1419  outputs the current time of day to the arithmetic unit  1421 . The correspondence table  1420  of the time of day and the length of a time period contains one or more sets of time-of-day information defined by the time of day and information of the length of a time period at that time of day. The arithmetic unit  1421  searches the correspondence table  1420  of the time of day and the length of a time period by using the current time of day detected by the clock  1419  as a key, and based on the search result, determines and outputs a time period that includes the occurrence time of day of the abnormal event indicated by the abnormal event detection information and that has a length corresponds to the current time of day. 
       FIG. 11  is a diagram illustrating an example of the correspondence table  1420  of the time of day and the length of a time period. The correspondence table  1420  of this example contains sets of time-of-day information defined by the start time of day and the end time of day and the length of a time period to be used at the time of day in the section. For example, on the second line, it is stored that the length of a time period is set toT 1  in a section from a start time-of-day t 11  to an end time-of-day t 12 . 
     The arithmetic unit  1421  searches the correspondence table  1420  for time-of-day information in which the current time of day detected by the clock  1419  is included in the section. Then, when the search succeeded, the arithmetic unit  1421  outputs a time period that includes the occurrence time of day of the abnormal event indicated by the abnormal event detection information and that has a length stored in the correspondence table  1420  corresponding to the searched time-of-day information. Meanwhile, when the search failed, the arithmetic unit  1420  outputs a time period that includes the occurrence time of day of the abnormal event indicated by the abnormal event detection information and that has a preset standard length. 
     The time-of-day information to be recorded on the correspondence table  1420  may be the time of day at which accidents occur frequently, for example, and the length of the time period corresponding thereto may be a value longer than the standard. Thereby, it is possible to save the video of a longer time at the time of day when accidents occur frequently, compared with other time of day. The time-of-day information to be recorded on the correspondence table  1420  may be the time of day representing the night, for example, and the length of the time period corresponding thereto may be a value longer than the standard. Thereby, it is possible to save a video of a longer time than the standard, in the case of an abnormal event such as an accident that occurs at night of low visibility. 
     &lt;Example 5 of Time Period Determination Unit  140 &gt; 
       FIG. 12  is a block diagram illustrating another example of the time period determination unit  140 . The time period determination unit  140  of this example includes an illuminance sensor  1422 , a correspondence table  1423  of the illuminance and the length of a time period, and an arithmetic unit  1424 . The illuminance sensor  1422  detects the current illuminance around the vehicle, and outputs the detected result to the arithmetic unit  1424 . The correspondence table  1423  of the illuminance and the length of a time period contains one set or more sets of illuminance information defined by the illuminance and information of the length of a time period in the illuminance. The arithmetic unit  1424  searches the correspondence table  1423  of the illuminance and the length of a time period by using the illuminance detected by the illuminance sensor  1422  as a key, and based on the search result, the arithmetic unit  1424  determines and outputs the time period that includes the occurrence time of day of the abnormal event indicated by the abnormal event detection information and that has a length corresponds to the current illuminance. 
       FIG. 13  is a diagram illustrating an example of the correspondence table  1423  of the illuminance and the length of a time period. The correspondence table  1423  contains sets of illuminance information defined by the lower limit illuminance and the upper limit illuminance, and the length of a time period used with the illuminance of the section. For example, on the second line, it is stored that the length of a time period is T 1  in the section from lower limit illuminance i 11  to upper limit luminance i 12 . 
     The arithmetic unit  1424  searches the correspondence table  1423  for illuminance information in which the illuminance detected by the illuminance sensor  1422  is included in the section. Then, when the search succeeded, the arithmetic unit  1424  outputs the time period that includes the occurrence time of day of the abnormal event indicated by the abnormal event detection information and that has a length stored in the correspondence table  1423  corresponding to the searched time-of-day information. Meanwhile, when the search failed, the arithmetic unit  1424  outputs the time period that includes the occurrence time of day of the abnormal event indicated by the abnormal event detection information and that has a preset standard length. 
     The Illuminance information to be recorded on the correspondence table  1423  may be illuminance with which accidents occur frequently, for example, and the length of the time period corresponding thereto may be a length longer than the standard. Thereby, with the illuminance in which accidents occur frequency (e.g., illuminance in which it is hesitated whether or not to light the headlamp), it is possible to store a video of a longer time than other points of place. Further, the time-of-day information to be recorded on the correspondence table  1420  may be illuminance at night or in a dark tunnel, for example, and the length of the time period corresponding thereto may be a value longer than the standard. Thereby, in the case of an abnormal event such as an accident that occurred at night or in a tunnel of low visibility, it is possible to store a video of a longer time than the standard. 
