Abstract:
A multimedia system comprising at least two multimedia devices having differing filesystems and/or no filesystem(s), one or more applications, and a media filesystem adapted to communicate with the at least two multimedia devices and the one or more applications is disclosed. The one or more applications are adapted to issue filesystem commands and/or receive filesystem responses in a common filesystem representation with respect to files of the at least two multimedia devices. The media filesystem may accept the filesystem commands from the one or more applications and may provide responses to filesystem commands to the one or more applications using the common filesystem representation.

Description:
PRIORITY CLAIM 
       [0001]    This application claims the benefit of priority from U.S. Ser. No. 60/841,804, filed Sep. 1, 2006, and from U.S. Ser. No. 60/840,246, filed Aug. 25, 2006, both of which are incorporated by reference. 
     
     BACKGROUND OF THE INVENTION 
       [0002]    1. Technical Field 
         [0003]    The present invention relates to a filesystem for use in a computer, embedded controller, or the like. More particularly, this invention is directed to a filesystem that represents content from various, disparate multimedia devices in a unified filesystem representation for access by one or more higher-level applications. 
         [0004]    2. Related Art 
         [0005]    Multimedia systems may employ multiple media players for playback of multimedia content. Such players include cell phones with Secure Digital (SD) Cards that play encoded music files, Sony® PlayStationPortable® units that use Sony® Memory Stick technology for storage and playback of encoded music files, iPod® devices that employ internal hard disk drives for storage and playback of media files, including video media files, and other media players, including those that employ Universal Serial Bus (USB) flash memory. Media files may be encoded on these devices using a variety of different formats such as MPEG layer III (MP3) encoding, Windows Media Audio (WMA) encoding, Windows Media Video encoding, RealAudio encoding, RealVideo encoding, DVD video, CD audio, and the like files. 
         [0006]    Such devices do not include filesystems that are organized in a readily accessible manner. Rather, these systems may use proprietary formats, often with digital rights management (DRM) protection, which makes it very difficult to access and manage their data content with a generic personal computer or embedded processor. As a result, many software and hardware systems that interact with these devices and systems must be custom designed to accommodate their proprietary device formats. These multimedia systems and devices therefore are not readily adaptable to today&#39;s interconnected world in which a vast interactive network of personal computing devices reside in almost every home and office, as well as a quickly growing proportion of automobiles, wireless personal digital assistants and telephones. 
       SUMMARY 
       [0007]    A multimedia system that comprises a plurality of multimedia devices having differing filesystems and/or no filesystem(s), one or more applications, and a media filesystem adapted to communicate with the plurality of multimedia devices and the one or more applications areis disclosed. The one or more applications may be adapted to issue filesystem commands and/or receive filesystem responses in a common filesystem representation with respect to files of the plurality of multimedia devices. The media filesystem may accept the filesystem commands from the one or more applications and may provide responses to filesystem commands to the one or more applications using the common filesystem representation. 
         [0008]    In one construction of the system, the common filesystem is in the form of a POSIX, UNIX, or the like, interface. Still further, the one or more applications may include a human machine interface (HMI) module and/or a multimedia engine (MME) module. 
         [0009]    Other systems, methods, features and advantages of the invention will be, or will become, apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention, and be protected by the following claims. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The invention can be better understood with reference to the following drawings and description. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Moreover, in the figures, like referenced numerals designate corresponding parts throughout the different views. 
           [0011]      FIG. 1  is a block diagram of an exemplary multimedia system  100  that may include a unified filesystem representation of media files on a plurality of media devices. 
           [0012]      FIG. 2  illustrates one manner of implementing the filesystem shown in  FIG. 1  and its relationship to other modules/components. 
           [0013]      FIG. 3  illustrates one manner in which a media filesystem may access the content of a PFS device. 
           [0014]      FIG. 4  illustrates an exemplary directory structure for a first occurrence of an iPod(R) in the system of  FIG. 1 . 
