Abstract:
A video playback device includes a processor that executes a procedure. The procedure includes: for each of plural videos, receiving designations of positions in display regions of the videos; and adjusting a placement position in the display regions of the plural videos such that the positions designated for each of the plural videos are aligned at the same position in a vertical direction or a horizontal direction.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2015-145346, filed on Jul. 22, 2015, the entire contents of which are incorporated herein by reference. 
       FIELD 
       [0002]    The embodiments discussed herein are related to a storage medium storing a video playback program, a video playback device, and a video playback method. 
       BACKGROUND 
       [0003]    Hitherto, instruction methods have been proposed for instruction on how to move the body in sports, performances, actions, or the like that are performed by moving the body. In such methods, a sport, performance, action or the like performed by a student under instruction is captured using a video camera, and instruction is given while comparing plural video images on a screen. Moreover, the sport, performance, action or the like as performed by an instructor is compared on the same screen, so as to give the student an understanding of the correct form and timing therefor. 
       Related Patent Documents 
       [0004]    Japanese Laid-Open Patent Publication No. H07-144038 
       SUMMARY 
       [0005]    According to an aspect of the embodiments, a video playback device includes a processor that executes a procedure. The procedure includes, for each of plural videos, receiving designations of positions in display regions of the videos; and adjusting a placement position in the display regions of the plural videos such that the positions designated for each of the plural videos are aligned at the same position in a vertical direction or a horizontal direction. 
         [0006]    The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
         [0007]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0008]      FIG. 1  is a block diagram illustrating a schematic configuration of a video playback system according to a first to a third exemplary embodiment; 
           [0009]      FIG. 2  is a diagram illustrating an example of a video playback screen of the first exemplary embodiment; 
           [0010]      FIG. 3  is a diagram illustrating an example of a video playback screen with a horizontal bar displayed; 
           [0011]      FIG. 4  is a diagram illustrating an example of a video playback screen with the heights of two videos adjusted; 
           [0012]      FIG. 5  is a block diagram illustrating a schematic configuration of a computer that functions as a video playback device according to the first to the third exemplary embodiments; 
           [0013]      FIG. 6  is a flowchart illustrating an example of height adjustment processing; 
           [0014]      FIG. 7  is a diagram illustrating an example of a video playback screen with a vertical bar displayed; 
           [0015]      FIG. 8  is a diagram illustrating an example of a video playback screen with horizontal positions of two videos adjusted; 
           [0016]      FIG. 9  is a diagram illustrating an example of a video playback screen of the second exemplary embodiment; 
           [0017]      FIG. 10  is a diagram illustrating an example of a video playback screen with a superimposition mark displayed; 
           [0018]      FIG. 11  is a diagram illustrating an example of a video playback screen with two videos displayed superimposed; 
           [0019]      FIG. 12  is a diagram illustrating an example of a video playback screen with positions of superimposed display adjusted; 
           [0020]      FIG. 13  is a flowchart illustrating an example of superimposed display processing; 
           [0021]      FIG. 14  is a diagram illustrating an example of a shared information table; 
           [0022]      FIG. 15  is a diagram illustrating an example of a sharing user table; 
           [0023]      FIG. 16  is a diagram illustrating an example of a video playback screen of the third exemplary embodiment; 
           [0024]      FIG. 17  is a diagram illustrating an example of a video playback screen with a display share list button displayed; 
           [0025]      FIG. 18  is a diagram illustrating an example of a share list screen; 
           [0026]      FIG. 19  is a sequence chart representing a flow of processing for exchange between a video playback device of a transmission side user, a video management device, and a video playback device of a reception side user; 
           [0027]      FIG. 20  is a flowchart illustrating an example of shared information transmission processing. 
           [0028]      FIG. 21  is a flowchart illustrating an example of shared information reception processing; 
           [0029]      FIG. 22  is a flowchart illustrating an example of shared video transmission processing; and 
           [0030]      FIG. 73  is a flowchart illustrating an example of shared video playback processing. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0031]    Detailed explanation follows regarding an exemplary embodiment according to technology disclosed herein, with reference to the drawings. 
       First Exemplary Embodiment 
       [0032]    As illustrated in  FIG. 1 , a video playback system  10  according to a first exemplary embodiment includes a video playback device  20  and a video management device  30 . The video playback device  20  and the video management device  30  are connected to each other by a network. 
         [0033]    The video management device  30  includes a controller  31  that controls distribution and the like of video data to the video playback device  20 , and a video database (DB)  32  that stores plural items of video data that can be provided to users. In the present exemplary embodiment, the video data is distributed to the video playback device  20  using a method in which split files obtained by splitting a single item of video data at specific time intervals (for example, 10 seconds) are sequentially distributed using hypertext transfer protocol (HTTP). This method is a method such as HTTP live streaming (HLS), or moving picture experts group-dynamic adaptive streaming over HTTP (MPEG-DASH). A playlist describing, for example, a playback sequence for the split files is therefore also stored in the video DB  32  for each item of video data. Management information for managing identification information (for example, usernames) of users to which each item of video data can be distributed is also stored in the video DB  32 . 
         [0034]    When a user logs in to a video playback application on the video playback device  20 , the controller  31  receives identification information (for example, the username) of the logged-in user. The controller  31  transmits, to the video playback device  20 , a playlist listing of video data items permitted for distribution to the logged-in user. The playlist listing is a listing of playlist names for respective video data permitted for distribution to the logged-in user, and in addition to the playlist names, the playlist listing may include metadata other than that of the video data, thumbnail images, and the like. Thumbnail images pre-generated from one of the frame images included in the video data may also be stored in the video DB  32 , or the thumbnail images may be generated when transmitting the playlist listing. 
         [0035]    When the controller  31  receives a request for video data from the video playback device  20 , the controller  31  acquires the playlist corresponding to the requested video data from the video DB  32 , and transmits the acquired playlist to the video playback device  20 . Moreover, the controller  31  acquires, from the video DB  32 , the split files sequentially requested by the video playback device  20  according to the playlist, and sequentially transmits the acquired split files to the video playback device  20 . 
         [0036]    The video playback device  20  functions as a display section that displays a video playback screen  60  (described in detail below), and as a video playback application that is installed to a user terminal provided with an input section for input of information. The user terminal is, for example, an information processing device such as a personal computer (PC), a notebook PC, a tablet terminal, or a smartphone. 
         [0037]    As illustrated in  FIG. 1 , the video playback device  20  functionally includes an acquisition section  21  and a display controller  22 . The display controller  22  is an example of a reception section and an adjustment section of technology disclosed herein. 
         [0038]    The acquisition section  21  transmits the identification information (for example, the username) of the logged-in user to the video management device  30 , and thereby acquires, from the video management device  30 , the playlist listing of the video data permitted for distribution to the logged-in user, and passes the acquired playlist listing to the display controller  22 . Moreover, the acquisition section  21  transmits, to the video management device  30 , the playlist names for videos that have been selected from the playlist listing by the user, and thereby requests video data from the video management device  30 , and acquires the playlist corresponding to that video data. Moreover, the acquisition section  21  issues sequential requests to the video management device  30  for split files in accordance with the acquired playlist, and sequentially acquires the split file from the video management device  30 . The acquisition section  21  sequentially passes the acquired split file to the display controller  22 . 