     &lt;Example 6 of Time Period Determining Section  140 &gt; 
       FIG. 14  is a block diagram illustrating another example of a time period determination unit  140 . The time period determination unit  140  of this example includes a weather sensor  1425 , a correspondence table  1426  of the weather conditions and the length of a time period, and an arithmetic unit  1427 . The weather sensor  1425  detects weather conditions at the point of place where the vehicle travels, and outputs the detection result to the arithmetic unit  1424 . The weather conditions include one or a combination of temperature, humidity, wind speed, weather (sunny, rain, snow, cloudy, etc.), and the like. The weather sensor  1425  may be one that senses the weather conditions by itself, or one that is connected with a server device that provides the weather conditions, and acquires the weather conditions of the point of place where the own vehicle is traveling through a network. The point of place where the own vehicle is traveling can be acquired from a car navigation system mounted on a vehicle, for example. The correspondence table  1426  of the weather conditions and the length of a time period contains one or more sets of weather condition information defined by the weather conditions and information of the length of a time period under such weather conditions. The arithmetic unit  1427  searches the correspondence table  1426  of the weather conditions and the length of a time period by using the weather conditions detected by the weather sensor  1425  as a key, and based on the search result, determines and outputs the time period that includes the occurrence time of day of the abnormal event indicated by the abnormal event detection information and that has a length corresponding to the weather conditions of the current point of place. 
       FIG. 15  is a diagram illustrating an example of a correspondence table  1426  of the weather conditions and the length of a time period. The correspondence table  1426  of this example contains sets of the weather condition information defined by one or a plurality of weather conditions and the length of a time period used under such weather conditions. For example, on the second line, it is stored that at the point of place of a weather condition w 1 , the length of a time period is T 1 . 
     The arithmetic unit  1427  searches the correspondence table  1426  for weather condition information that matches the weather conditions detected by the weather sensor  1425 . Then, when the search succeeded, the arithmetic unit  1427  outputs a time period that includes the occurrence time of day of the abnormal event indicated by the abnormal event detection information, and that has a length stored in the correspondence table  1426  corresponding to the searched weather condition information. Meanwhile, when the search failed, the arithmetic unit  1427  outputs a time period that includes the occurrence time of day of the abnormal event indicated by the abnormal event detection information and that has a preset standard length. 
     The weather condition information to be recorded on the correspondence table  1426  may be rain in which accidents occur frequently, for example, and the length of the time period corresponding thereto may be a value longer than the standard. Thereby, in the case where the vehicle travels in the rain in which accidents frequently occur, a video of a longer time can be stored compared with the case of sunny weather. Also, the weather condition information recorded on the correspondence table  1426  may be a combination of rain and wind of a certain value or higher, for example, and the length of the time period corresponding thereto may be longer than the standard. Thereby, in the case of an abnormal event such as an accident that occurred in strong wind and rain such as typhoon, it is possible to save a video of a longer time than the standard. 
     &lt;Example 7 of Time Period Determination Unit  140 &gt; 
       FIG. 16  is a block diagram illustrating another example of the time period determination unit  140 . The time period determination unit  140  of this example includes a biological sensor  1428 , a correspondence table  1429  of biological information and the length of a time period, and an arithmetic unit  1430 . The biological sensor  1428  detects biological information of the driver (operator) of the vehicle, and outputs the detection result to the arithmetic unit  1430 . The biological information includes one or a combination of body temperature, blood pressure, heart rate, blood glucose level, consumed calories, brain waves, oxygen concentration, expiration, posture, and the like. The biological sensor  1428  may be a wearable sensor for sensing biological information in real time by itself, or may be one that is connected with a server that provides biological information of the driver, and acquires recent biological information of the driver through a network. The correspondence table  1429  of the biological information and the length of a time period contains one or more sets of biological information and information of the length of a time period relating to the biological information. The arithmetic unit  1430  searches the correspondence table  1429  of the biological information and the length of a time period by using the biological information detected by the biological sensor  1428 , and based on the search result, determines and outputs a time period that includes the occurrence time of day of the abnormal event indicated by the abnormal event detection information and that has a length corresponding to the biological information of the driver. 
       FIG. 17  is a diagram illustrating an example of a correspondence table  1429  of biological information and the length of a time period. The correspondence table  1429  of this example contains one or more sets of biological information and the length of a time period used in the biological information. For example, on the second line, it is stored that for biological information B 1 , the length of a time period is T 1 . 
     The arithmetic unit  1430  searches the correspondence table  1429  for biological information that matches the biological information detected by the biological sensor  1428 . Then, when the search succeeded, the arithmetic unit  1430  outputs a time period that includes the occurrence time of day of the abnormal event indicated by the abnormal event detection information and that has a length stored in the correspondence table  1429  corresponding to the searched biological information. Meanwhile, when the search failed, the arithmetic unit  1430  outputs a time period that includes the occurrence time of day of the abnormal event indicated by abnormal event detection information and that has a preset standard length. 
     The biological information recorded on the correspondence table  1429  may be one of or a combination of body temperature, blood pressure, heart rate, blood glucose level, consumed calories, brain waves, oxygen concentration, expiration, posture, and the like that are out of normal values. The length of a time period corresponding thereto may be a value longer than the standard. Thereby, when the driver is operating in a state of poor physical condition, it is possible to save a video of a longer time than usual. 
     &lt;Another Example of Time Period Determination Unit  140 &gt; 
     In the above example, the time period determination unit  140  determines the length of a time period of a video signal to be saved based on the magnitude of acceleration of the vehicle, a change pattern in the acceleration of the vehicle, the traveling location of the vehicle, the time of day when an abnormal event is detected, illuminance around the vehicle, weather conditions, or biological information of the driver of the vehicle. However, it is also possible to determine the length of a time period based on another type of information, that is, a road width, the number of persons existing in front, presence or absence of conversation in the vehicle, or the like. Furthermore, the time period determination unit  140  may determine the length of a time period based on a combination of the aforementioned information and the vehicle speed. 
