Airtime

Measure jump height from video, frame by frame, in the browser.

Airtime turns a clip of a jump into flight time, contact time and jump height. Open a local video, step to the frame the feet leave the ground and the frame they touch down, and Airtime does the math (h = g·t²/8), including for slow-motion footage.

Airtime has two pages:

• / is a time tool for a clip you just took: mark an in point and an out point and read the time and frame count between them. It saves nothing.
• /alpha is the full app described below: jump marking, analysis, saved sessions and trends. It's still in alpha.

Privacy first: videos are loaded from your device into the browser using local object URLs. Airtime does not include an upload API or application backend.

What it does

• Open a video from the file picker or drag and drop it into the app.
• Step one frame at a time, and slow playback to ½× or ¼× to find the moment quickly.
• Mark takeoff and landing frames; marks show on the timeline and can be nudged a frame at a time.
• Report flight time, contact time, jump height and RSI for every jump in the clip, with the best jump highlighted.
• Correct for slow-motion footage (2×, 4×, 8×) so times are real-world.
• Detect the source frame rate from MP4, M4V and MOV files, or measure it during playback for other formats. A video whose frame rate can't be read or measured can be watched but not marked.
• Save sessions to the browser, reopen them by opening the same video again, and export or import them as JSON.
• Correct when each video was recorded, so sessions sort in the right order.
• Zoom into the video up to 5x and pan around the frame.

Quick start

Use the hosted app

Open the deployed Airtime site in a modern desktop or mobile browser, then choose Open video or drag a video onto the player.

Run locally

Requirements:

• Bun 1.x
• A modern browser with HTML video support

git clone https://github.com/andresaclan/airtime.git
cd airtime
bun install
bun run dev -- --open

The development server starts at http://localhost:5173.

Basic workflow

Airtime is built around an approach jump: three marks give contact time, flight time, jump height and RSI. A marking guide under the video shows which step you're on and lights up the button that marks it.

1. Open a local video with Open video, or drag it onto the app.
2. Play (press R to slow down) until you're near your last step before the jump, then pause.
3. Plant step: step with , and . to the first frame your plant foot touches the ground and press Landing (L).
4. Takeoff: step forward to the first frame both feet are off the ground and press Takeoff (T).
5. Landing: step forward to the first frame your feet touch back down and press Landing (L). The analysis panel shows the jump.
6. Press ⌘S / Ctrl+S to save. Open the same file later to pick up where you left off.

Hide the guide with Hide; bring it back from the keyboard shortcuts dialog (?).

Keyboard shortcuts

Press ? in the app to see these at any time.

Shortcut	Action
Space or K	Play or pause
, / .	Step one frame backward / forward
Shift + ← / →	Step one frame backward / forward
R	Cycle playback speed 1× / ½× / ¼×
↑ / ↓	Volume up / down
M	Mute or unmute
T	Mark takeoff on this frame
L	Mark landing on this frame
[ / ]	Jump to previous / next mark
Backspace / Delete	Delete the mark at the playhead
⌘ / Ctrl + Z	Undo a mark change
⌘ / Ctrl + Shift + Z	Redo a mark change
A	Show or hide the analysis panel
⌘ / Ctrl + S	Save the session to this browser
← / →, Home / End	Scrub the timeline when it has focus

Supported files and browser behavior

Airtime accepts common video extensions such as MP4, M4V, MOV, WebM, MKV, AVI, WMV, FLV, MPEG, 3GP, and OGV. Actual playback depends on the codecs supported by the browser and operating system.

Source frame-rate parsing is currently implemented for ISO Base Media File Format containers, including MP4, M4V, and MOV. Other formats can still play when supported by the browser, and their frame rate is measured during playback. If that fails too, Airtime won't mark the video rather than guess its frame rate.

For best results:

• Use an up-to-date Chromium-, Firefox-, or Safari-based browser.
• Use a browser with requestVideoFrameCallback support for the most accurate runtime playback detection.
• Keep very large files in mind: the browser must read and decode them locally, and available memory varies by device.
• If a file opens but cannot play, the codec is likely unsupported or the file may be damaged.

Privacy and data handling

Airtime is designed for local review:

• Selected files are represented with browser-generated object URLs.
• Video bytes are not sent to an Airtime server by the app.
• Marks, titles and notes are saved only when you save, to this browser's IndexedDB. The video itself is never stored.
• Exports are JSON files you download yourself.
• Clearing site data deletes saved sessions. The Sessions dialog shows whether the browser has agreed to protect them from automatic clearing, and how many sessions haven't been exported yet; the Sessions button shows a dot when a backup is overdue.
• Exports from older versions of Airtime can always be imported; sessions are upgraded to the current format automatically.
• Object URLs are released when the active video is replaced or the page is unloaded.

If you use a hosted deployment, the hosting provider may still collect normal website and infrastructure metadata. See the deployment configuration and hosting provider policies for those details.

Development

Install dependencies with Bun:

bun install

Useful commands:

bun run dev -- --open  # Start the Vite development server
bun run check          # Run Svelte and TypeScript diagnostics
bun run test           # Run unit tests
bun run lint           # Check formatting and ESLint rules
bun run format         # Format the repository
bun run build          # Create the static production build
bun run preview        # Preview the production build locally

The project uses:

• Svelte 5
• SvelteKit
• Vite
• Tailwind CSS
• TypeScript
• @sveltejs/adapter-static

Before opening a pull request, run:

bun run check
bun run test
bun run lint
bun run build

These checks also run in GitHub Actions for pull requests targeting main.

Project structure

src/
├── lib/
│   ├── components/       # Video viewer, controls, scrubber, analysis panel, dialogs
│   ├── session/          # Saved sessions (IndexedDB), fingerprinting, export/import
│   └── video/            # Frame-rate detection, timecode, marks and jump analysis
└── routes/
    ├── +page.svelte     # The time tool: in and out points, nothing saved
    ├── alpha/+page.svelte  # The full app and its local file lifecycle
    └── layout.css       # Application theme and shared styles

Deployment

Airtime is built as a static SvelteKit site:

bun run build