         [0039]    When the display controller  22  receives the playlist listing from the acquisition section  21 , the display controller  22 , for example, displays a video playback screen  60  like that illustrated in  FIG. 2  on the display section. In the example of  FIG. 2 , plural videos can be played back in a video playback region  61  provided in the center of the video playback screen  60 . Note that in the present exemplary embodiment, explanation is given regarding an example of a case in which two videos are played back. The video at the left side of the video playback screen  60  is referred to as a left video  62 L and the video at the right side of the video playback screen  60  is referred to as a right video  62 R. In states in which desired videos have not yet been selected from the playlist listing, neither a left video  62 L nor a right video  62 R is displayed on the video playback region  61 . 
         [0040]    The display controller  22  displays, in a specific region of the video playback screen  60 , a left video playlist listing  63 L for selecting the left video  62 L to play back, and a right video playlist listing  63 R for selecting the right video  62 R to play back.  FIG. 2  illustrates an example in which thumbnail images of the videos represented by the respective playlists are displayed as the respective playlist listings  63 L,  63 R. The display controller  22  displays the respective playlist listings  63 L,  63 R in a state in which all of the thumbnail images can be checked by scrolling or the like. The display state of the playlist listing is not limited to cases employing thumbnail images as illustrated in  FIG. 2 . Playlist names included in the playlist listing may be displayed in a listing, or playlist names may be displayed together with the thumbnail images. When other metadata is also included in the playlist listing acquired from the video management device  30 , that metadata may also be displayed together with the playlist listing. 
         [0041]    When thumbnail images have been selected by operations such as double clicks or double taps that respectively correspond to the left video playlist listing  63 L and the right video playlist listing  63 R, the display controller  22  emphatically displays the selected thumbnails images. As the emphatic display, the display controller  22  can control display such that, for example, a border is thickened, size is increased, or brightness is increased. Moreover, the display controller  22  notifies the acquisition section  21  of the playlist name corresponding to the thumbnail image selected from the left video playlist listing  63 L, and the playlist name corresponding to the thumbnail image selected from the right video playlist listing  63 R. 
         [0042]    Moreover, when the display controller  22  receives the split file from the acquisition section  21 , the video corresponding to the thumbnail image that was selected from the left video playlist listing  63 L is displayed in the video playback region  61  as the left video  62 L. Moreover, the video corresponding to the thumbnail image that was selected from the right video playlist listing  63 R is displayed in the video playback region  61  as the right video  62 R. 
         [0043]    In general methods for streaming playback of video using hypertext markup language (HTML), the position and size of a region where a video is to be played back is set in advance. In the present exemplary embodiment, control information regarding the display sizes and display positions of the respective left video  62 L and the right video  62 R is awaited, and the display controller  22  uses the control information to respectively dispose the left video  62 L and the right video  62 R at freely selected positions and at freely selected sizes in the video playback region  61 . The display size, which is control information, is, for example, information respectively designating the widths and heights for the left video  62 L and the right video  62 R. The display position, which is control information, is information respectively designating x-coordinates and y-coordinates of freely selected points (for example, the top left corners) of the left video  62 L and the right video  62 R. Note that the x-coordinate and the y-coordinate may employ coordinate values of a coordinate system in which the rightward direction is set as the positive direction of the x-axis, and the downward direction is set as the positive direction of the y-axis, with the top left corner of the video playback region  61  serving as the origin. 
         [0044]    The display controller  22  also displays a left video operation button group  64 L for controlling playback of the left video  62 L, and a right video operation button group  64 R for controlling playback of the right video  62 R, in specific regions of the video playback screen  60 . The display controller  22  also displays a shared operation button group  64 C for simultaneously controlling playback of the left video  62 L and playback of the right video  62 R. As operation buttons, each of the respective operation button groups  64 L,  64 C,  64 R includes, for example, a rewind button, a play button, a pause button, a fast forward button, a previous-frame button, a slow playback button, and a next-frame button. 
         [0045]    When an operation button of the left video operation button group  64 L has been operated by the user, the display controller  22  controls playback of the left video  62 L based on the button operated and the amount of operation. Moreover, when an operation button of the right video operation button group  64 R has been operated by the user, the display controller  22  controls playback of the right video  62 R based on the button operated and the amount of operation. Moreover, when an operation button of the shared operation button group  64 C has been operated by the user, the display controller  22  controls playback of both the left video  62 L and the right video  62 R based on the button operated and the amount of operation. This not only enables respective control of playback of the left video  62 L and the right video  62 R, but also enables both of the videos  62 L,  62 R to be played back synchronized. For example, the left video  62 L is paused at a desired timing, and the playback button of the shared operation button group  64 C is selected in a state in which a frame image of the right video  62 R to be aligned with the timing of the paused frame image has been searched for using frame-by-frame advancing or the like and then displayed. This enables playback synchronized so as to match the playback timing of a desired frame image to be realized. 
         [0046]    The display controller  22  also displays a display horizontal bar button  65  in a specific region of the video playback screen  60 . The horizontal bar is a mark for respectively designating positions in the height direction for the left video  62 L and the right video  62 R. When the display horizontal bar button  65  has been selected, the display controller  22 , for example, displays a left video horizontal bar  66 L above the left video  62 L and displays a right video horizontal bar  66 R above the right video  62 R as illustrated in  FIG. 3 . The respective positions at which the horizontal bars  66 L,  66 R are displayed when the display horizontal bar button  65  has been selected may be predetermined initial positions (for example, positions at half of the height of the respective left video  62 L and right video  62 R). 
         [0047]    The display controller  22  also displays a left video horizontal bar position adjusting button  67 L and a right video horizontal bar position adjusting button  67 R in a specific region of the video playback screen  60 . The horizontal bar position adjusting buttons  67 L,  67 R are buttons for instructing changes to the respective heights of the respective horizontal bars  66 L,  66 R. For example, the display controller  22  moves the display positions of the respective horizontal bars  66 L,  66 R upward or downward by a specific amount of pixels (for example, one pixel) each time a button indicating an upward direction or a downward direction of the respective horizontal bar position adjusting buttons  67 L,  67 R is selected. Note that the respective horizontal bars  66 L,  66 R may also be moved in the upward and downward directions directly by an operation such as dragging or swiping. 
         [0048]    In place of the display horizontal bar button  65 , the display controller  22  displays a execute height adjustment button  68  in a specific region of the video playback screen  60 . When the execute height adjustment button  68  has been selected, as illustrated in  FIG. 4 , the display controller  22  adjusts the display position of at least one out of the left video  62 L and the right video  62 R such that positions inside the respective videos  62 L,  62 R indicated by the respective horizontal bars  66 L,  66 R are set at the same height as each other. Note that the positions at which the left video horizontal bar  66 L and the right video horizontal bar  66 R were displayed are indicated by the dotted line P in  FIG. 4 . 
         [0049]    More specifically, the display controller  22  acquires information regarding the difference between the height of the left video horizontal bar  66 L and the height of the right video horizontal bar  66 R, the respective current display positions of the left video  62 L and the right video  62 R, and the size of the video playback region  61 . Based on the acquired information, the display controller  22  derives display positions by adjusting at least one out of the left video  62 L or the right video  62 R. For example, the display controller  22  derives display positions for a case in which the left video  62 L has been moved to a position where the movement amount is the difference in the heights of the horizontal bars  66 L,  66 R, in a direction to match the heights of the horizontal bars  66 L and  66 R, within a range that does not exceed the video playback region  61 . When the movement amount does not amount to this difference, display positions are derived for a case in which the right video  62 R has been moved to a position where the movement amount that is the remaining difference in the heights of the of the horizontal bars  66 L,  66 R, in a direction to match the heights of the horizontal bars  66 L,  66 R, within a range not exceeding the video playback region  61 . The display controller  22  updates the information indicating the display positions included in the respective control information of the left video  62 L and the right video  62 R to the display positions derived as described above. The display controller  22  then changes at least one display position out of that of the left video  62 L or the right video  62 R, based on the updated control information. 