     Next, the data saving unit  160  will be described in more detail. 
     &lt;Example 1 of Data Saving Unit  160 &gt; 
       FIG. 18  is a diagram illustrating an exemplary format of a file created by the data saving unit  160 . In this example, the data saving unit  160  creates a file having a file name  161 , time period information  162 , and video data  163 . The file name  161  may be any character string as long as it is uniquely identifiable. The time period information  162  is information of a time period determined by the time period determination unit  140 . The video data  163  is a video extracted by the video extraction unit  150 . According to this format, the video data  163  can be uniquely identified by the file name  161 . Further, according to this format, as the time period information  162  is provided independently, it is possible to immediately recognize the time period that the video data  163  is captured by referring to the time period information  162 . However, in addition to providing the time period information  162  independently, it is also possible to add time-of-day information to each video frame of the video data  163 . 
     &lt;Example 2 of Data Saving Unit  160 &gt; 
       FIG. 19  is a diagram illustrating another exemplary format of a file created by the data saving unit  160 . In this example, the data saving unit  160  creates two types of files. One is a file having the file name  161 , the time period information  162 , and size information  165  of video data. Hereinafter, this file is referred to as a sub-file. The other one is a file having a file name  164  and the video data  163 . Hereinafter, this file is referred to as a main file. The file name  161  and the file name  164  are configured such that different branch numbers are added to the same file name. For example, in the case where the same file name is AAA and branch numbers are 1 and 2, the file name  161  is AAA-1 and the file name  164  is AAA-2. The size information  165  of the video data represents the size of the video data  163 . According to this format, the time period information  162  and the size information of the video data, and the video data  163  can be recorded and transmitted as separate files. Further, according to this format, it is possible to mechanically determine the file name  164  of the main file from the file name  161  of the sub-file. On the contrary, it is also possible to mechanically determine the file name  161  of the sub-file from the file name  164  of the main file. 
     Second Exemplary Embodiment 
     Next, a second exemplary embodiment of the present invention will be described. FIG.  20  is a block diagram of a drive recorder according to the present exemplary embodiment. Referring to  FIG. 20 , a drive recorder  200  according to the present embodiment is mounted on a vehicle such as an automobile, and has a function of recording the driving condition of the vehicle. The drive recorder  200  includes a camera  210 , a communication I/F unit (communication interface unit)  220 , an operation input unit  230 , a screen display unit  240 , sensors  250 - 1  to  250 - n , a storage unit  260 , and an arithmetic processing unit  270 . 
     The camera  210  has the same function as that of the camera  110  of  FIG. 1 . The communication I/F unit  220  is configured of a dedicated data communication circuit, and has a function of performing data communication with an external device connected via a wireless communication line, for example. The operation input unit  230  is configured of an operation input device such as operation buttons, and has a function of detecting an operation by an operator and outputting it to the arithmetic processing unit  270 . The screen display unit  240  is configured of a screen display device such as an LCD or PDP, and has a function of displaying, on a screen, various kinds of information such as a monitor screen of the camera  210 , according to an instruction from the arithmetic processing unit  270 . The sensors  250 - 1  to  250 - n  include an acceleration sensor, a vehicle speed sensor, a GPS sensor, a time-of-day sensor (clock), an illuminance sensor, a weather sensor, a biological sensor, and the like. 
     The storage unit  260  is configured of a storage device such as a hard disk or a memory, and has a function of storing processing information, a storage area, and a program  261  necessary for various kinds of processing performed in the arithmetic processing unit  270 . The program  261  is a program for implementing various processing unit by being read into the arithmetic processing unit  270  and executed, and is read in advance from an external device (not illustrated) or a storage medium (not illustrated) via a data input/output function such as the communication I/F unit  220 , and is saved in the storage unit  260 . The main processing information and the storage area, stored in the storage unit  260 , include a video buffer  262  and a video saving area  263 . 
     The video buffer  262  is a storage area for temporarily storing the video captured by the camera  210 . The image saving area  263  is a storage area for recording a video extracted from the video buffer  262  as an erasure prohibited object. 
     The arithmetic processing unit  270  includes a microprocessor such as a CPU and its peripheral circuits, and has a function of reading the program  261  from the storage unit  260  and executing it to implement various types of processing units by allowing the hardware and the program  261  to cooperate with each other. The main processing units implemented by the arithmetic processing unit  270  include a video recording unit  271 , an abnormal event detection unit  272 , a time period determination unit  273 , a video extraction unit  274 , and a data saving unit  275 . 
     The video recording unit  271  has a function of recording a video captured by the camera  210  in the video buffer  262  in association with the time of day. In addition, the video recording unit  271  also has the same function as that of the video recording unit  120  of  FIG. 1 . 
     The abnormal event detection unit  272  has a function of detecting an abnormal event based on the detection results of the sensors  250 - 1  to  250 - n . In addition, the abnormal event detection unit  272  also has the same function as that of the abnormal event detection unit  130  of  FIG. 1 . 
     The time period determination unit  273  has a function of determining a time period that includes the time of day when the abnormal event detection unit  272  detects an abnormal event and that has a length determined based on the driving condition other than the speed of the vehicle. In addition, the time period determination unit  273  also has the same function as that of the time period determination unit  140  of  FIG. 1 . 
