Windows (Host)

This is for using a Windows PC as the host, streaming from it. The Linux client, Android app, and Steam Deck plugin are unchanged: they connect to this host the same way they connect to a Linux one.

New here? Read Security & Safe Use first. A streaming host is remote control of the machine, so keep it on a trusted LAN or VPN and require pairing.

There is no installer in this repository. Build slipstream-host and slipstream-tray on Windows (MSVC or the GNU toolchain), then register the host with the Service Control Manager if you want it running when you are not logged into a console.

What this host does

AMD AMF and Intel Quick Sync are not encode backends on Windows. SLIPSTREAM_ENCODER=vaapi, vulkan, pyrowave, amf, or qsv fails at open instead of silently picking another encoder.

Build

From a Windows checkout, with the pinned toolchain in rust-toolchain.toml:

cargo build --release -p slipstream-host -p slipstream-tray

The Windows host always compiles the NVENC backend. nvEncodeAPI64.dll is loaded at runtime, so the same binary runs on AMD and Intel: those GPUs use the software H.264 encoder.

A Linux CI job cross-checks this crate graph with x86_64-pc-windows-gnu. That job does not open a GPU or a display.

Config and the service

Config, pairing state, and the console password live in %APPDATA%\slipstream (SLIPSTREAM_CONFIG_DIR overrides that).

The service name is slipstream-host. The tray looks that name up in the Service Control Manager and can start or stop it. Register it once, from an elevated prompt, with the path to the binary you built:

sc create slipstream-host binPath= "C:\path\to\slipstream-host.exe" start= auto
sc start slipstream-host

slipstream-host.exe with no arguments tries the service dispatcher first. Started by the SCM, it runs the default serve plane (management API and slipstream/1, GameStream off). Started from a console, the dispatcher declines and the normal CLI runs, so slipstream-host serve and slipstream-host serve --gamestream still work. The tray is slipstream-tray.exe.

Encode

SLIPSTREAM_ENCODER selects the backend:

The probe asks the driver which of H.264, HEVC, and AV1 that chip can open, plus the HEVC 4:4:4 and 10-bit capability bits. The host advertises that set on both the native handshake and the Moonlight ServerCodecModeSupport mask. If the probe does not answer, both planes advertise H.264 only.

auto plus H.264 falls back to openh264 when NVENC refuses to open. HEVC and AV1 do not: those sessions fail with the driver error.

openh264 accepts up to 3840×2160, or 2160×3840 in portrait. NVENC is not held to that ceiling. Frame rate follows the session request (1–1000). 4K/120 is a legal request on NVENC; it has not been measured on a Windows GPU from this repository.

Picture

Windows capture is 8-bit BGRA, so the frame already has full chroma.

• 4:4:4 is offered on the native plane only when the session is HEVC, the client asks for it, and the NVENC probe reported NV_ENC_CAPS_SUPPORT_YUV444_ENCODE. GameStream stays 4:2:0.
• HDR / 10-bit is not offered. The encoder refuses a 10-bit session, and capture cannot produce a PQ frame, so the handshake stays at 8-bit even if the GPU's 10-bit bit is set.
• Cursor. Capture embeds the pointer. The host does not advertise a separate cursor blend, because it cannot also deliver a pointer-free frame plus a cursor bitmap.

Display

The default is a mirror: the session changes the mode of an existing monitor with ChangeDisplaySettingsExW and restores it when the session ends.

A headless virtual monitor needs SLIPSTREAM_VIRTUAL_DISPLAY=idd (also 1, on, true, yes, or virtual) and the RustDesk indirect display driver installed and loaded. The host speaks that driver's userspace plug/unplug protocol (device interface {781EF630-72B2-11d2-B852-00C04EAF5272}). The driver is not shipped here: Windows will not load an unsigned indirect-display driver. If you ask for idd and the driver is absent, the session fails and names the install. It does not fall back onto someone else's monitor. mirror, 0, off, false, no, or an unset variable keeps the mirror.

Network

SLIPSTREAM_PERFORMANCE_PROFILE=low_latency registers the capture, encode, send, and input threads with MMCSS (Games on the critical path, Playback on the rest) and raises the thread priority when MMCSS refuses. Generic segmentation offload and TXTIME pacing stay Linux-only. Video and audio DSCP (CS5 / CS6) are applied through qWAVE when qwave.dll loads; the IP TOS byte is still set when it does not. NVENC bitrate changes are applied in place. The software encoder cannot retarget without rebuilding the session.

Limits

These are current gaps, not settings you can flip:

• No on-glass Windows GPU run is part of this repository's CI. The cross compile checks that the host builds.
• HDR capture is not implemented.
• The pointer stays inside the captured frame.
• No AMF, Quick Sync, or PyroWave backend.
• No virtual gamepad.
• The software encoder is H.264 only and resolution-capped as above.