Patent Publication Number: US-2011072113-A1

Title: Local server and content transmission method

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2009-219805 filed on Sep. 24, 2009; the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a local server connected to a local reproduction device via a local network and connected to a public server via a public network, and relates to a content transmission method. 
     2. Description of the Related Art 
     In recent years, technologies aimed to promote utilization of content data such as video and audio data in DLNA (Digital Living Network Alliance) have been under development. For example, studies have been in progress on technologies promoting utilization of content data by transmitting the content data from a local server, so-called DMS (Digital Media Server) to a local reproduction device, so-called DMP (Digital Media Player). 
     Here, the content transmitted from the local server to the local reproduction device is managed by use of a content list called CDS (Content Directory Service). In the CDS, content is managed in tiers. Users view and listen to desired content using CDS (content list) displayed by the local reproduction device. 
     SUMMARY OF THE INVENTION 
     Content data is also stored in a public server (for example, NAS (Network Attached Storage)) connected to a public network such as the Internet. Users have a need to view and listen to the content downloaded from the public server connected to the public network. 
     However, in the public network, information including content data is written in a language such as HTML, XML, or JSON, for example. Unfortunately, it is generally assumed that the local reproduction device does not have a function to display the information written in any of these languages. 
     In such a case, the local reproduction device cannot acquire content data from the public server connected to the public network. In short, users&#39; need is not satisfied. 
     Thus, the present invention is made in order to solve the problem described above, and it is an object of the present invention to provide a local server and a content transmission method that enables acquisition of content data from a public server connected to a public network. 
     In an aspect of the present invention, a local server (local server  400 ) connected to a local reproduction device (local reproduction device  300 ) via a local network (local network  100 ) and to a public server (public server  500 ) via a public network (public network  200 ), the local server comprising: a local communication unit (local communication unit  410 ) configured to communicate with the local reproduction device via the local network; a public communication unit (public communication unit  420 ) configured to communicate with the public server via the public network; and a converter (list generator  440 ) configured to convert a language format compatible with the public server to another language format compatible with the local reproduction device. The local communication unit receives a list request from the local reproduction device, the list request requesting a list of content data stored in the public server. The public communication unit receives the list of content data stored in the public server from the public server in response to the list request. The converter converts the list of content data stored in the public server to a list of content data written in a language format compatible with the local reproduction device. The local communication unit transmits the resultant list of content data converted by the converter to the local reproduction device. 
     In aforementioned aspect, the local communication unit receives a content data request from the local reproduction device, the content data request requesting content data selected from the resultant list of content data converted by the converter. The public communication unit receives content data from the public server in response to the content data request, the content data corresponding to the content data request. The local communication unit transmits the content data received from the public server to the local reproduction device. 
     In an aspect of the present invention, a content transmission method for a local server (local server  400 ) to transmit content data stored in a public server (public server  500 ) to a local reproduction device (local reproduction device  300 ) connected to the local server via a local network (local network  100 ), the public server being connected to the local server via a public network (public network  200 ), the content transmission method comprising the steps of: transmitting (step S 101 ) a list request to the local server by the local reproduction device, the list request requesting a list of content data stored in the public server; receiving (steps S 105 , S 109 ) a list of content data from the public server by the local server in response to the list request, the content data being stored in the public server; converting (steps S 106 , S 110 ) the list of content data stored in the public server to a list of content data written in a language format compatible with the local reproduction device by the local server; and transmitting (step S 111 ) the resultant list of content data converted in the step of converting to the local reproduction device by the local server. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram showing a content transmission system according to a first embodiment. 
         FIG. 2  is a diagram showing a local reproduction device according to the first embodiment. 
         FIG. 3  is a diagram showing a local server according to the first embodiment. 
         FIG. 4  is a diagram showing an example of a configuration of a content list according to the first embodiment. 
         FIG. 5  is a diagram showing a generation process of the content list according to the first embodiment (# 1 ). 
         FIG. 6  is a diagram showing the generation process of the content list according to the first embodiment (# 2 ). 
         FIG. 7  is a diagram showing the generation process of the content list according to the first embodiment (# 3 ).  FIG. 8  is a diagram showing the generation process of the content list according to the first embodiment (# 4 ). 
         FIG. 9  is a diagram showing the generation process of the content list according to the first embodiment (# 5 ). 
         FIG. 10  is a diagram showing a public server according to the first embodiment. 
         FIG. 11  is a sequence diagram showing operations of the content transmission system according to the first embodiment (generation and transmission of the content list). 
         FIG. 12  is a sequence diagram showing operations of the content transmission system according to the first embodiment (transmission of local content data). 
         FIG. 13  is a sequence diagram showing operations of the content transmission system according to the first embodiment (transmission of public content data). 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Next, an embodiment of the present invention is described with reference to the drawings. In the following description of the drawings, same or similar components are labeled with the same of similar reference numerals. However, it should be noted that the drawings are schematic, and ratios between dimensions are different from actual ones. Accordingly, specific dimensions should be determined in consideration of the following description. Of course, the drawings include parts between which dimensional relationship and ratios are different from each other. 
