obs-streamer-tools-plugin/README.md

# obs-streamer-tools-plugin

Native OBS Studio source plugin that pulls streamer-tools camera feeds
directly from LiveKit over WebRTC, replacing the current SRT/RTSP-via-VLC-or-
Media-Source path for directors. Full design:
`docs/superpowers/specs/2026-09-06-obs-camera-plugin-design.md` in the
`streamer-tools` repo.

## Status

**Release/distribution of built binaries is blocked pending owner sign-off.**
This plugin statically/dynamically pulls in Google WebRTC and OpenH264 code
through the LiveKit SDK — a real patent/royalty question (OpenH264/WebRTC)
that only the project owner can decide. Nothing in this repo should be built
into a package and handed out, posted, or attached to a public release until
that sign-off happens. See `third_party/livekit/README.md` for the specifics
of what is and is not currently known/shipped on the licensing side —
including a 2026-09-07 finding, sourced from Cisco's own OpenH264 FAQ, that
the way LiveKit's WebRTC build normally links OpenH264 (statically, from
source, not Cisco's runtime-downloaded binary) is specifically the case Cisco
says voids their MPEG-LA royalty coverage and shifts it to the redistributor.
That finding has not been confirmed against LiveKit's actual pinned build —
see the third_party doc for exactly what is and isn't verified. (CI in
`.gitea/workflows/build.yml` only builds, tests, and uploads CI-internal
build artifacts — it does not create a Gitea Release or otherwise publish
anything publicly.

`.gitea/workflows/release.yml` is the mechanism that *would* publish a
release, but it does not run automatically: it is gated on someone pushing a
`v*` tag, which is the actual sign-off gate in practice — don't push one
until the owner has actually signed off on C1. When it does run, it packages
each platform's `build/package/` (or macOS's bundle output, once that lands)
into a zip and creates a **draft** Gitea Release, whose generated release
notes lead with the same C1 reminder as this section, so whoever opens the
draft to publish it sees the open question again before doing so. Building
that mechanism is not the same as clearing C1 — it still requires the same
owner sign-off before a tag gets pushed.)

The separate license-compatibility question — this repository's own top-level
`LICENSE` was GPLv2 while the vendored LiveKit binaries are Apache-2.0, which
are incompatible — is **resolved**: the project owner has relicensed this
project's own first-party code to Apache-2.0, matching LiveKit. Everything in
this repo is now Apache-2.0, so there is no remaining GPL/Apache
incompatibility.

The plugin is **functionally complete on Linux and verified end to end there**
(module loads into real libobs, connects to a real LiveKit server through the
real streamer-tools API shape, and pushes decoded frames into
`obs_source_output_video`/`_audio`).

It has **not been run in the OBS GUI on any platform.** macOS builds the real
module in CI but its artifact is not yet loadable (see the macOS packaging gap
under CI).

**Windows CI is now green.** The run at `f27b1c0` is the first completed
green Windows job on this repository: the from-source libobs bootstrap
configures, builds and installs, `find_package(libobs)` resolves, all 6 CTest
suites pass, and `build\package\bin\64bit\streamer-tools-camera.dll`
(136,192 bytes) is staged next to `livekit.dll` and `livekit_ffi.dll` — read
out of the job's own log body, not inferred from the job status. That also
retires three previously-unproven items in one go: the `-A x64` argument fix,
the PowerShell rewrite of the Windows steps, and the `add_subdirectory`
patch for `OBS::w32-pthreads`. Windows is still **unverified in the OBS GUI**,
exactly like the other two platforms. See "Where the Windows bootstrap got
to" under CI below for the whole trace, and check current CI status rather
than trusting this paragraph's age.

See "What is verified, and how" below for exactly what has and has not been
checked, and "Testing this by hand" for what a human still needs to do.

