Multimedia data recording apparatus, monitor system, and multimedia data recording method

A monitoring system comprising:

• a multimedia data recording apparatus comprising:
• a layer classifier that classifies multimedia data into a plurality of hierarchical layers according to data contents or data precision;
• a recorder that continuously records data classified into said layers in a memory;
• and
• a data amount reducer that, when vacant capacity of said memory is at or below a threshold value, performs deletion in an order starting with data classified into a lower layer of said hierarchical layers among data recorded in said memory;
• said monitoring system further comprising:
• a measurer that measures frequency of access to data recorded in said memory;
• and
• a changer that changes at least one or a plurality of layers in which data whose frequency of access is greater than or equal to a predetermined value among data recorded in said memory to a protected layer that is not subject to data amount reduction by said data amount reducer.