Patent Publication Number: US-2011072479-A1

Title: System and method for reporting a position of a video device and network video transmitter thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefits of U.S. provisional application Ser. No. 61/245,016, filed on Sep. 23, 2009 and Taiwan patent application serial no. 99124320, filed on Jul. 23, 2010. The entirety of each of the above-mentioned patent applications is hereby incorporated by reference herein and made a part of specification. 
    
    
     BACKGROUND 
     1. Field of the Disclosure 
     The disclosure relates to a system and a method for reporting the position of a video device. More particularly, the disclosure relates to a system and a method for reporting the position of a mobile video device, as well as a network video transmitter using such method. 
     2. Description of Related Art 
     Along with the development of wireless communication technologies, various mobile devices can be easily connected to the Internet. A mobile Internet protocol (IP) camera is connected to the Internet through a wireless communication technique (for example, WiMAX, 3G or long term evolution (LTE), etc.), so as to transmit video streams captured on the move to a client or a back-end server. For example, the mobile IP cameras can be used for military reconnaissance, rescue search, police patrols, traffic status notification, and pollution investigation, etc. 
     Conventionally, a camera of a video surveillance system is disposed at a fixed position, so that a user can clearly know the position where the video frames are captured. However, since the mobile IP camera captures video frames in a mobile approach, a client user has to identify the position of a captured video frame through specific buildings or other landmarks on the video frame. Therefore, regarding such video frames, it is inconvenient to identify the position of each video frame to be captured. 
     SUMMARY 
     The disclosure is directed to a system and a method for reporting the position of a video device, which can report geographic coordinate information corresponding to the position of a network video transmitter. 
     The disclosure is directed to a network video transmitter, which can report geographic coordinate information of the current position where video frames are taken. 
     An exemplary embodiment of the disclosure provides a system for reporting the position of a video device. The system includes a network video transmitter and a network video client. The network video transmitter is configured for taking a video frame and transmitting the video frame through a network. The network video transmitter includes a geographic coordinate detecting device for detecting geographic coordinate information corresponding to the network video transmitter. The network video client is configured for receiving the video frame through the network, wherein the network video transmitter transmits the geographic coordinate information corresponding to the network video transmitter to the network video client through the network. 
     An exemplary embodiment of the disclosure provides a method for reporting the position of a video device, which is used for reporting the geographic coordinate information corresponding to a network video transmitter to a network video client. The method for reporting the position of a video device includes detecting the geographic coordinate information corresponding to the network video transmitter, and transmitting the geographic coordinate information corresponding to the network video transmitter to the network video client through a network. 
     An exemplary embodiment of the disclosure provides a network video transmitter including an image sensor, a geographic coordinate detecting device, a communication interface and a position reporting module. The image sensor is configured for taking a video frame. The geographic coordinate detecting device is configured for detecting geographic coordinate information. The position reporting module is coupled to the image sensor, the geographic coordinate detecting device and the communication interface, and is configured for transmitting the geographic coordinate information through the communication interface by using a web service discovery procedure. 
     An exemplary embodiment of the disclosure provides a network video transmitter including an image sensor, a geographic coordinate detecting device, a communication interface and a position reporting module. The image sensor is configured for taking a video frame. The geographic coordinate detecting device is configured for detecting geographic coordinate information. The position reporting module is coupled to the image sensor, the geographic coordinate detecting device and the communication interface, and is configured for transmitting the geographic coordinate information through the communication interface by using a Real-time Transport Protocol (RTP) streaming service. 
     An exemplary embodiment of the disclosure provides a method for reporting the position of a video device, which is used for reporting geographic coordinate information corresponding to a network video transmitter to a network video client. The method for reporting the position of a video device includes detecting the geographic coordinate information corresponding to the network video transmitter, defining a geographic coordinate attribute in a location scope of a hello message of a web service discovery procedure, and transmitting the geographic coordinate information to the network video client through the geographic coordinate attribute. 
     An exemplary embodiment of the disclosure provides a method for reporting the position of a video device, which is used for reporting geographic coordinate information corresponding to a network video transmitter to a network video client. The method for reporting the position of a video device includes detecting the geographic coordinate information corresponding to the network video transmitter, and transmitting the geographic coordinate information to the network video client through a Real-time Transport Protocol (RTP) streaming service. 