     The video extraction unit  274  has a function of extracting a video of a time period determined by the time period determination unit  273 , from the video buffer  262 . In addition, the video extraction unit  274  also has the same function as that of the video extraction unit  150  of  FIG. 1 . 
     The data saving unit  275  has a function of recording the video extracted by the video extraction unit  274  as an erasure prohibited object, in the video saving area  263 . Further, the data saving unit  273  has a function of transmitting the video extracted by the video extraction unit  274 , to an external device through the communication I/F unit  220 . The data saving unit  275  can be implemented by an SD cart having a wireless communication function such as Wi-Fi or Bluetooth (registered trademark), for example, together with the communication I/F unit  220 , the video buffer  262 , and the video saving area  263 . 
     Next, operation of the drive recorder  200  will be described with reference to  FIG. 2 . 
     When the ignition switch of the vehicle is turned on, the drive recorder  200  starts operation illustrated in  FIG. 2 . 
     First, the camera  210  of the drive recorder  200  starts operation of capturing a video of the front side in the traveling direction of the vehicle at a predetermined frame rate (step S 101 ). Then, the video recording unit  271  starts operation of recording the video captured by the camera  210  in the video buffer  262  in association with capturing time-of-day information (step S 102 ). Capturing of the video by the camera  210  and recording of the video by the video recording unit  271  are continued until the ignition switch of the vehicle is turned off. 
     On the other hand, the operation described below is performed in parallel with the operation described above. First, the abnormal event detection unit  272  detects presence or absence of an abnormal event (step S 103 ). When the abnormal event detection unit  272  detects an abnormal event, the abnormal event detection unit  272  notifies the time period determination unit  273  of the abnormal event detection information including the detection time of day. When the time period determination unit  273  is notified of the abnormal event detection information, the time period determination unit  273  determines a time period that includes the time of day when the abnormal event is detected and that has a predetermined time length, based on the traveling condition other than the speed of the vehicle (step S 104 ). Then, the time period determination unit  273  notifies the video extraction unit  274  of the determined time period. The video extraction unit  274  extracts a video of the notified time period from the video buffer  262  (step S 105 ). Then, the video extraction unit  274  notifies the data saving unit  275  of the extracted video. The data saving unit  275  records, in the video saving area  263 , a file including the video extracted by the video extraction unit  274  and information of the time period as an erasure prohibited object (S 106 ), and transmits it to an external device through the communication I/F unit  220  (S 107 ). 
     As described above, according to the present embodiment, it is possible to save necessary video information without excess and deficiency. This is because the time period of the video to be saved is determined based on the traveling condition other than the speed of the vehicle. 
     Third Exemplary Embodiment 
     Next, a third exemplary embodiment of the present invention will be described.  FIG. 21  is a block diagram of a driving condition recording device  300  according to the present exemplary embodiment. Referring to  FIG. 21 , the driving condition recording device  300  includes a drive recorder  400  and an information terminal device  500 . 
     The drive recorder  400  is mounted on a vehicle such as an automobile, and has a function of recording the driving condition of the vehicle. The drive recorder  400  records, on a recording medium, a video captured by a camera mounted on the vehicle in association with the time of day, and when detecting an abnormal event, extracts the video of a predetermined time period including the time of day when the abnormal event is detected from the recording medium, and transmits a file including the extracted video and information of the predetermined time period to the information terminal device  500  through wireless communication. As the drive recorder  400 , the drive recorder  100  of  FIG. 1  or the drive recorder  200  of  FIG. 20  may be used, for example. 
     The information terminal device  500  acquires driving condition information of the vehicle, creates and records a file including the video received from the drive recorder  400  and the acquired driving condition information, or transmits it to an external device. More specifically, the information terminal device  500  acquires driving condition information of the vehicle and records it on a recording medium in association with the time of day. When receiving a file from the drive recorder  400 , the information terminal device  500  extracts driving condition information of the time period that is the same as the information of the time period included in the received file, creates a file including the extracted driving condition information, the video included in the received file, and information of the predetermined time period, and records it as an erasure prohibited object or transmits it to an external device. The information terminal device  500  may be configured of a smart phone terminal, a personal computer, or the like, held by the driver who operates the vehicle. 
       FIG. 22  is a block diagram illustrating an example of the information terminal device  500 . Referring to  FIG. 22 , the information terminal device  500  of the present example includes communication interface units (communication I/F units)  510  and  520 , an operation input unit  530 , a screen display unit  540 , sensors  550 - 1  to  550 - n , a storage unit  560 , and an arithmetic processing unit  570 . 
     The communication I/F unit  510  is configured of a dedicated data communication circuit, and has a function of performing data communication with an external device such as a drive recorder  400  by wireless communication such as Wi-Fi or Bluetooth (registered trademark). The communication I/F unit  520  is configured of a dedicated data communication circuit, and has a function of performing data communication with an external device such as a server device, not illustrated, connected through a mobile communication network such as 3G or LTE. The operation input unit  530  is configured of an operation input device such as a keyboard, and has a function detecting an operation by an operator and outputting it to the arithmetic processing unit  570 . The screen display unit  540  is configured of a screen display device such as an LCD or a PDP, and has a function of displaying various types of information such as a video on the screen, according to an instruction from the arithmetic processing unit  570 . The sensors  550 - 1  to  550 - n  are sensors for acquiring driving condition information of the vehicle. The sensors  550 - 1  to  550 - n  include an acceleration sensor, a vehicle speed sensor, a GPS sensor, a time-of-day sensor (clock), an illuminance sensor, a weather sensor, a biological sensor, and the like, for example. 
