Hierarchical storage scheme and data playback scheme for enabling random access to realtime stream data

A data playback device, comprising:

• an output unit configured to playback and output either one or both of input audio data and input video data;
• a command unit configured to command playback, stop, or shifting of a playback position forwards/backwards, to the output unit according to a user input;
• a memory unit configured to store a plurality of playback start indexes;
• and
• a control unit configured to record information regarding a playback position that is determined according to the user input as a playback start index in the memory unit when the user input received by the command unit is in a prescribed pattern, and to present the plurality of playback start indexes recorded in the memory unit to a user so as to urge the user to select a desired playback position.

A method for controlling playback and output of either one or both of input audio data and input video data according to a user input indicating playback, stop, or shifting of a playback position forwards/backwards, the method comprising the steps of:

• recording a plurality of playback start indexes, each playback start index being information regarding a playback position that is determined according to the user input which is recorded when the user input is in a prescribed pattern;
• presenting the plurality of playback start indexes recorded by the recording step to a user so as to urge the user to select a desired playback position;
• and
• starting playback from the desired playback start position selected by the user using the plurality of playback start indexes presented by the presenting step.

A server client system, comprising:

• a hierarchical memory server having a library storage device storing realtime stream data in units of segments subdividing each realtime stream data and a cache storage device storing selected segments among the segments stored in the library storage device;
• and
• a data playback client for playbacking and outputting a desired segment of a desired realtime stream data obtained from the hierarchical memory server according to a user input indicating playback, stop, or shifting of a playback position forwards/backwards;
• wherein the hierarchical memory server includes:
• a server side memory unit configured to store random access point segment information from which a possibility for each segment to contain a point that can potentially be random accessed in future can be estimated;
• a control unit configured to control a selection of the selected segments to be stored in the cache storage device according to the random access point segment information stored in the server side memory unit;
• and
• a segment transfer management unit configured to read out the desired segment of the desired realtime stream data requested from the data playback client, either from the cache storage device when the desired segment is stored in the cache storage device, or from the library storage device when the desired segment is not stored in the cache storage device, and to transfer the desired segment to the data playback client;
• and
• the data playback client includes:
• a client side memory unit configured to store a plurality of playback start indexes, each playback start index being information regarding a playback position that is determined according to the user input which is recorded when the user input is in a prescribed pattern;
• and
• a control unit configured to present the plurality of playback start indexes recorded in the client side memory unit to a user so as to urge the user to select a desired playback position, and to request a segment containing the desired playback position selected by the user as the desired segment to the hierarchical memory server.