     According to the above descriptions, the geographic coordinate information of the network video transmitter can be reported to the network video client, so as to effectively identify the position where a video frame is captured. 
     In order to make the aforementioned and other features and advantages of the disclosure comprehensible, several exemplary embodiments accompanied with figures are described in detail below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanied drawings are included to provide a further understanding of the disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate the embodiments of the disclosure and serve to explain the principles of the disclosure in together with the description. 
         FIG. 1  is a schematic block diagram illustrating a system for reporting the position of a video device according to the first exemplary embodiment of the disclosure. 
         FIG. 2  is a schematic block diagram illustrating a system for reporting the position of a video device according to another exemplary embodiment of the disclosure. 
         FIG. 3A  is a schematic block diagram illustrating a network video transmitter according to the first exemplary embodiment of the disclosure. 
         FIG. 3B  is a schematic block diagram illustrating a network video transmitter according to another exemplary embodiment of the disclosure. 
         FIG. 4  is a schematic diagram illustrating an example of reporting geographic coordinate information through a hello message according to the first exemplary embodiment of the disclosure. 
         FIG. 5  is a flowchart illustrating a method for reporting the position of a video device according to the first exemplary embodiment of the disclosure. 
         FIG. 6  is a schematic diagram of an XML schema used for recording the geographic coordinate information in a location information stream according to the second exemplary embodiment of the disclosure. 
         FIG. 7  is a schematic diagram illustrating an example of reporting geographic coordinate information through a Real-time Transport Protocol (RTP) metadata stream according to the second exemplary embodiment of the disclosure. 
         FIG. 8  is a flowchart illustrating a method for reporting the position of a video device according to the second exemplary embodiment of the disclosure. 
         FIG. 9  is a schematic diagram illustrating an example of an RTP packet according to the third exemplary embodiment of the disclosure. 
         FIGS. 10A and 10B  are schematic diagrams illustrating a 32-bit representing method according to the third exemplary embodiment of the disclosure. 
         FIG. 11  is a flowchart illustrating a method for reporting the position of a video device according to the third exemplary embodiment of the disclosure. 
         FIG. 12  is a schematic diagram illustrating an RTP packet according to another exemplary embodiment of the disclosure. 
     
    
    
     DETAILED DESCRIPTION OF DISCLOSED EMBODIMENTS 
     In the disclosure, geographic coordinate information of a network video transmitter can be transmitted to a network video client (for example, a back-end processing server) through a network during a communication process between the network video transmitter and the network video client, so as to identify the position where a video frame is captured by the network video transmitter. A plurality of exemplary embodiments is provided below to describe the disclosure in detail. 
     The First Exemplary Embodiment 
       FIG. 1  is a schematic block diagram illustrating a system for reporting the position of a video device according to the first exemplary embodiment of the disclosure. 
     Referring to  FIG. 1 , the system for reporting the position of a video device (hereafter referred to as the system  100 ) includes an Network Video Transmitter (NVT)  102  and an Network Video Client (NVC)  104 . 
     The NVT  102  is configured for capturing a video frame and then transmitting the video frame to the NVC  104 . For example, the NVT  102  is a mobile Internet Protocol (IP) camera, a video encoding device or other video/audio capturing devices. The NVC  104  is configured for receiving the video frame from the NVT  102 . Particularly, the NVT  102  reports its own geographic coordinate information to the NVC  104  according to a method for reporting the position of a video device disclosed in the exemplary embodiment of the disclosure. 
     In the present exemplary embodiment, the NVT  102  and the NVC  104  are complied with an Open Network Video Interface Forum (ONVIF) specification. In the ONVIF specification, the NVT  102  and the NVC  104  are mutually communicated through a web service, and transmit video frames (i.e. video streams) according to a Real-time Transport Protocol (RTP). Here, the web service is a machine to machine communication interface in an IP-based network, which can be formed by components such as a Simple Object Access Protocol (SOAP) component, a Web Service Description Language (WSDL) component and a Universal Description Discovery and Integration (UDDI) component based on an eXtensible Markup Language (XML). 
     Moreover, the NVT  102  and the NVC  104  are mutually communicated by exchanging IP packets through an IP-based network  106 . For example, the video frames captured by the NVT  102  are transmitted to the NVC  104  through the IP-based network  106 . 