           [0015]      FIG. 5  is a flowchart showing a number of interrelated operations that may be associated with the media filesystem of  FIG. 2  pursuant to obtaining a list of files from an arbitrary media device. 
           [0016]      FIG. 6  is a table illustrating exemplary fields that may be employed in media file records of the database shown in  FIG. 1 . 
           [0017]      FIG. 7  is a table illustrating exemplary fields that may be employed in playlist file records of the database shown in  FIG. 1 . 
           [0018]      FIG. 8  is a table illustrating exemplary fields that may be employed in a media stores table of the database shown in  FIG. 1 . 
           [0019]      FIG. 9  is a table illustrating exemplary fields that may be employed in a slots table of the database shown in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0020]      FIG. 1  is a block diagram of an exemplary multimedia system  100  that may include a unified filesystem representation of media files on a plurality of media devices. As shown, the exemplary system  100  may include a Multimedia Engine (MME) module  105  that interacts with a human machine interface (HMI) module  110 , as well as interacting with an IO media module  115 , that provides an interface between a plurality of different multimedia devices  120  and the MME module  105 . The HMI module  110  provides an interface that may include multimodal user inputs such as voice, touch buttons and touch screens that are employed by the user to identify the content to be played and to request certain playback operations. The information acquired by the HMI module  110  as a result of these user interactions is passed to the MME module  105 . The MME module  105  obtains media file information for a requested file name, file type, genre, artist, etc., using metadata from consolidated media file information stored, for example, in a database  130 . Database  130  is used by the MME module  105  to store and retrieve metadata for media files that client applications, such as the HMI module  110 , access. The client applications may use this information to display media files to a user or otherwise arrange for playback of the media files in a desired manner on one or more playback output devices/zones  125 . Database  130  may support multiple connections from multiple clients in a concurrent manner. The information in database  130  may be divided between multiple files. Each database file can be stored in RAM, flash, or hard drives in a configurable manner that does not affect access by higher level applications. 
         [0021]    The HMI module  110  may be used to implement a variety of different functions, including the following: 
         [0022]    1. Sending requests to the MME  105  for playback and copying of media files on the devices  120 . It may be allocated to the HMI module  110 , as manipulated by a user, to decide which media is to be played and in what order. The resulting request is then sent to the MME  105  for processing. Playback of the selected media to one or more of the playback output devices/zones  125  may be placed under the control of the media playback module  165  of the MME module  105 . 
         [0023]    2. Browsing the media file contents of devices  120 . The MME module  105  may access database  130  to expose some or all of the available media to the HMI module  110 . User commands may be input to the HMI module  110  to direct the MME module to return information relating to selected media to the HMI module  110 . 
         [0024]    3. Supporting the MME module  105  browsing interface. Some devices require that the client application browse them directly. For example, when a DVD Video is played, its on-screen navigation menu appears. The HMI module  110  may be used to send navigation commands (such as up, down, left, right, play, etc.) to the device through the MME module  105  to navigate the DVD menu. 
         [0025]    4. Accepting notifications from the MME module  105  and responding accordingly. The MME module  105  provides event notifications to a client application. Some examples of events that generate notifications are “song changed,” “new device inserted,” and so on. The HMI module  110  may remain synchronized with the MME module  105  and media by, for example, accepting such messages and updating itself accordingly. 
         [0026]    The MME module  105  may be implemented as a resource manager that handles device discovery and synchronization using, for example, a synchronization module  170 . The synchronization module  170  may be used to synchronize the consolidated media file information of database  130  with the media content of devices  120 . The MME module  105  also may provide a high-level API for managing playback (play, stop, and seek commands) using the media playback module  165 . 
         [0027]    The MME module  105  may be responsible for a wide range of functions, including the following: 