## Layout

```
cmake/LiveKitSDK.cmake   - downloads + unpacks the pinned client-sdk-cpp release
core/                    - core library (C++17, no OBS dependency, headless-testable)
  include/stplugin/
    core.h                 version + ConnectionConfig
    json.h                 small strict JSON reader
    http.h                 injectable HTTP client interface
    api_client.h           the two /api/obs/:slug/* calls
    session_types.h        media/state types + the pure session logic
    session.h              LiveKitSession, the livekit::Room wrapper
  src/
    http_curl.cpp          libcurl backend (Linux/macOS)
    http_winhttp.cpp       WinHTTP backend (Windows)
  tests/                   dependency-free CTest suites
obs-adapter/             - thin OBS glue (C++)
  src/plugin-main.cpp      obs_source_info, properties UI, frame output
  data/locale/en-US.ini
scripts/livekit-dev-room.py - mints tokens for the integration test
third_party/livekit/     - redistribution notices for the LiveKit binaries
.gitea/scripts/          - the actual per-platform build commands, shared by build.yml and release.yml
.gitea/workflows/build.yml    - 3-platform CI matrix (every push/PR; never publishes)
.gitea/workflows/release.yml  - packages + creates a draft Gitea Release (only on a `v*` tag push; see Status above)
```

## How it works

1. The operator fills in the streamer-tools server URL, room slug and read key,
   and picks a camera from the dropdown.
2. The source's own worker thread calls `POST /api/obs/:slug/token?key=…` to
   mint a hidden, subscribe-only LiveKit token
   (identity `obs:<slug>:<nonce>` — a fresh nonce per mint, so two OBS
   installs watching the same room can never kick each other).
3. `LiveKitSession` connects `livekit::Room` to the returned `wsUrl`, waits for
   the chosen participant's `Source.Camera` video track (and their microphone),
   and reads decoded frames off `VideoStream`/`AudioStream`.
4. The adapter hands those straight to `obs_source_output_video` /
   `obs_source_output_audio`.

Nothing on the OBS UI thread ever blocks on the network. The one deliberate
exception is the "Refresh camera list" button, which the operator pressed and
is waiting on; it uses a shortened 5s timeout.

### Design decisions worth knowing before changing this

- **Frames come from `VideoStream::fromTrack` with our own reader threads, not
  from `Room::setOnVideoFrameCallback`.** The dispatcher API is keyed by
  (participant identity, track *name*), which is only knowable once the track
  is published — and disassembly of `liblivekit.so` 1.10.1 confirms that
  neither `Room::setOnVideoFrameCallback` nor the dispatcher's own version
  starts a reader for an already-subscribed track; they only record the
  registration. Registering at the only moment the name exists would therefore
  have silently produced no video.
- **Every stream operation runs on one owned worker thread**, never on a
  LiveKit room event thread: `Room::disconnect()` from inside a delegate
  callback is documented to deadlock.
- **`VideoStream::Options::capacity` is 3**, making the SDK queue a
  drop-oldest ring buffer. A stalled consumer can only fall three frames
  behind and then sees the *newest* frame, not a backlog — the structural
  answer to the stale-media bug that motivated this plugin.
- **Video and audio are both timestamped with `os_gettime_ns()` at arrival.**
  The SDK gives video a WebRTC capture timestamp and audio none; mixing two
  epochs inside one OBS source would guarantee A/V drift. This relies on the
  SDK's jitter buffering having already aligned them — the assumption the
  design doc flags for verification on real hardware. **Still unverified.**
- **WebRTC changes resolution mid-stream.** Observed directly in the
  integration test: the first frames after (re)subscribing arrive at a
  downscaled spatial layer before ramping to the published size. The adapter
  passes each frame's own geometry through, and logs geometry changes.

## Building

Linux (the platform that is fully verified). `STPLUGIN_BOOTSTRAP_OBS=OFF`
skips the macOS/Windows OBS-SDK bootstrap, which Linux does not need:

```
sudo apt-get install -y cmake ninja-build libobs-dev libcurl4-openssl-dev
cmake -S . -B build -G Ninja -DCMAKE_BUILD_TYPE=Release -DSTPLUGIN_BOOTSTRAP_OBS=OFF
cmake --build build
ctest --test-dir build --output-on-failure
```

The configure step downloads the pinned `client-sdk-cpp` release (~13 MB) into
`build/_deps/livekit-sdk`. Point `-DSTPLUGIN_LIVEKIT_SDK_DIR=<path>` at a
persistent directory to cache it across builds; `-DSTPLUGIN_LIVEKIT_SDK_VERSION`
and `-DSTPLUGIN_LIVEKIT_SDK_TRIPLE` override the pin and the release triple.