     In the IP-based network  106 , the NVT  102  and the NVC  104  can be simultaneously located in either a public network or an administrative domain. Otherwise, the NVT  102  and the NVC  104  can be respectively located in a public network and in an administrative domain. 
     It should be noticed that in another exemplary embodiment of the disclosure, the system  100  further includes a network video storage device  108  (shown in  FIG. 2 ). The network video storage device  108  is configured for directly receiving the video frames from the NVT  102  or indirectly receiving the video frames captured by the NVT  102  from the NVC  104 , and storing the received video frames. 
       FIG. 3A  is a schematic block diagram illustrating an NVT according to the first exemplary embodiment of the disclosure. 
     Referring to  FIG. 3A , the NVT  102  includes a media processor  302 , an image sensor  304 , a geographic coordinate detecting device  306 , a communication interface  308  and a position reporting module  310 . 
     The media processor  302  is configured for controlling the whole operation of the NVT  102 . 
     The image sensor  304  is coupled to the media processor  302 , and is configured for capturing video frames. For example, the image sensor  304  is a Charge-Coupled Device (CCD) image sensor or a Complementary Metal-Oxide Semiconductor (CMOS) image sensor. 
     The geographic coordinate detecting device  306  is coupled to the media processor  302 , and is configured for detecting geographic coordinate information. In the present exemplary embodiment, the geographic coordinate detecting device  306  supports the Global Positioning System (GPS), so as to receive position information from a plurality of satellites to calculate the geographic coordinate information corresponding to the NVT  102 . However, it should be noticed that the disclosure is not limited thereto, and in another exemplary embodiment, the geographic coordinate detecting device  306  can also support the Galileo positioning system, the GLObal NAvigation Satellite System (GLONASS) or the Assisted Global Positioning System (AGPS). 
     It should be noticed that in the present exemplary embodiment, the geographic coordinate detecting device  306  is integrated in the NVT  102 , but the disclosure is not limited thereto. For example, in another exemplary embodiment of the disclosure, the geographic coordinate detecting device  306  can also be independently disposed at the external of the NVT  102 , and is coupled to the NVT  102  through a suitable interface. 
     The communication interface  308  is coupled to the media processor  302 , and is configured for transmitting and receiving data through the IP-based network  106 . Here, the communication interface  308  can be an Ethernet interface, or other wireless communication interfaces. For example, the wireless version of the communication interface  308  is complied with a WiMAX specification, a Wi-Fi specification, a WLAN specification or other wireless communication specifications. Particularly, in case that the NVT  102  and the NVC  104  are complied with the ONVIF specification, the communication interface  308  transmits data according to the ONVIF specification. 
     The position reporting module  310  is coupled to the media processor  302 , and is configured for transmitting the geographic coordinate information detected by the geographic coordinate detecting device  306  through the communication interface  308  according to the method for reporting a position of a video device in the exemplary embodiment of the disclosure. 
     In another exemplary embodiment of the disclosure, the NVT  102  further includes an audio input device  312 , a storage device  314  and a power management circuit  316  (shown in  FIG. 3B ). 
     The audio input device  312  is coupled to the media processor  302 , and is configured for sound capturing. The storage device  314  is coupled to the media processor  302 , and is configured for storing data (for example, the video frames captured by the image sensor  304 , the audio data captured by the audio input device  312 , and the geographic coordinate information detected by the geographic coordinate detecting device  306 , etc.). The power management circuit  316  is coupled to the media processor  302 , and is configured for managing the supply of power in the NVT  102 . 
     As described above, the NVT  102  and the NVC  104  are mutually communicated through the web service. Therefore, when the NVT  102  enables the web service, the NVT  102  may enable a web service discovery procedure through the UDDI component to release and register the web service. In the web service discovery procedure, the NVT  102  may transmit a hello message through the IP-based network  106  to start communicating with the NVC  104 . 
       FIG. 4  is a schematic diagram illustrating an example of reporting the geographic coordinate information through the hello message according to the first exemplary embodiment of the disclosure. 