         [0028]    1. Playing media. Such media operations may be executed by the media playback module  165  and may include seeking, pausing, stopping, changing volume, adjusting balance and fade, and so on. The playback module  165  may abstract the type of media and how it is played from the client application level, such as HMI module  110 . For example, when the HMI module  110  instructs the MME module  105  to play some media in a DVD player, the HMI module  110  does not need to know whether the media is stored on an audio CD or DVD in the drive. In most cases the playback is handled by the media playback module  165  of the MME module  105 . However, for some devices like iPod® players or PlaysForSure® devices, the MME module  105  passes the playback request to the device itself. 
         [0029]    2. Synchronizing devices  120  and the database  130 . The synchronization module  170  of the MME module  105  may be used to update the database  130  with metadata corresponding to all the media files and devices that it detects. Client applications may browse the database  130  either directly or through, for example, the MME module  105  to browse music, create playlists, and so on. When a media device  120  is connected to the system  100 , the MME module  105  detects its presence and begins synchronizing the information on the device with the database  130 . The information in database  130  may consolidate metadata from multiple, diverse devices  120  into a single format that is independent of the types of devices attached to system  100 . 
         [0030]    3. Providing a browsing interface for devices. Because of the large list of devices that the MME module  105  may support, it may be provided with a browsing abstraction layer that is the same for all devices. This allows a client application, such as the HMI module  110 , to browse all devices supported by the MME  105  without having to support them directly. 
         [0031]    A number of diverse multimedia devices may be attached to the system  100  shown in  FIG. 1 . The devices  120  may include one or more MP3 players  135 , one or more DVD players  140 , one or more iPod® players  145 , one or more PSP devices  150 , one or more USB storage devices  155 , and/or one or more memory stick devices  160 . At least some of the media devices  120  may include their own proprietary filesystem while others may be accessed using conventional file systems such as POSIX, UNIX, or the like. IO-media module  115  may include a plurality of device drivers  175  to facilitate hardware interaction between each high-level application and media devices  120 . 
         [0032]    High-level applications, such as the HMI module  110  and MME module  105  may require direct access to the files on devices  120 . For example, MME module  105  may access the files on each device in order to synchronize the metadata in database  130 . Since the filesystems of media devices  120  may differ substantially from one another, the MME module  105 , as well as each high-level application attempting to access all of the devices  120 , may require individual modules providing an interface between the high-level application and the individual devices. Such architectures may prove to be quite inefficient and difficult to implement, particularly when a wide range of multimedia devices are attached to system  100 . 
         [0033]    Rather than requiring implementation of specific drivers in each of the high-level modules for each of the attached media devices, system  100  employs device drivers  175  that cooperate with a unified filesystem module  180  to present a common filesystem for presentation to the high-level modules. To this end, high-level modules may access the media content of devices  120  using a single set of filesystem commands, such as those associated with POSIX, UNIX, and the like. 
         [0034]      FIG. 2  illustrates one manner of implementing the filesystem  180  and its relationship to other modules/components. In this exemplary implementation, filesystem  180  is comprised of a high-level interface io-fs, such as a POSIX interface, that is accessible to user applications  205 , such as the HMI module  110 , using filesystem commands. The filesystem  180  also may include a number of low-level interface modules/components that interface with a device access layer  225 . The modules/components of filesystem  180  may include a TMPFS module  210 , a devf-generic module  215 , and a media filesystem  220 . 
         [0035]    The media filesystem  220  may be an io-fs module that presents a POSIX-like file system view of media devices  120 . The filesystem may be implemented as a QNX® Neutrino® resource manager that handles file system semantics, including path name resolution, file and directory access, symbolic links, permissions, and block caching. Media devices that the media filesystem  220  may access include portable music devices such as iPod® players and PlaysForSure® devices, as well as UPnP devices that attach to a network. 
         [0036]    In the system shown in  FIG. 2 , a high-level portion of the media filesystem  220  interfaces with a device access layer  225  that may be implemented separate from the media filesystem  220  or integrated with it. The device access layer  225 , in turn, interfaces with individual drivers that are tailored to access individual media device types. Here, a serial port driver  230  is used to interface with an iPod® device  235 , a USB driver  240  is used to interface with a PlaysforSure® device  245 , and a TCP/IP driver  250  is used to interface with a universal plug and play (UPnP) device  255 . The media filesystem  220  allows access to the contents of devices  235 ,  245 , and  255  using, for example, POSIX functions related to file and directory operations. 
