TraceWeaver CLI — stitch Chrome step traces into videos 🎞️

TraceWeaver CLI is a command-line tool that stitches the Screenshot frames contained in Chrome step trace files that mabl collects during test execution into a single MP4 video.

• ✅ Works great with Chrome step traces gathered by mabl
• 🧩 Input: a .zip of JSON trace files (or - to read from stdin)
• 🎬 Output: .mp4 (only)
• 📐 Default size: 1920×1080 (customizable)
• ⏱️ Traces shorter than 400 ms are skipped by default
• 🗂️ Files are processed in name-ascending order; frames within each file follow the event order

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Table of contents

• Prerequisites
  • Node.js + npm
  • ffmpeg
• Install (public npm) > The installed command is traceweave.
• Get a mabl step trace .zip
• Make a video!
• Command reference
• Examples
• Troubleshooting
• Uninstall

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Prerequisites

Node.js + npm

TraceWeaver CLI is a Node.js CLI. We support Node 18+.

macOS (pick one):

• 👉 Easiest: download and run the macOS installer from https://nodejs.org/
• or via Homebrew:

  brew install node
  node -v && npm -v

Windows (pick one):

• 👉 Easiest: download and run the Windows installer from https://nodejs.org/
• or using winget (Windows 10/11):

  winget install OpenJS.NodeJS.LTS
  node -v
  npm -v

• or using Chocolatey:

  choco install nodejs-lts -y

If you already have Node, verify with node -v. You should see v18.x or higher.

ffmpeg

TraceWeaver CLI uses ffmpeg to encode the video.

macOS

brew install ffmpeg
ffmpeg -version

Windows

# winget (recommended)
winget install --id Gyan.FFmpeg -e
ffmpeg -version

# or Chocolatey
choco install ffmpeg -y

If your shell says ffmpeg: command not found, ensure it’s installed and on your PATH, then restart your terminal.

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Install (public npm)

The installed command is traceweave.

# globally
npm i -g traceweaver-cli
traceweave -h

# OR project-local, then use npx
npm i -D traceweaver-cli
npx traceweave -h

If traceweave isn’t found, see Troubleshooting for adding npm’s global bin to your PATH.

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Get a mabl step trace .zip

Use the mabl CLI to export step traces from a test run:

mabl test-runs export <id> --types step

Where to find <id>:

• On the mabl test run results page, click the kebab (⋮) menu in the top-right → View CLI Info.
• Or query via mabl CLI to list your test runs and copy the Test Run ID.

This command will download a .zip containing the step trace JSON files — that’s the input for TraceWeaver CLI.

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Make a video!

Basic usage:

traceweave -i mabl.zip -o output.mp4

• -i, --input <filename>: your .zip of mabl step trace files (or - to read from stdin)
• -o, --output <filename>: output MP4 file (defaults to output.mp4)

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Command reference

Usage: traceweave -i <zip> [options]

Options:
  -i, --input <file>   zip of JSON trace files (or - for stdin)           (required)
  -o, --output <file>  output MP4 filename (defaults to output.mp4)
  --min-ms <ms>        minimum total duration per trace (default: 400)
  --width <px>         output width (default: 1920)
  --height <px>        output height (default: 1080)
  -h, --help           display help for command

Behavior details

• Files are read from the zip in name-ascending order.
• Frames inside each file follow the original event order (no timestamp re-sort).
• Traces totaling < 400 ms are skipped by default (--min-ms).
• MP4 encoding uses H.264 (libx264, -preset veryfast, -crf 23, +faststart).

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Examples

traceweave -i steps.zip -o stitched.mp4
cat steps.zip | traceweave -i - -o out.mp4
traceweave -i steps.zip --width 1280 --height 720 -o out-720p.mp4
traceweave -i steps.zip --min-ms 0 -o video.mp4

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Troubleshooting

“ffmpeg was not found on your PATH”

Install ffmpeg (see ffmpeg above), then restart your terminal. Verify with:

which ffmpeg   # macOS/Linux
where ffmpeg   # Windows
ffmpeg -version

“command not found: traceweave” after npm i -g

Your global npm bin directory may not be on PATH.

• macOS (zsh):

  echo 'export PATH="$(npm config get prefix)/bin:$PATH"' >> ~/.zshrc
  source ~/.zshrc
  which traceweave

• Windows: add your global npm bin path to System → Environment Variables → Path, then open a new terminal.

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Uninstall

npm un -g traceweaver-cli

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Happy weaving! ✨