     First Embodiment  
     A first embodiment of the present invention is described below with reference to the drawings. Specifically, the followings are described: (1) Schematic Configuration of Content Transmission System, (2) Configuration of Local Reproduction Device, (3) Configuration of Local Server, (4) Configuration of Public Server, (5) Operation of Content Transmission System, and (6) Operations and Effects. 
     (1) Schematic Configuration of Content Transmission System 
     First, a schematic configuration of a content transmission system according to the first embodiment of the present invention is described with reference to  FIG. 1 .  FIG. 1  is a diagram showing a content transmission system  1  according to the first embodiment. 
     As shown in  FIG. 1 , the content transmission system  1  includes a local network  100 , a public network  200 , a local reproduction device  300 , a local server  400 , and public servers  500 . 
     The content transmission system  1  is a system that transmits the local content data and the public content data to the local reproduction device  300  where the local content data is the content data stored in the local server  400 , and the public content data is the content data stored in the public servers  500 . 
     The local network  100  is a network such as a LAN or a wireless LAN. The local network  100  is provided independently from the public network  200 . 
     The public network  200  is a network such as the Internet, for example. 
     The local reproduction device  300  is a device that is connected to the local network  100  and reproduces e.g., video or audio content data. 
     Specifically, the local reproduction device  300  receives a content data list (hereinafter referred to as a content list) from the local server  400  via the local network  100 . The local reproduction device  300  transmits a content data request requesting content data selected from the received content list, to the local server  400  via the local network  100 . The local reproduction device  300  receives content data transmitted in response to the content data request via the local network  100 . The local reproduction device  300  reproduces the received content data. 
     The local server  400  is a server that is connected to the local reproduction device  300  via the local network  100 , as well as to the public servers  500  via the public network  200 . The local server  400  serves as a content server that provides the local reproduction device  300  with the local content data stored in itself, and also serves as a gateway between the local network  100  and public network  200 . 
     The local server  400  generates a content list that has a language format compatible with the local reproduction device  300 , and transmits the generated content list to the local reproduction device  300 . The local server  400  receives a content data request from the local reproduction device  300  via the local network  100 , the content data request requesting content data selected from the content list. 
     When the received content data request indicates a request to the local content data, the local server  400  transmits the local content data stored therein to the local reproduction device  300  via the local network  100 . 
     When the content data request received from the local reproduction device  300  indicates a request to the public content data, the local server  400  transfers the received content data request to one of the public servers  500  via the public network  200 . In response to the transferred content data request, the local server  400  receives public content data from the public server  500  via the public network  200 . The local server  400  transmits the received public content data to the local reproduction device  300  via the local network  100 . 
     The public server  500  is a content server that is connected to the public network  200 , and provides the public content data stored in itself. The public server  500  receives a content data request from the local reproduction device  300  via the local network  100  and the public network  200 . In response to the received content data request, the public server  500  transmits public content data to the local reproduction device  300  via the public network  200  and the local network  100 . 
     (2) Configuration of Local Reproduction Device 
     Next, a configuration of a local reproduction device according to the first embodiment of the present invention is described with reference to  FIG. 2 .  FIG. 2  is a diagram showing the local reproduction device  300  according to the first embodiment. 
     As shown in  FIG. 2 , the local reproduction device  300  includes a local communication unit  310 , a receiver  320 , a processor  330 , a reproduction unit  340 , and a display  350 . 
     The local communication unit  310  is a hardware interface to connect the local reproduction device  300  to the local network  100 . For the local communication unit  310 , a LAN port or a wireless LAN port may be used. 
     The receiver  320  receives a request to operate the local reproduction device  300  from the outside of the local reproduction device  300 . 
     The receiver  320  receives, for example, a name assignment request to the public server  500  and a content list acquisition request. The receiver  320  inputs the received request to the processor  330 . 
     The name assignment request to the public server  500  is a request to assign a name to each public server  500  to identify the same, as well as to associate the assigned name with the address of the public server  500  for management in the local server  400 . The name assignment request to the public server  500  includes a name assigned by a user of the local reproduction device  300 , and the address of the public server  500  as the target to which the name is assigned. The public server name assigned to the public server  500  only needs to be managed in the local reproduction device  300  and the local server  400 , and does not need to be notified to the public server  500 . 
     The content list acquisition request is a request to acquire a list of content names assigned to respective pieces of content data stored in a predetermined server. The configuration of the content list is described in detail hereinafter. 
     The receiver  320  receives information to select item(s) from the content list displayed on the display  350 . Specifically, the content list is configured with one or multiple items, and the receiver  320  receives information to select at least one item. The receiver  320 , when receiving the information to select item(s), inputs selected item information to the processor  330 , the selected item information indicating the selected items. 
     As the receiver  320 , a touch panel or a keyboard that is an operation device operable by a user of the local reproduction device  300 , or a radio signal receiver from a remote controller, or a button that can be pressed by a user and arranged on the outer surface of the local reproduction device  300  may be used. 