         [0037]    The MME  105  may use the media filesystem  220  to control and browse media devices  120 . When a physical device is detected to be in some way attached to the media filesystem  220  (via USB, serial port, wired network or wireless network for example), a filesystem representing the device appears under the /fs directory of the filesystem. The contents of each device is made available as a filesystem with, for example, the root directory of the device mounted on /fs/dev_id, where dev_id is a name that indicates the type of device with a numeric suffix representing the instance number of the device. The first device discovered, for example, may have an instance number of 0. For example: 
         [0038]    if the first device is an iPod® device, then the media filesystem  220  may make its contents accessible at /fs/ipod0. 
         [0039]    if the first device is a PFS/MTP device, then the media filesystem  220  may make its contents accessible at /fs/psf0. 
         [0040]    if the first device is a UPnP device, then the media filesystem  220  may make its contents accessible at /fs/upnp0. 
         [0041]    The device access layer  225  will generate a device information file that can be accessed as if it were a file in a traditional filesystem. The information file is located at a root directory for each device as .FS_info./info.xml. This device information file may be in the form of an XML-formatted information file which is used by higher level applications and also may be useful for human viewing. 
         [0042]    The following sections list some file-related POSIX functions that may be supported by the media filesystem  220  and that may be used in a user application. For example, the following directory access operations may be supported: 
         [0043]    opendir( ) 
         [0044]    readdir( ) 
         [0045]    closedir( ) 
         [0046]    Additionally, the following file access operations also may be supported: 
         [0047]    open( ) 
         [0048]    read( ) 
         [0049]    write( ) 
         [0050]    lseek( ) 
         [0051]    devctl( ) 
         [0052]    close( ) 
         [0053]    The media filesystem module  220  makes disparate media devices  120  appear, for example, as POSIX-compliant filesystems to the MME  105  and other high-level applications. Further, it may provide some proprietary extensions specific to one or more of the media devices  120 . The exemplary media filesystem module  220  shown in  FIG. 2  includes a PFS module  260  for connecting with PlaysForSure® devices, and an iPod® module  265  for connecting with Apple® iPod® devices. PlaysForSure® is a Microsoft media standard for devices using the Media Transport Protocol (MTP). It implements Digital Rights Management (DRM). 
         [0054]    Devices that support MTP provide a view of media content that comprises objects with properties. These objects and their properties may be accessed via a command and response protocol with an optional data transfer phase. Commands that deal with objects may be executed in the context of a session. When a session is started, each command within the session has a sequential transaction identifier. Within any particular session, each item of media content is assigned a 32 bit “object handle,” which is unique for the duration of the session. Given the object handle, properties such as the object&#39;s name, format, and metadata can be obtained. Each object has a parent object, which facilitates viewing of the media in a hierarchical file structure. Certain object types may serve as folders or directories, where the objects contained in these object types may share the same parent object. 
         [0055]    Separate processes  305 ,  310 , and  325  associated with accessing PFS devices are shown in  FIG. 3 . The process  305  includes an instance of the MME  105 , which may be used to connect to, browse, and play media from a PFS device  245  via the io-fs module  180  shown in connection with process  310 . PlaysForSure® connectivity may be comprised of three layers: 
         [0056]    1. At the top layer may be the PFS module  160 , which may be responsible for presenting a filesystem view of the device to io-fs  305  for further access by the MME  105 . When io-fs  180  initializes the PFS module  160 , it may set up a structure filled with function pointers that it can call into. In this way, the PFS module  160  can “translate” POSIX commands into MTP requests, and vice versa. 
         [0057]    2. An MTP layer  315  may be Microsoft-supplied software that handles MTP messages. 
         [0058]    3. A PTP layer  320  may handle Picture Transfer Protocol (PTP) messages, an implementation of the Still Image class of USB service. Though originally a protocol developed for use with digital cameras, it has been extended and may be used as a foundation for accessing multimedia content of PFS devices. The PTP layer  320  may communicate directly with a USB driver  240  that, in turn, communicates with PFS device  245 . 