     Referring to  FIG. 4 , the hello message  402  includes a location scope, i.e. “onvif://www.onvif.org/location/”. Particularly, in the present exemplary embodiment, a geographic coordinate attribute is defined for recording the geographic coordinate information in the location scope. For example, a proposed name of the geographic coordinate attribute is “geographic_coordinate”, and the parameters of latitude, longitude and altitude of the geographic coordinate information are recorded in the geographic coordinate attribute in the form of plain text. As shown in the example of  FIG. 4 , “onvif://www.onvif.org/location/geographic_coordinate/33.8,−117.916,12” represents that the latitude of the geographic coordinate information of the NVT  102  is 33.8, the longitude thereof is −117.916, and the altitude thereof is 12. It should be noticed that in the geographic coordinate attribute, the altitude can be expressed in meters or feet. The unit of altitude can be provided by the NVT in an out-of-band approach. For example, a new web service with the name “GetAltituteUnit” is provided by the NVT, and this web service can return whether the unit of altitude employed by the NVT is meters or feet. 
     Accordingly, when the NVT  102  enables its web service, the position reporting module  310  records the geographic coordinate information currently detected by the geographic coordinate detecting device  306  in the location scope of the hello message  402 , and the hello message  402  containing the geographic coordinate information is transmitted through the IP-based network  106 , so that the NVC  104  can identify the location scope of the hello message  402  to obtain the geographic coordinate information corresponding to the NVT  102 . 
     It should be noticed that the hello message  402  is only transmitted during an initialisation phase of the web service. In another exemplary embodiment of the disclosure, a parameter “variable” is further defined in the geographic coordinate attribute to show whether the NVT  102  is a mobile device or not. In detail, during the web service discovery procedure, the NVT  102  adds a description of “onvif://www.onvif.org/location/geographic_coordinate/variable” in the location scope of the hello message  402  to notify the other devices in the IP-based network  106  that the position of the NVT  102  is variable (i.e. the NVT is movable). 
       FIG. 5  is a flowchart illustrating a method for reporting a position of a video device according to the first exemplary embodiment of the disclosure. 
     Referring to  FIG. 5 , in step S 501 , the NVT  102  detects the current geographic coordinate information. For example, the geographic coordinate detecting device  306  calculates the geographic coordinate information corresponding to the NVT  102  according to information received from the satellites. 
     In step S 503 , the position reporting module  310  of the NVT  102  adds the detected geographic coordinate information in the location scope of the hello message  402  according to the defined geographic coordinate attribute. 
     Next, in step S 505 , the position reporting module  310  of the NVT  102  transmits the hello message  402  to the NVC  104  through the IP-based network  106  in the web service discovery procedure. 
     It should be noticed that in the present exemplary embodiment, the geographic coordinate information corresponding to the NVT  102  is transmitted through the hello message in the web service discovery procedure, but the disclosure is not limited thereto. In another exemplary embodiment, the geographic coordinate information corresponding to the NVT  102  can also be transmitted through other communication messages in the web service discovery procedure. 
     The Second Exemplary Embodiment 
     A structure of a system for reporting the position of a video device in the second exemplary embodiment is substantially the same to that of the system for reporting the position of the video device in the first exemplary embodiment, and the differences between them are that in the second exemplary embodiment, the geographic coordinate information is transmitted through a metadata stream of a Real-time Transport Protocol (RTP) streaming service. Only the differences between the second exemplary embodiment and the first exemplary embodiment are described with reference to  FIG. 1  and  FIG. 3  in the following. 
     As described above, the NVT  102  and the NVC  104  transmit the video frames (i.e. the video streams) according to the RTP specifications. In the present exemplary embodiment, the geographic coordinate information corresponding to the NVT  102  is transmitted through the metadata stream within the RTP streaming service. 
     To be specific, the metadata stream is delivered by a series of RTP packet in which the XML-based metadata are carried in the payload of the RTP packets. Particularly, in the present exemplary embodiment, the metadata transmitted by the RTP metadata stream contains a location information stream type declared by a complex type component of XML schema, so as to provide a format required for recording the geographic coordinate information. 
       FIG. 6  is a schematic diagram of the XML schema used for recording the geographic coordinate information according to the second exemplary embodiment of the disclosure. 