     The processor  330  processes a request and information which are acquired from the receiver  320  or the local communication unit  310 . 
     First, the processor  330  acquires a name assignment request to the public server  500  from the receiver  320 . 
     The processor  330  transmits the acquired name assignment request to the local server  400  via the local communication unit  310 , the acquired name assignment request being made to the public server  500 . 
     Second, the processor  330  acquires a content list acquisition request from the receiver  320 . The processor  330  transmits the acquired content list acquisition request to the local server  400  via the local communication unit  310 . In response to the content list acquisition request, the processor  330  receives a content list from the local server  400  via the local communication unit  310 . The processor  330  inputs the received content list to the display  350 . 
     Third, the processor  330  acquires selected item information from the receiver  320 , the selected item information indicating selected items from the items of the content list displayed on the display  350 . 
     The processor  330  transmits the acquired selected items to the local server  400  via the local communication unit  310 . According to the selected items, the processor  330  receives other items included in the content list or content data from the local server  400  via the local communication unit  310 . The processor  330 , when receiving other items, inputs the received other items to the display  350 . The processor  330 , when receiving content data, inputs the received content data to the reproduction unit  340 . 
     The reproduction unit  340  performs reproduction processing of the content data acquired from the processor  330 . The reproduction unit  340  is configured with, for example, a display that displays a video or data, and/or a speaker that outputs audio. 
     The display  350  displays the content list acquired from the processor  330 . Specifically, the display  350  displays the items of the content list acquired from the processor  330 . 
     Although not shown, the local reproduction device  300  may include a program holder that holds programs for causing a CPU to execute processing of the local communication unit  310 , the receiver  320 , the processor  330 , the reproduction unit  340 , and the display  350 . As a program holder, a recording media such as a RAM, a ROM, a hard disk, a flexible disk, a compact disc, an IC chip, a cassette tape, and the like, may be used, for example. 
     (3) Configuration of Local Server 
     Next, a configuration of a local server according to the first embodiment of the present invention is described with reference to  FIGS. 3 to 9 . 
     (3.1) Schematic Configuration of Local Server 
       FIG. 3  is a diagram showing the local server  400  according to the first embodiment. As shown in  FIG. 3 , the local server  400  includes a local communication unit  410 , a public communication unit  420 , a processor  430 , a list generator  440 , and a storage  450 . 
     The local communication unit  410  is a hardware interface to connect the local server  400  to the local network  100 . As the local communication unit  410 , a LAN port or a wireless LAN port may be used. 
     The public communication unit  420  is an interface to connect the local server  400  to the public network  200 . 
     The processor  430  performs processing in response to a request and selected item information received from the local reproduction device  300  via the local communication unit  410 . 
     The processor  430  acquires e.g., a name assignment request to the public server  500 , a content list acquisition request from the local communication unit  410 . According to the acquired request, the processor  430  assigns a name to the public server  500 , and/or transmits a content list to the local reproduction device  300 . The processor  430  also acquires selected item information from the local communication unit  410 , the selected item information indicating the items selected from the items of the content list. According to the acquired selected item information, the processor  430  transmits other items or content data. 
     Specifically, the processor  430 , when acquiring a name assignment request to the public server  500 , assigns the name included in the name assignment request thereto as a public server name. Specifically, the processor  430  extracts the name included in the name assignment request, as well as the address included in the same. The processor  430  inputs the extracted name as a public server name to the storage  450 , as well as the extracted address to the same. After assigning the name to the public server, the processor  430  transmits a name assignment completion notification to the local reproduction device  300  via the local communication unit  410 , the name assignment completion notification indicating the completion of assignment of the public server name. 
     The processor  430 , when acquiring a content list acquisition request, inputs a content list generation instruction to the list generator  440 , the content list generation instruction instructing generation of a content list. In response to the content list generation instruction, the processor  430  acquires a generation completion notification from the list generator  440 , the generation completion notification indicating the completion of generation of the content list. In response to the acquisition of the generation completion notification from the list generator  440 , the processor  430  acquires the generated content list from the storage  450 . The processor  430  transmits the acquired content list to the local reproduction device  300  via the local communication unit  410 . At this point, the processor  430  transmits only a portion of the items of the content list to the local reproduction device  300  as a response to the content list acquisition request. The processor  430  transmits the items other than those transmitted as a response to the content list acquisition request as a response to the selected item information. The processor  430 , when acquiring the selected item information, transmits other items included in the content list or content data to the local reproduction device  300  with reference to the content lists stored in the storage  450 . 
     The description of the processing of the processor  430  at the time of transmission of the items or content data of the content list is described in detail hereinafter. 
     The list generator  440  generates a content list in response to the content list generation instruction acquired from the processor  430 . The list generator  440  inputs the generated content list to the storage  450 . After inputting the generated content list to the storage  450 , the list generator  440  inputs a generation completion notification to the processor  430 , the generation completion notification indicating the completion of generation of the content list. The configuration of the list generator  440  is described in detail hereinafter. 