         [0059]    The PFS module  160  may be used to identify which media objects have been encrypted using Microsoft&#39;s WMDRM technology. It may use the DRM extensions to MTP to register itself with the PlaysForSure® device—this registration may re-occur periodically to maintain digital rights in the content. 
         [0060]    The iPod® module  265  provides a filesystem view of a connected Apple® iPod® device to the MME  105  or to other high-level application. An iPod® device can connect via its 30 pin Omni connector to either a USB or RS232 serial UART connection and system  100 . When the device is connected to a RS232 serial UART port, the ipod module  265  may communicate directly with a communications manager for the hardware. When the device is connected to a USB port, the ipod module  265  may communicate with a usb device communications manager, which simulates a serial connection on a USB port. 
         [0061]    The iPod® module  265  may create a directory structure from a connected iPod(R) by querying the internal database of the device. Each item on an iPod® module&#39;s  265  menu is a database query. For example, selecting Albums queries the database for albums. Each item on an iPod&#39;s menu is a sub-query of the query represented by the parent menu item. Using this organizing principle, the ipod module  265  generates a filesystem directory structure that resembles an iPod® menu structure. This means that commandline operations can be performed on the iPod. For example, performing the POSIX command “cd Music; Is” may have the same effect as a user selecting the Music option on the iPod®. Both yield the same listing of items. An exemplary directory structure for a first occurrence of an iPod® is shown in  FIG. 4  and includes the folder “music,” where the folder “music” includes the subfolders “playlist,” “artist,” “albums,” “genre,” “songs,” “composer,” “audiobooks” and “podcasts.” In this example, each subfolder terminates in a further subfolder containing “songs”. 
         [0062]    iPod® devices do not export their digital content. Consequently, music files on an iPod® connected to the MME  105  may be played by the iPod® itself, while the MME  105  may be responsible for sending control commands to the device to initiate playback, stop, pause, etc. The analog audio output from the iPod(R) can be routed to an amplifier directly. 
         [0063]    On some devices like the iPod(R), there may be duplicate song names or songs that use characters that are not compatible with the common filesystem representation used by the media filesystem  220  to interact with higher-level applications. In POSIX, for example, the character “/” is reserved, so it cannot be used. Incompatible characters can be converted to a character string of a “%” followed by two hex digits corresponding to the specific character. For example, “/” could be converted to “%2F,” and the character “%” could be converted to “%25.” Any file starting with “.” would also change, for example, “.file” may become “%2Efile”. Duplicate song names may be represented using a “˜” character and an instance number added to the filename. These operations allow the media filesystem  220  to return unique names in a POSIX type filesystem that can be matched in the future. A display program implemented in the HMI  110  may be used to display the original names by removing any “˜” followed by numbers from the end of a file and converting any % xx to the original character before displaying the name to the user. 
         [0064]    The tmpfs module  210  may be used to provide a filesystem interface to shared memory. It may allow RAM to be used as a storage medium with a full POSIX filesystem running on top of it. By simply pointing database  130  at the filesystem mount path of tmpfs  210 , the database  130  may be accessed in RAM only, avoiding the performance costs of running on slower devices like flash. Similarly, the devf-generic module  175  provides a POSIX based filesystem for flash-like media devices. 
         [0065]    Device control codes may be defined for controlling physical devices  120  accessed via the media filesystem  220 . The control codes may be divided into those that direct the device driver to perform some action, and those that obtain information or metadata from the device. If a code is not supported by the device access layer, then either it is ignored and the call returns successfully with null data, or an error code may be returned (ENOTTY—Inappropriate I/O control operation). 
         [0066]    The device control function codes are applied to opened files. In the following descriptions, a data transfer buffer is not used unless specified. If a data buffer is used to receive data, the number of bytes written to the buffer exceeds the specified buffer size, and the number of bytes written to the buffer is returned as the informative value (in a dev_info_ptr argument). If the return data is a UTF string, then it may be null-terminated, even if the string had to be truncated because the receive buffer was not large enough. For example, in the following code the assert( ) should be true even if the song title is larger than the buffer: 
         [0000]    
       