         [0050]    Note that in cases in which the movement amounts of the videos  62 L,  62 R does not amount to the difference even when both of the videos  62 L,  62 R have been moved to the limit within the range not exceeding the video playback region  61 , display position height adjustment may be executed with the display size of both of the videos  62 L,  62 R reduced. 
         [0051]    As described above, in the present exemplary embodiment, the left video  62 L and the right video  62 R can each be disposed in freely selected regions at freely selected sizes since control information is held for the respective left video  62 L and the right video  62 R This enables the respective display positions of the left video  62 L and the right video  62 R to be adjusted based on the designated positions (respective positions within the videos  62 L,  62 R indicated by the horizontal bars  66 L,  66 R). Adjusting the display positions of the videos in this manner can be realized using a combination of frameworks each capable of implementing precise functionality, rather than using a large, easy to handle framework such as that of a media player. For example, the functionality described above can be implemented using a combination of a framework for displaying videos, a framework for displaying lines, and a framework that detects operations such as touches, and the like. For example, the AVPlayer, AVPlayerItem layer of AVfoundation, which is a framework related to audio, can be employed as a framework for displaying videos on iOS (registered trademark). 
         [0052]    The video playback device  20  may, for example, be implemented by the computer  40  illustrated in  FIG. 5 . The computer  40  includes a CPU  41 , memory  42  serving as a temporary storage region, and a non-volatile storage section  43 . The computer  40  also includes an input/output interface (I/F)  44  to which input/output devices  48 , such as a display device and an input device, are connected. The computer  40  also includes a read/write (R/W) section  45  for controlling reading and writing of data from and to a recording medium  49 , and a network I/F  46  connected to a network such as the internet. The CPU  41 , the memory  42 , the storage section  43 , the input/output I/F  44 , the R/W section  45 , and the network I/F  46  are connected to one another through a bus  47 . 
         [0053]    The storage section  43  may be implemented by a hard disk drive (HDD), a solid state drive (SSD), flash memory, or the like. A video playback program  50  that causes the computer  40  to function as the video playback device  20  is stored in the storage section  43 , which serves as a storage medium. The video playback program  50  includes an acquisition process  51  and a display control process  52 . 
         [0054]    The CPU  41  reads the video playback program  50  from the storage section  43 , expands the video playback program  50  into the memory  42 , and sequentially executes the processes included in the video playback program  50 . The CPU  41  operates as the acquisition section  21  illustrated in  FIG. 1  by executing the acquisition process  51 . The CPU  41  also operates as the display controller  22  illustrated in  FIG. 1  by executing the display control process  52 . The computer  40 , which executes the video playback program  50 , thereby functions as the video playback device  20 . 
         [0055]    The functionality implemented by the video playback program  50  can also be implemented by, for example, a semiconductor integrated circuit, and more specifically, by an application specific integrated circuit (ASIC). 
         [0056]    Next, explanation follows regarding operation of the video playback system  10  according to the first exemplary embodiment. 
         [0057]    In the video playback device  20 , when the user has logged-in to the video playback application, the acquisition section  21  transmits the identification information (for example, the username) of the logged-in user to the video management device  30 . 
         [0058]    In the video management device  30 , when the user identification information has been received, the controller  31  transmits, to the video playback device  20 , a playlist listing of video data permitted for distribution to the logged-in user. 
         [0059]    In the video playback device  20 , the acquisition section  21  passes the acquired playlist listing to the display controller  22 . The display controller  22 , for example, displays a video playback screen  60  like that illustrated in  FIG. 2  (the left video  62 L and the right video  62 R are not displayed). 
         [0060]    When respective thumbnail images have been selected by the user from the left video playlist listing  63 L and the right video playlist listing  63 R, the display controller  22  emphatically displays the selected thumbnail images. The display controller  22  then notifies, to the acquisition section  21 , the playlist name corresponding to the thumbnail image selected from the left video playlist listing  63 L, and the playlist name corresponding to the thumbnail image selected from the right video playlist listing  63 R. The acquisition section  21  then requests video data from the video management device  30  by transmitting the playlist names indicated by the respectively notified left video  62 L and right video  62 R to the video management device  30 . 
         [0061]    In the video management device  30 , the controller  31  acquires the playlist corresponding to the requested video data from the video DB  32 , and transmits the acquired playlist to the video playback device  20 . 
         [0062]    In the video playback device  20 , the acquisition section  21  acquires the playlist, and sequentially requests the split files from the video management device  30  in accordance with the acquired playlist. 
         [0063]    In the video management device  30 , the controller  31  acquires the requested split files from the video DB  32 , and sequentially transmits the acquired split files to the video playback device  20 . 
         [0064]    In the video playback device  20 , the acquisition section  21  sequentially passes the acquired split files to the display controller  22 . Then, when the display controller has received the split files from the acquisition section  21 , the left video  62 L and the right video  62 R are each played back in the video playback region  61 . The respective display sizes and display positions of the left video  62 L and the right video  62 R are defined by the respective control information held for the left video  62 L and right video  62 R. Note that at this stage, a predetermined initial value is set in the control information. The display controller  22  then respectively controls playback of the left video  62 L and the right video  62 R based on operation of the operation buttons of the respective operation button groups  64 L,  64 C,  64 R by the user. 
         [0065]    Then, in a state in which the video playback screen  60  is displayed with the display horizontal bar button  65  included, when the display horizontal bar button  65  is selected by the user, the height adjustment processing illustrated in  FIG. 6  is executed in the video playback device  20 . 
         [0066]    At step S 11  of the height adjustment processing illustrated in  FIG. 6 , the display controller  22 , for example, displays the left video horizontal bar  66 L at a predetermined initial position on the left video  62 L, and displays the right video horizontal bar  66 R at a predetermined initial position on the right video  62 R, as illustrated in  FIG. 3 . 
         [0067]    Next, at step S 12 , the display controller  22  determines whether or not the execute height adjustment button  68  has been selected by the user. Processing transitions to step S 13  in cases in which the execute height adjustment button  68  has not been selected. 
         [0068]    At step S 13 , the display controller  22  determines whether or not a change in the position of either the left video horizontal bar  66 L or the right video horizontal bar  66 R has been received. For example, in cases in which either of the horizontal bar position adjusting buttons  67 L,  67 R have been selected, and in cases in which either of the horizontal bars  66 L,  66 R have been operated by dragging or swiping, the display controller  22  receives a change in the position of either of the horizontal bars  66 L,  66 R. Processing then transitions to step S 14 . However, processing returns to step S 12  in cases in which no change in position has been received. 
         [0069]    At step S 14 , the display controller  22  changes the display position of the horizontal bars  66 L,  66 R such that the horizontal bars  66 L,  66 R are displayed at the position received at step S 13  above, and processing returns to step S 12 . 