     The storage  450  is a storage, such as a HDD, that stores predetermined information. As shown in  FIG. 3 , the storage  450  includes a content data storage  451 , a list storage  452 , and an address table storage  453 . 
     The content data storage  451  stores local content data. The content data storage  451  stores the local content data and a content name assigned to the local content data with the local content data being associated with the content name. 
     The list storage  452  stores a content list generated by the list generator  440 . 
     The address table storage  453  stores an address table which associates a public server name assigned by the processor  430  with the address of the public server  500 . 
     Although not shown, the local server  400  may include a program holder that holds a program for causing a CPU to execute processing of the local communication unit  410 , the public communication unit  420 , the processor  430 , the list generator  440 , and the storage  450 . As a program holder, a recording media such as a RAM, a ROM, a hard disk, a flexible disk, a compact disc, an IC chip, and a cassette tape, and the like, may be used, for example. 
     (3.2) Configuration of Content List and Description of Processing by Processor 
     In the following, a configuration of a content list according to the first embodiment of the present invention, and the description of processing of the processor  430  when acquiring selected item information are described with reference to  FIG. 4 . 
     The content list has a tree structure in which multiple items are in tiers. Each of the multiple items is classified into two types, i.e., directory name and content name according to the location of the item in the tree structure. Each item located in the bottom tiers of the tree structure represents a content name, and any item other than the one representing a content name represents a directory name. 
     The processor  430 , when acquiring the selected item information, determines the information to be transmitted to the local reproduction device  300  according to the location of the item indicated by the selected item information. 
     Specifically, when the acquired selected item information matches a directory name, the processor  430  transmits the items located in the immediate lower tier of the matched directory name to the local reproduction device  300 . 
     When the acquired selected item information matches a content name, the processor  430  transmits the content data corresponding to the matched content name to the local reproduction device  300 . 
     When an item indicating a predetermined directory name is located between the item matched with the selected item information and the items in the top tier of the content list, the processor  430  transmits a content data acquisition request to a predetermined public server  500 . The content data acquisition request is for acquiring the content data corresponding to the content name. In response to the content data acquisition request, the processor  430  receives the content data corresponding to the content name from the predetermined public server  500 , the content name being indicated by the selected item information, and transmits the received content data to the local reproduction device  300 . For example, when a directory name indicating the public server name is located in the immediate upper tier of the item matching the selected item information, the processor  430  transmits a content data acquisition request to the public server  500  corresponding to the public server name. The content data acquisition request includes content names. 
       FIG. 4  is a diagram showing an example of a content list configuration. As shown in  FIG. 4 , the content list  600  has a tree structure with the root directory being the top tier, and each content name being in the bottom tier. 
     Root directory R, menu directories A, B, C, content names A- 1  to A- 3 , B- 1  to B- 3 , public server names PS 1 , PS 2 , content names PS 1 - 1  to PS 1 - 3 , PS 2 - 1  to PS 2 - 3  included in the content list  600  shown in  FIG. 4  are collectively referred to as items of the content list. 
     The root directory R is used to display the menu directories A, B, C. In response to the content list acquisition request, the processor  430  transmits the root directory R to the local reproduction device  300 . 
     The processor  430 , when receiving the selected item information indicating the root directory R from the local reproduction device  300 , transmits the menu directories A, B, C, i.e. the items located in the immediate lower tier of the root directory R to the local reproduction device  300 . 
     The menu directories A, B, C indicate the types of content which can be provided to the local reproduction device  300  by the local server  400 . For example, the menu directory A indicates the provision of the audio content data, the menu directory B indicates the provision of the video content data, and the menu directory C indicates the provision of the content data stored in the public server  500  connected to the public network  200 . 
     The processor  430 , when receiving selected item information indicating the menu directory A from the local reproduction device  300 , transmits the content names A- 1  to A- 3 , i.e., the items located in the immediate lower tier of the menu directory A to the local reproduction device  300 . The processor  430 , when receiving selected item information indicating the menu directory B from the local reproduction device  300 , transmits the content names B- 1  to B- 3 , i.e., the items located in the immediate lower tier of the menu directory B to the local reproduction device  300 . The processor  430 , when receiving selected item information indicating the menu directory C from the local reproduction device  300 , transmits the public server names PS 1 , PS 2 , i.e., the items located in the immediate lower tier of the menu directory C to the local reproduction device  300 . 
     The content names A- 1  to A- 3  indicate the ones assigned to the local content data that is stored in the storage  450  of the local server  400 , and corresponds to the type of content indicated by the menu directory A. For example, when the menu directory A indicates the provision of the audio content data, the content names A- 1  to A- 3  indicate the content names assigned to audio content data of the local content data that is stored in the storage  450  of the local server  400 . 
     The content names B- 1  to B- 3  indicate the ones assigned to the local content data that is stored in the storage  450  of the local server  400 , and corresponds to the type of content indicated by the menu directory B. For example, when the menu directory B indicates the provision of the video content data, the content names B- 1  to B- 3  indicate the content names assigned to video content data of the local content data that is stored in the storage  450  of the local server  400 . 