     The storage unit  560  is configured of a storage device such as a hard disk, a memory, or the like, and has a function of storing processing information, a storage area, and a program  561  that are necessary for various kinds of processing performed in the arithmetic processing unit  570 . The program  561  is a program for implementing various processing units by being read into the arithmetic processing unit  570  and executed, and is read in advance from an external device (not illustrated) or a storage medium (not illustrated) via a data input/output function such as the communication I/F units  510  and  520 , and is saved in the storage unit  560 . The main processing information and the storage area stored in the storage unit  560  include the driving condition information buffer  262 , a received file buffer  563 , and a file saving area  564 . 
     The driving condition information buffer  262  is a storage area in which driving condition information acquired with use of the sensors  550 - 1  to  550 - n  are temporarily recorded. The received file buffer  563  is a storage area for temporarily storing a file received from the drive recorder  400 . The file saving area  564  is a storage area for storing a file including driving condition information extracted from the driving condition information buffer  562 , the video extracted from the received file buffer  563 , and information of the time period, as an erasure prohibited object. 
     The arithmetic processing unit  570  includes a microprocessor such as a CPU and its peripheral circuits, and has a function of reading the program  561  from the storage unit  560  and executing it to thereby allow the hardware and the program  561  to cooperate with each other to implement various processing units. The main processing units implemented by the arithmetic processing unit  570  include a driving condition information recording unit  571 , a file receiving unit  572 , a driving condition information extraction unit  573 , and a data saving unit  574 . 
     The driving condition information recording unit  571  has a function of acquiring driving condition information with use of the sensors  550 - 1  to  550 - n , and a function of recording the acquired driving condition information in the driving condition information buffer  562  in association with the time of day. For example, the driving condition information recording unit  571  measures acceleration of the vehicle by using an acceleration sensor, and records measured acceleration in the driving condition information buffer  562  in association with the time of day. Further, the driving condition information recording unit  571  measures the speed of the vehicle by using a vehicle speed sensor, and records the measured vehicle speed in the driving condition information buffer  562  in association with the time of day, for example. Further, the driving condition information recording unit  571  acquires the current position (latitude and longitude) of the vehicle by using a GPS sensor, and records the acquired position in the driving condition information buffer  562  in association with the time of day, for example. Further, the driving condition information recording unit  571  acquires illuminance inside and outside the vehicle by using an illuminance sensor, and records the acquired illuminance in the driving condition information buffer  562  in association with the time of day, for example. Further, the driving condition information recording unit  571  detects weather conditions of the point of place where the vehicle is traveling by using a weather sensor, and records the detection result in the driving condition information buffer  562  in association with the time of day, for example. The weather conditions include one or a combination of temperature, humidity, wind speed, weather (sunny, rain, snow, cloudy, etc.), and the like. The weather sensor may be one that senses weather conditions by itself, or one that acquires weather conditions of the point of place where the own vehicle is travelling by connecting with a server that provides weather conditions, through a network. Further, the driving condition information recording unit  571  acquires biological information of the driver by using a biological sensor, and records the acquired biological information in the driving condition information buffer  562  in association with the time of day, for example. The biological information includes one or a combination of body temperature, blood pressure, heart rate, blood glucose level, consumed calories, brain waves, oxygen concentration, expiration, posture, and the like. 
     The file receiving unit  572  has a function of receiving, via the communication I/F unit  510 , a file including a video transmitted from the drive recorder  400  through Wi-Fi communication or the like and information of a time period, and records it in the received file buffer  563 . Exemplary formats of a file including the video transmitted from the drive recorder  400  and the information of the time period are illustrated in  FIGS. 18 and 19 . 
     The driving condition information extraction unit  573  has a function of reading, from the received file buffer  563 , a file including information of the time period received from the drive recorder  400 , and extracting the driving condition information of the same time period as that of the information of the time period from the driving condition information buffer  562 . 
     The data saving unit  574  has a function of creating a file including the driving condition information extracted by the driving condition information extraction unit  573  and information including the video of the same time period recorded in the received file buffer  563  and the corresponding time period, and recording the created file in the file saving area  564  as an erasure prohibited object. The data saving unit  574  also has a function of transmitting the created file to a server device via the communication I/F unit  520  through a mobile communication network. 
     Next, operation of the driving condition recording device  300  will be described. As the operation of the drive recorder  400  constituting the driving condition recording device  300  is the same as the operation of the drive recorder  100  of  FIG. 1  or the drive recorder  200  of  FIG. 20 , the description thereof is omitted. Hereinafter, operation of the information terminal device  500  constituting the driving condition recording device  300  will be described. 
       FIG. 23  is a flowchart illustrating an exemplary operation of the information terminal device  500 . During startup, the information terminal device  500  performs the operation described below. 
     First, the driving condition information recording unit  571  of the information terminal device  500  uses the sensors  550 - 1  to  550 - n  to acquire driving condition information (S 201 ), and stores the acquired driving condition information in the driving condition information buffer  562  in association with the time of day (S 202 ). Then, the driving condition information recording unit  571  returns to step S 201 , and repeats the same operation as that described above. 