The build stages a runnable layout into `build/package/`:

```
build/package/bin/64bit/streamer-tools-camera.so   (RPATH=$ORIGIN)
build/package/bin/64bit/liblivekit.so
build/package/bin/64bit/liblivekit_ffi.so
build/package/data/locale/en-US.ini
build/package/licenses/...
```

That is exactly the layout OBS searches on Linux and Windows —
`<config>/obs-studio/plugins/<name>/bin/64bit` plus a sibling `data/`, per
`AddExtraModulePaths()` in obs-studio's `UI/window-basic-main.cpp` — so
`build/package/` is a straight drop-in. The module resolves the LiveKit
libraries from `$ORIGIN` (verified: `ldd` on the staged copy resolves both
to `bin/64bit/`), not from the build tree. macOS is not this shape; see the
macOS packaging gap under CI.

## Testing this by hand

**Nobody has yet run this in the OBS GUI. That test is still outstanding on
all three platforms.** To do it on Linux:

```
mkdir -p ~/.config/obs-studio/plugins/streamer-tools-camera
cp -r build/package/bin build/package/data \
      ~/.config/obs-studio/plugins/streamer-tools-camera/
obs
```

(That yields `.../streamer-tools-camera/bin/64bit/streamer-tools-camera.so`
and `.../streamer-tools-camera/data/locale/en-US.ini`, which is what OBS
looks for.)

Then: Sources → `+` → "streamer-tools Camera" → fill in the server URL, room
slug and read key from the room's settings page → "Refresh camera list" → pick
a camera. Check `~/.config/obs-studio/logs/` for
`[streamer-tools-camera] connected to …` and `[streamer-tools-camera] video
frame WxH I420`.

What to look for that automated testing could not answer:
- Does video actually *appear*, right way up, right colours?
- Is A/V sync acceptable? (see the timestamp caveat above)
- What is the end-to-end latency versus the existing egress path?
- Does a publisher restarting mid-show recover cleanly on screen?

### Running the LiveKit integration test

`core/tests/test_integration_livekit` publishes a synthetic camera into a real
room and subscribes to it through the wrapper. It skips unless
`STPLUGIN_IT_*` is set:

```
livekit-server --dev --bind 127.0.0.1 &
eval "$(python3 scripts/livekit-dev-room.py)"
ctest --test-dir build -R test_integration_livekit --output-on-failure
```

## What is verified, and how

Verified on Ubuntu 24.04 (libobs 30.0.2, client-sdk-cpp 1.10.1,
livekit-server 1.13.6 in dev mode):

| Claim | How it was checked |
|---|---|
| The pinned LiveKit SDK links and is callable | `test_livekit_smoke`: `initialize()`/`shutdown()` round-trip, header version asserted equal to the CMake pin |
| The JSON reader handles real and hostile input | `test_json`, 158 checks, including truncated bodies, HTML error pages, binary garbage, lone surrogates, and a depth-limit case |
| The API client parses the real response shapes and every error branch | `test_api_client`, 127 checks, against a fake HTTP client **and** a real loopback HTTP server driving the actual platform backend |
| A dead/stalled/garbage server cannot hang or crash the plugin | loopback cases: truncated JSON, connection closed with no reply, non-HTTP bytes, dead port, stalled server cut off by the client timeout |
| Session state transitions, track selection, frame geometry | `test_session`, 81 checks, plus real `connect()` failures against the real SDK |
| **Media actually flows** | `test_integration_livekit` against a real LiveKit server: 36 video frames + 323 audio frames, correct I420 geometry and plane pointers, publisher unpublish → `hasVideo()` false with **no further frames from the dead publisher**, republish → video resumes |
| **The module loads into real libobs and pushes frames** | a headless libobs harness (`obs_startup` + `obs_reset_audio`/`obs_reset_video` + `obs_open_module`) driving the built module against a stand-in streamer-tools API in front of a real LiveKit server. Log: `connected to ws://…  watching cam-test` then `video frame 640x360 I420`; the camera dropdown populated as `Test Camera` / `Dark Camera (offline)`; status `connected`; clean destroy and unload |
| A wrong read key is reported, not silently swallowed | same harness with a bad key: status `unknown room slug, or the read key is wrong or has been rotated`, warning info type, retry with backoff, no crash |
| Changing the selected camera reconnects cleanly | same harness: switch to a dark slot and back. Each switch mints a fresh `obs:<room>:<nonce>` identity and reconnects; video returns; status stays `connected`; no crash, no stale frame |
| Two sources in one OBS process | same harness with a second source added: both connect with distinct nonce identities, both receive frames, both tear down cleanly |

