Format intake
The file extension matters, but the recorded fields matter more. This guide explains what OVRLEY can usually read from each activity format and why two files with the same extension can produce different widgets.
OVRLEY reads FIT, GPX, SRT and CSV, plus specialist IGC flight logs, VBO motorsport logs, and telemetry embedded in supported MP4 videos.
Each format was built for a slightly different job and understanding the differences will help you choose the telemetry source to get the exact overlay you want. OVRLEY also supports IGC flight logs and VBO motorsport logs; those specialist formats are covered by the same aviation and motorsport workflows described below. It also works with exports from RaceBox, RaceChrono, AiM Race Studio, AirData UAV, Torque Pro, TrackAddict and LapLegend.
There are two types of widgets - some directly display recoreded data. Others, such as speed or heading, can be calculated by OVRLEY from basic data such as GPS coordinates. In both cases, a widget can only show a metric if the file contains the source telemetry data.
| Metrics / widgets | FIT | GPX | SRT | CSV |
|---|---|---|---|---|
| Course, Elevation, Altitude, Time, GPS coordinates | Direct | Direct | Direct | Direct |
| Gradient, Distance to home, Total ascent | Calculated | Calculated | Calculated | Calculated |
| Speed | Direct | Calculated | Calculated | Direct |
| Pace, Vertical speed | Direct | Calculated | Calculated | Calculated |
| Heart rate, Cadence, Power, Calories, Temperature, Air pressure, Ground contact time, Left/right balance, Stride length, Stroke rate, Vertical oscillation, Core temperature | Direct | Possible | Unavailable | Unavailable |
| G-force, Torque, Gear position | Direct | Possible | Unavailable | Direct |
| RPM, Engine power, Throttle / brake, Lean angle, Lap timing | Unavailable | Unavailable | Unavailable | Direct |
| Vertical ratio | Possible | Possible | Unavailable | Unavailable |
| ISO, Aperture, Shutter speed, Focal length, EV, White balance | Unavailable | Possible | Direct | Unavailable |
Course, Elevation, Altitude, Time, GPS coordinates
Gradient, Distance to home, Total ascent
Speed
Pace, Vertical speed
Heart rate, Cadence, Power, Calories, Temperature, Air pressure, Ground contact time, Left/right balance, Stride length, Stroke rate, Vertical oscillation, Core temperature
G-force, Torque, Gear position
RPM, Engine power, Throttle / brake, Lean angle, Lap timing
Vertical ratio
ISO, Aperture, Shutter speed, Focal length, EV, White balance
Decision order
When you have more than one export available, start with the original file if possible, or a one that preserves the most original data.
Build your overlay Original recordings usually beat re-exported copies.
sensor-rich activity
Use FIT for any sports activity if you have it available. It is most consistent.
track and elevation
Use GPX when the overlay mainly needs a map line, elevation profile, timestamps, or GPS-derived speed.
subtitle telemetry
Use SRT when the camera exported it alongside the clip and when you want high update frequency.
motorsport and custom data
Use CSV for supported logger exports with vehicle, motion, or lap data.
Two files with the same extension can contain very different telemetry. The file format tells OVRLEY how to open the file, but the device and export settings determine what data is actually inside.
FIT is largely standardized, so metrics such as heart rate, cadence,
power, and GPS data are stored consistently across supported devices.
GPX is less standardized. It primarily defines GPS coordinates, elevation,
and timestamps, while additional metrics are up to vendor, stored under custom tags in
extensions. As a result, two GPX files may contain very different telemetry.
The same applies to SRT files. There is no standard for telemetry stored
in SRT subtitles, and even the same manufacturer may use multiple formats. For example,
DJI devices use different SRT layouts depending on the product.
CSV and VBO are even less consistent. Logger apps choose their own column
names, units, timestamps and available channels. OVRLEY recognizes many common exports,
but an unfamiliar file may only provide some of its metrics.
Supported CSV layouts include RaceBox, RaceChrono, AiM Race Studio, AirData UAV, Torque Pro, TrackAddict and LapLegend, plus RaceBox and RaceChrono VBO logs. App versions
and custom presets can still differ. If a file only imports partly,
please send me a sample. OVRLEY support for formats grows from
the real files people share.
This is why two files that look similar in your file browser may support very different metrics in OVRLEY.
Embedded telemetry
Some action cameras store GPS, motion, or camera metadata inside the video file instead of a separate activity file. OVRLEY can read telemetry from MP4 files of GoPro, DJI, Insta360, Sony, Cannon and other cameras, so you do not need an external separate telemetry file to create your overlays.
Telemetry data inside MP4 files is unfortunately not standardized which makes the
process challenging. Different manufacturers, and even devices from the same
manufacturer, may store telemetry differently.
GoPro primarily uses different versions of GPMF metadata. DJI is the most fragmented: many drones record telemetry as separate SRT files, while others
embed telemetry directly in CAMM tracks, often encoded with protocol buffers
(protobuf). Insta360 cameras use their own proprietary metadata embedded
streams, with different generations of protobuf schemas and metadata layouts.
Because of this, one cannot simply "read telemetry from MP4", but it requires device-specific
parsers accounting for several generations of metadata formats and layouts. See current supported files.
A camera clip can hold separate streams inside the same file. Video and audio are standard tracks. Some vendors include metadata like GPS, gyro, and camera settings in a vendor-specific metadata track.
Good overlays start with good source data. You do not need to become a file-format expert, but it helps to know whether your export came from the original device and whether timestamps line up with the video. Compare export formats when you are ready to render.
Use the original activity export where possible instead of a re=export from service such as Strava or Komoot.
Ensure that the clock of your devices and camera are in sync to avoid drift. Account for timezones.
Check that sensors were connected before recording; OVRLEY handles temporary disconnects.
If you export from another app, make sure you export actual activity, and not GPS-plan.
OVRLEY is built for local telemetry overlay work: import the activity, choose the widgets the file can actually support, line it up with the footage, and export the result.
Free, local, and built for action camera footage.