saphid--frame-control/docs/mac-in-headset.md

Mac in the headset

Frame Control can show any Mac window, or a whole Mac screen, as its own panel in the Steam Frame. You place each panel anywhere in the room with the SteamVR dashboard. The laser clicks and drags, the thumbstick scrolls, and you type on the Mac's own keyboard. Find it under Tools → Mac in the headset (macOS only).

The confidence labels are the same as in ssh.md.

Why this design

First-party options come first, as the repo's rule asks, with the reason each one was or wasn't chosen. The full list for every device is in streaming.md. Checked 2026-09-28.

Goal	First-party option	Chosen?	Why
One Mac screen in the headset	Apple Screen Sharing (VNC) → Remmina (Remmina 1.4.43 is already installed on this Frame)	Kept as the fallback (panel-on-frame.sh mac-screen)	It's the closest to first-party and needs nothing new. But VNC sends compressed tiles rather than video, so moving content is slow. It shows only whole screens
One Mac screen	Steam Remote Play, Mac as host (Valve)	No	macOS isn't a SteamVR host, and Mac-hosted Remote Play is reported broken (Steam forum). It streams games, not the desktop. Not tested here; one real try is still worth doing
One Mac screen	AirPlay (Apple)	No	Apple licenses AirPlay receivers only to TV and speaker makers, and nothing official runs on Linux. UxPlay is an unofficial receiver, and it mirrors a whole screen, not single windows
One Mac screen	Sidecar / Mac Virtual Display (Apple)	No	These work only with an iPad or Apple Vision Pro
Each Mac window as its own panel	None	–	No first-party way does this: Apple's per-app streaming is only for Vision Pro, and Valve's desktop streaming needs a Windows SteamVR host. So Frame Control does it itself
Mac keyboard and trackpad driving the headset	Bluetooth HID	No	macOS can't act as a Bluetooth keyboard or mouse. A real Bluetooth keyboard paired with the Frame still works
Mac keyboard and trackpad	KDE Connect (KDE)	No	The Frame has no kdeconnectd and it isn't on Flathub. Its Mac app has no keyboard or mouse sharing (inferred), and on Wayland it can only reach the desktop panel
Mac keyboard and trackpad	xrdp (Valve, Developer Mode)	No	It runs a separate Linux session that you view on the Mac. It isn't the headset's view, and it doesn't carry input the other way

What that leaves is our own stream: nothing to install on the Mac or the Frame, and whole screens or single windows. Here the Mac's own keyboard and trackpad need no forwarding, because the windows are still on the Mac. The laser is the only input that has to be sent back.

Other routes that were compared:

Option	One screen	Each window	Speed	Verdict
Sunshine → Moonlight	✓	–	Good	Sunshine's macOS support is still experimental (discussion #777), and it captures whole screens only
Virtual Desktop, Immersed	–	–	–	No Frame client as of September 2026
Frame Control's own stream	✓	✓	Hardware H.264, sending only changed frames	Built

To type into VR surfaces other than these panels (SteamVR's dashboard, games), the Frame supports a uinput keyboard and mouse without sudo (verified 2026-09-27: steamos is in input, and /dev/uinput is root:input 660). That's a separate feature, not part of this one.

How it works

Mac                                              Frame
ScreenCaptureKit (one window or display)
  → VideoToolbox H.264 (hardware, low-latency,
    no B-frames)
  → frame-mac-view, 127.0.0.1 ──ssh -R──→ 127.0.0.1:479xx
                                             → Chromium app window per stream
                                               (WebCodecs decode), on gamescope's
                                               X display, tagged STEAM_GAME
                                             → its own SteamVR panel
  ← CGEvent (clicks, drags, wheel, keys) ←──── pointer, wheel and key events

• The agent is mac/bin/frame-mac-view, built from mac/frame-mac-view (Swift, no dependencies; build.sh). Frame Control's server starts it on first use and stops it on quit.
  • It captures with ScreenCaptureKit, which sends frames only when something changes, so idle windows cost nothing.
  • It encodes in hardware with VideoToolbox's low-latency rate control (plain real-time mode where that's unavailable).
  • While anyone is watching, it keeps the Mac's display awake. A sleeping display isn't drawn, so there would be nothing to capture.
• The link is an ssh -R tunnel on its own connection. It's encrypted and works anywhere ssh frame works, Tailscale included, with no firewall changes on the Mac. If the headset sleeps or the network drops, Frame Control reopens the tunnel on the same port, and open viewers reconnect by themselves.
• Access.
  • Frame Control's own key never leaves the Mac.
  • Each viewer is opened with a single-use ticket. It's tied to one window or display and expires after a minute. It's spent as soon as the viewer confirms it has received its reconnect key. Until then, a retry gets the same key, so a connection lost at that moment doesn't strand the viewer. Stop revokes tickets that haven't been used yet.
  • After that, the viewer holds a reconnect key for that one source, in memory only. Stop revokes it.
  • Remaining risk: a program running as steamos on the Frame could read a ticket from Chromium's command line in the first second or so and use it first. That gets it the one source being opened, not the Mac, and the real viewer would then fail to connect. Android apps in Lepton run in their own podman container, so they shouldn't see the Frame's process list (inferred, not checked).
• The viewer is ui/mac-view.html, served by the agent. It opens on the Frame as a Chromium app window, preferring Chromium XR (~/chromium-xr, built with H.264) over Flathub Chromium.
  • The page puts [fcNNNNN] in its title. The launcher finds the window by that tag and sets STEAM_GAME to a stable id per source, which gives it its own panel (see panels.md). The same Mac window gets the same panel id each time.
  • It decodes with WebCodecs. If it falls behind, it skips to the next keyframe instead of showing old frames late.
  • It falls back to JPEG stills (Compatible quality) where H.264 isn't available.
• Flow control. When the link backs up, the agent skips capture frames before encoding, so no reference frame goes missing. Once the link drains, it sends the newest picture.
• Input.
  • A click on a window's panel brings that Mac window to the front (Accessibility API), then clicks at the same point. Double clicks, right clicks, drags and the wheel work too.
  • Keys typed into the panel are sent as Mac key codes. Any keys or buttons still held down are released if the viewer loses focus or disconnects, or when the stream stops. Characters the key table doesn't know, such as those from other keyboard layouts, are typed as text.
  • The Mac's own keyboard and trackpad keep working as normal. Click a panel with the laser, then type on the Mac.

