Add a 'Volume While Recording' slider, duck audio instead of hard-muting (also works on USB interfaces)

[newideas99]

The problem

"Mute While Recording" on macOS toggles the system output mute flag via AppleScript. Two issues with that:

1. It silently does nothing on a lot of hardware. USB audio interfaces (Focusrite Scarlett, Native Instruments Traktor, etc.) and HDMI/DisplayPort outputs don't expose a software mute/volume control to macOS — the log says "Mute applied" but nothing happens. This is exactly [BUG] macOS 26.3 - 'Mute While Recording' doesn't work when using USB Audio Interface. Can handy have 'Pause While Recording' as an alternative? #998.
2. Full mute is all-or-nothing. Often the goal is just to keep music from drowning out the mic — lowering it to ~10% achieves that while keeping playback alive (no abrupt cutoff/snap-back; related: [Feature] Smooth fade in/out option for "Mute While Recording" #1431).

I listen to music a lot, especially while coding, and it was always annoying to pause or turn down whatever I'm playing just to dictate. I wanted the music to dip while I talk and come right back when I let go.

Proposed solution (working implementation)

Add a "Volume While Recording" slider next to the existing toggle (macOS):

• 0% = mute, stays the default — existing setups behave exactly as before.
• Higher values duck other apps' audio to that level and restore the previous state on key release.

Under the hood, macOS now tries three strategies in order:

1. Core Audio process tap (macOS 14.2+): a tap over every process except Handy, replayed at the chosen gain through an aggregate device wrapping the default output. Ducks every audio source (browsers, players, games) and works regardless of the output device's capabilities — including the USB interfaces from [BUG] macOS 26.3 - 'Mute While Recording' doesn't work when using USB Audio Interface. Can handy have 'Pause While Recording' as an alternative? #998, and at 0% it gives those devices a mute that actually works. Needs the system-audio-recording permission; without it the tap is detected as inert and we fall through.
2. System output volume / mute flag via AppleScript (the devices where today's mute already works).
3. Per-app AppleScript: Spotify / Apple Music volume, plus browser tab media elements for users who enabled "Allow JavaScript from Apple Events".

Windows/Linux keep the current hard mute (slider hidden there). The setting keeps its existing key and stays opt-in.

This complements PR #1028 (pause-while-recording): pause is great for resumable media, ducking covers non-resumable audio (live streams, calls) and people who want their music to keep flowing.

Status

Implemented and tested on macOS (Apple Silicon), on both a Traktor Kontrol S4 USB interface (the #998 scenario — works) and regular outputs. I've already opened #1501 separately for two pre-existing mute bugs we hit along the way (audio stuck muted after cancel / quick taps). Happy to open the PR if there's interest — the branch is ready.

[benediktkraus]

Update from a current v0.9.0/main rebase: I ported the combined branch back on top of cjpais/Handy@dad37ba (v0.9.0 + current main as of 2026-07-06):

https://github.com/benediktkraus/Handy/tree/feature/media-pause-fade-toggle-lock

Scope in that branch:

• Keeps the current mute compatibility path, but replaces the setting UI with Media while recording: None / Mute / Pause / Fade Volume.
• Fade Volume uses a macOS Core Audio Process Tap bridge to duck other processes to ~30% while Handy records, then stops/restores when recording ends; if ducking fails it falls back to mute.
• Pause uses state-aware app pause/resume for Spotify/Music and a fire-and-forget media pause path for browser/system media to avoid blindly resuming something that was already paused.
• Also includes the separate toggle-lock shortcut discussed in Feature Request: Separate Shortcuts for Toggle Talk and Push-to-Talk (e.g. Ctrl+Space / Ctrl+Shift+Space) #170, because the two workflows fit together: hold-to-talk remains available, but users can bind a non-hold recording shortcut.

Local verification after the rebase:

• npm run build passes.
• git diff --check origin/main...HEAD passes.
• Full Rust/Tauri/macOS verification still needs to run before a PR, because this environment did not have Cargo/Rust or a real Tauri WebView available.

Posting here instead of opening a duplicate idea because this thread already captures the Core Audio ducking proposal.