     Referring to  FIG. 6 , a name of the location information stream type  602  is “LocationInformationStream”. In the location information stream type  602 , a component named “longitude” is declared to record the longitude of the geographic coordinate information, and the longitude has a range of value from “−180” to “180” (shown by a dot line  610 ). Moreover, in the location information stream type  602 , a component named “latitude” is declared to record the latitude of the geographic coordinate information, and the latitude has a range of value from “−90” to “90” (shown by a dot line  620 ). Moreover, in the location information stream type  602 , a component named “altitude” is declared to record the altitude of the geographic coordinate information (shown by a dot line  630 ). The unit of altitude can be provided by the NVT in an out-of-band approach. For example, a new web service with the name “GetAltituteUnit” is provided by the NVT, and this web service can return whether the unit of altitude employed by the NVT is meters or feet. 
       FIG. 7  is a schematic diagram illustrating an example of the metadata for reporting the geographic coordinate information through the RTP metadata stream according to the second exemplary embodiment of the disclosure. 
     Referring to  FIG. 7 , the geographic coordinate information is added in a metadata stream  702  according to the location information stream type  602  defined in  FIG. 6 , wherein the longitude of the geographic coordinate information corresponding to the NVT  102  is 41.02, and the latitude thereof is 28.58 (shown by a dot line  710 ). Furthermore, in another embodiment of the present disclosure, the version number “ver10” in the XML namespace “http://www.onvif.org/ver10/schema” in  FIG. 7  can be changed to other version numbers. 
     In this way, when the NVT  102  transmits the video frames, the position reporting module  310  records the geographic coordinate information currently detected by the geographic coordinate detecting device  306  in the RTP metadata stream  702 , and the RTP metadata stream  702  containing the geographic coordinate information is transmitted through the IP-based network  106 , so that the NVC  104  can identify the geographic coordinate information recorded in the RTP metadata stream  702 , so as to obtain the positions where the video frames are captured. Furthermore, the relationship between a copy of the geographic coordinate information and a captured video frame is expressed and maintained by RTCP (Real-time Transport Control Protocol) according to both the RTP timestamp in the header of the RTP packet that contains the copy of the geographic coordinate information and the RTP timestamp in the header of the RTP packet that contains the captured video frame. 
       FIG. 8  is a flowchart illustrating a method for reporting the position of a video device according to the second exemplary embodiment of the disclosure. 
     Referring to  FIG. 8 , in step S 801 , the NVT  102  detects the current geographic coordinate information. For example, the geographic coordinate detecting device  306  calculates the geographic coordinate information corresponding to the NVT  102  according to information received from the satellites. 
     In step S 803 , the position reporting module  310  of the NVT  102  adds the detected geographic coordinate information in the RTP metadata stream  702  according to the defined location information stream type. 
     Next, in step S 805 , the position reporting module  310  of the NVT  102  transmits the RTP metadata stream  702  to the NVC  104  through the IP-based network  106  during video frame transmission. 
     The Third Exemplary Embodiment 
     The structure of a system for reporting the position of a video device in the third exemplary embodiment is substantially the same to that of the system for reporting the position of the video device in the first exemplary embodiment, and the differences between them are that in the third exemplary embodiment, the geographic coordinate information is transmitted through an RTP header extension in an RTP packet. Only the differences between the third exemplary embodiment and the first exemplary embodiment are described with reference of  FIG. 1  and  FIG. 3  in the following. 
     As described above, the NVT  102  and the NVC  104  transmit the video frames (i.e. the video streams) according to the RTP specifications. In the present exemplary embodiment, the geographic coordinate information corresponding to the NVT  102  is transmitted through an RTP header extension of a packet transmitted by the RTP streaming service. To be specific, when the RTP is employed to transmit a video frame or audio data, a transmitter adds an RTP header to the video frame (or a fragment of the video frame) or the audio data to form an RTP packet. Then, a receiver can correctly decode and play the received video frame or the audio data according to the RTP header (or the related RTP headers if the video frame is transmitted in multiple fragments). For example, the RTP header includes several fixed fields of bits for recording the information related to the video frame or the audio data. Particularly, in the fixed part of the RTP header, an extension bit is defined to indicate that the RTP header contains a header extension. In the present exemplary embodiment, a binary coded coordinate header extension is defined in the RTP header to transmit the geographic coordinate information corresponding to the NVT  102 . 
       FIG. 9  is a schematic diagram illustrating an example of a RTP packet according to the third exemplary embodiment of the disclosure. 