**Not verified anywhere:**
- The OBS GUI, on any platform. No human has looked at this in OBS.
- macOS beyond "CI builds and links the real module and the core tests pass".
  Its artifact is a bare `.so` with a relative libobs install name and will
  not load in OBS.app — see the macOS packaging gap under CI.
- Windows beyond "the core library and the WinHTTP backend compile and their
  tests pass", from runs predating the current fixes. The WinHTTP backend has
  never run against a real streamer-tools server, only against the loopback
  test server in `test_api_client`.
- A/V sync and end-to-end latency against the existing egress path.
- Behaviour against the real production streamer-tools server (only against a
  stand-in serving the same shapes).
- Token expiry after an hour. Expiry is handled *reactively*: a fatal
  disconnect makes the worker mint a fresh token and reconnect. The design
  doc's "proactively refreshed before expiry" is **not** implemented —
  `client-sdk-cpp` 1.10.1 exposes no way to hand a live `Room` a new token.

## CI

`.gitea/workflows/build.yml` runs on every push, matrixed across the three
runners available to this repo under the `CyberCoveLLC` org.

| Job | `runs-on` | Runner | State |
|---|---|---|---|
| `linux` | `ubuntu-24.04` | `localhost.localdomain` | **Green.** Builds the real adapter against Ubuntu's libobs-dev 30.0.2, runs all six test suites, uploads `build/package` as an artifact |
| `macos` | `macos-latest` | `home-mac` (Global) | **Green.** Builds libobs 30.0.2 from source, then the real adapter; 6/6 tests; artifact uploaded. But see the macOS packaging gap below |
| `windows` | `windows-latest` | `winvm-builder` (org-scoped) | **Failing, fix pushed and awaiting a completed run.** Every completed run so far has failed; the latest got as far as building libobs and stopped on an OBS-side `OBS::w32-pthreads` target that its own modern CMake path never defines. A bootstrap patch for that gap has been pushed but not yet confirmed by a green run; see below |

The Linux job is pinned to `ubuntu-24.04` rather than `ubuntu-latest`: this
instance's two Linux runners answer `ubuntu-latest` with different releases,
and 22.04's `libobs-dev` is OBS 27 — a different API surface, and the LiveKit
SDK's own `linux-x64` asset does not even link there (hence the
`ubuntu-22.04` SDK triple; see `cmake/LiveKitSDK.cmake`).

macOS and Windows use the `obsproject/obs-plugintemplate` buildspec
bootstrap, trimmed to drop `qt6` (this plugin's properties UI is plain
`obs_properties_*`), with `obs-studio.version` pinned to 30.0.2 — the same
version Linux builds against, and deliberately low, because OBS rejects a
module built against a newer libobs than the one running it.

**Both jobs fall back to a core-library-only build if the bootstrap fails**,
rather than going red, with a workflow `::warning::` and a "Show what was
built" step that reports no module. That fallback exists because the
bootstrap is the least verifiable part of this project — there is no way to
exercise a macOS or Windows OBS build from the Linux development machine —
and a permanently red CI teaches people to ignore CI. **Do not remove the
warning:** a green job that quietly stopped building the plugin is worse than
a red one.

### Windows runner: persistent build tools (2026-09-07)

`winvm-builder`'s Windows job used to install its own CMake + Ninja on every
single run via `uses: lukka/get-cmake@latest`. That action has its own
caching (routed through this act_runner's built-in cache server, the same
mechanism `.deps/`'s `actions/cache` step above relies on and that one does
work) but it never hit: every run logged `Cloud cache miss` against the same
cache key, even immediately after a run that logged a successful save under
that exact key -- some incompatibility between `lukka/get-cmake`'s bundled
cache client and this act_runner's cache-server implementation, not
"caching isn't configured." Separately, and the larger cost: the archive
extraction step alone measured **~7.5 minutes** for a 45MB zip on this VM
(13:11:14 to 13:18:48 in one captured run) -- consistent with Windows
Defender real-time-scanning every extracted file, not raw disk I/O, though
that specific cause is not confirmed. Together this was the dominant cost of
every Windows CI run, cold cache or not.

