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wrec implementation notes

Current backend

Cargo compiles the Swift capture engine from crates/macos/native/capture_engine.swift into the build output. The daemon starts that compiled capture engine at runtime. Packaged app builds copy daemon and capture-engine into Wrec*.app/Contents/MacOS; standalone CLI packages copy wrec, daemon, and capture-engine into the CLI runtime.

Why this route:

  • Uses real native macOS ScreenCaptureKit immediately.
  • Keeps the frame path inside Apple's native stack.
  • Rust does not receive, copy, or retain raw pixels.
  • Uses SCStreamOutput and AVAssetWriter with HEVC/AAC .mov output.

Current recording path:

SwiftUI menu-bar app / Rust CLI / agents
  -> control protocol
  -> daemon
  -> spawn compiled Swift capture engine
  -> ScreenCaptureKit SCStream
  -> SCStreamOutput CMSampleBuffer
  -> AVAssetWriter / VideoToolbox
  -> HEVC/AAC .mov

The capture engine accepts the selected display/window target, fps, cursor setting, codec, quality mode, resolution, system audio setting, Wrec-window hiding, microphone setting, and mic-indicator setting from the daemon. It keeps ScreenCaptureKit queue depth low and drops samples when the writer is backpressured rather than allowing memory to grow.

The app and CLI stay above the control crate. The daemon owns target listing, job queueing, recording state, store writes, permission operations, and macOS recorder startup. The app owns the user-facing permission flow; keeping the daemon and capture engine in its launch chain makes macOS attribute Screen Recording permission to the matching Wrec channel rather than an internal helper.

The capture engine routes normal stops, macOS Stop Sharing, stream failures, stdin closure, and SIGINT/SIGTERM through one AVAssetWriter finalization path. It also writes ten-second movie fragments. SIGKILL or machine failure cannot run finalization, but the .mov remains playable through its last committed fragment.

Requirements

  • Apple Silicon Mac
  • macOS 15+
  • Full Xcode selected with xcode-select
  • Screen Recording permission granted for the app/terminal during development

Run

cargo dev
cargo run -p cli -- targets --json

If Swift or the native capture engine cannot find the Apple toolchain, select full Xcode:

sudo xcode-select -s /Applications/Xcode.app/Contents/Developer

Package

./scripts/package-macos.sh

By default this creates an ad-hoc signed dist/dev/Wrec Dev.app with the debug Cargo profile. Release packaging is explicit:

./scripts/package-macos.sh release

Release packaging creates dist/release/Wrec.app with the release Cargo profile and a .dmg. Builds are ad-hoc signed; we do not notarize. Set CODESIGN_IDENTITY for Developer ID signing and NOTARIZE=1 with App Store Connect credentials if that ever changes.

The standalone CLI runtime is packaged separately:

./scripts/package-cli-macos.sh release

That archive contains wrec, daemon, and capture-engine so the CLI can be installed without installing the app bundle.