Every frame of your dash cam footage contains more information than the image itself. Timestamps, GPS coordinates, speed data, and heading information are embedded in or overlaid on the video — and knowing how to read this data is what makes your footage genuinely useful as evidence rather than just a video recording.
What Timestamp Data Is in Your Footage
Dash cam footage contains two types of timestamp information:
1. File metadata timestamps: Stored in the video file's header — the date and time the file was created. This is the timestamp your operating system shows when you look at file properties. This timestamp is set by the camera's internal clock, which may have drifted from real time if the battery was disconnected or the camera was never synced.
2. GPS-synchronized timestamps: If your camera has GPS, the timestamp is synchronized to GPS time on every startup with signal. GPS time is accurate to within 100 milliseconds — essentially perfect for evidence purposes. A GPS-synced timestamp overwrites any clock drift and is authoritative regardless of when the camera was last synced manually.
In the Nexar app, timestamps visible in footage are GPS-synchronized on cameras with GPS enabled. When reviewing footage for evidence purposes, confirm the GPS indicator was active at the time of the incident — in the app, this appears as an active satellite icon in the status bar.
How to Verify a Timestamp
For legal or insurance purposes, you may need to verify that a timestamp is authentic and unaltered. The process:
- Cross-reference with external sources: Compare the footage timestamp against the time of the police report (which is logged by the dispatcher), the time on the other driver's cell phone, or the time of any nearby business's security camera that captured the same event. Consistency across multiple sources establishes authenticity.
- Check the file metadata: Right-click the video file, select Properties (Windows) or Get Info (Mac), and check the "Date Created" and "Date Modified" fields. The creation date should match the footage timestamp. If the file was modified after creation, the Modified date will be different — not necessarily a problem (app metadata updates can modify files) but worth noting.
- Use a video analysis tool: MediaInfo (free, open-source) displays full file metadata including the embedded creation timestamp, codec, and any GPS data embedded in the file. This provides a complete, independent view of the file's metadata without relying on the camera's app display.
Reading the GPS Overlay
Most cameras with GPS display data as an overlay on the recorded video — visible in the footage itself, not just in metadata. A standard GPS overlay shows:
- Speed: Displayed in mph or km/h, updated approximately once per second. The speed shown is the instantaneous speed at that moment — not an average.
- Coordinates: Latitude/longitude in decimal degrees (e.g., 37.7749° N, 122.4194° W). Some cameras display in degrees/minutes/seconds format instead.
- Heading: Direction of travel in degrees (0° = North, 90° = East, 180° = South, 270° = West) or as a compass bearing (N, NE, E, etc.).
- Altitude: Some cameras include altitude above sea level, primarily relevant for mountain driving.
- Satellite count: Some overlays display the number of GPS satellites locked. Fewer than 4 satellites indicates reduced position accuracy; 8+ is optimal.
What Speed Data Means in an Accident Claim
The speed displayed on GPS overlay is your vehicle's speed at that moment. In an accident claim, this data serves specific purposes:
- Confirming speed limit compliance: If your speed at the moment of impact matches or is below the posted speed limit, GPS data corroborates that you were not speeding. Note that GPS speed is accurate to approximately ±2–3 mph under good satellite conditions.
- Establishing the speed differential: In a rear-end collision where the other driver claims you braked suddenly, your speed in the seconds leading up to impact — visible frame by frame in the overlay — shows whether you were decelerating normally or erratically.
- Disproving false speed claims: If the other party claims you were traveling at 80 mph when you were doing 45 mph, GPS data from every second of the footage provides a definitive counter-record.
GPS speed is admissible in most US jurisdictions as documentary evidence, similar to a vehicle's speedometer reading — but more credible because it's independently verified by satellite signal rather than a potentially uncalibrated mechanical instrument.
Reading GPS Coordinates as Evidence
GPS coordinates in dash cam footage establish precisely where an incident occurred. To use coordinates effectively:
- Convert to a readable location: Copy the coordinates from your footage and paste them into Google Maps or Google Earth. The pin that drops is the exact location where the footage was recorded.
- Cross-reference with the police report: The police report will describe the location verbally (e.g., "intersection of Oak Ave and Main St"). GPS coordinates should place you at or very near that location, confirming the footage is from the claimed incident.
- Establish the approach direction: GPS coordinates from the 30 seconds before an incident show your approach direction and speed. This reconstructs the approach vector that's relevant to fault determination in intersection collisions.
When GPS Data Is Missing
GPS signal can be absent if:
- The camera doesn't have GPS capability (check specs)
- The camera hadn't acquired satellite lock yet (cold start — takes 30–90 seconds)
- The incident occurred in a GPS-blocked area (tunnel, parking garage, dense urban canyon)
- GPS was disabled in the camera's settings
If GPS data is absent, the footage still has evidentiary value — video of the incident itself is the primary evidence. GPS data is supplementary, not mandatory. A clear video showing the sequence of events is useful with or without GPS overlay.
Exporting GPS Data for External Analysis
For complex legal cases, you may want to export raw GPS data for independent analysis. The Nexar app allows GPS data export as a GPX file — a standard GPS exchange format readable by Google Earth, GIS applications, and forensic analysis tools.
A GPX file from your incident trip shows the complete route with timestamps, speeds, and coordinates — this can be overlaid on a satellite map to reconstruct your exact path in the seconds before, during, and after an incident. This level of reconstruction is standard in serious accident litigation and becomes possible with GPS-enabled dash cam footage.
The Practical Checklist
After any incident, when reviewing footage for evidence purposes:
- Confirm the GPS satellite indicator was active in the footage
- Note the speed at the moment of impact (visible in the overlay)
- Note the GPS coordinates at the moment of impact
- Compare the footage timestamp against the police report timestamp
- Export the GPS data as a GPX file if the case may involve legal proceedings
- Keep the original file — don't compress, convert, or edit it
This information, properly documented, converts raw video into structured evidence that adjusters and courts can use directly.