         
               
             
           
               
                   
               
             
             
               
                 char buffer[16]; 
               
               
                 int fd, len; 
               
               
                 status = devctl(fd, DCMD_MEDIA_SONG, buffer, sizeof(buffer),&amp;len); 
               
               
                 if (status == 0) 
               
               
                 assert((strlen(buffer) + 1) == len); 
               
               
                   
               
             
          
         
       
     
         [0067]    Several exemplary device control codes are described below.
       DCMD_MEDIA_PLAY—This control code may be used to direct the device to play the current file (a song, recording or video). The devctl( ) call returns:   ENOTTY if playback is not supported by the device   EINVAL if the file can&#39;t be played for some reason   DCMD_MEDIA_PAUSE—This control code may be used to direct the device to pause the play of the current file. The devctl( ) call returns EINVAL if a file is not currently playing.   DCMD_MEDIA_RESUME—This control code may be used to direct the device to resume the play of the current file. The devctl( ) call returns EINVAL if the file is not currently paused.       
 
         [0073]    DCMD_MEDIA_NEXT_TRACK—This control code may be used to direct the device to skip to the next file (track, song, or recording) in the device&#39;s playlist or album. The devctl( ) call returns EINVAL if the object is not currently playing or paused. 
         [0074]    DCMD_MEDIA_PREV_TRACK—This control code may be used to direct the device to skip to the previous file in the device&#39;s playlist or album. The devctl( ) call returns EINVAL if the object is not currently playing or paused. 
         [0075]    DCMD_MEDIA_FASTFWD—This control code may be used to transfer an integer value to the device access layer via the data buffer (the buffer size should be sizeof(int), which may be, for example, 4 bytes). The integer value indicates the rate, as a multiple of the normal playback rate, at which the device should fast forward. A value of 2 specifies moving forward at double the normal playback speed. 
         [0076]    DCMD_MEDIA_FASTRWD—This control code may be used to transfer a 32 bit integer value to the device access layer via the data buffer (the buffer size may be, for example, 4 bytes). The value indicates the rate at which the device should rewind, as be a multiple of the normal playback rate. A value of  2  specifies moving backward at double the normal playback speed. 
         [0077]    DCMD_MEDIA_PLAYBACK_INFO—This control code may be used to obtain information about the currently playing song. The devctl( ) call returns EINVAL if the file identified by the file descriptor is not currently playing or paused. The data written to the specified buffer may be a media_playback_t structure with at least the following members: 
         [0078]    uint32_t count; The total number of tracks in the playback list 
         [0079]    uint32_tindex; The track index currently in playback 
         [0080]    Uint8_tstate; The device&#39;s playback state selected from the following:
       PLAYBACK_STATE_STOP   PLAYBACK_STATE_PLAY   PLAYBACK_STATE_PAUSE       
 
         [0084]    uint32_tlength; The length of the track (in, for example, seconds) 
         [0085]    uint32_telapsed; The elapsed time for the current track 
         [0086]    uint32_tmetaflags; Bit mask 
         [0087]    DCMD_MEDIA_GET_SHUFFLE—This code gets the shuffle setting for the device. The data buffer contains a single byte, which can be one of:
       SHUFFLE_OFF   SHUFFLE_TRACKS   SHUFFLE_ALBUMS       
 
         [0091]    DCMD_MEDIA_SET_SHUFFLE—This control code may be used to set the shuffle setting for the device. The first byte of the data buffer may be interpreted as the shuffle setting. 
         [0092]    DCMD_MEDIA_GET_REPEAT—This control code may be used to obtain the repeat setting for the device. The data buffer may contain a single byte, which can be one of the following:
       REPEAT_OFF   REPEAT_ONE_TRACK   REPEAT_ALL_TRACKS       
 
