FIT Telemetry Converter – Add Live Ride Data to Your Videos (No Re-Encoding Required)

FIT Telemetry Converter is a simple yet powerful tool that turns your .FIT activity files (from Garmin, Wahoo, Bryton, Suunto, or any FIT-compatible device) into subtitles that overlay your speed, heart rate, cadence, power, and elevation directly on your ride or run videos — without re-encoding the video.

That means you can record your action camera footage and your cycling computer or smartwatch activity separately, then easily synchronize them later for YouTube or local playback — all without touching the video quality.

Don’t want to deal with command-line tools? Try the web version - it even supports YouTube sync! Click here for the web-based app - telemetry-subtitles.

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What It Does

This tool reads data from your recorded .FIT file (fitness telemetry) and exports:

• .VTT subtitles – directly usable by YouTube or media players (VLC, MPC-HC, etc.)
• .JSON files – for web previews, advanced integration, or custom overlays

You can then:

• Upload the .vtt file to YouTube as captions (see YouTube captions upload guide)
• Or place the .vtt file next to your video locally for any modern player to show real-time telemetry while watching

No conversion or editing of the video file itself — subtitles simply "float" over playback.

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Why It's Useful

Whether you're a cyclist, runner, or triathlete, you often record two things:

1. A video of your ride or run
2. A .fit activity file with telemetry (speed, power, heart rate, etc.)

FIT Telemetry Converter combines those worlds by letting you overlay your performance data directly on your video timeline — perfect for:

• YouTube uploads of races or rides with live metrics
• Training analysis videos
• Action camera footage synced with fitness sensors

All with zero video re-encoding, so your footage stays 100% original quality.

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Usage

usage: fitconvert -i input_file -o output_file -t output_type -f offset -s N

Parameters

Flag	Description
-i	Path to .fit file (input data)
-o	Path to output file (.vtt or .json)
-t	Output type (vtt or json) – default is vtt
-f	Offset in milliseconds (optional, syncs telemetry start with video start)
-s	Smoothness value (optional, 0–5) – controls interpolation between data points for smoother graphs or frequent updates
-v	Values format: metric or imperial (optional, default metric)

Example of offset

• Positive offset: your video started after the activity → move telemetry earlier
• Negative offset: you started recording the video before the FIT recording → delay telemetry to match

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Example Workflow

1. Record a ride with your Garmin (or similar) and your action camera.
2. Export the .fit file from your device.
3. Run:

   fitconvert -i ride.fit -o ride.vtt -f 3000 -s 3

   (This applies a 3-second sync offset and smooths telemetry)
4. Put ride.vtt next to your video file with the same name as video but with .vtt extension and play it — or upload it to YouTube as subtitles.

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Optional: Embed Subtitles into a Video

You can also "bake" subtitles into your MP4 file without re-encoding:

ffmpeg -i video.mp4 -i ride.vtt -c copy -c:s mov_text output.mp4

This process is instant and keeps the original quality.

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Example Results

Local playback (Media Player Classic):

YouTube upload: Watch on YouTube

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Building from Source

Works on Windows and Linux. Tested with:

• Visual Studio 2019/2022 (Open as Folder)
• GCC on Ubuntu
• Uses Conan for dependencies and CMake as the build system

Example setup for Visual Studio 2022:

 conan install . -s build_type=Release --build=missing
 conan install . -s build_type=Debug --build=missing
 cmake -B build -S . -G "Visual Studio 17 2022" -DCMAKE_TOOLCHAIN_FILE=build/generators/conan_toolchain.cmake
 # Open build\fit2srt.sln

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License

MIT License Copyright © 2025pavel.sokolov@gmail.com / CEZEO Software Ltd.

Part of this repository includes Garmin's FIT SDK (in the fitsdk/ folder), distributed under its respective license.

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About This Project

FIT Telemetry Converter is part of the CEZEO Software ecosystem — focused on creating efficient, portable, and open tools.

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 C E Z E O  S O F T W A R E (c) 2025   FIT telemetry to subtitles converter