         [0070]    At step S 12 , processing transitions to step S 15  when the display controller  22  determines that the execute height adjustment button  68  has been selected by the user. At step S 15 , the display controller  22 , for example, as illustrated in  FIG. 4 , adjusts the display position of at least one out of the left video  62 L or the right video  62 R such that respective positions within the videos  62 L,  62 R respectively indicated by the horizontal bar  66 L and the horizontal bar  66 R are at the same height. The height adjustment processing then ends. 
         [0071]    As explained above, in the video playback system  10  according to the first exemplary embodiment, the video playback device  20  adjusts the display positions of the left video and the right video such that positions designated by the horizontal bars are aligned at the same position in the vertical direction, namely, such that the designated positions are at the same height. This facilitates comparison of the left video and the right video. 
         [0072]    Note that although explanation has been given in the first exemplary embodiment regarding a case in which the left video  62 L right video  62 R are disposed side-by-side in the horizontal direction and the heights of their display positions are adjusted, there is no limitation thereto. For example, as illustrated in  FIG. 7 , configuration may be made such that an upper video  62 U and a lower video  62 D are disposed side-by-side in the vertical direction and their display positions are adjusted in the horizontal direction in a video playback screen  160 . In the video playback screen  160 , configuration similar to that of the respective configurations of the video playback screen  60  in  FIG. 3  are allocated similar reference numerals with only the suffixes of the reference numerals changed from “L” or “R” to “U” or “D”, and detailed explanation is omitted. Note that the reference numeral “U” is allocated to configuration related to the upper video  62 U, and the reference numeral “D” is allocated to configuration related to the lower video  62 D. 
         [0073]    More specifically, when a display vertical bar button  165  (see also  FIG. 8 ) provided to the video playback screen  160  has been selected, the display controller  22  displays an upper video vertical bar  66 U on the upper video  62 U, and displays a lower video vertical bar  66 D on the lower video  62 D. Similarly to the horizontal bars  66 L,  66 R, the respective vertical bars  66 U,  66 D can be moved in the horizontal direction by operation of an upper video vertical bar position adjustment button  67 U and a lower video vertical bar position adjustment button  67 D. Moreover, the respective vertical bars  66 U,  66 D may also be moved in the horizontal direction directly by a dragging or swiping operation. When a horizontal position adjustment execution button  168  provided to the video playback screen  160  has been selected, as illustrated in  FIG. 8 , the display controller  22  adjusts the display position of at least one out of the upper video  62 U or the lower video  62 D, such that respective positions in the videos  62 U,  62 D respectively indicated by the vertical bars  66 U,  66 D are at the same position in the horizontal direction. Note that the positions at which the upper video vertical bar  66 U and the lower video vertical bar  66 D were displayed are indicated by the dotted line Q in  FIG. 8 . 
         [0074]    This enables the display positions of the upper video  62 U and the lower video  62 D in the horizontal direction to also be adjusted similarly to in the case of adjusting the display positions of the left video  62 L and the right video  62 R in the vertical direction. 
       Second Exemplary Embodiment 
       [0075]    Next, explanation follows regarding a video playback system according to a second exemplary embodiment. In the video playback system according to the second exemplary embodiment, portions similar to those of the video playback system  10  according to the first exemplary embodiment are allocated the same reference numerals, and detailed explanation thereof is omitted. 
         [0076]    As illustrated in  FIG. 1 , a video playback system  210  according to the second exemplary embodiment includes a video playback device  220 , and the video management device  30 . The video playback device  220  and the video management device  30  are connected to each other through a network. As illustrated in  FIG. 1 , the video playback device  220  functionally includes the acquisition section  21  and a display controller  222 . Note that the display controller  222  is an example of a reception section and an adjustment section of technology disclosed herein. 
         [0077]    When the display controller  222  has received a playlist listing from the acquisition section  21 , the display controller  222 , for example, displays a video playback screen  260  like that illustrated in  FIG. 9  on a display section. The video playback screen  260  includes a display superimposed mark button  265  instead of the display horizontal bar button  65  of the video playback screen  60  of the first exemplary embodiment. A superimposed mark is a mark for designating a position to serve as a reference for overlaying when performing superimposed display of the left video  62 L and the right video  62 R. When the display superimposed mark button  265  has been selected, the display controller  222 , for example, displays a left video superimposition mark  266 L on the left video  62 L, and displays a right video superimposition mark  266 R on the right video  62 R, as illustrated in  FIG. 10 . In the example of  FIG. 10 , marks represented by respective squares and lines across the diagonals of the squares serve as the superimposition marks  266 L,  266 R, and positions (coordinates) of the respective superimposition marks  266 L,  266 R are specified by the respective positions of the intersection points of the diagonal lines. The positions of the respective superimposition marks  266 L,  266 R displayed when the display superimposed mark button  265  has been selected may be predetermined initial positions (for example, the respective centers of the left video  62 L and the right video  62 R). 
         [0078]    The display controller  222  also displays a left video superimposition mark position adjustment button  267 L and a right video superimposition mark position adjustment button  267 R in a specific region of the video playback screen  260 . The respective superimposition mark position adjustment buttons  267 L,  267 R are buttons for instructing changes in the positions of the respective superimposition mails  266 L,  266 R in both the horizontal direction and the vertical direction. For example, each time a button of the respective superimposition mark position adjustment buttons  267 L,  267 R indicating a direction out of up, down, left, or right has been selected, the display controller  222  moves the display positions of the respective superimposition marks  266 L,  266 R by a specific amounts of pixels (for example, one pixel) in the designated direction. Note that the respective superimposition marks  266 L,  266 R may be directly moved in the up, down, left, or right direction by a dragging or a swiping operation. 
         [0079]    Moreover, the display controller  222  displays a execute superimposition button  268  in place of the display superimposed mark button  265  in a specific region of the video playback screen  260 . When the execute superimposition button  268  has been selected, as illustrated in  FIG. 11 , the display controller  222  adjusts the display position of at least one out of the left video  62 L and the right video  62 R such that positions inside the videos  62 L,  62 R indicated by the left video superimposition mark  266 L and the right video superimposition mark  266 R are at the same position. Note that in the example of  FIG. 11 , the right video  62 R is disposed in the center of the video playback region  61 , and the left video  62 L is superimposed thereon after being set with transparency. The dotted line S in  FIG. 11  indicates the position where the superimposition mark  266 L or the superimposition mark  266 R has been displayed on the left video  62 L or the right video  62 R. Information related to the overlay sequence (which video is the video to be overlayed on), and the transparency setting can be held as control information of the respective videos  62 L,  62 R. 
         [0080]    The display controller  222  acquires information related to the respective positions of the superimposition marks  266 L,  266 R in each video, the current respective display positions of the left video  62 L and the right video  62 R, and the size of the video playback region  61 . Based on the acquired information, the display controller  222  derives a display position obtained by adjusting at least one out of the left video  62 L or the right video  62 R. For example, the display controller  222  derives the position of the right video superimposition mark  266 R when the right video  62 R has been disposed in the center of the video playback region  61 . The display controller  222  then derives the differences between the position of the derived right video superimposition mark  266 R and the current position of the left video superimposition mark  266 L in the horizontal direction and the vertical direction, and derives a position obtained by moving by this difference as the display position of the left video  62 L. In cases in which either of the videos  62 L,  62 R exceeds the video playback region  61 , adjustment may be performed such that the videos  62 L,  62 R do not exceed the video playback region  61 , and the display positions may be readjusted with the display sizes of both of the videos  62 L,  62 R reduced. 
