How dash cam loop recording works
Loop recording splits dash cam footage into fixed-length clips, usually 1 to 3 minutes, and automatically overwrites the oldest clip once the card fills; a 128GB card recording 4K front plus 1080p rear at 42 Mbps combined holds about 6.3 hours before the loop starts overwriting.
VIOFO 64GB Industrial Grade High Endurance microSDXC Card for Dash Cam
64GB / high endurance
The main piece of gear for this job. The rest of what you need is below.
What does loop recording actually mean?
A dash cam does not save one giant video file. Instead it records in short segments, commonly 1, 2, or 3 minutes long, and writes each finished segment to the memory card as its own file. Once the card's storage fills up, the camera deletes the oldest segment and keeps recording into a new one, looping through the same amount of storage indefinitely instead of stopping when the card is full.
This is what lets a dash cam run for months without you ever managing files by hand: the camera is always making room for the newest footage by discarding the oldest.
How much footage fits on a card before it loops?
The rough formula is: minutes = card capacity in GB times 0.93, to account for formatting overhead, times 8000, divided by the total bitrate in Mbps across all channels, divided by 60 for hours. A 128GB card recording a 4K front channel at 32 Mbps plus a 1080p rear channel at about 10 Mbps, 42 Mbps combined, works out to roughly 6.3 hours of footage before the oldest clips start getting overwritten.
A 64GB card with a single 1080p front channel at 12 Mbps holds roughly 11 hours by the same math, since a single lower-resolution channel uses far less data per minute than a multi-channel 4K setup.
- 1080p: about 12 Mbps per channel
- 2K or 1440p: about 16 Mbps per channel
- 2.5K or 2.7K: about 20 Mbps per channel
- 4K: about 32 Mbps per channel
- A secondary 1080p rear or cabin channel: about 10 Mbps
Does loop recording delete footage I actually need?
Yes, if you do not lock it first. Loop recording only protects itself by overwriting the oldest unlocked clip, so an important clip left unlocked will eventually get looped over once the card fills again, however long that takes. Most cams give three ways to lock a clip: the G-sensor automatically flags and locks the clip around a hard braking or collision event, a manual button press locks whatever is recording right now, and the companion app lets you export or lock a clip after the fact.
Locked clips are stored in a separate folder or partition on the card so the loop never touches them, but that locked storage is a fixed slice of the card's total capacity. Once the locked folder itself fills up, most cams either stop locking new clips or start overwriting the oldest locked ones, so it is worth clearing out old locked clips you no longer need.
Why does a bigger card mean longer loop coverage, not unlimited storage?
A bigger card does not change how loop recording works, it just gives the loop more room to run before it starts overwriting. A 256GB card at the same 42 Mbps combined bitrate as the earlier example would hold roughly 12.6 hours instead of 6.3, doubling the window before old footage disappears, but it still eventually loops.
This is why the card size question and the loop recording question are really the same question: how many hours of buffer do you want before the oldest unlocked footage is gone for good.
What segment length should I set?
Most cams let you choose the loop segment length, typically 1, 2, or 3 minutes. Shorter segments mean less footage is at risk if a segment gets corrupted by a card write error, and they make it easier to find a specific moment in the companion app or file browser. Longer segments mean fewer file boundaries to deal with but slightly more footage lost if one segment is damaged. A 1 to 2 minute segment length is a reasonable default for most drivers.
Does adding a rear or cabin channel change the math a lot?
Yes, because loop recording time depends on the combined bitrate of every channel writing to the same card, not just the front camera. A single 4K front channel alone runs about 32 Mbps, but adding a 1080p rear channel at roughly 10 Mbps brings the combined total to about 42 Mbps, which is why a three or four channel dash cam with front, rear, and cabin cameras fills the same size card noticeably faster than a front-only camera.
This is worth checking before buying a card size for a multi-channel cam. A 128GB card that would hold around 11 hours behind a single 1080p front channel only holds around 6.3 hours once a second 1080p channel is added, so sizing the card to the actual combined bitrate of the setup matters more than sizing it to the front channel alone.
What you need to keep loop recording reliable
Prices change often.
SANDISK 128GB High Endurance Video microSDXC Card with Adapter for dash cam and home...128GB / high endurance$36.99Check price on Amazon
REDTIGER F7N 4K Dash Cam Front and Rear, 5.8GHz WiFi6-20 MB/s, APP Control4K / 2 channel / Wi-Fi$99.99Check price on Amazon
Frequently asked questions
Will loop recording delete an accident clip automatically?
No, as long as the impact triggered the cam's G-sensor, which locks that clip into a protected folder the loop cannot overwrite. If the G-sensor did not trigger, for example in a low speed bump, you should manually lock or export the clip as soon as possible, since an unlocked clip will eventually be overwritten once the card loops back around to it.
How often does a card get overwritten with loop recording?
That depends on total recording bitrate and card size. Using card GB times 0.93 times 8000, divided by combined Mbps, divided by 60 for hours: a 128GB card at 42 Mbps combined loops roughly every 6.3 hours of driving, while a 64GB card recording only a single 1080p channel at 12 Mbps loops roughly every 11 hours.
Can I turn off loop recording?
Some cams allow it, but doing so means the camera simply stops recording once the card is full instead of continuing to capture new footage, which defeats the point of a dash cam left running unattended. Leaving loop recording on and locking important clips as needed is the safer default for most drivers.
Does a faster microSD card change how loop recording works?
It does not change the loop logic itself, but a card with a low or inconsistent write speed can cause dropped frames or corrupted segments at higher bitrates like 4K's roughly 32 Mbps. A high endurance card, built for the continuous write cycles loop recording puts on a card, holds up better over months of daily overwriting than a standard consumer microSD card.
What happens if the locked clips folder fills up?
Most dash cams either stop locking any new clips until you delete some, or begin overwriting the oldest locked clips once that reserved folder is full, since the camera still needs the loop to keep functioning. It is worth periodically pulling locked clips off the card onto a computer or cloud storage and clearing space.
Does recording in 4K instead of 1080p shorten how long the loop lasts?
Yes, significantly. A 4K channel runs roughly 32 Mbps compared to about 12 Mbps for 1080p, so at the same card size the 4K setup loops through its storage more than twice as fast. If longer coverage before overwriting matters more to you than 4K detail, recording the front channel at 1080p or 2K instead of 4K stretches the same card size considerably further.