     The processor  430 , when receiving selected item information indicating the content names A- 1  to A- 3 , B- 1  to B- 3 , transmits the local content data to the local reproduction device  300 , the local content data corresponding to the content name indicated by the selected item information. 
     The public server names PS 1  and PS 2  indicate the ones assigned to servers that provide the content data other than the local content data stored in the storage  450  of the local server  400 . For example, when the menu directory C indicates the provision of the content data stored in the public server  500  connected to the public network  200 , the public server names PS 1  and PS 2  indicate the names of public server  500  assigned in the local server  400  according to a name assignment request to the public server  500 . 
     The processor  430 , when receiving selected item information indicating the public server name PS 1 , transmits the content names PS 1 - 1  to PS 1 - 3  to the local reproduction device  300 , the content names PS 1 - 1  to PS 1 - 3  being the items located in the immediate lower tier of the public server name PS 1 . The processor  430 , when receiving selected item information indicating the public server name PS 2 , transmits the content names PS 2 - 1  to PS 2 - 3  to the local reproduction device  300 , the content names PS 2 - 1  to PS 2 - 3  being the items located in the immediate lower tier of the public server name PS 2 . 
     The content names PS 1 - 1  to PS 1 - 3  are the items located in the immediate lower tier of the public server name PS 1 . The content names PS 1 - 1  to PS 1 - 3  indicate the ones assigned to the public content data stored in the public server  500  corresponding to the public server name PS 1 . 
     The content names PS 2 - 1  to PS 2 - 3  are the items located in the immediate lower tier of the public server name PS 2 . The content names PS 2 - 1  to PS 2 - 3  indicate the ones assigned to the public content data stored in the public server  500  corresponding to the public server name PS 2 . 
     The processor  430 , when receiving selected item information indicating the content names PS 1 - 1  to PS 1 - 3 , PS 2 - 1  to PS 2 - 3 , transmits a content data acquisition request requesting acquisition of the content data corresponding to the content names indicated by the selected item information to the public server  500  corresponding to the public server name located in the immediate upper tier of the content name. The content data acquisition request includes the content names indicated by the selected item information. In response to the content data acquisition request, the processor  430  receives the public content data corresponding to the content names included in the content data acquisition request from the public server  500 . The processor  430  transmits the received public content data to the local reproduction device  300 . 
     (3.3) Configuration of List Generator 
     In the following, a configuration of a list generator provided on the local server according to the first embodiment of the present invention is described with reference to  FIGS. 5 to 9 . 
     The list generator  440  generates a content list by using the information stored in the storage  450  and the information received from the public server  500  in response to a content list generation instruction acquired from the processor  430 . The list generator  440  generates a content list that has the language format compatible with the local reproduction device  300 . 
       FIGS. 5 to 9  are diagrams showing a generation process of a content list by the list generator  440 . 
     First, the list generator  440  generates items in the immediate lower tier of the root directory R. Specifically, as shown in  FIG. 5 , the list generator  440  places the menu directories A, B, C in the immediate lower tier of the root directory R. As described above, the root directory R is used to display the menu directories A, B, C. The menu directories A, B, C also indicate the types of content that can be provided to the local reproduction device  300  by the local server  400 . For example, the menu directory A indicates the provision of the audio content data, the menu directory B indicates the provision of the video content data, and the menu directory C indicates the provision of the content data stored in the public server  500  connected to the public network  200 . 
     Second, the list generator  440  generates items in the immediate lower tier of the menu directory A with reference to the local content stored in the storage  450 . Specifically, as shown in  FIG. 6 , the list generator  440  acquires the content names assigned to the content data corresponding to the type of content indicated by the menu directory A, and places the acquired content names in the immediate lower tier of the menu directory A. For example, when the menu directory A indicates the provision of the audio content data, the list generator  440  acquires the content names A- 1  to A- 3  which are assigned to the audio content data in the local content data stored in the storage  450 . The list generator  440  then places the acquired content names A- 1  to A- 3  in the immediate lower tier of the menu directory A. 
     Third, the list generator  440  generates items in the immediate lower tier of the menu directory B with reference to the local content stored in the storage  450 . Specifically, as shown in  FIG. 7 , the list generator  440  acquires the content names assigned to the content data corresponding to the type of content indicated by the menu directory B, and places the acquired content names in the immediate lower tier of the menu directory B. For example, when the menu directory B indicates the provision of the video content data, the list generator  440  acquires the content names B- 1  to B- 3  which are assigned to the video content data in the local content data stored in the storage  450 . The list generator  440  then places the acquired content names B- 1  to B- 3  in the immediate lower tier of the menu directory B. 
     Fourth, the list generator  440  generates items in the immediate lower tier of the menu directory C. Specifically, as shown in  FIG. 8 , the list generator  440  acquires the server names of the servers that store the content data corresponding to the type of content indicated by the menu directory C, and places the acquired public server names in the immediate lower tier of the menu directory C. For example, when the menu directory C indicates the provision of the content data stored in the public server  500  connected to the public network  200 , the list generator  440  acquires the public server names PS 1  and PS 2  set in the local server  400  from the storage  450 . The list generator  440  then places the acquired public server name PS 1  and PS 2  in the immediate lower tier of the menu directory C. 
