Audio Cutter

Documentation

Audio Cutter docs

How to cut audio locally, what the extension supports, and how to audit its privacy boundaries.

Using Audio Cutter

Audio Cutter is a browser extension. Click its toolbar icon to open the durable editor page. No account or additional setup is needed.

Cutting audio

  1. Drop a WAV or MP3 onto the drop zone, or focus it and press Enter or Space to choose a file.
  2. Wait while the file is decoded locally and its waveform appears.
  3. Drag the gold handles, or enter exact In and Out times, to select the audio you want to keep.
  4. Choose WAV or MP3 output and select Cut & download.
  5. The editor encodes the selection in a worker and saves it through a standard browser download.

Joining and changing speed

Join mode combines tracks in your chosen order and normalizes differing channel layouts or sample rates when needed. Speed mode supports 0.25× through 4× and shows the estimated result duration; pitch changes with speed.

Cancelling work

Select Cancel during a worker job to stop it. Audio Cutter reports progress and does not create a partial download after cancellation or failure.

Local processing and privacy boundaries

The precise promise is:

Your audio never leaves your device; no uploads, no accounts, no telemetry; all processing local.

Audio Cutter has no server dependency. WAV and MP3 input, waveform analysis, editing, encoding, and output all stay in the extension page and its workers. Encoder assets ship inside the extension.

The claim rests first on auditable behavior: the extension declares zero permissions, CI scans both production bundles for fetch, XMLHttpRequest, WebSocket, sendBeacon, and EventSource, and source review verifies that its only tab-opening call resolves to its own bundled page. The CSP is defense in depth rather than proof on its own, because it does not restrict top-level navigation.

“Offline” and “no network” describe the extension's audio-processing behavior. This public documentation is a normal HTTPS website, so visiting it uses your network normally.

Verify the contract

  • Review the peer review and capability contract.
  • Inspect both built manifests for the permission list and content-security policy.
  • Search the production bundles for network primitives, as CI does.
  • Observe the extension's network panel while editing: no requests should be made.

Permissions and CSP

Permission When requested Why
None Never The manifest declares "permissions": []. Blob downloads use the browser's standard page download and need no downloads permission.

Extension-page content-security policy

default-src 'none'; script-src 'self'; style-src 'self' 'unsafe-inline'; img-src 'self' data: blob:; media-src 'self' blob:; worker-src 'self'; connect-src 'none'; form-action 'none'; frame-src 'none'; object-src 'none'; base-uri 'none'

connect-src 'none' blocks outbound connections from extension pages. form-action 'none' blocks form submissions, and frame-src 'none' blocks frames. CI checks the literal policy in both built manifests.

Formats and output behavior

  • Input: WAV and MP3 for cutting, joining, speed changes, and conversion.
  • WAV output: lossless PCM audio.
  • MP3 output: 192 kbps encoded audio.
  • Speed range: 0.25× to 4×, with speed and pitch changing together.
  • Channels: mono and stereo are accepted; joins normalize mismatched layouts.

Safety limits

Limits keep unexpectedly large or malformed audio from consuming unbounded browser resources.

  • Input file: 64 MiB maximum.
  • Decoded and in-flight PCM: 256 MiB limits.
  • Channels: mono or stereo only.
  • Processing: cancellable workers and a watchdog bound active jobs.
  • Failure behavior: corrupt or unsupported input reports an error and produces no misleading or partial download.

Install, support, and source

Audio Cutter is a developer preview for Firefox and Chrome. Signed store listings are coming; current packages are available from the latest GitHub release.