Fix: CMake 4.4.2 and Ninja 1.12.1 are now installed once, directly on the
`winvm-builder` VM (Proxmox VMID 110, host pve4/192.168.1.145), not fetched
per-run:

- `C:\BuildTools\cmake\` (from
  `cmake-4.4.2-windows-x86_64.zip`, Kitware's GitHub releases) and
  `C:\BuildTools\ninja\` (from `ninja-win.zip`, `ninja-build/ninja` v1.12.1
  release) — plain `Expand-Archive` drops, nothing installed via an
  installer/MSI.
- Both added to the **Machine**-level `PATH`
  (`[Environment]::SetEnvironmentVariable('PATH', ..., 'Machine')`, not
  `setx`, which silently truncates a `PATH` this long).
- The `GiteaRunner-winvm-builder` scheduled task (`C:\gitea-runner\
  gitea-runner.exe daemon`, runs as SYSTEM) was stopped and restarted after
  the `PATH` change — a already-running process does not pick up an updated
  Machine environment variable, only processes started after the change do,
  and every CI job is a child process of this one long-running daemon.

Both workflows' Windows jobs now just run `cmake --version` / `ninja
--version` as a "Verify build dependencies" step and fail loudly if either
is missing, instead of silently falling back to the slow per-run install.

**This is VM state, not something `git clone` reproduces.** If
`winvm-builder` is ever rebuilt or reimaged, redo the three steps above
(download+extract both zips under `C:\BuildTools\`, extend the Machine
`PATH`, restart the scheduled task) before expecting Windows CI to pass
again — there is nothing in this repo that does it automatically.

### Where the macOS bootstrap actually got to

Six CI iterations, each fixing a real failure visible in the logs:

1. Upstream's Xcode generator → `No CMAKE_C_COMPILER could be found` (the
   runner has the Command Line Tools, not Xcode). Switched to Ninja.
2. OBS's SDK version regex only matches a full-Xcode SDK path. Synthesised a
   `MacOSX.platform/Developer/SDKs/MacOSX<ver>.sdk` symlink to the same SDK.
3. The install walked into `UI/obs-frontend-api`, whose binary is
   deliberately never built. The install's exit code is now tolerated.
4. Restricting the install to `libobs/` fixed that but lost the
   per-configuration export file.
5. `xattr -r -d com.apple.quarantine` followed the SDK symlink into the
   read-only system SDK. Symlink moved to the build directory; the xattr step
   is no longer fatal.
6. `IMPORTED_LOCATION or IMPORTED_IMPLIB not set for imported target
   OBS::libobs configuration Release` — OBS 30.0.2 installs
   `libobsTargets.cmake` without the per-config file that carries the library
   path. The top-level `CMakeLists.txt` now detects a locationless
   `OBS::libobs` and points it at the framework the bootstrap just built.

All six are confirmed fixed: the macOS job now downloads obs-deps and
obs-studio, builds libobs from source, builds and links the real adapter,
passes 6/6 tests, and uploads its artifact. `otool -L` on the result shows it
linked against libobs and `@rpath/liblivekit.dylib`.

### macOS packaging gap (known, unfixed)

**The macOS artifact will not load in OBS.app as it stands.** Two reasons,
neither of which CI can catch, because CI only proves it compiles and links:

1. It is a bare `streamer-tools-camera.so`. OBS on macOS loads plugins as
   `<name>.plugin` bundles (`Contents/MacOS/<name>`, `Contents/Resources/`,
   an `Info.plist`), which is what obs-plugintemplate's
   `cmake/macos/helpers.cmake` builds and which this project deliberately did
   not vendor.
2. `otool -L` shows the libobs dependency recorded as the relative path
   `libobs/libobs.framework/Versions/A/libobs`, inherited from the
   from-source libobs's own install name. A real plugin needs
   `@rpath/libobs.framework/Versions/A/libobs` plus an `LC_RPATH` pointing at
   `OBS.app/Contents/Frameworks`.

