c2-overlay

Generate PM5-style overlays for rowing videos from Concept2 FIT files.

Creates accurate ASS subtitle overlays matching the Concept2 PM5 monitor display, synchronized with your workout video using metadata timestamps.

Features

• PM5-style display: Shows time, split pace, stroke rate, distance, watts, and heart rate in a familiar layout
• Automatic synchronization: Aligns workout data with video using creation timestamps
• Interval workout support: Displays work/rest lap information with visual indicators
• Rest overlay: Shows previous lap statistics during rest periods
• Flexible output: Generate ASS subtitles or burn them directly into video

Installation

uvx c2-overlay video.mp4 workout.fit

Or install locally:

uv tool install c2-overlay

Usage

Basic usage (generates ASS subtitle file):

uvx c2-overlay video.mp4 workout.fit

Generate and lint the ASS output:

uvx c2-overlay video.mp4 workout.fit --lint

Lint an existing ASS file:

uvx c2-overlay-lint video.ass

Burn overlay into video:

uvx c2-overlay video.mp4 workout.fit --burn-in output.mp4

Adjust timing manually:

uvx c2-overlay video.mp4 workout.fit --offset 2.5

Override the video start timestamp (when metadata is missing/incorrect):

uvx c2-overlay video.mp4 workout.fit --video-start 2025-12-14T10:41:31Z

Options

• -o, --out-ass PATH: Output .ass file path (default: same name as video)
• --video-start ISO8601: Override video start timestamp (e.g. 2025-12-14T10:41:31Z)
• --offset SECONDS: Manual offset adjustment in seconds (positive = later, negative = earlier)
• --burn-in OUT_VIDEO: Burn overlay into video using ffmpeg
• --label-font FONT: Font for labels (default: PragmataPro)
• --value-font FONT: Font for values (default: PragmataPro Mono)
• --fontsize SIZE: Value font size (default: scaled from resolution)
• --left-margin PX: Left margin in pixels
• --top-margin PX: Top margin (positions overlay from top)
• --bottom-margin PX: Bottom margin (default positioning)
• --box-alpha 0-255: Background transparency (0=opaque, 255=transparent, default: 112)
• --no-interp: Disable per-second/per-meter interpolation (smaller ASS output)
• --lint: Lint the generated ASS output and exit non-zero on errors
• --lint-strict: Like --lint, but also fails on warnings
• --crf VALUE: Video quality for burn-in (default: 18)
• --preset PRESET: Encoding preset (default: veryfast)

Requirements

• Python 3.12+
• ffprobe (for video metadata)
• ffmpeg (optional, for burn-in)

How it Works

1. Extracts video creation timestamp from metadata
2. Reads FIT file trackpoints with absolute timestamps
3. Computes synchronization offset
4. Generates ASS subtitle file with PM5-style overlay
5. Optionally burns subtitles into video with ffmpeg

Display Layout

The overlay shows a bottom-left panel with two rows:

Row 1: TIME | SPLIT | S/M Row 2: METERS | WATTS | BPM

During rest intervals, the overlay displays:

• Previous lap statistics
• Rest countdown timer
• Visual tinting and border highlighting

License

MIT