MultiMon

A multi-monitor video-wall performance tool for Windows and macOS — load video and audio onto monitor slots, set up routing, then enter a fullscreen perform mode that spans or subdivides a single canvas across all selected monitors.

Status: 1.0.0 — released 2026-10-18 for Windows (x64) and macOS (Apple Silicon). Stable on AMD and NVIDIA; the real-Intel (QuickSync) acceptance pass and a multi-vendor 4+ screen rig remain to be run on hardware — see CHANGELOG known limitations.

On Windows, MultiMon is built on a persistent Direct3D 11 pipeline (Vortice.Windows), Media Foundation hardware decode with automatic software fallback, and from-scratch HAP support. The D3D11 device and swapchains are created once at application start and reused for the entire session — no per-cycle teardown.

On macOS (Apple Silicon, macOS 14+), the same portable core (MultiMon.Core, MultiMon.Hap) drives a Metal render core, HAP and VideoToolbox decode, CoreAudio output and an Avalonia control panel, with display refresh matching and a performance readout. The platform choices are recorded in ADR 0005.

Features

• Three playback modes
  • Span — one video source sampled equally across all selected monitors
  • Individual — one independent video source per monitor
  • Split — one high-resolution source divided into a configurable grid of outputs (e.g. 4K → 2×2 1080p)
• HAP / HapQ playback — from-scratch BCn texture upload and YCoCg-to-RGB shader; no third-party HAP library
• Hardware decode — Windows: H.264 and HEVC via Media Foundation (DXGI device manager) with automatic software-decode fallback; macOS: VideoToolbox. No LibVLC
• Audio per output device, clocked to the master timeline — WASAPI shared mode on Windows, CoreAudio on macOS
• Project I/O — save and load monitor assignments and routing as .mmproj files
• Convert to HAP — optional dialog to transcode a source to HAP via FFmpeg (see below)
• Identify screens — numbered overlays on every monitor to confirm assignment before performing
• AMD / NVIDIA / Intel / integrated GPU support on Windows — any Direct3D 11 Feature Level 11.0 GPU

Screenshots

Screenshots will be added before the 1.0.0 GA release.

System requirements

See REQUIREMENTS.md for the full Windows list. In short:

• Windows: Windows 10 version 1809 or later, or Windows 11 (64-bit); any GPU with Direct3D 11 Feature Level 11.0 or higher
• macOS: macOS 14 or later on Apple Silicon. Intel Macs are deferred to 1.1.
• No .NET runtime to install on either platform — it's bundled in the distribution kit

Install and run

Windows

1. Download MultiMon-<version>-win-x64.zip from the Releases page and unzip it to any folder.
2. Run MultiMon.Control.exe (or the included Launch MultiMon App.bat).

macOS

1. Download MultiMon-<version>-macos-arm64.dmg from the Releases page and drag MultiMon to Applications.
2. The app is signed with a Developer ID but not yet notarized: right-click → Open on first launch, or run xattr -dr com.apple.quarantine /Applications/MultiMon.app.

Windows SmartScreen prompt

This release is unsigned, so Windows may show a SmartScreen warning on first run: click More info → Run anyway. Code-signing is planned for a future release (see docs/adr/0004).

FFmpeg — only for "Convert to HAP"

The Convert to HAP feature calls FFmpeg to transcode source files; FFmpeg is not bundled and is not required for any playback feature. To enable it, install FFmpeg from ffmpeg.org (or a trusted build) and add the folder containing ffmpeg.exe to your PATH. On macOS it also looks in the usual install locations (a user-local bin, then Homebrew).

Build from source

One master branch holds both platforms. Each platform has its own solution, sharing the portable projects (MultiMon.Core, MultiMon.Hap, MultiMon.Core.Tests); neither solution references the other platform's projects. CI (.github/workflows/ci.yml) builds both on every push to master and every pull request. How the two development machines share the branch: docs/DEV_PATHS.md.

Windows

Prerequisites: .NET 9 SDK, Windows 10/11, and Visual Studio 2022 or VS Code with the C# extension.

git clone https://github.com/Fiavaion/MultiMon.git
cd MultiMon
dotnet build MultiMon.sln -c Release -warnaserror
dotnet test MultiMon.Core.Tests -c Release --no-build
dotnet test MultiMon.Tests -c Release --no-build

Run the stress harness (the primary verification gate):

dotnet run --project MultiMon.Stress -- --cycles=50 --windows=1

Produce a self-contained release zip:

pwsh scripts/publish-release.ps1

macOS (Apple Silicon)

Prerequisites: .NET 9 SDK, Xcode 15+ with the command-line tools, and the macOS workload (sudo dotnet workload install macos). Full setup: docs/MAC_SETUP.md.

dotnet build MultiMon.Mac.sln -c Release -warnaserror
dotnet test MultiMon.Core.Tests -c Release --no-build
dotnet run --project MultiMon.Stress.Mac -- --cycles=50 --windows=1

Produce the DMG (signed and notarized when the variables in docs/RELEASE.md are set):

bash scripts/publish-release-mac.sh

Releases for both platforms are cut from a tag; see docs/RELEASE.md.

Known limitations

Outside the local-desktop / single-performer threat model for 1.0.0, documented rather than patched:

1. HAP conversion resolves FFmpeg from PATH. If an ffmpeg.exe sits in a world-writable or temporary directory earlier on your PATH, it will be used. Install FFmpeg only from a trusted source and keep your PATH clean.
2. Project file media paths are accepted as-is, including UNC paths. Only open .mmproj files you created; don't open project files from untrusted sources.

Contributing

Contributions are welcome — see CONTRIBUTING.md. Found a bug? Use the in-app Report a bug button or open an issue.

Licence

Licensed under the European Union Public Licence v1.2 (EUPL-1.2) — see LICENSE. Third-party attributions are in THIRD-PARTY-NOTICES.md.

Changelog

See CHANGELOG.md.