Fixing this means either vendoring the template's macOS bundle helpers or
adding an `install_name_tool` pass and a bundle layout — bounded work, but
work that has to be done and checked on an actual Mac. It is deliberately not
attempted here rather than guessed at.

### Where the Windows bootstrap got to

Windows is by far the slowest job — the `lukka/get-cmake` step alone takes
7-15 minutes on `winvm-builder`, and the runner serialises jobs, so a burst of
pushes leaves a queue that takes an hour to drain.

**The honest record, as it stood before `f27b1c0`: every completed Windows CI
run on this branch had failed.** (`f27b1c0` is the one that finally went
green — see "After the w32-pthreads target" at the end of this section. The
history below is kept because each dead end in it is a real constraint
someone will otherwise rediscover.) The first 7 failures were all at commits
predating the `-A x64` fix
below. The 8th, at `edb0c02` — the first commit that actually carries that fix
— has since completed, and it is the informative one: **the `-A x64` fix
worked, and Windows failed further along, on something else.** A later run
(`58f4832`) then failed for an unrelated reason — its Windows steps still used
`shell: bash`, which on this runner is WSL and cannot run as local system —
so it never reached cmake at all and tells us nothing about the bootstrap.
The PowerShell rewrite that fixes that is still queued and remains unproven.
Do not read any fix below as "confirmed" beyond what is stated; check current
CI status rather than trusting this paragraph's age.

What `edb0c02` showed: obs-deps and Qt6 downloaded, CEF skipped, the OBS
sub-configure ran for 53s and correctly reported "Plugin Support" and "User
Interface" disabled — then failed at generate time:

```
CMake Error at libobs/cmake/os-windows.cmake:46 (target_link_libraries):
  Target "libobs" links to:
    OBS::w32-pthreads
  but the target was not found.
```

**That looks like a genuine hole in OBS 30.0.2's opt-in modern CMake path on
Windows, not something this repo is doing wrong.** Traced at the 30.0.2 tag:

- `libobs/cmake/os-windows.cmake` links `OBS::w32-pthreads`;
- that target is defined only by `deps/w32-pthreads/CMakeLists.txt`, reached
  only through `deps/CMakeLists.txt`;
- `deps/` is added only by the **legacy** branch of the top-level
  `CMakeLists.txt`. The modern branch — the one `-DOBS_CMAKE_VERSION=3.0.0`
  selects — adds `libobs`, `libobs-d3d11`, `libobs-winrt`, `libobs-opengl`,
  `plugins`, `test/test-input` and `UI`, never `deps`;
- `libobs/CMakeLists.txt` adds only `deps/libcaption` and `deps/uthash`;
- `plugins/CMakeLists.txt` returns immediately under `ENABLE_PLUGINS=OFF`, and
  does not add `deps/` even when enabled.

macOS is unaffected because its libobs does not link w32-pthreads. At 30.0.2
the modern path was the *default* only on macOS
(`if(CMAKE_HOST_SYSTEM_NAME MATCHES "(Darwin)" OR OBS_CMAKE_VERSION ...)`),
which is consistent with the Windows side of it being under-exercised
upstream.

Deliberately **not** "fixed" by bumping the pin: 30.0.2, 30.1.2, 30.2.3,
31.0.3 and 31.1.1 were all checked, and every one still links
`OBS::w32-pthreads` from `libobs/cmake/os-windows.cmake` while none of them
add `deps/w32-pthreads` from `libobs/CMakeLists.txt`. A version bump is
therefore not obviously the answer and needs checking rather than assuming.

Option 1 (build `obs-frontend-api`, matching obs-plugintemplate's own CI, and
accept the Qt dependency on Windows only) was investigated and **rejected**:
`UI/obs-frontend-api/CMakeLists.txt` only links `OBS::libobs`, nothing else —
it does not itself pull in `deps/w32-pthreads`. What actually satisfies the
target upstream is that `UI/CMakeLists.txt` returns early when
`ENABLE_UI=OFF`, *before* reaching `include(cmake/os-windows.cmake)` — the
file that (via its own `if(NOT TARGET OBS::w32-pthreads)` guard) adds
`deps/w32-pthreads`. Upstream's CI never sets `ENABLE_UI=OFF`, so that
add-as-a-side-effect-of-Qt always happens for them. Building
`obs-frontend-api` instead of `libobs` would not change any of that; the only
way to get the same side effect is to stop passing `-DENABLE_UI:BOOL=OFF`,
which is exactly the ~100 MB Qt6 download this bootstrap was trimmed to avoid
(see the Windows `buildspec.cmake` comment) and buys this plugin nothing,
since its properties UI is plain `obs_properties_*`.

