What does the MDVR recording plan show?
Most fleet MDVR units do not record every channel the same way. The road camera may record all the time, the cabin camera only with the ignition on, and a rear camera only when an alarm fires. Many units also write the main stream to a hard disk and a lighter copy to an SD card.
This planner adds up each channel on the disk it writes to. It shows how many calendar days each disk holds before the oldest video is overwritten, how much space locked alarm files take, and which disk size or bitrate meets the retention you must keep.
Record modes and the space they take
Continuous
Records while the unit has power
- Records
- Ignition-on hours plus the delay-off timer
- Space
- Highest
- Suits
- Road and driver cameras
Ignition on only
Records while the engine runs
- Records
- Ignition-on hours only
- Space
- Medium
- Suits
- Cabin and cargo cameras
Alarm only
Records seconds around each alarm
- Records
- Pre-alarm and post-alarm seconds
- Space
- Lowest
- Suits
- Side, rear and reversing cameras
- Mirror recording. The unit writes a second copy to the SD card, often at a lower bitrate. If the hard disk fails or is removed, the card still holds recent video.
- Alarm lock. Some units keep alarm files out of the loop for a set number of days. That space is no longer free for continuous video.
- Sub-stream recording. A lower bitrate saves space and loses detail. Check that the picture is still readable before you lower it.
Inputs you need from the unit
| Input | Where to find it | Tip |
|---|---|---|
| Bitrate per channel | Unit video settings, per channel | Use the recording stream, not the live-view stream. |
| Record mode per channel | Unit recording settings | Continuous, ignition on only or alarm only. |
| Disks fitted | Unit label or the installer's job card | Hard disk or SSD size and SD card size, in decimal GB. |
| Mirror bitrate | Unit storage or backup settings | Only if the unit copies channels to the SD card. |
| Pre-alarm and post-alarm time | Unit alarm settings | Seconds before and after each alarm. |
| Alarms per day | Your event report | Count every alarm that starts a recording. |
How the days are calculated
Sizes are decimal: 1 GB = 1,000 MB and 1 TB = 1,000 GB, as printed on disks and cards.
The lamp compares the calendar days of the shorter disk with your target. Green means at least 10% more, amber means it just reaches it, and red means it falls short. The 10% line is a convention.
Worked example: four channels, a 1 TB disk and a 64 GB mirror
- Road camera at 2 Mbps, continuous for 11 hours: 0.9 GB an hour and 9.9 GB a day. Driver at 1 Mbps, continuous: 4.95 GB. Cabin at 1 Mbps for 10 ignition hours: 4.5 GB. Rear at 0.5 Mbps on 20 alarms of 20 seconds: 0.025 GB.
- Hard disk: 19.375 GB a day, of which 0.225 GB is alarm video. A 30-day lock at 6 days a week holds 5.79 GB. Loop space is 900 - 5.79 = 894.2 GB. Days: 894.2 / (19.15 x 6 / 7) = about 54 calendar days.
- SD mirror at 0.5 Mbps for the road camera: 2.475 GB a day. Loop space is 57.6 - 0.64 = 56.96 GB. Days: 56.96 / (2.45 x 6 / 7) = about 27 calendar days.
- Against a 45-day target the hard disk passes and the card falls short. A 128 GB card meets it, or a mirror bitrate of about 60% of the current value.
These are the values the planner opens with.
How to read the results
- Days on each disk. The shorter one decides what you can still find after an incident.
- Locked space. Alarm files protected from overwrite. A long lock with many alarms can take most of a card.
- Size that meets the target. The next standard size above what you need. Check that the unit supports that size.
- Bitrate share. How far every bitrate on that disk must drop to meet the target with the disks you have.
Set the unit up for the days you need
Read the settings from the unit
Note the bitrate, frame rate and record mode of each channel from the unit menu or its configuration file.
Decide the target per disk
The hard disk usually carries the full retention. The SD mirror often only needs a few days as a backup.
Change one setting at a time
Lower the bitrate of the channel with the most data first, or move a side camera to alarm only.
Check the footage after a week
Open the oldest file on each disk and check that its date matches the plan.
Common mistakes
- Mixing working days and calendar days. A 30-day target usually means 30 calendar days.
- Using the live-view bitrate. Recording often uses the main stream at a higher bitrate.
- Forgetting the delay-off timer. Minutes recorded after the ignition is off add up every day.
- Leaving locked files out. A 90-day lock on many alarms can leave little space for the loop.
- Expecting the mirror to match the hard disk. A small card at a lower bitrate covers fewer days.
Assumptions and limits
Results are estimates. The bitrates on this page are typical values, not Tracom device specifications, so replace them with the values in your unit. Variable bitrate changes with the scene and the light, so real days can be shorter at night or in heavy traffic. The planner assumes the same duty on every operating day and counts alarm segments separately, so overlapping alarms are counted twice. Check the oldest file on a sample of units before you commit to a retention figure in a contract.