         [0096]    DCMD_MEDIA_SET_REPEAT—This control code may be used to set the repeat setting for the device. The first byte of the data buffer is the shuffle setting and may use the states listed under the DCMD_MEDIA_GET_REPEAT command. 
         [0097]    DCMD_MEDIA_SONG—This control code may be used to obtain the name or title of the track identified by the file descriptor parameter. A devctl( ) module may copy a UTF-8 character string of n_bytes bytes, to the data buffer. 
         [0098]    DCMD_MEDIA_ALBUM—This control code may be used to obtain the album name associated with the track identified by the file descriptor parameter. a devctl( ) module may copy a UTF-8 character string of n_bytes bytes to the data buffer. 
         [0099]    DCMD_MEDIA_ARTIST—This control code may be used to obtain the name of the artist who performed the track identified by the file descriptor parameter. A devctl( ) module may copy a UTF-8 character string of n_bytes bytes to the data buffer. 
         [0100]    DCMD_MEDIA_GENRE—This control code may be used to obtain the name of the genre to which the track belongs. The devctl( ) module may copy a UTF-8 character string of n_bytes bytes to the data buffer. 
         [0101]    DCMD_MEDIA_COMPOSER—This control code may be used to obtain the name of the composer of the track identified by the file descriptor parameter. The devctl( ) may copy a UTF-8 character string of n_bytes bytes to the data buffer. 
         [0102]    DCMD_MEDIA_RELEASE_DATE—This control code may be used to obtain the release date of the track identified by the file descriptor parameter. The data buffer may have a 48-byte data structure written to it. This structure may include fields for the year, month (1-12) and day (1-31) of the release of the song. There also may be a text field that is filled in with a UTF-8 string representing the date in a device-dependent date format. The structure may have the following format: 
         [0000]    
       
         
               
               
             
               
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 struct _media_date { 
               
             
          
           
               
                   
                 uint16_t 
                 year; 
                   
               
               
                   
                 uint8_t 
                 seconds; 
                 // (0-59) 
               
               
                   
                 uint8_t 
                 minutes; 
                 // (0-59) 
               
               
                   
                 uint8_t 
                 hours; 
                 // (0-23) 
               
               
                   
                 uint8_t 
                 day; 
                 // (1-31) 
               
               
                   
                 uint8_t 
                 month; 
                 // (1-12) 
               
               
                   
                 uint8_t 
                 weekday; 
                 // (0-6, where 0=Sunday, 1=Monday ... 
               
               
                   
                 6=Saturday) 
               
               
                   
                 char 
                 text[40]; 
                 // ASCII date as formatted by device 
               
               
                   
                 }; 
               
               
                   
                   
               
             
          
         
       
     
         [0103]    DCMD_MEDIA_TRACK_NUM—This control code may be used to obtain the original track number for the song. The track number may be returned as an integer value in the data buffer. 
         [0104]    DCMD_MEDIA_PUBLISHER—This control code may be used to obtain the name of the publisher of the track. The devctl( ) may copy a UTF-8 character string of n_bytes bytes to the data buffer. 
         [0105]    DCMD_MEDIA_DEVINFO—This control code may be used to obtain device information in a UTF-8 character string format. The content of this string may be device-dependent. The following is an example device information string from an MTP device: 
         [0000]    
       
         
               
               
             
           
               
                   
               
             
             
               
                 Standard Version = 
                 100 
               
               
                 Vendor ext id = 
                 0x6 
               
               
                 Vendor ext ver = 
                 100 
               
               
                 Vendor ext desc = 
                 microsoft.com/WMDRMPD: 10.1; 
               
               
                   
                 microsoft.com:1.0; 
               
               
                 Ops supported = 
                 0x1014, 0x1015, 0x1001, 0x1002, 0x1003, 0x1004, 
               
               
                   
                 0x1005, 0x1007, 0x1008, 0x1009, 0x101B, 0x100C, 0x100D, 0x100B, 
               
               
                   
                 0x1012, 0x1016, 0x9801, 0x9802, 0x9803, 0x9805, 0x9806, 0x9810, 0x9811, 
               
               
                   
                 0x9201, 0x9101, 0x9102, 0x9103, 0x9104, 0x9105, 0x9106, 0x9107, 0x9108, 
               
               
                   
                 0x9109, 0x910A, 0x910B, 0x9170, 0x9171, 0x9172, 0x9173, 0x9180, 
               
               
                   
                 0x9181, 0x9182, 0x9183, 0x9184, 0x9185, 0x9800, 
               
               
                 Events supported = 
               
               
                 Props supported = 
                 0x5001, 0xD101, 0xD102, 0xD103, 0xD401, 
               
               
                   