Went with Option 2 instead: `cmake/common/buildspec_common.cmake` now carries
`_patch_obs_studio_w32_pthreads()`, called for `OS_WINDOWS` right before
`_setup_obs_studio()`. It patches the freshly-extracted
`libobs/CMakeLists.txt` to add the one missing subdirectory itself, using the
exact same `if(NOT TARGET OBS::w32-pthreads)` guard
`UI/cmake/os-windows.cmake` already relies on upstream:

```cmake
if(OS_WINDOWS)
  if(NOT TARGET OBS::w32-pthreads)
    add_subdirectory("${CMAKE_SOURCE_DIR}/deps/w32-pthreads" "${CMAKE_BINARY_DIR}/deps/w32-pthreads")
  endif()
  include(cmake/os-windows.cmake)
...
```

It is idempotent (checks for `deps/w32-pthreads` already present in the file
before patching, so re-running against a previously-patched extraction is a
no-op) and fails loudly with `FATAL_ERROR` if the anchor text it expects to
find is not there, rather than silently doing nothing on a future OBS version
whose `libobs/CMakeLists.txt` has changed shape. Verified locally (this is a
Linux sandbox, so only the CMake string-patching logic itself could be
checked, not a real Windows configure/build): ran the same `string(FIND)`
/`string(REPLACE)` sequence against the real `libobs/CMakeLists.txt` fetched
from the obs-studio 30.0.2 tag, confirmed it produces the intended
`if(OS_WINDOWS) / if(NOT TARGET ...) / add_subdirectory(...) / endif() /
include(...)` block, and confirmed a second run against the already-patched
file is a no-op. Whether this actually gets libobs through CMake generate and
building on a real Windows runner is the thing the next CI run needs to
prove — option 3 (dropping the from-source libobs on Windows for a prebuilt
SDK) remains the fallback if it does not.

Two bugs of its own were found; the first is now proven fixed by `edb0c02`
getting past it, the second is still unproven:

1. Upstream passes `-A x64,version=<Windows SDK>` to the OBS sub-configure,
   and with a current CMake that `,version=` suffix reappears verbatim in the
   sub-build's `CMAKE_VS_PLATFORM_NAME` — which obs-studio's own dependency
   downloader uses as the architecture, sending it after
   `windows-deps-2023-11-03-x64,version=10.0.26100.0.zip`:

   ```
   string sub-command JSON member 'hashes windows-x64,version=10.0.26100.0' not found
   Unable to download .../windows-deps-2023-11-03-x64,version=10.0.26100.0.zip
   ```

   Plain `-A x64` now. **Confirmed fixed:** the `edb0c02` run got past this
   and downloaded `windows-deps-2023-11-03-x64.zip` correctly.
2. The Windows CI steps were originally written in bash (via `shell: bash`)
   and were rewritten in PowerShell. **The bash version is now proven broken**
   by the `58f4832` run: on `winvm-builder`, `bash` resolves to WSL, and WSL
   refuses to run under the service account the runner uses —

   ```
   Running WSL as local system is not supported.
   Error code: Bash/WSL_E_LOCAL_SYSTEM_NOT_SUPPORTED
   ##[error]Process completed with exit code 1.
   ```

   so the step died on the shell without ever invoking cmake. The PowerShell
   rewrite is therefore necessary, but **still unproven in the other
   direction** — no completed run has yet included it. Note this also means
   `58f4832`'s failure says nothing about the `w32-pthreads` blocker; that
   result comes from `edb0c02` alone.

(Superseded by the next subsection: the `w32-pthreads` blocker described above
*was* the next thing solved, and the `add_subdirectory` patch and the
PowerShell rewrite are both now proven by a completed green run. What stands
from this subsection is its reasoning — why `ENABLE_UI=OFF` exposes the gap,
and why re-enabling Qt or bumping the OBS pin is not the answer.)