     Referring to  FIG. 9 , the RTP packet  900  includes a RTP header  902  and a payload  950 . The RTP header  902  is used for recording related information of the RTP packet  900 , and the payload  950  is for storing the user data to be transmitted (For example, the video frame). 
     The RTP header  902  includes a version information field  904 , a padding field  906 , an extension field  908 , a CSRC (Contributing SouRCe) count field  910 , a marker field  912 , a payload type field  914 , a sequence number field  916 , a timestamp field  918  and an SSRC (Synchronization SouRCe) identifier field  920 . 
     The version information field  902  has 2 bits for recording the version of RTP. The padding field  906  has 1 bit for recording whether the end of the packet contains padding bits. The extension field  908  has 1 bit for recording whether the RTP header includes a header extension. The CSRC count field  910  has 4 bits for recording the number of CSRC. The marker field  912  has 1 bit for marking the information to be explained by the user. The payload type field  914  has 7 bits for recording the type of the RTP payload. The sequence number field  916  has 16 bits for recording a serial number of the RTP packet. The timestamp field  918  has 32 bits for recording a sampling time of the RTP packet. The SSRC identifier field  920  has 32 bits for recording the identifier of the synchronization source. 
     Particularly, if an RTP header  902  contains a binary coded coordinate header extension  980 , the extension field  908  of the RTP header  902  is marked by “1”. 
     The binary coded coordinate header extension  980  has an identifier field  922 , an extension header length field  924 , a mobility field (MO)  926 , an encoding method field (BE)  928 , an altitude identification field (A)  930 , an altitude unit field (AU)  932 , a reserved field  934 , a longitude field (X)  936 , a latitude field (Y)  938  and an altitude field (Z)  940 . 
     The identifier field  922  has 16 bits for recording an identification value of the binary coded coordinate header extension  980 . For example, the identification value of the binary coded coordinate header extension  980  is “0xFBEC” in hexadecimal integer representation. 
     The extension header length field  924  has 16 bits for recording the length of the binary coded coordinate header extension  980 . In detail, the extension header length field  924  records the number of 32-bit words belonged to the binary coded coordinate header extension  980  behind the extension header length field  924 . 
     The mobility field  926  has 1 bit for recording whether the NVT  102  is a fixed device or a mobile device. For example, when the mobility field  926  is marked by “0”, it represents that the NVT  102  is a fixed device. When the mobility field  926  is marked by “1”, it represents that the NVT  102  is a mobile device. 
     The encoding method field  928  has 1 bit for recording whether the longitude filed  936 , the latitude field  938  and the altitude field  940  are of a 32-bit representation or a 64-bit representation. For example, when the encoding method field  928  is marked by “0”, it means that the longitude filed  936 , the latitude field  938  and the altitude field  940  are of the 32-bit representation. In contrast, when the encoding method field  928  is marked by “1”, it means that the longitude filed  936 , the latitude field  938  and the altitude field  940  are of the 64-bit representation. 
     In detail, when the encoding method field  928  is marked by “1”, it means that the longitude filed  936 , the latitude field  938  and the altitude field  940  are represented by the format of the 64-bit floating numbers defined in IEEE 764 specification. Moreover, when the encoding method field  928  is marked by “0”, it means that the longitude filed  936 , the latitude field  938  and the altitude field  940  are represented by a 32-bit representation method designed by the exemplary embodiment of the disclosure. 
       FIGS. 10A and 10B  are schematic diagrams illustrating the 32-bit representation method according to the third exemplary embodiment of the disclosure. 
     Referring to  FIG. 10A , according to the 32-bit representation method, a sign field  1002 , an integer field  1004  and a decimal field  1006  are used to represent the longitude and the latitude. 
     The sign field  1002  has 1 bit for recording a plus sign (positive sign) or a minus sign (negative sign) of the longitude (or the latitude). For example, when the sign field  1002  is marked by “0”, it represents the plus sign, and when the sign field  1002  is marked by “1”, it represents the minus sign. The integer field  1004  has 8 bits for recording the integer part of the longitude (or the latitude). The decimal field  1006  has 23 bits for recording the decimal part of the longitude (or the latitude). A method for calculating the value represented by the decimal part is to treat the 23-bit decimal field as an integer, and then the integer is divided by 2 23 . For example, “−23.5” is represented by “1 0001 0111 100 0000 0000 0000 0000 0000” if the 32-bit representation method for longitude and latitude is employed. 
