Definition
DVR (Digital Video Recorder, vehicle-mounted hard disk recorder) is a video monitoring device installed on vehicles. It records videos of the front, rear, cabin, and blind spots of the vehicle through multiple cameras (usually 4 to 8 channels) and stores them on a local hard drive or SD card, supporting loop recording. DVR supports extended functions such as ADAS and DSM, and can interface with FMS and T-Box to achieve remote video retrieval, real-time preview, and alarm-triggered uploads.
DVR uses H.264/H.265 encoding and supports 1080P and above resolutions. Through 4G IoT SIM cards, alarm videos, thumbnails, or real-time streams can be uploaded to the cloud. IoT SIM cards provide high-traffic connectivity for DVR, supporting video uploads, remote retrieval, and real-time preview, with high requirements for network stability and bandwidth.
Technical Features
DVR features collision locking, emergency recording, GPS track overlay, and ADAS/DSM linkage. When an alarm is triggered, related video segments can be automatically uploaded to the cloud for accident evidence and remote handling. It supports OTA upgrades, allowing remote updates of algorithms and firmware.
Use Cases
DVR Applied to commercial vehicles, logistics vehicles, buses, taxis, ride-hailing cars, and vehicles carrying passengers or hazardous materials. Typical scenarios include: driving recording, in-cabin monitoring, accident evidence collection, remote retrieval, ADAS/DSM warnings, fleet safety management, etc. SimtoLink provides IoT SIM cards, dedicated APN, large data plans, and telematics solutions for DVR vehicle monitoring.
Loop overwrite and the order in which locked clips return
A vehicle DVR writes multi-channel pictures into local loop storage first. The IoT SIM carries only the part that was selected: an alarm clip, a thumbnail, playback, or a small preview. Local disk overwrite and the cellular upload queue run on two clocks. Loop overwrite drops the oldest ordinary recording by time. A clip locked by a collision or an alarm should not be overwritten, but the lock itself does not mean the clip has been uploaded. If the queue puts playback and a full-time preview ahead of the locked clip, the incident recording can be pushed out of the memory queue by a new playback task before it finishes uploading, and a wrong policy can also release the locked area on the disk. Estimate the SIM plan for events and occasional playback. Estimating it for always-on high definition produces a completely different system.
The storage medium needs an explicit lock quota. After cellular returns, send the locked clip’s index and time range first, then the pictures, so the platform knows what is still missing. Time comes from a reliable clock, or the clip start and end cannot be lined up with the alarm and the track. Weak-coverage stretches rely on local retention, not on a live stream. With two SIMs or a restricted upload window, write the rule down: there must be a chance to upload before the lock expires. Do not set the upload window shorter than the lock retention. Remote playback should be rate-limited and concurrency-limited, and an alarm upload must be able to interrupt it. Bind the SIM to the plate and the terminal id. When a vehicle is transferred or the terminal is replaced, export locked indexes that have not been uploaded first. Whether in-cabin audio is uploaded should be authorized on its own. Do not turn it on by default with the picture.
A common error is to treat online rate as recording integrity. The device is attached all day, the disk is full and overwriting, or one camera has no signal, and the platform only sees a heartbeat. Another is playback pulling a stream from the disk while loop overwrite deletes the playback start, so the user sees half a clip. A third is a firmware upgrade reboot that loses the lock mark, so the clip from before the incident returns to the area that may be overwritten. Uploading many channels at once with no total bandwidth cap fills both the cell and the plan, and the new urgent clip fails. Acceptance should create one lockable event and, before upload finishes, apply overwrite pressure and one playback, then confirm the locked clip can still be retrieved at its original time. How a driver alarm joins the upload is described under DSM. Event and slice policy is described under ADAS and DVR integrated upload.
Each day, form a local integrity summary: whether each channel has signal, how many locked clips are still unsent, and up to what time ordinary recording has been overwritten. Upload the summary before the pictures. The platform then knows which interval is missing, not only that the device is online. Before the lock quota is exhausted, refuse a new non-urgent lock or prompt a manual export. Do not start quietly overwriting an old incident clip. A playback task may be preempted by a new locked upload. A failed playback can be retried. A failed lock has to be visible immediately. If the upload window is set for the early morning and the vehicle is not in a covered parking place then, the window does not exist, and the lock never gets out during its retention. When two SIMs switch, a clip already in transfer continues from the break. Do not resend from the first second and spend the quota again. Before a transfer or a removal, export unfinished indexes. After the SIM is stopped, the old vehicle produces no new clips. The audio channel stays off by default, and when it is on it is listed separately in the summary. When reviewing an incident, look at the locked time range in the summary first, then fetch the pictures. Do not keep requesting playback in an interval that has already been overwritten.
If the summary upload fails, keep the summary locally until it succeeds or is exported. Keeping only pictures and not the summary leaves the platform unable to say which interval to ask for. After a locked-clip upload breaks, resume from the break, and after it finishes check that the duration matches the locked range. The last ordinary recording before a vehicle enters a basement may be overwritten quickly. If the service needs that stretch, lock it as the vehicle enters the basement. Do not wait for signal to return in the basement and then try to lock a file that is already gone.