     In parallel with the operation described above, the file receiving unit  572  of the information terminal device  500  determines whether or not a file is received from the drive recorder  400  by the communication I/F unit  510  (S 203 ), and when it is received, the file receiving unit  572  records the received file in the received file buffer  563  (S 204 ). Then, the file receiving unit  572  returns to step S 203 , and repeats the same operation as that described above. 
     In parallel with the above operation, the data saving unit  574  of the information terminal device  500  determines whether or not an unprocessed file exists in the received file buffer  563  (S 205 ), and if any, the data saving unit  574  reads one unprocessed file (S 206 ). Here, in the case where a file including the file name  161 , the time period information  162 , and the video data  163  as illustrated in  FIG. 18  is transmitted from the drive recorder  400 , the data saving unit  574  handles the file as a single file. Further, in the case where a sub-file including the file name  161 , the time period information  162 , and the size information  165  of video data, and a main file including the file name  164  and the video data  163 , as illustrated in  FIG. 19 , are transmitted from the drive recorder  400 , the data saving unit  574  handles that in which the two files are combined as a single file. Next, the data saving unit  574  extracts driving condition information from the driving condition information buffer  562 , by using the driving condition extraction unit  573 , based on the information of the time period included in the readout file (S 207 ). That is, the data saving unit  574  extracts driving condition information of the same time period as the received time period information. Next, the data saving unit  574  creates a file including the information of the time period and the video data included in the file and the extracted driving condition information, and records it in the file saving area as an erasure prohibited object (S 208 ). The data saving unit  574  returns to step S 205 , and repeats the same operation as that described above. 
       FIG. 24  illustrates an exemplary format of a file recorded in the data saving unit  574 . In this example, the data saving unit  574  creates a file including the file name  161 , the time period information  162 , the video data  163 , and the driving condition information  165 . 
     In parallel with the above-described operation, the data saving unit  574  performs the operation described below. First, the data saving unit  574  determines whether or not a non-transmitted file exists in the file saving area  564  (S 209 ), and if any, reads out one non-transmitted file (S 210 ). Next, the data saving unit  574  uses the communication I/F unit  520  to transmit the readout file to the server device (S 211 ). Then, the data saving unit  574  returns to step S 209 , and repeats the same operation as that described above. 
     According to the present exemplary embodiment, it is possible to enrich the types of driving condition information of the vehicle to be acquired without modifying the drive recorder  400 . This is because the information terminal device  500  uniquely acquires driving condition information, and combines the acquired driving condition information and the video and the like received from the drive recorder  400 . 
     Further, it is possible to reduce the driving condition information to be transmitted to the server device to a minimum amount required relating to the video. This is because the information terminal device  500  extracts the driving condition information of the same time period as that of the video of the drive recorder  400 , and combines it with the video. 
     Fourth Exemplary Embodiment 
     Next, a driving condition recording device according to a fourth exemplary embodiment of the present invention will be described. The driving condition recording device according to the present exemplary embodiment is similar to that of the third exemplary embodiment except for points (a) and (b) described below. 
     (a) The drive recorder  400  uses two types of files (main file and sub-file) illustrated in  FIG. 19 , and in the transmission at step S 107  of  FIG. 2 , a sub file is transmitted in preference to a main file. For example, in the case where there are one or more sets of a main file and a sub-file of the same file name but having different branch numbers, all of the sub-files are transmitted first, and then the main files are transmitted. As the sub-file does not include video data, the file size thereof is much smaller than that of the main file. Therefore, transmission of the sub-file from the drive recorder  400  to the information terminal device  500  is completed in a shorter period compared with the main file. 
     (b) The data saving unit  574  of the information terminal device  500  executes steps S 301  to S 307  illustrated in  FIG. 25 , instead of steps S 205  to S 208  in the flowchart of  FIG. 23 . 
     Hereinafter, operation of the driving condition recording device according to the present exemplary embodiment will be described focusing on differences from the third exemplary embodiment. 
     When the data saving unit ( 160  or  275 ) of the drive recorder  400  creates a file including the video extracted by the video extraction unit ( 150  or  274 ) and information of the time period, the data saving unit creates two types of files (main file and sub-file) illustrated in  FIG. 19 . Then, in the transmission at step S 107  of  FIG. 2 , the data saving unit ( 160  or  275 ) transmits the sub-file in preference to the main file, to the information terminal device  500 . 
     Referring to  FIG. 25 , the data saving unit  574  of the information terminal device  500  determines whether or not an unprocessed sub-file exists in the received file buffer  563  (S 301 ), and if any, reads out one unprocessed sub-file (S 302 ). Next, the data saving unit  574  uses the driving condition extraction unit  573  to extract driving condition information from the driving condition information buffer  562 , based on the information of the time period included in the unprocessed sub-file (S 303 ). Next, the data saving unit  574  creates a file including the information of the time period included in the sub-file, a blank area for the video size, and the extracted driving condition information, and records it in the file saving area (S 304 ). Then, the data saving unit  574  returns to step S 301 , and repeats the same operation as that described above. The format of the file created at step S 304  is the same as that illustrated in  FIG. 24 , for example. However, the video data  163  part is blank. In addition, the file name  161  may be the same as the file name of the sub-file or one in which the branch number is deleted, for example. 