     Fifth, as shown in  FIG. 9 , the list generator  440  generates items in the immediate lower tier of the public server name PS 1 . 
     Specifically, first, the list generator  440  acquires the address corresponding to the public server name PS 1  with reference to the address table stored in the storage  450 . Next, by using the acquired address, the list generator  440  transmits a public content list acquisition request to the public server  500  via the public communication unit  420 . The public content list acquisition request is for acquiring the list of the public content stored in the public server  500  corresponding to the public server name PS 1 . 
     The list generator  440  receives a public content list from the public server  500 , the public content list being the list of the public content stored in the public server  500 . 
     Here, the received public content list is written in a language format such as HTML, XML, or JSON, for example, compatible with the public server  500 . Then, the list generator  440  extracts content names assigned to the public content data from the received public content list. The list generator  440  places the extracted content names in parallel as the items in the immediate lower tier of the public server name PS 1 . Accordingly, the language format of the public content list stored in the public server  500  is converted to a language format compatible with the local reproduction device  300 , and the public content list stored in the public server  500  is incorporated into a part of the content list having the language format compatible with the local reproduction device  300 . That is, the list generator  440  serves as a converter that converts the language format compatible with the public server  500  to the language format compatible with the local reproduction device  300 . 
     Items in the immediate lower tier of the public server name PS 2  is generated in a similar manner to that of the public server name PS 1 , thus the description of the generation is omitted. 
     (4) Configuration of Public Server 
     Next, a configuration of a public server according to the first embodiment of the present invention is described with reference to  FIG. 10 .  FIG. 10  is a diagram showing the public server  500  according to the first embodiment. 
     As shown in  FIG. 10 , the public server  500  includes a public communication unit  510 , a storage  520 , a manager  530 , and a list generator  540 . 
     The public communication unit  510  is an interface to connect the public server  500  to the public network  200 . 
     The storage  520  is a storage such as a HDD that stores predetermined information. As shown in  FIG. 10 , the storage  520  has a content data storage  521 , a list storage  522 , and a setup information storage  523 . 
     The content data storage  521  stores public content data. The content data storage  521  stores the public content data and a content name assigned to the public content data with the public content data being associated with the content name. 
     The list storage  522  stores content lists generated by the list generator  540 . 
     The setup information storage  523  stores information set in the public server  500 . The setup information storage  523  stores e.g., an identifier that identifies the public server  500 , and the address of the public server  500  as the information set in the public server  500 . 
     The manager  530  manages the information stored in the storage  520  in response to a request received from the local server  400  via the public communication unit  510 . The manager  530  acquires e.g., a public content list acquisition request and a content data acquisition request from the public communication unit  510 . 
     The manager  530 , when acquiring a public content list acquisition request, inputs an instruction for generating a public content list to the list generator  540 , the public content list including the content names of the public content data stored in the storage  520 . In response to a public content list generation instruction, the manager  530  acquires a generation completion notification from the list generator  540 , the generation completion notification indicating the completion of generation of the public content list. In response to the acquisition of the generation completion notification from the list generator  540 , the manager  530  acquires the generated public content list from the storage  520 . The manager  530  transmits the acquired content list to the local server  400  via the public communication unit  510 . 
     The manager  530 , when acquiring a content data acquisition request, acquires the public content data corresponding to the content name included in the content data acquisition request from the storage  520 . The manager  530  transmits the acquired public content data to the local server  400  via the public communication unit  510 . The public content data transmitted to the local server  400  is transferred to the local reproduction device  300  by the local server  400 . 
     The list generator  540  generates a public content list including the content names of the public content data in response to the public content list generation instruction acquired from the manager  530 . The list generator  540  generates a public content list having the language format compatible with the public server  500 . Such public content list is written in a language such as HTML, XML, or JSON, for example. 
     The list generator  540  inputs the generated list to the storage  520 , and inputs a generation completion notification to the manager  530 , the generation completion notification indicating the completion of generation of the list. 
     Although not shown, the public server  500  may include a program holder that holds a program for causing a CPU to execute processing of the public communication unit  510 , the storage  520 , the manager  530 , and the list generator  540 . As a program holder, a recording media such as a RAM, a ROM, a hard disk, a flexible disk, a compact disc, an IC chip, and a cassette tape, and the like, may be used, for example. 
     (5) Operations of Content Transmission System 
     In the following, operations of the content transmission system according to the first embodiment of the present invention are described with reference to  FIGS. 11 to 13 . In the following, the case where the public server names PS 1  and PS 2  are already assigned to the public server names of a first and a second public servers  500 , respectively, in the local server  400  is described. In the following, the case where the content list shown in  FIG. 4  is generated as a content list is described. 
