Add Linux support (Avalonia): FFmpeg discovery, packaging & docs

[Hangell]

Add Linux support (Avalonia): FFmpeg discovery, packaging & docs

Summary

ScreenForge currently builds and runs on Windows. We want to add Linux (x64) support next. If you have experience running Avalonia on Linux (X11/Wayland) and handling FFmpeg on Linux, your help would be greatly appreciated.

Why

The goal of ScreenForge is to be cross-platform. Linux support unblocks a large part of our users and contributors and keeps the codebase portable from day one.

Scope (Linux first)

• Target: linux-x64, .NET 8, Avalonia (Skia).
• Out of scope for this issue: macOS packaging. (We’ll file a separate issue later.)

Proposed approach

1. FFmpeg discovery (cross-platform)
   • Resolve path in this order:
     1. SCREENFORGE_FFMPEG env var (absolute path to ffmpeg),
     2. user tools dir (e.g., ~/.local/share/ScreenForge/tools/ffmpeg/bin/ffmpeg),
     3. app-local tools/ffmpeg/bin/ffmpeg (if we add optional tooling later),
     4. system PATH (via which ffmpeg).
   • Throw a clear error with instructions if not found.
2. Process execution
   • Use UseShellExecute=false, capture stderr/stdout, and ensure UTF-8 compatibility.
3. Build tweaks
   • Ensure ScreenForge.App builds with -r linux-x64 on .NET 8.
   • Remove/guard any Windows-only assumptions (e.g., path separators, Win32 specifics).
4. Packaging (first step)
   • Start with a portable publish (no FFmpeg bundled):

     dotnet publish ScreenForge.App -c Release -r linux-x64 --self-contained false

   • Document how to install FFmpeg via distro package manager.
5. Docs
   • Add a new README › Linux section (install .NET SDK 8 + FFmpeg, run instructions).
6. CI (nice to have)
   • Add a Linux job to GitHub Actions that builds linux-x64 and runs a smoke test (launch and exit).

Getting started (suggested)

• Prereqs on Linux:
  • .NET 8 SDK (dotnet --list-sdks should include 8.x).
  • FFmpeg available on PATH (ffmpeg -version).
• Install examples:
  • Debian/Ubuntu: sudo apt update && sudo apt install ffmpeg
  • Fedora: sudo dnf install ffmpeg
  • Arch: sudo pacman -S ffmpeg
• Build:

  dotnet restore
  dotnet publish ScreenForge.App -c Release -r linux-x64 --self-contained false
  

Acceptance criteria

• ✅ App builds on linux-x64 (.NET 8) without code changes to Windows-only bits.
• ✅ When FFmpeg is installed on the system PATH, recording works (manual smoke test: select region, start/stop, output file created).
• ✅ FFmpeg path resolution covers:
  • SCREENFORGE_FFMPEG pointing to a valid binary,
  • user tools dir fallback,
  • system PATH via which.
• ✅ README updated with Linux instructions (install, build, run, troubleshooting).
• ✅ No binary artifacts committed (keep **/bin, **/obj, **/runtimes ignored).

Nice-to-haves (future follow-ups)

• Optional downloader that offers to fetch FFmpeg on first run (e.g., using SharpCompress).
• Packaging as AppImage or Flatpak/Snap once basic linux-x64 runtime is solid.
• Wayland vs X11 notes (overlays, screen capture APIs, permissions).

Where to look in the codebase

• FFmpeg path resolution: ScreenForge.FFmpeg/FFmpegLocator.cs (or equivalent place in App startup).
• App services: ScreenForge.App/Services/*.
• UI/ViewModels: ScreenForge.App/ViewModels/* and Views/*.

How to contribute

• Please comment below if you’re familiar with Avalonia on Linux and FFmpeg.
• Open a Draft PR early if you start implementing this.
• Suggested labels: help wanted, platform:linux, avalonia.

Thanks in advance to anyone who can help us bring ScreenForge to Linux!