         [0081]    The display controller  222  updates information related to the display positions included in the respective control information of the left video  62 L and the right video  62 R to the display positions derived above. The display controller  222  also sets the sequence of overlaying in the control information for the respective videos  62 L,  62 R. The display controller  222  also sets a predetermined transparency ratio for the transparency setting included in the control information of the video at the front side of the overlay. The display controller  222  then changes the display position of at least one out of the left video  62 L or the right video  62 R based on the updated control information, and displays the left video  62 L and the right video  62 R superimposed with each other. 
         [0082]    The display controller  222  also displays superimposed display position adjustment buttons  69  in a specific region of the video playback screen  260 . The superimposed display position adjustment buttons  69  are buttons for instructing an adjustment to the display position of at least one out of the left video  62 L or the right video  62 R, which are displayed superimposed with each other. The superimposed display position is made adjustable since, depending on the size of the display sections and the contents of the videos, it is easier to compare the two videos  62 L,  62 R when slightly offset from each other than in cases in which the superimposition marks  266 L,  266 R are displayed superimposed so as to completely match with each other. In the example of  FIG. 11 , the superimposed display position adjustment buttons  69  are provided for adjusting the display position of the left video  62 L at the front side of the overlay. In this case, each time a button of the superimposed display position adjustment buttons  69  indicating either the up, down, left, or right direction has been selected, for example, the display controller  222  moves the display position of the left video  62 L by a specific amount of pixels (for example, one pixel) in the designated direction, as illustrated in  FIG. 12 . 
         [0083]    The display controller  222  also displays a release superimposed display button  70  in a specific region of the video playback screen  260  in place of the execute superimposition button  268 . In cases in which the release superimposed display button  70  has been selected, the display controller  222  restores the video playback screen  260  to a state prior to execution of superimposed display (for example, the video playback screen  260  illustrated in  FIG. 9 ). 
         [0084]    The video playback device  220  may, for example, be implemented by the computer  40  illustrated in  FIG. 5 . A video playback program  250  that causes the computer  40  to function as the video playback device  220  is stored in the storage section  43  of the computer  40 . The video playback program  250  includes the acquisition process  51  and a display control process  252 . 
         [0085]    The CPU  41  reads the video playback program  250  from the storage section  43 , expands the video playback program  250  into the memory  42 , and sequentially executes the processes included in the video playback program  250 . The CPU  41  operates as the acquisition section  21  illustrated in  FIG. 1  by executing the acquisition process  51 . The CPU  41  also operates as the display controller  222  illustrated in  FIG. 1  by executing the display control process  252 . The computer  40 , which executes the video playback program  250 , thereby functions as the video playback device  220 . 
         [0086]    The functionality implemented by the video playback program  250  can also be implemented by, for example, a semiconductor integrated circuit, and more specifically, by an ASIC or the like. 
         [0087]    Next, explanation follows regarding operation of the video playback system  210  according to the second exemplary embodiment. The second exemplary embodiment differs from the first exemplary embodiment in that the superimposed display processing illustrated in  FIG. 13  is executed in place of the height adjustment processing ( FIG. 6 ) executed in the first exemplary embodiment. When the display superimposed mark button  265  has been selected by the user in a state in which the video playback screen  260  is displayed with the display superimposed mark button  265  included, the superimposed display processing is executed in the video playback device  220 . 
         [0088]    At step S 21  of the superimposed display processing illustrated in  FIG. 13 , the display controller  222 , for example, displays the left video superimposition mark  266 L at a predetermined initial position on the left video  62 L as illustrated in  FIG. 10 . The display controller  222  also displays the right video superimposition mark  266 R at a predetermined initial position on the right video  62 R. 
         [0089]    Next, at step S 22 , the display controller  222  determines whether or not the execute superimposition button  268  has been selected by the user. Processing transitions to step S 23  in cases in which the execute superimposition button  268  has not been selected. 
         [0090]    At step S 23 , the display controller  222  determines whether or not a change in the position of either the left video superimposition mark  266 L of the right video superimposition mark  266 R has been received. For example, in cases in which either out of the superimposition mark position adjustment buttons  267 L,  267 R has been selected, and in cases in which either out of the superimposition marks  266 L,  266 R has been drag operated, the display controller  22  receives a change in the position of either out of the superimposition marks  266 L,  266 R. Processing then transitions to step S 24 . However, processing returns to step S 22  in cases in which a change in position has not been received. 
         [0091]    At step S 24 , the display controller  222  changes the display positions of the superimposition marks  266 L,  266 R such that the superimposition marks  266 L,  266 R are displayed at the position received at step S 23  above, and processing returns to step S 22 . 
         [0092]    At step S 22 , processing transitions to step S 25  when the display controller  222  has determined that the execute superimposition button  268  has been selected by the user. At step S 25 , the display controller  22 , for example, sets transparency for the left video  62 L, and displays the left video  62 L superimposed on the right video  62 R such that the left video superimposition mark  266 L and the right video superimposition mark  266 R are at the same position, as illustrated in  FIG. 11 . 
         [0093]    Next, at step S 26 , the display controller  222  determines whether or not a change in the position of the superimposed display has been received. In cases in which, for example, the superimposed display position adjustment buttons  69  have been selected, the display controller  222  receives the change in the position of the superimposed display, and processing transitions to step S 27 . However, in cases in which no change in position has been received, processing returns to step S 26 . 
         [0094]    At step S 27 , the display controller  222  changes the display position of at least one out of the left video  62 L or the right video  62 R based on the position received at step S 26  above, and processing returns to step S 26 . 
         [0095]    At step S 26 , in cases in which the display controller  222  has determined that no change in position of superimposed display has been received, processing transitions to step S 28 , and the display controller  222  determines whether or not the release superimposed display button  70  has been selected by the user. Processing returns to step S 26  in cases in which the release superimposed display button  70  has not been selected. In cases in which the release superimposed display button  70  has been selected, the superimposed display of the left video  62 L and the right video  62 R is released, and superimposed display processing ends. 
         [0096]    As explained above, in the video playback system  210  according to the second exemplary embodiment, the video playback device  220  adjusts the display position of the left video and the right video such that the positions designated by aligning the superimposition marks at the same position in the horizontal direction and the vertical direction. Namely, the left video and the right video are displayed superimposed with reference to the position of the respective superimposition marks. This facilitates comparison of the left video and the right video. 
         [0097]    Moreover, comparison of the left video and the right video is further facilitated by enabling adjustment of the superimposed display positions of the left video and the right video displayed superimposed with reference to the position of the respective superimposition marks. 
         [0098]    Note that although explanation has been given regarding a case in which the left video is set with transparency and superimposed on the right video in the second exemplary embodiment, there is no limitation thereto. Superimposition may be performed with the right video at the front, and transparency may be set for both videos. 
         [0099]    Moreover, although explanation has been given regarding a case in which the display positions of the videos that are displayed superimposed are offset in the horizontal direction and the vertical direction by operating the superimposed display position adjustment buttons in the second exemplary embodiment, there is no limitation thereto. For example, when superimposed display is executed, a preset may be applied such that superimposed display is performed at a position at a predetermined offset distance in the horizontal direction or the vertical direction, from a position where the superimposition marks of both videos completely match. 
