Expose a host-backed hardware video encoder to Windows guests #104

Problem

Windows 11 ARM64 guests receive 3D acceleration through VMPal VirtIO GPU 3D, but no hardware video encoder is exposed to the guest. Applications that require hardware H.264 encoding fail even though the Apple silicon host provides hardware encoding through VideoToolbox.

Environment

• VMPal 0.111
• Windows 11 Pro 24H2 ARM64
• VMPal VirtIO GPU 3D driver 100.6.101.58114
• Apple silicon host

Reproduction

ffmpeg -hide_banner -loglevel error -f lavfi -i "testsrc2=size=1280x720:rate=30" -t 1 -c:v h264_mf -hw_encoding 1 -f null NUL

Result:

could not find any MFT for the given media type
could not create MFT

The common vendor backends are also unavailable:

• NVENC: Cannot load nvcuda.dll
• AMD AMF: DLL amfrt64.dll failed to open
• Intel QSV: Error creating a MFX session: -9

Software encoding with libx264 works.

One affected application is GoTestify Contribute 2.1.9, which reports:

GPU hardware encoding is not available on this system

GoTestify currently detects vendor-specific encoders, so it would also need to support a standard virtual encoder backend. However, the guest currently has no hardware encoder surface at all.

Feature request

Could VMPal expose host-backed H.264/HEVC encoding to Windows guests using Apple VideoToolbox, preferably as a Windows Media Foundation hardware MFT or a documented virtual-device API?

Suggested verification:

• Windows enumerates a hardware H.264 encoder.
• The FFmpeg command above encodes 1280x720 at 30 fps.
• Supported guest versions, formats, resolutions, and limitations are documented.

This would complement the existing 3D acceleration for recording, streaming, and other applications that require hardware-only video encoding.