VHS produces blank frames on Windows, canvas renderer fails in headless Chrome

[djdarcy]

VHS on Windows produces blank or missing GIF frames. After a little debugging, I identified there were two issues:

1. ttyd ConPTY failure on Windows 11: The bundled ttyd.win32.exe (MinGW cross-compiled) fails with CreateProcessW error 123 on Windows 11 25H2. No child process spawns, so there's nothing to render. Fixed upstream in tsl0922/ttyd#1501 / PR #1502. Pre-built MSVC binary available at djdarcy/ttyd-msvc.

2. Canvas renderer unavailable in headless Chrome: Even with a working ttyd, CanvasToImage() returns empty data because WebGL isn't available in headless Chrome on Windows (particularly in RDP sessions and CI environments). The xterm.js canvas layers (xterm-text-layer, xterm-cursor-layer) exist but produce blank screenshots.

Fix:

• Switch default renderer from canvas to dom in ttyd client options
• Add SwiftShader/ANGLE browser flags as WebGL fallback
• Detect missing canvas layers and fall back to .xterm-screen element screenshots

Working fork with fix: djdarcy/vhs-windows-fixes (branch fix/windows-ttyd-rendering)

Related:

• Recording doesn't work on windows 11. #631 -- VHS broken on Windows
• ConPTY fails on Windows 11 25H2, MinGW cross-compiled binary can't spawn child process tsl0922/ttyd#1501 -- ConPTY failure in MinGW build
• Add MSVC native build support for Windows tsl0922/ttyd#1502 -- MSVC build fix PR