         [0100]    Moreover, there is no limitation to cases in which overlaying is performed with the superimposition mark serving as a reference, and one of the videos may be directly moved in at least one out of the horizontal direction and the vertical direction by, for example, button operating or drag operating the video, and superimposed display of both videos may be realized by overlaying the video onto the other video. 
       Third Exemplary Embodiment 
       [0101]    Next, explanation follows regarding a video playback system according to the third exemplary embodiment. In the third exemplary embodiment, explanation is given regarding a case in which display positions of videos are shared between users. Note that in the video playback system according to the third exemplary embodiment, portions similar to those of the video playback system  10  according to the first exemplary embodiment are allocated the same reference numerals and detailed explanation thereof is omitted. 
         [0102]    As illustrated in  FIG. 1 , a video playback system  310  according to the third exemplary embodiment includes a video playback device  320  and a video management device  330 . The video playback device  320  and the video management device  330  are connected to each other through a network. 
         [0103]    A controller  331  of the video management device  330  controls distribution of video data to the video playback device  320 , similarly to the controller  31  of the first exemplary embodiment. Additionally, the controller  331  manages shared information for sharing the display position of videos between users. The shared information includes a username, two playlist names, and information related to display positions of videos indicated by the respective playlists, and this is explained in more detail below. Hereafter, the user at the side registering the shared information to the video management device  330  is sometimes referred to as the “transmission side user”, and the user at the side using the shared information managed by the video management device  330  to play back the videos is sometimes referred to as the “reception side user”. 
         [0104]    More specifically, the controller  331  receives the shared information transmitted from the video playback device  320  due to instruction from the transmission side user. The controller  331  holds, for example, a shared information table  332 A like that illustrated in  FIG. 14  in a video DB  332  that stores plural items of video data and the respective playlists of the video data, and the controller  331  manages the received shared information. In the example of  FIG. 14 , each row corresponds to one item of shared information. Moreover, “playlist  1 ” and “playlist  2 ” are two respective playlist names included in the shared information. Note that in the third exemplary embodiment also, video playback can be performed in the video playback device  320  in a state in which the left video  62 L and the right video  62 R are aligned, similarly to in the first exemplary embodiment. The two playlist names are therefore the playlist name of the left video  62 L and the playlist name of the right video  62 R, respectively. However, since both of the videos  62 L,  62 R are identifiable as either the left video  62 L or the right video  62 R based on the display position, there is no need to specify which out of the left video  62 L and the right video  62 R the playlist  1  or playlist  2  corresponds to. 
         [0105]    The controller  331  also manages the shared information for each transmission side user. When shared information is registered in the shared information table  332 A, the controller  331  allocates, to each item of shared information, a number for identifying the item of shared information for each username as a “user-distinct shared information number”. 
         [0106]    As illustrated in  FIG. 15 , for each user, shared information transmitted by that user when they are the transmission side user is also stored in a sharing user table  332 B in the video DB  332  in association with identification information (for example, usernames) of users that are capable of using the shared information as reception side users. The sharing user table  332 B may be preregistered when application use is registered, and usernames of users capable of using the shared information may be included in the shared information and registered when the shared information has been received by the controller  331 . 
         [0107]    When shared information usable by a logged-in user is present, the controller  331  notifies this to the video playback device  320  in addition to transmitting the playlist listing of the video data permitted for distribution to the logged-in user. More specifically, the controller  331  references the sharing user table  332 B, searches the “reception side user” column for usernames of logged-in users, and acquires the usernames of corresponding transmission side users. In cases in which shared information being managed in association with an acquired username is present in the shared information table  332 A, the controller  331  then determines that shared information usable by a logged-in user is present in the shared information table  332 A. 
         [0108]    Moreover, when the controller  331  has received a request for a share list (described in detail below) from the video playback device  320 , the controller  331  acquires shared information usable by the logged-in user from the shared information table  332 A, and transmits a share list listing the acquired shared information to the video playback device  320 . At least the usernames and the user-distinct shared information numbers for each item of shared information are included in the share list. Other than the above information included in the shared information, metadata, a thumbnail image, and the like of video data indicated by the playlist name included in each item of shared information may also be included in the shared information. 
         [0109]    Moreover, when the controller  331  has received a request for a shared video from the video playback device  320 , the controller  331  acquires shared information for the requested video, and the two playlists respectively indicated by the two playlist names included in the shared information, from the video DB  332 . The controller  331  then transmits the acquired shared information and playlists to the video playback device  320 . 
         [0110]    As illustrated in  FIG. 1 , the video playback device  320  functionally includes an acquisition section  321  and a display controller  322 . Note that the display controller  322  is an example of a reception section and an adjustment section of technology disclosed herein. 
         [0111]    Similarly to the acquisition section  21  of the first exemplary embodiment, the acquisition section  321  acquires video data from the video management device  330 . Additionally, the acquisition section  321  transmits the shared information to the video management device  330  according to instruction by the transmission side user. 
         [0112]    The acquisition section  321  also acquires video data shared from the video management device  330 , according to instruction by the reception side user. More specifically, when a user has logged-in, in cases in which a notification has been received from the video management device  330  stating that shared information usable by the logged-in user is present, the acquisition section  321  notifies this to the display controller  322 . Moreover, when a notification (described in detail below) has been made from the display controller  322  stating that a display share list button has been selected, the acquisition section  321  requests a share list from the video management device  330 . The acquisition section  321  also passes the share list received corresponding to the request to the display controller  322 . Moreover, when the display controller  322  has notified the acquisition section  321  of a username and a user-distinct shared information number of shared information selected from the share list (this is described in more detail below), the acquisition section  321  requests the shared video by transmitting the username and the user-distinct shared information number to the video management device  330 . The acquisition section  321  then acquires the shared information and the playlist received corresponding to the request, sequentially acquires the split files from the video management device  330  according to the playlist, and passes the acquired split files to the display controller  322  together with the shared information. 
         [0113]    Similarly to the display controller  22  of the first exemplary embodiment, the display controller  322  displays a video playback screen on the display section, and performs height adjustment on the left video  62 L and the right video  62 R. Additionally, the display controller  322 , for example, displays a share button  71  on a video playback screen  360  after having performed height adjustment on the left video  62 L and the right video  62 R, as illustrated in  FIG. 16 . When the share button  71  has been selected, the display controller  322  acquires the respective playlist names of the left video  62 L and the right video  62 R from the playlist listing during playback, and acquires information related to the display positions from the respective control information held by the videos  62 L,  62 R. The display controller  322  appends the identification information (for example, the username) of the logged-in user to the respective playlist names of the acquired left video  62 L and right video  62 R and the information related to the display position, and passes this to the acquisition section  321  as the shared information. 
         [0114]    Moreover, when the display controller  322  has been notified by the acquisition section  321  that shared information usable by the logged-in user is present, the display controller  322  displays the display share list button  72  on the video playback screen  360 , as illustrated in  FIG. 17 . When the display share list button  72  has been selected, the display controller  322  notifies this to the acquisition section  321 . 