     When there is no unprocessed sub-file in the received file buffer  563 , the data saving unit  574  determines whether or not an unprocessed main file exists (S 305 ), and if any, reads out one unprocessed main file (S 306 ). Next, the data saving unit  574  overwrites the video data included in the readout main file on the blank area of the corresponding file saved in the file saving area (S 307 ). Here, the corresponding file is a file having a file name in which only the branch number is different from the file name of the main file. 
     As described above, according to the present exemplary embodiment, even if a communication delay occurs between the drive recorder  400  and the information terminal device  500 , it is possible to prevent necessary driving condition information from being lost from the information terminal device  500 . The reason for this is as described below. 
     In the driving condition information buffer  562  of the information terminal device  500 , driving condition information is written sequentially from the head of the buffer, and when information is written up to the end of the buffer, writing is performed again from the head of the buffer. Therefore, driving condition information is lost from the buffer  562  when a certain time has passed. Thus, it is necessary to complete extraction of necessary driving condition information from the buffer before it is lost. However, driving condition information of which time period should be extracted is unknown until information of the time period is received from the drive recorder  400 . Therefore, if time period information is received with a delay, there is a possibility that driving condition information of the time period has already been lost from the buffer. In particular, as illustrated in  FIG. 18 , in the configuration of transmitting time period information in the same file with video data, it takes a long communication time because the volume of the video data is large. Therefore, receiving of the time period information delays significantly. In contrast, by previously transmitting time period information by means of a small-sized sub-file from the drive recorder  400  to the information terminal device  500  as illustrated in  FIG. 19 , it is possible to quickly transmit time period information from the drive recorder  400  to the information terminal device  500 . As a result, it is possible to prevent the time period information from being received with a delay, which enables extraction processing to be completed before necessary driving condition information is lost from the buffer. 
     While the present invention has been described with reference to the exemplary embodiments described above, the present invention is not limited to the above-described embodiments. Various additions and changes can be made within the scope of the present invention. For example, in the drive recorder of the exemplary embodiments described above, information of vehicle speed and acceleration of the vehicle and the position information of the vehicle, acquired on the drive recorder side, may be added as additional information of the video data. The present invention is based upon and claims the benefit of priority from Japanese patent application No. 2016-172465, filed on Sep. 5, 2016, the disclosure of which is incorporated herein in its entirety by reference. 
     INDUSTRIAL APPLICABILITY 
     The present invention is applicable to a field of recording driving condition of a vehicle for analysis of causes of an accident of a vehicle such as an automobile, monitoring of driving condition, and safe driving guidance. 
     The whole or part of the exemplary embodiments disclosed above can be described as, but not limited to, the following supplementary notes. 
     [Supplementary Note  1 ] 
     A drive recorder comprising: 
     a video recording unit that records a video captured by a camera mounted on a vehicle, in association with a time of day; 
     an abnormal event detection unit that detects an abnormal event; 
     a time period determination unit that determines a time period, the time period including a time of day when the abnormal event is detected and having a length determined based on a traveling condition other than speed of the vehicle; 
     a video extraction unit that extracts a video of the time period determined, from the video recording unit; and 
     a data saving unit that records or transmits to an external device a file including the video extracted, as an erasure prohibited object. 
     [Supplementary Note  2 ] 
     The drive recorder according to supplementary note  1 , wherein 
     the time period determination unit determines the length of the time period based on magnitude of acceleration of the vehicle. 
     [Supplementary Note  3 ] 
     The drive recorder according to supplementary note  1 , wherein 
     the time period determination unit determines the length of the time period based on a change pattern of acceleration of the vehicle. 
     [Supplementary Note  4 ] 
     The drive recorder according to supplementary note  1 , wherein 
     the time period determination unit determines the length of the time period based on a change pattern of acceleration of the vehicle around the time of day when the abnormal event is detected. 
     [Supplementary Note  5 ] 
     The drive recorder according to supplementary note  1 , wherein 
     the time period determination unit determines the length of the time period based on a change pattern of acceleration of the vehicle from when an ignition switch of the vehicle is turned on last time until the abnormal event is detected. 
     [Supplementary Note  6 ] 
     The drive recorder according to supplementary note  1 , wherein 
     the time period determination unit determines the length of the time period based on a place where the vehicle travels at the time of day when the abnormal event is detected. 
     [Supplementary Note  7 ] 
     The drive recorder according to supplementary note  1 , wherein 
     the time period determination unit determines the length of the time period based on the time of day when the abnormal event is detected. 
     [Supplementary Note  8 ] 
     The drive recorder according to supplementary note  1 , wherein 
     the time period determination unit determines the length of the time period based on illuminance around the vehicle at the time of day when the abnormal event is detected. 
     [Supplementary Note  9 ] 
     The drive recorder according to supplementary note  1 , wherein 
     the time period determination unit determines the length of the time period based on a weather condition of the time of day when the abnormal event is detected. 
     [Supplementary Note  10 ] 
     The drive recorder according to supplementary note  1 , wherein 
     the time period determination unit determines the length of the time period based on biological information of a driver of the vehicle. 