     Referring to  FIG. 10B , the 32-bit representing method uses 2&#39;s complement to represent the altitude. For example, “150” is represented by “0000 0000 0000 0000 0000 0000 1001 0110”. 
     Referring to  FIG. 9  again, the altitude identification field  930  has 1 bit for recording whether the geographic coordinate information contains the altitude information. For example, when the altitude identification field  930  is marked by “0”, it represents that the geographic coordinate information does not contain the altitude information, and when the altitude identification field  930  is marked by “1”, it represents that the geographic coordinate information contains the altitude information. 
     The altitude unit field  932  has 1 bit for recording the unit of the altitude. For example, when the altitude unit field  932  is marked by “0”, it represents that the altitude is expressed by meters, and when the altitude unit field  932  is marked by “1”, it represents that the altitude is expressed by feet. 
     The reserved field  934  has 28 bits. The longitude field  936 , the latitude field  938  and the altitude field  940  are respectively used for recording the longitude, the latitude and the altitude of the geographic coordinate information. 
     According to the above configuration, the extension header length field  924  can be set according to different situations. In the present exemplary embodiment, the extension header length field  924  can be marked by 3, 4, 5 or 7. 
     In detail, if the transmitted geographic coordinate information does not contain the altitude information, and the longitude and the latitude are represented by the 32-bit representation method, the length of the binary coded coordinate header extension  980  is 96 bits. Consequently, the extension header length field  924  is marked by 3. 
     If the transmitted geographic coordinate information contains the altitude information, and the longitude and the latitude are represented by the 32-bit representation method, the length of the binary coded coordinate header extension  980  is 128 bits. Consequently, the extension header length field  924  is marked by 4. 
     If the transmitted geographic coordinate information does not contain the altitude information, and the longitude and the latitude are represented by the 64-bit representation method, the length of the binary coded coordinate header extension  980  is 160 bits. Consequently, the extension header length field  924  is marked by 5. 
     If the transmitted geographic coordinate information contains the altitude information, and the longitude and the latitude are represented by the 64-bit representation method, the length of the binary coded coordinate header extension  980  is 224 bits. Consequently, the extension header length field  924  is marked by 7. 
     According to the above descriptions, in the exemplary embodiment of the disclosure, during the process of transmitting the video frames, the geographic coordinate information of the NVT  102  is transmitted to the NVC  104  through the IP-based network  106  by using the binary coded coordinate header extension  980  of the RTP header  902 . 
       FIG. 11  is a flowchart illustrating a method for reporting the position of a video device according to the third exemplary embodiment of the disclosure. 
     Referring to  FIG. 11 , in step S 1101 , the NVT  102  detects the current geographic coordinate information. For example, the geographic coordinate detecting device  306  calculates the geographic coordinate information corresponding to the NVT  102  according to information received from the satellites. 
     In step S 1103 , the position reporting module  310  of the NVT  102  adds the detected geographic coordinate information in the RTP header according to the defined binary coded coordinate header extension  980 . 
     Next, in step S 1105 , the NVT  102  packetizes the video frame to be transmitted by the RTP header, and transmits the video frame containing the RTP header to the NVC  104  through the IP-based network  106 . 
     It should be noticed that in another exemplary embodiment of the disclosure, in the binary coded coordinate header extension  980 , other header extension can be further defined, so as to transmit the other related information. For example, an RTP header extension for Joint Photographic Experts Group (JPEG) can be further included in the binary coded coordinate header extension  980 . As shown in  FIG. 12 , an RTP header extension for JPEG  960  with the identifier of “0xFFD8” and the length of N is included in the binary coded coordinate header extension  980 . It should be noticed that the value of the extension header length field  924  is equal to the length of the binary coded coordinate header extension  980  plus the length of the RTP header extension for JPEG  960 . 
     In summary, the geographic coordinate information of the mobile NVT can be detected, and the detected geographic coordinate information can be transmitted to the NVC or a video storage device, so as to effectively identify the positions of the video frames captured by the mobile NVT. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the disclosure without departing from the scope or spirit of the disclosure. In view of the foregoing, it is intended that the disclosure cover modifications and variations of this disclosure provided they fall within the scope of the following claims and their equivalents.