Live H.264 video of the headset view in Frame Control

Live in the headset view now streams video instead of polling stereo
screenshots (~2 fps). SteamVR's steamvr-v4l2cam.service mirrors the headset
view into /dev/video99; ffmpeg on the Frame encodes it with x264 (720p30 by
default, AUD + repeated SPS/PPS), /api/stream relays the raw H.264 over SSH,
and the page splits it on access unit delimiters and decodes it with
WebCodecs into the existing viewer. Capture still takes a stereo still; the
desktop panel keeps capture polling, and the page falls back to it if the
video can't start.

The remote ffmpeg runs under a shell that kills it when the SSH channel
closes, stderr goes to a temp file, and a 10 s stall ends the stream. One
stream at a time; a new one supersedes the last.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

docs/how-the-frame-works.md

@@ -30,6 +30,7 @@ Lepton (Android 11, podman container "lepton-dev") ← its own panel, app 305600
 | Handy gamescope root properties on `:0`: `GAMESCOPE_FOCUSABLE_APPS`, `GAMESCOPE_FOCUSABLE_WINDOWS` (triples: window, app id, pid), `GAMESCOPE_FOCUSED_APP`. Read them with `DISPLAY=:0 xprop -root`. | Debugging panels |
 | `gamescopectl screenshot <file>` (with `WAYLAND_DISPLAY=gamescope-0`) captures gamescope's flat layer. | Frame Control's capture |
 | The **headset view** (both eyes, fully composited: room, panels, dashboard, controllers) comes from OpenVR `IVRScreenshots::RequestScreenshot(VRScreenshotType_Stereo)`. It's callable from `python3` with `ctypes` against `/opt/steamvr/bin/linuxarm64/libopenvr_api.so` as an overlay app. The compositor appends `.png`, writing a 1920×1080 side-by-side image (960×1080 per eye) plus a left-eye preview, in about 0.3s. In standby the frame is blank. `vrcmd --screenshot` and `vrcmd --compositorcmd screenshot_request` wrote nothing, even with `steamvr/rawCapturePath` set. | `ui/frame_vrshot.py` |
+| SteamVR's `steamvr-v4l2cam.service` (`/opt/steamvr/bin/linuxarm64/v4l2cam --output=99`) copies the headset view (the `system.HeadsetView` mirror, one undistorted image) into the v4l2loopback device `/dev/video99` ("SteamVR"), 1920×1080 RGB24. `ffmpeg -f v4l2 -i /dev/video99` reads it at about 70 new frames/s; the first frame read can be black. The Frame's hardware encoder (`iris_encoder`, `/dev/video-enc0`) crashes ffmpeg's `h264_v4l2m2m`, so encode with `libx264 -preset ultrafast -tune zerolatency`: 720p30 takes about 0.7 of a core and 1080p60 about 1.7 (of 8). gamescope also publishes a PipeWire `gamescope` video source, but the Frame's GStreamer has no `pipewiresrc`. **Verified 2026-09-26.** | Frame Control's live video (`/api/stream`) |
 | Battery: `/sys/class/power_supply/max1720x_bat_7-36` gives µV/µA (current is positive while charging), `time_to_full_now`/`time_to_empty_now` in seconds, and `temp` in tenths of °C. The charger shows up as `tcpm-source-psy-…` (`type=USB`, `usb_type=C PD [PD_PPS]`), for example 12 V × 1.67 A. | Frame Control's battery card |
 | `vrcmd --stats` reports `activity_level` (3 = standby). | Telling whether the headset is being worn |
 | The SteamVR dashboard has docking: Float in World, Move, Size, Curvature, controller docking, Theater, Multitasking View. **Inferred** from `/opt/steamvr/resources/webinterface/dashboard/` and not yet driven by hand. | [panels.md](panels.md) |