Window Recording Bug On Windows

[7Wdev]

Window capturing is recording the region itself the app is taking on the screen, that means pulling another window on top of it appears in the video. or switching between virtual desktops too.

I am on the latest release, on a Windows 11 machine.

[linear]

CAP-794

[matthewdonsemail-lab]

Additional Report: cap targets windows returns empty list on Windows

Same bug as reported but with more detail on root cause.

Environment

• Cap version: 0.1.0 (bundled CLI from C:\Users\0\AppData\Local\Cap\cap-cli.exe)
• OS: Windows 11
• Browser window: Camoufox (Chromium-based)

Issue

cap targets windows returns an empty array:

$ cap targets windows --json
[]
$ cap targets --json
{
  "screens": [{"id": "65537", "name": "Generic PnP Monitor", "fps": 144, "size": "1920x1080"}],
  "windows": [],
  "cameras": [...],
  "mics": [...]
}

When we find the HWND ourselves via Python win32gui.EnumWindows and pass it to --window:

$ cap record start --window 2952884 --json
{"type":"error","error":"Window with id '2952884' not found. Run `cap targets windows` to list window ids"}

Root Cause Analysis

Looking at the Cap source code for Windows (crates/scap-targets/src/platform/win.rs), window enumeration uses:

pub fn list() -> Vec<WindowImpl> {
    // Uses EnumChildWindows(GetDesktopWindow(), ...)
    unsafe {
        let _ = EnumChildWindows(
            Some(GetDesktopWindow()),
            Some(enum_windows_proc),
            LPARAM(std::ptr::addr_of_mut!(context) as isize),
        );
    }
    context.list
}

This differs from our Python approach which uses EnumWindows (scans all top-level windows including owned windows).

The enum_windows_proc filter also skips:

• Windows owned by the current process (Cap CLI itself)
• Windows from ignored EXEs (webview2, msedgewebview2, cap)
• Invisible/iconic windows
• Child windows
• Tool windows

Likely causes for empty list:

1. The Camoufox window may be an owned window (not a direct child of desktop) — EnumChildWindows only returns direct children
2. DPI awareness mismatch — Cap sets PROCESS_PER_MONITOR_DPI_AWARE in main.rs, may affect window enumeration on some systems
3. Window class or ownership hierarchy prevents it from appearing in the child enumeration

Reproduction Steps

1. Launch any Chromium-based browser window (Camoufox, Chrome, Brave)
2. Run cap targets windows --json
3. Observe empty list despite visible browser window

Expected Behavior

cap targets windows should list all visible top-level windows on the system, including browser windows.

Impact

This makes --window recording impossible on Windows when using Cap CLI programmatically, as there's no way to get a valid window ID from the CLI itself.

[AshokTechie]

Hi, I'd like to investigate and work on this Windows window-recording issue.

I'm setting up the Cap development environment on Windows and will first reproduce the issue locally, then investigate the Windows capture path and submit a PR if I can identify and fix the root cause.

[matthewdonsemail-lab]

@AshokTechie opened a PR #2173 have a look through to see if this resolve it for yourself I've been fighting LLVM install on windows 11 so I've not been able to build cap locally.