Memory management in event recording systems
In vehicle event recorders which capture video as discrete image frames, a managed loop memory and management system is provided to realize a virtual ‘timeline dilation’ effect. For a buffer memory of limited size, the maximum extent of a video series in time is extended by trading a reduction in temporal resolution for an increase in temporal range. Memory cells are overwritten in an ‘interleaved’ fashion to effect a reduced frame rate for certain periods in relation to an event moment. In time periods furthest from the event moment, an effective frame rate is minimized while at time periods closest to the event moment, an effective frame rate is maximized.
1 ) Vehicle event recorders comprising.
a camera; a managed loop buffer memory; and an overwrite mechanism,
said camera is operable for converting optical images to electronic signals suitable for recording in said managed loop buffer memory,
said managed loop buffer memory is a random access, re-writ able, electronic storage medium of finite size suitable for storing data, and in particular data arranged as discrete video frame data,
said overwrite mechanism electronically coupled to said managed loop buffer memory and arranged to manage data overwrite operations whereby a first video frame older than a second video frame is saved in the memory while the second frame is overwritten.
2 ) Vehicle event recorders of claim 1 , said overwrite mechanism being arranged to overwrite data associated with a frame not the oldest frame in memory.
3 ) Vehicle event recorders of claim 1 , said overwrite mechanism being arranged to overwrite data in an interleaved fashion whereby an effective frame rate is preserved by performing overwrite operations on alternate frames or frame sets.
4 ) Vehicle event recorders of claim 1 , said overwrite mechanism further is comprised of an overwrite pointer arranged to point to a cell to be overwritten in a future overwrite action.
5 ) Vehicle event recorders of claim 1 , said overwrite mechanism further comprising a timeline definition which defines an expanded timeline and virtual frame rates and periods for those frame rates.
6 ) Vehicle event recorders of claim 5 , said timeline definition includes one having three distinct periods and an event moment at the timeline midpoint whereby the frame rates associated with the periods at the timeline extremities is lower than the frame rate associated with the period including the event moment.
7 ) Vehicle event recorders of claim 5 , said timeline definition includes one having five distinct periods and an event moment at the timeline midpoint whereby the frame rates associated with the periods at the timeline extremities is lowest, and the frame rate associated with the period including the event moment is the highest.
8 ) Vehicle event recorders of claim 5 , said timeline definition includes an asymmetry whereby the frame rate is different for the periods after an event moment than the periods before an event moment.
9 ) Vehicle event recorders of claim 1 , further comprising a second memory, a high capacity, long-term memory coupled to the managed loop buffer memory.
10 ) Vehicle event recorders of claim 9 , further comprising an event trigger arranged to cause a transfer of data from said managed loop buffer memory and said high capacity long-term memory in an expanded timeline format.
11 ) Vehicle event recorders of claim 9 , said transfer of data step resets the managed loop memory into an initial state and a new timeline is initiated.
12 ) Vehicle event recorders of claim 9 , data in long term memory is not overwritten in successive data transfer steps as it includes capacity sufficient for a plurality of events.
13 ) Methods of dilating a timeline of a video series in a vehicle event recorder video managed loop buffer memory comprising the steps:
receiving electronic signal data associated with video frames from a video camera; and
overwriting previously written data with newly received data, whereby previously written data is comprised of that belonging to a frame which is not the oldest frame in memory.
14 ) Methods of dilating a timeline of claim 13 , said overwriting previously written data step includes overwriting data in an interleaved fashion whereby successive frames are skipped with reference to their capture times to effect an effective reduced frame rate.
15 ) Methods of dilating a timeline of claim 14 , further comprising the step of moving an overwrite pointer to a cell not a member of a timeline definition.
16 ) Methods of dilating a timeline of claim 15 , further comprising applying an overwrite operation to the cell associated with the pointer and further moving the pointer to another cell not part of the timeline definition.
17 ) In a vehicle event recorder system, a managed loop memory comprising:
a coupling to a video camera output whereby images from the camera are received at said managed loop memory;
a plurality of memory cells each being associated with a single video frame;
an overwrite pointer associated with precisely one memory cell; and
a timeline definition, whereby said timeline definition directs the overwrite pointer to be associated with a cell which no longer remains a member of the timeline definition thus subjecting that cell to an impending overwrite action.
18 ) Managed loop memory of claim 17 , said timeline definition comprising two 24 second periods of 1 frame per second and one 48 second period of 4 frames per second, either of said 12 second periods falling before and after the 48 second period.