         [0115]    When the display controller  322  has received the share list from the acquisition section  321 , the display controller  322  also displays, for example, a share list screen  80  like that illustrated in  FIG. 18 . The share list screen  80  may be displayed by switching from video playback screen  360 , or may be displayed superimposed over the video playback screen  360 . In the example of  FIG. 18 , the share list screen  80  includes a share list  81  and a select button  82 . Each row of the share list  81  corresponds to one item of shared information and each row is displayed in a selectable state. Moreover, each row of the share list  81  is linked to at least a username and a user-distinct shared information number, and selecting at least one row from the share list  81  causes the shared information specified by the username and user-distinct shared information number linked to that row to be selected. In the example of  FIG. 18 , a case is illustrated in which the items included in the share list  81  are the username, playlist  1 , and playlist  2 ; however, there is no limitation thereto. In cases in which metadata, a thumbnail image, and the like of the video data indicated by each playlist name is included in the share list acquired from the video management device  330 , this information may also be displayed. 
         [0116]    When the select button  82  has been selected in a state in which at least one row has been selected from the share list  81 , the display controller  322  notifies, to the acquisition section  321 , the username and the user-distinct shared information number linked to the row selected in the share list  81 . The display controller  322  also closes the share list screen  80  and returns to displaying the video playback screen  360 . 
         [0117]    Moreover, when the display controller  322  has received the shared information together with the split files from the acquisition section  321 , the display controller  322  sets, in the control information of the video represented by the split files, the information related to the display position included in the shared information. More specifically, for example, in a case in which the shared information in the first row of the shared information table  332 A illustrated in  FIG. 14  has been received, (x 1 , y 1 ) is set as the display position included in the control information of the video represented by the split files acquired in accordance with playlist  1 . Similarly, (x 2 , y 2 ) is set as the display position included in the control information of the video represented by the split files acquired in accordance with playlist  2 . When the reception side user plays back the video, the display controller  322  can display the video in the same display position as that of the video playback screen  360  when the transmission side user selected the share button  71  by disposing the respective videos  62 L,  62 R in accordance with the control information. 
         [0118]    The video playback device  320  may, for example, be implemented by the computer  40  illustrated in  FIG. 5 . A video playback program  350  that causes the computer  40  to function as the video playback device  320  is stored in the storage section  43  of the computer  40 . The video playback program  350  includes an acquisition process  351  and a display control process  352 . 
         [0119]    The CPU  41  reads the video playback program  350  from the storage section  43 , expands the video playback program  350  into the memory  42 , and sequentially executes the processes included in the video playback program  50 . The CPU  41  operates as the acquisition section  321  illustrated in  FIG. 1  by executing the acquisition process  351 . The CPU  41  also operates as the display controller  322  illustrated in  FIG. 1  by executing the display control process  352 . The computer  40 , which executes the video playback program  350 , thereby functions as the video playback device  320 . 
         [0120]    Note that the functionality implemented by the video playback program  350  can also be implemented by, for example, a semiconductor integrated circuit, and more specifically, by an ASIC or the like. 
         [0121]    Next, explanation follows regarding operation of the video playback system  310  according to the third exemplary embodiment. In the third exemplary embodiment, processing other than processing that shares display positions of videos between users is similar to that of the first exemplary embodiment, and explanation therefore follows regarding the processing to share the display positions of videos between users. 
         [0122]    After first explaining a flow of processing for exchanges between a video playback device  320 A operated by the transmission side user, the video management device  330 , and a video playback device  320 B operated by the reception side user, explanation follows regarding details of processing executed by each of these devices. Note that it is convenient to treat the video playback device  320 A and the video playback device  320 B as being distinct for the sake of explaining differences in behavior between the transmission of shared information and the use of shared information, but this does not imply that these devices are configured differently from each other. 
         [0123]      FIG. 19  illustrates a sequence chart representing a flow of processing for exchanges between the video playback device  320 A, the video management device  330 , and the video playback device  320 B. In the video playback device  320 A, the height adjustment processing for the left video  62 L and the right video  62 R (S 10 ) is, for example, executed similarly to the height adjustment processing of the first exemplary embodiment ( FIG. 6 ). When the share button  71  has been selected from the video playback screen  360  in this state, the display controller  322  generates shared information (S 30 ) and transmits the shared information to the video management device  330  (S 33 ). The received shared information is managed in the video management device  330  (S 40 ). 
         [0124]    Due to a user logging in to the video playback device  320 B, the username of the logged-in user is transmitted from the video playback device  320 B to the video management device  330  (S 71 ). In cases in which shared information usable by the logged-in user is present, the video management device  330  notifies this to the video playback device  320 B ( 572 ). When this notification has been received and the share list has been requested by the video playback device  320 B (S 63 ), the share list is transmitted from the video management device  330  (S 54 ). The video playback device  320 B then makes a request to the video management device  330  for the shared video (S 66 ). The video management device  330  transmits, to the video playback device  320 B, shared information for the requested video and the playlists indicated by the playlist names included in the shared information (S 56 ). 
         [0125]    In the video playback device  320 B, the acquired shared information is analyzed, and the username, the respective playlist names, and information related to the display position of the video indicated by each of the playlist names is extracted. The video playback device  320 B also makes sequential requests to the video management device  330  for the split files in accordance with the acquired playlist (S 68 ). The video management device  330  sequentially transmits the split files to the video playback device  320 B in accordance with the request (S 73 ). In the video playback device  320 B, the video represented by the acquired split files is disposed and played back at a position according to the display position of the playlist included in the shared information (S 69 ). 
         [0126]    Explanation follows regarding processing executed by the video playback device  320 A, the video management device  330 , and the video playback device  320 B, respectively. In each processing, steps that perform processing similar to processing explained with reference to  FIG. 19  are allocated the same reference numerals. 
         [0127]    First, in the video playback device  320 A, when the share button  71  displayed by the video playback screen  360  has been selected, the shared information transmission processing illustrated in  FIG. 20  is executed. 
         [0128]    At step S 31 , the display controller  322  respectively acquires the playlist names for the left video  62 L and the right video  62 R during playback, from the playlist listing received from the acquisition section  321 . Next, at step S 32 , the display controller  322  acquires information related to the display position of the respective videos  62 L,  62 R from the respective control information of the left video  62 L and the right video  62 R. Next, at step S 33 , the display controller  322  appends the identification information of the logged-in user (for example, their username) to the two items of acquired information, these being the playlist names and the display positions, and this is passed to the acquisition section  321  as the shared information. The acquisition section  321  then transmits the shared information to the video management device  330  and then ends the shared information transmission processing. 
         [0129]    Next, in the video management device  330 , when the shared information transmitted from the video playback device  320 A has been received, the shared information reception processing illustrated in  FIG. 21  is executed. 
         [0130]    At step S 41 , the controller  331  allocates a user-distinct shared information number to the received shared information. Next, at step S 42 , the controller  331  stores the shared information allocated with the user-distinct shared information number in the shared information table  332 A of the video DB  332 , and then ends the shared information reception processing. 
         [0131]    Moreover, in the video playback device  320 B, when a username transmitted from the video playback device  320 B due to a user logging in has been received by the video management device  330 , the shared video transmission processing illustrated in  FIG. 22  is executed by the video management device  330 . 
         [0132]    At step S 51 , the controller  331  references the sharing user table  332 B and the shared information table  332 A of the video DB  332 , and determines whether or not shared information usable by the logged-in user is present. In cases in which shared information usable by the logged-in user is present, processing transitions to step S 52 , and the video playback device  320 B is notified that shared information usable by the logged-in user is present. However, in cases in which no shared information usable by the logged-in user is present, the shared video transmission processing ends. 
         [0133]    Next, at step S 53 , the controller  331  determines whether or not a request for a share list from the video playback device  320 B has been received. Processing transitions to step S 54  in cases in which a request for a share list has been received, or the determination of the current step is repeated in cases in which a request for a share list has not been received. 