     (5.1) Generation and Transmission of Content List 
     First, operations of the content transmission system  1  in the case where a content list is transmitted to the local reproduction device  300  in response to a content list acquisition request are described with reference to  FIG. 11 .  FIG. 11  is a sequence diagram showing operations of the content transmission system  1  in the case where a content list is generated in response to a content list acquisition request and the generated content list is transmitted to the local reproduction device  300 . 
     As shown in  FIG. 11 , in step S 101 , the local reproduction device  300  transmits the content list acquisition request to the local server  400 . 
     In step S 102 , the local server  400  generates a part of the content list. Specifically, the local server  400  places the menu directories A, B, C in the immediate lower tier of the root directory R. Here, the menu directory A indicates the provision of the audio content data, the menu directory B indicates the provision of the video content data, and the menu directory C indicates the provision of the content data stored in the public server  500  connected to the public network  200 . Next, the local server  400  places the content names A- 1  to A- 3  in the immediate lower tier of the menu directory A, the content names A- 1  to A- 3  being assigned to the audio content data in the local content data stored in the storage  450 . Next, the local server  400  places the content names B- 1  to B- 3  in the immediate lower tier of the menu directory B, the content names B- 1  to B- 3  being assigned to the video content data in the local content data stored in the storage  450 . Next, the local server  400  places the public server names PS 1  and PS 2  stored in the storage  450  in the immediate lower tier of the menu directory C. 
     In step S 103 , the local server  400  transmits a public content list acquisition request to a first public server  500  corresponding to the public server name PS 1 . 
     In step S 104 , the first public server  500  generates a public content list including the content names of the public content data stored in the first public server  500  itself. 
     In step S 105 , the first public server  500  transmits the public content list generated in step S 104  to the local server  400 . 
     In step S 106 , the local server  400  converts the language format of the received public content list. Specifically, the local server  400  extracts the content names of the public content data stored in the first public server  500  from received public content list, and places extracted content names in the immediate lower tier of the public server name PS 1 . 
     In step S 107 , the local server  400  transmits a public content list acquisition request to the second public server  500  corresponding to the public server name PS 2 . 
     In step S 108 , the second public server  500  generates a public content list including the content names of the public content data stored in the second public server  500  itself. 
     In step S 109 , the second public server  500  transmits the public content list generated in step S 108  to the local server  400 . 
     In step S 110 , the local server  400  converts the language format of received public content list. Specifically, the local server  400  extracts the content names of the public content data stored in the second public server  500  from received public content list, and places extracted content names in the immediate lower tier of the public server name PS 2 . The content list is generated by the above steps S 102  to S 110 . 
     In step S 111 , the local server  400  transmits generated content list to the local reproduction device  300 . Specifically, as a response to the content list acquisition request received in step S 101 , the local server  400  transmits the root directory R of the items included in the content list to the local reproduction device  300 . 
     In step S 112 , the local reproduction device  300  displays received root directory R. 
     (5.2) Transmission of Local Content 
     Next, operations of the content transmission system  1  from transmission of a content list to transmission of a local content list are described with reference to  FIG. 12 .  FIG. 12  is a sequence diagram showing operations of the content transmission system  1  in the case where local content data is transmitted. 
     As shown in  FIG. 12 , in step S 201 , the local server  400  transmits a content list to the local reproduction device  300 . Specifically, the local server  400  transmits the root directory R of the items included in the content list to the local reproduction device  300 . 
     In step S 202 , the local reproduction device  300  displays received root directory R. 
     In step S 203 , the local reproduction device  300  transmits selected item information indicating the root directory R to the local server  400 . 
     In step S 204 , the local server  400  transmits the content list to the local reproduction device  300 . Specifically, the local server  400  transmits the menu directories A, B, C to the local reproduction device  300 , the menu directories A, B, C being the items included in the content list and located in the immediate lower tier of the root directory R indicated by received selected item information. 
     In step S 205 , the local reproduction device  300  displays received menu directories A, B, C. 
     In step S 206 , the local reproduction device  300  transmits selected item information indicating the menu directory A to the local server  400 . 
     In step S 207 , the local server  400  transmits the content list to the local reproduction device  300 . Specifically, the local server  400  transmits the content names A- 1  to A- 3  to the local reproduction device  300 , the content names A- 1  to A- 3  being the items included in the content list and located in the immediate lower tier of the menu directory A indicated by received selected item information. 
     In step S 208 , the local reproduction device  300  displays received content names A- 1  to A- 3 . 
     In step S 209 , the local reproduction device  300  transmits selected item information indicating the content name A- 1  to the local server  400 . 
     In step S 210 , the local server  400  reads content data. Specifically, the local server  400  reads local content data corresponding to the content name A- 1  indicated by the received selected item information. 
     In step S 211 , the local server  400  transmits the read local content data to the local reproduction device  300 . 
     In step S 212 , the local reproduction device  300  reproduces received local content data. 