                 0xD402, 
               
               
                 Capture fmts supp = 
               
               
                 Img formats supp = 
                 0x3001, 0x3009, 0x3008, 0x3801, 0xBA05, 0xBA03, 
               
               
                 0xB901, 
               
               
                 Manufacturer = 
                 IRIVER 
               
               
                 Model = 
                 IRIVER Device 
               
               
                 Device Version = 
                 PP5020AF-02.51-ENG-MT-DT, (Build 157.13) 
               
               
                 Serial Number = 
                 3ME5G7QX 
               
               
                   
               
             
          
         
       
     
         [0106]      FIG. 5  is a flow chart showing a number of interrelated operations that may be associated with the media filesystem  220  pursuant to obtaining a list of files from an arbitrary media device. As shown, a high-level application, such as the HMI module  110 , issues a command at block  510  using, for example, a POSIX command, to obtain a list of files/content from a media device. The media filesystem  220  identifies this command and uses the corresponding driver to access the data and/or metadata from the media device. The data and/or metadata from the media device is parsed at block  515  to collect the filenames, date created, date modified, file type, file size and other attributes that might be available and useful. Any data or headers that are not required may simply be disregarded or discarded. The data content is then converted from the format in which it was received from the device to a desired filesystem representation at block  520  and reported to the requesting application at block  525 . The filesystem representation provided at block  525  corresponds to an arrangement of the data for presentation to the requesting application in a manner mimicking a similar request made using a common file system or otherwise conventional filesystem, such as POSIX. In the course of doing this, the media filesystem  220  may identify where the file was obtained and the manner in which it may be accessed for later use. 
         [0107]    When a list of songs is obtained from a media device, the media filesystem  220  may generate and store an internal 32-bit number that may be used to find the actual file in the future. It may report a unique name to the user for each song on the media device and may be capable of converting that unique name back to the 32-bit number later on. This number can be used to retrieve the song name again, or tell the media device to play the song or get metadata, or even the raw song data if the media device supports it. For example, on PlayForSure devices, every song may have a 32-bit object identification that can be used. On an iPod device, the number of down presses from the top of the menu needed to get to the entry may be used for identification purposes. 
         [0108]    The records in database  130  may have a number of different structures depending on the requirements of the system. Some fields that may be used in such database records and their corresponding meaning are shown in the table of  FIG. 6 . Exemplary fields that may be used in connection with a playlist table in database  130  are shown in  FIG. 7 . 
         [0109]    Database  130  also may include a media stores table. Each mediastore in the mediastores table may be used to describe one physical device containing media that the engine has seen. This could be an iPod® device, hard drive, USB stick, DVD Video disc, etc. Mediastores come and go as they are inserted and removed and this table is updated by the MME  105  accordingly as that happens. All entries in the library table may belong to one mediastore which is where the media is located. Mediastores may be uniquely identified by an identifier that can be used to later attain the msid for the mediastore which links to the other tables.  FIG. 8  shows exemplary fields that may be used in connection with the media stores table. 
         [0110]    Still further, the database  130  may include a slots table. Slots may be used to define fileystem locations where mediastores can be connected and removed. For example, an audiocd may be found in the filesystem at location /fs/cd0. If it were a networked audiocd, it may be found at /net/remote_host/fs/cd0. The MME  205  may be designed to support an unlimited number of slots.  FIG. 9  shows exemplary fields that may be used in connection with the slots table. 
         [0111]    The metadata corresponding to a file may be available on the media containing the file. However, it is also possible for an external source to add metadata to a file. Metadata for a file may include information regarding the music type and the group that produced the music. It is also possible to incorporate various additional types of metadata. For example, the metadata may include information on the quality of the content stored in the file. This quality information may be used in the selection of contents to be played for a user, or with certain license or other restrictions associated with the content. 
         [0112]    While various embodiments of the invention have been described, it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible within the scope of the invention. Accordingly, the invention is not to be restricted except in light of the attached claims and their equivalents.