         [0134]    At step S 54 , the controller  331  acquires shared illumination usable by the logged-in user from the shared information table  332 A, and transmits the share list listing the acquired shared information to the video playback device  320 B. 
         [0135]    Next, at step S 55 , the controller  331  determines whether or not a request from the video playback device  320 B for shared videos has been received. Processing transitions to step S 56  in cases in which a request for shared videos has been received, or the determination of the current step is repeated in cases in which a request for shared videos has not been received. 
         [0136]    At step S 56 , the controller  331  acquires, from the video DB  332 , shared information for the requested videos and the two playlists respectively indicated by the two playlist names included in the shared information, and transmits these to the video playback device  320 B. 
         [0137]    Next, at step S 57 , the controller  331  determines whether or not a request from the video playback device  320 B for split files has been received. Processing transitions to step S 58  in cases in which a request for split files has been received, or the determination of the current step is repeated in cases in which request for split files has not been received. 
         [0138]    At step S 58 , the controller  331  acquires the requested split files from the video DB  332 , sequentially transmits the acquired split files to the video playback device  320 B, and then the shared video transmission processing ends. 
         [0139]    However, when a notification has been made from the video management device  330  to the video playback device  320 B stating that shared information usable by the logged-in user is present, the shared video playback processing illustrated in  FIG. 23  is executed in the video playback device  320 B. 
         [0140]    At step S 61 , the acquisition section  321  notifies the display controller  322  that shared information usable by the logged-in user is present, and having received this notification, the display controller  322  displays the display share list button  72  on the video playback screen  360 . 
         [0141]    Next, at step S 62 , the display controller  322  determines whether or not the display share list button  72  has been selected by the user. Processing transitions to step S 63  in cases in which the display share list button  72  has been selected, or the determination of the current step is repeated in cases in which the display share list button  72  has not been selected. 
         [0142]    At step S 63 , the display controller  322  notifies the acquisition section  321  that the display share list button  72  has been selected, and having received the notification, the acquisition section  321  makes a request to the video management device  330  for the share list. Next, at step S 64 , the acquisition section  321  acquires the share list transmitted from the video management device  330  according to the request, and passes the acquired share list to the display controller  322 . The display controller  322 , for example, displays a share list screen  80  like that illustrated in  FIG. 18 . 
         [0143]    Next, at step S 65 , in a state in which at least one row has been selected from the share list  81  of the share list screen  80 , the display controller  322  determines whether or not shared information has been selected by the user by determining whether or not the select button  82  has been selected. Processing transitions to step S 66  in cases in which shared information has been selected, or the determination of the current step is repeated in cases in which shared information has not been selected. 
         [0144]    At step S 66 , the display controller  322  notifies, to the acquisition section  321 , the username and the user-distinct shared information number linked to the row selected in the share list  81 . Having received the notification, the acquisition section  321  makes a request to the video management device  330  for the shared videos. The display controller  322  also closes the share list screen  80  and returns to displaying the video playback screen  360 . 
         [0145]    Next, at step S 67 , the acquisition section  321  acquires the shared information and the playlist transmitted from the video management device  30  according to the request. Next, at step S 68 , the acquisition section  321  sequentially acquires the split files from the video management device  330  in accordance with the playlist, and passes the acquired split files to the display controller  322  together with the shared information acquired at step S 67  above. 
         [0146]    Next, at step S 69 , the display controller  322  sets, in the control information of the videos indicated by the acquired split files, the information related to the display position included in the shared information, disposes and plays back the respective videos  62 L,  62 R in accordance with the control information, and ends the shared video playback processing. 
         [0147]    As explained above, in the video playback system  310  according to the third exemplary embodiment, the video playback device  320  transmits, to the video management device  330 , information regarding the respective display positions related to the left video and the right video after height adjustment was performed, and this information is managed as the shared information in the video management device  330 . Then, when the shared videos are played back, in the video playback device  320 , the shared information is also acquired together with the playlist, and the videos are disposed at the display positions indicated by the shared information. This enables a user who has compared plural videos to share the display positions for each video with another user such that playback is performed at the same display position, without using editing tools or the like to generate new videos in the height adjusted state. 
         [0148]    In the third exemplary embodiment, explanation has been given regarding a case in which, similar to the first exemplary embodiment, the display position of each video obtained by adjusting the height of the left video and the right video is shared; however, there is no limitation thereto. Similarly to in the second exemplary embodiment, display positions from a case in which the left video and the right video are displayed superimposed may be shared. In such cases, similarly to in the exemplary embodiments above, display positions, transparency settings, and the like of each video at the time of superimposed display may be managed as shared information. 
         [0149]    Explanation has been given regarding a case in which display positions of videos are shared in the third exemplary embodiment. However, in cases in which the shared operation button group  64 C is operated and two video playback timings are synchronized by the transmission side user, this synchronization state may also be shared. In such cases, information for specifying respective frame images of the left video  62 L and the right video  62 R being displayed at the timing when the share button  71  was selected may be acquired (for example, timestamps or frame numbers), and this information may be included in the shared information. When shared videos are played back by the reception side user, the playback timing of the left video  62 L and the right video  62 R is controlled such that frame images of the left video  62 L and frame images of the right video  62 R specified by information such as timestamps included in the shared information are displayed at the same timing. 
         [0150]    In each of the exemplary embodiments above, explanation has been given regarding cases in which split files obtained by splitting a single item of video data at specific time intervals are sequentially acquired and played back in accordance with a playlist, namely, cases in which the subject is video data managed while split into plural segments; however, there is no limitation thereto. For example, video data managed with each segment as an individual file could be the subject, as in MPEG-4. In such cases, the filename of each file may be included in the shared information in place of the playlist name. 
         [0151]    Although explanation has been given regarding examples of cases in which two videos are compared in each of the exemplary embodiments above, technology disclosed herein may also be applied when comparing three or more videos. 
         [0152]    Although the drawings illustrate cases in which baseball videos are played back in each of the exemplary embodiments above, the videos that are made the subject may be videos of another sport such as tennis or golf, or may be videos other than a sports videos. Although technology disclosed herein is particularly applicable to videos captured in similar settings, technology disclosed herein is also applicable to comparisons of videos created with, for example, slight differences in camera angle. For example, in the case of baseball videos, although compositions captured in the batter direction from behind the pitcher are often included, subtle discrepancies may arise in such compositions due to differences between stadiums, difference in the position where the pitcher or batter is standing, and the like, despite the compositions being of the same sort. Even in cases in which such discrepancies arise in videos being compared, comparison of minute portions, such as the position of a specific part of the pitcher or batter, is facilitated as long as the display positions can be adjusted as in each of the exemplary embodiments above. 
         [0153]    Although explanation was given above regarding a mode in which the video playback program  50 ,  250 ,  350  was pre-stored (installed) to the storage section  43 , there is no limitation thereto. The program according to technology disclosed herein may be provided in a mode recorded onto a recording medium such as a CD-ROM, DVD-ROM, or USB memory. 
         [0154]    An aspect of technology disclosed herein enables comparison of plural videos to be facilitated. 
         [0155]    All examples and conditional language provided herein are intended for the pedagogical purposes of aiding the reader in understanding the invention and the concepts contributed by the inventor to further the art, and are not to be construed as limitations to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although one or more embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.