     [Supplementary Note  11 ] 
     The drive recorder according to any of supplementary notes  1  to  10 , wherein 
     the abnormal event detection unit detects the abnormal event based on acceleration of the vehicle. 
     [Supplementary Note  12 ] 
     A processing method executed by a drive recorder, the method comprising: 
     recording a video captured by a camera mounted on a vehicle, in association with a time of day; 
     detecting an abnormal event; 
     determining a time period, the time period including a time of day when the abnormal event is detected and having a length determined based on a traveling condition other than speed of the vehicle; 
     extracting a video of the time period determined, from the video recording unit; and 
     recording or transmitting to an external device a file including the video extracted, as an erasure prohibited object. 
     [Supplementary Note  13 ] 
     The processing method according to supplementary note  12 , wherein 
     the determining the time period includes determining the length of the time period based on magnitude of acceleration of the vehicle. 
     [Supplementary Note  14 ] 
     The processing method according to supplementary note  12 , wherein 
     the determining the time period includes determining the length of the time period based on a change pattern of acceleration of the vehicle. 
     [Supplementary Note  15 ] 
     The processing method according to supplementary note  12 , wherein 
     the determining the time period includes determines the length of the time period based on a change pattern of acceleration of the vehicle around the time of day when the abnormal event is detected. 
     [Supplementary Note  16 ] 
     The processing method according to supplementary note  12 , wherein 
     the determining the time period includes determining the length of the time period based on a change pattern of acceleration of the vehicle from when an ignition switch of the vehicle is turned on last time until the abnormal event is detected. 
     [Supplementary Note  17 ] 
     The processing method according to supplementary note  12 , wherein 
     the determining the time period includes determining the length of the time period based on a place where the vehicle travels at the time of day when the abnormal event is detected. 
     [Supplementary Note  18 ] 
     The processing method according to supplementary note  12 , wherein 
     the determining the time period includes determining the length of the time period based on the time of day when the abnormal event is detected. 
     [Supplementary Note  19 ] 
     The processing method according to supplementary note  12 , wherein 
     the determining the time period includes determining the length of the time period based on illuminance around the vehicle at the time of day when the abnormal event is detected. 
     [Supplementary Note  20 ] 
     The processing method according to supplementary note  12 , wherein 
     the determining the time period includes determining the length of the time period based on a weather condition of the time of day when the abnormal event is detected. 
     [Supplementary Note  21 ] 
     The processing method according to supplementary note  12 , wherein 
     the determining the time period includes determining the length of the time period based on biological information of a driver of the vehicle. 
     [Supplementary Note  22 ] 
     The processing method according to supplementary note  12 , wherein 
     the detecting the abnormal event includes detecting the abnormal event based on acceleration of the vehicle. 
     [Supplementary Note  23 ] 
     A program for causing a computer to function as: 
     a video recording unit that records a video captured by a camera mounted on a vehicle, in association with a time of day; 
     an abnormal event detection unit that detects an abnormal event; 
     a time period determination unit that determines a time period, the time period including a time of day when the abnormal event is detected and having a length determined based on a traveling condition other than speed of the vehicle; 
     a video extraction unit that extracts a video of the time period determined, from the video recording unit; and 
     a data saving unit that records or transmits to an external device a file including the video extracted, as an erasure prohibited object. 
     REFERENCE SIGNS LIST 
     
         
           100  drive recorder 
           110  camera 
           120  video recording unit 
           130  abnormal event detection unit 
           140  time period determination unit 
           150  video extraction unit 
           160  data saving unit 
           131  acceleration sensor 
           132  comparator 
           161  file name 
           162  time period information 
           163  video data 
           164  file name 
           165  size information of video data 
           166  driving condition information 
           200  drive recorder 
           210  camera 
           220  communication I/F unit 
           230  operation input unit 
           240  screen display unit 
           250 - 1 ˜ 250 - n  sensor 
           260  storage unit 
           261  program 
           262  video buffer 
           263  video saving area 
           270  arithmetic processing unit 
           271  video recording unit 
           272  abnormal event detection unit 
           273  time period determination unit 
           274  video extraction unit 
           275  data saving unit 
           300  driving condition recording device 
           400  drive recorder 
           500  information terminal device 
           510  communication I/F unit 
           520  communication I/F unit 
           530  operation input unit 
           540  screen display unit 
           550 - 1 ˜ 250 - n  sensor 
           560  storage unit 
           561  program 
           562  driving condition information buffer 
           563  received file buffer 
           564  file saving area 
           570  arithmetic processing unit 
           571  driving condition information recording unit 
           572  file receiving unit 
           573  driving condition information extraction unit 
           574  data saving unit 
           1411  acceleration sensor 
           1412  maximum value detector 
           1413  comparator 
           1414  acceleration sensor 
           1415  pattern determination unit 
           1416  GPS sensor 
           1417  correspondence table of place and length of a time period 
           1418  arithmetic unit 
           1419  clock 
           1420  correspondence table of time and length of a time period 
           1421  arithmetic unit 
           1422  illuminance sensor 
           1423  correspondence table of illuminance and length of a time period 
           1424  arithmetic unit 
           1425  weather sensor 
           1426  correspondence table of weather conditions and length of a time period 
           1427  arithmetic unit 
           1428  biological sensor 
           1429  correspondence table of biological information and length of a time period 
           1430  arithmetic unit