     (5.3) Transmission of Public Content 
     Next, operations of the content transmission system  1  from transmission of a content list to transmission of a public content list are described with reference to  FIG. 13 .  FIG. 13  is a sequence diagram showing operations of the content transmission system  1  in the case where public content data is transmitted. Since the processing in step S 301  to S 305  in  FIG. 13  is similar to that in step S 201  to S 205  in  FIG. 12 , the description of the processing is omitted. 
     In step S 306 , the local reproduction device  300  transmits selected item information indicating the menu directory C to local server  400 . 
     In step S 307 , the local server  400  transmits a content list to the local reproduction device  300 . Specifically, the local server  400  transmits the public server names PS 1  and PS 2  to the local reproduction device  300 , the public server names PS 1  and PS 2  being the items included in the content list and located in the immediate lower tier of the menu directory C indicated by received selected item information. 
     In step S 308 , the local reproduction device  300  displays the received public server names PS 1  and PS 2 . 
     In step S 309 , the local reproduction device  300  transmits selected item information indicating the public server name PS 1  to the local server  400 . 
     In step S 310 , the local server  400  transmits a content list to the local reproduction device  300 . Specifically, the local server  400  transmits the content names PS 1 - 1  to PS 1 - 3  to the local reproduction device  300 , the content names PS 1 - 1  to PS 1 - 3  being the items included in the content list and located in the immediate lower tier of the public server name PS 1  indicated by received selected item information. 
     In step S 311 , the local reproduction device  300  displays the received content names PS 1 - 1  to PS 1 - 3 . 
     In step S 312 , the local reproduction device  300  transmits selected item information indicating the content name PS 1 - 1  to the local server  400 . 
     In step S 313 , the local server  400  transmits a content data acquisition request to the public server  500 , the content data acquisition request requesting acquisition of the content data corresponding to the content name PS 1 - 1  indicated by received selected item information. Specifically, the local server  400  transmits a content data acquisition request to the first public server  500  corresponding to the public server name PS 1  located in the immediate upper tier of the content name PS 1 - 1 , the content data acquisition request including the content name PS 1 - 1  indicated by the received selected item information. 
     In step S 314 , the first public server  500  reads the content data. Specifically, the first public server  500  reads the public content data corresponding to the content name PS 1 - 1  included in the received content data acquisition request. 
     In step S 315 , the first public server  500  transmits the read public content data to the local server  400 . 
     In step S 316 , the local server  400  transmits received public content data to the local reproduction device  300 . 
     In step S 317 , the local reproduction device  300  reproduces received public content data. 
     (6) Operations and Effects 
     According to the content transmission system  1  of the first embodiment of the present invention, when the local server  400  receives a content list from the public server  500 , the content list including the content names of the public content data stored in the public server  500 , the local server  400  generates a content list that has the language format compatible with the local reproduction device  300  by converting the language format of the received content list. The local server  400  then transmits the generated content list to the local reproduction device  300 . 
     According to such configuration, even if the content list acquired by the local reproduction device  300  is the one including a content name of the public content data stored in the public server  500 , the local reproduction device  300  can display the content list in the display  350 . Thus, the local reproduction device  300  can acquire public content data from the public server  500  connected to the public network  200 . 
     Other Embodiments  
     Although the invention has been disclosed through the embodiment according to the present invention as described above, it should be understood that the discussion and drawings which form a part of the disclosure are not intended to limit the invention. Various alternative embodiments, implementation examples, and application techniques will be apparent to those skilled in the art. 
     For example, although the first embodiment mentioned above is described for the case where one local reproduction device  300  is connected to the local network  100 ; however, the present invention is not limited to this case. For example, multiple local reproduction devices  300  may be connected to the local network  100 . In this case, respective users of the multiple local reproduction devices  300  may assign different names to the public server  500 . 
     In the first embodiment mentioned above, the local server  400  has been described in the case where a content list is generated when a content list acquisition request is received from the local reproduction device  300 , but the present invention is not limited to this case. For example, the local server  400  may periodically generate (i.e., update) a content list and transmit the same to the local reproduction device  300 . 
     In the first embodiment mentioned above, the invention is described in the case where the user of the local reproduction device  300  knows the address of the public server  500 , and an address table which associates the public server name assigned by the user of the public server  500  with the address of the public server  500  is managed in the local server  400 . However, the invention is not limited to this case. For example, a management device that manages multiple public servers  500  may be connected to the public network  200  so that an address table which associates a name assigned to each public server  500  by a user of the management device with the address of the public server  500  may be managed by the management device. In this case, a content list acquisition request, and a server name included in a content data acquisition request are inputted to the local reproduction device  300  based on an address table acquired from the management device. 
     Also, a program that causes a computer to execute the operations (i.e., the sequences shown in  FIGS. 11 to 13 ) of the content transmission system  1  may be provided, for example. Also, a storage in which such program is stored may be provided. A storage in which the program is stored is, for example, a CD-ROM attached to each of the local reproduction device  300 , the local server  400 , and the public server  500 . 
     In this manner, the present invention naturally includes various embodiments not specifically described herein. Accordingly, the technical scope of the present invention should be defined only by the specifications of the invention according to the claims based on the above description.