Permissions (Mac)

• Screen Recording, to see windows. Without it, the card asks for it.
• Accessibility, so input from the headset reaches the Mac. Without it the stream still works, and the viewer says clicks won't go through.

Both are granted to Frame Control. After granting, press Refresh, which restarts the helper so it picks them up. The app is ad-hoc signed, so macOS may ask again after an update.

Quality settings

Setting	Long side	fps	Codec	Use
Sharp	2560	60	H.264, ~0.14 bits/pixel	Text-heavy windows on a strong link
Balanced (default)	1920	60	H.264, ~0.1 bits/pixel	Most things
Light	1280	30	H.264	Weak Wi-Fi or Tailscale off the LAN
Compatible	1280	20	JPEG	A Frame browser without H.264

Checked so far (2026-09-28)

• Mac (checked by hand, macOS 26.5.2).
  • The agent builds, and lists windows and displays.
  • In a browser, the test pattern decoded at about 60 fps (H.264) and 30 fps (JPEG, about 22 Mbps).
  • A click in the viewer arrived at the same point in the source.
  • pmset -g assertions showed the display-awake assertion only while a stream was being watched.
• Automated (tests/test_macview.py, on CI's macOS runner): the agent builds (a build failure fails the job).
  • /ping and the page are open; everything else needs the key.
  • Tickets work once and only for their own source, and Stop revokes reconnect keys.
  • A WebSocket frame claiming 2^63 bytes closes that socket, and the agent keeps running.
  • A stream sends an SPS-led H.264 keyframe, and sends another when asked.
  • Stop ends the stream on the Mac even if the viewer ignores it.
  • The test doesn't decode video, time it, or check where clicks land.
• Linux aarch64 (verified in a stand-in, not on the Frame). In an Arch Linux ARM container with sshd, Xvfb as :0 and Chromium 153:
  • The real show path worked in 1–2.3 s: tunnel, ticket, launcher, window found and tagged STEAM_GAME.
  • Frame Control's key didn't appear anywhere in the stand-in's process list.
  • After the tunnel was killed, it came back on the same port within 4 s, and the viewer reconnected by itself.
  • Chromium decoded the stream in software with the GPU off.
  • Stop closed the window, and Chromium exited.
  • This test found and fixed a bug: in a C locale, xwininfo can't print a title with non-ASCII characters, so the launcher reads _NET_WM_NAME with xprop.
• On the Frame (verified 2026-09-28, SteamOS build 20260925.6191901, from the Mac, nobody wearing the headset). Frame Control's Show with the test pattern:
  • The panel was ready in 1.45 s. SteamVR logged [Overlays] Created: valve.steam.desktopgame.2001639889 (in vrwebhelper_systemui.txt).
  • The window was tagged STEAM_GAME, and gamescope sized it to 1920×1080 although 1280×720 was asked for.
  • Chromium XR decoded it live at about 60 fps: the frame counter advanced 62 in 1.04 s.
  • Over home Wi-Fi, the frames in the viewer window had been drawn on the Mac about 11–17 ms earlier, plus xwd's own time. That's measured against the two clocks, which were 37–39 ms apart (±4 ms, measured over one SSH session). SteamVR's compositor and the display come on top.
  • Clicks and keys injected with XTest into gamescope's Xwayland didn't reach the page. That's inconclusive, not a failure: XTest on gamescope isn't how real input arrives. The laser should arrive as a left mouse button and the thumbstick as a wheel, because the window has an app id (from gamescope's source; see panels.md).
• Not yet checked:
  • Clicking, dragging and scrolling with the laser while wearing the headset.
  • Real window capture and input on a Mac with both permissions granted.
  • Keys from SteamVR's on-screen keyboard.
  • Whether Flathub Chromium has H.264. Chromium XR is used when it's installed, as it is on this Frame.
  • Latency with real, busy windows at Sharp.

Limits

• Only windows on the Mac's current desktop (Space) are listed, and minimised windows can't be captured.
• A window's panel shows only that window. Its menus and sheets are separate windows on the Mac, so open them from the Mac or use Whole screen.
• Keys go to whichever Mac window is in front. Clicking a panel brings its window to the front first.
• Ctrl stays Ctrl. On the Mac, copy is ⌘C, so use Meta+C on a keyboard paired with the Frame.