### After the w32-pthreads target: the w32-pthreads *package*

The `add_subdirectory(deps/w32-pthreads)` patch above did its job — the
`edb0c02`-era generate error is gone, obs-studio 30.0.2 configures, builds
`w32-pthreads.dll` and `obs.dll`, and installs. Two further Windows-only
blockers then surfaced behind it, both the same underlying upstream mismatch
and neither one a defect in this repo:

1. **`find_package(libobs)` could not locate the package it had just
   installed.** obs-studio's `cmake/windows/defaults.cmake` sets
   `OBS_CMAKE_DESTINATION=cmake`, and `target_export()` installs each
   package to `<prefix>/${OBS_CMAKE_DESTINATION}/<target>/` — i.e.
   `.deps/cmake/libobs/`. That is not one of CMake's Config-mode search
   suffixes (`<prefix>/cmake/` is, but only for a config file sitting
   *directly* in it; `<prefix>/<name>*/cmake/` is, but the `<name>`
   directory has to come first). Fixed in `79de5e8f` by setting
   `libobs_DIR` explicitly; the long comment above that block in
   `CMakeLists.txt` has the full reasoning.

2. **…and then `libobsConfig.cmake` could not locate `w32-pthreads` for
   exactly the same reason.** `libobs/cmake/os-windows.cmake` links
   `PUBLIC OBS::w32-pthreads`, so upstream's `libobsConfig.cmake.in` carries
   a hard `find_dependency(w32-pthreads REQUIRED)` under `if(MSVC)`. Once
   fix 1 finally got that config file loaded, the dependency lookup inside
   it failed and killed the configure:

   ```
   By not providing "Findw32-pthreads.cmake" in CMAKE_MODULE_PATH this project
   has asked CMake to find a package configuration file provided by
   "w32-pthreads", but CMake did not find one.
     .deps/cmake/libobs/libobsConfig.cmake:30 (find_dependency)
   ```

   **This is not a missing export**, which was the first hypothesis and is
   worth recording as wrong: `deps/w32-pthreads/CMakeLists.txt` ends with
   `target_export(w32-pthreads)`, the same helper `libobs` itself uses, so
   it does emit `install(TARGETS … EXPORT w32-pthreadsTargets)`,
   `install(EXPORT … NAMESPACE OBS::)` and a generated
   `w32-pthreadsConfig.cmake`, all `COMPONENT Development`. Two independent
   arguments say those rules ran: CMake hard-errors at generate time if an
   exported target links a target that is in no export set at all (and OBS's
   generate step succeeded), and this repo's patch adds `deps/w32-pthreads`
   from `libobs/CMakeLists.txt`, making it part of the `libobs` subtree —
   which installs *before* the tolerated `UI/obs-frontend-api` install error
   aborts the rest. The package really is at `.deps/cmake/w32-pthreads/`;
   `find_package` was simply never going to look there.

   So the fix is the same one-liner as for `libobs`, and it is literally
   what CMake's own error message suggests: set `w32-pthreads_DIR` before
   the `find_package(libobs)` call that transitively triggers the
   `find_dependency`. Both `_DIR` blocks now sit next to each other in
   `CMakeLists.txt`.

   Behind that sits `cmake/windows/find-fallback/Findw32-pthreads.cmake`,
   used only if that export is genuinely absent from `.deps/`. It rebuilds
   `OBS::w32-pthreads` by hand from the bootstrap's own artifacts. It
   deliberately does *not* live in `cmake/windows/`, which
   `cmake/common/osconfig.cmake` already puts on `CMAKE_MODULE_PATH` for
   every Windows configure — a find module there would shadow OBS's real
   exported package on every build, since `find_package` tries MODULE mode
   before CONFIG mode. `CMakeLists.txt` appends the `find-fallback/`
   directory to `CMAKE_MODULE_PATH` only after it has established the real
   export is missing, and logs what *is* under `.deps/cmake/` when it does,
   so a future failure of this shape is answered by the CI log rather than
   by another run.

   Note this package is load-bearing for more than the dependency check:
   `libobs/util/threading.h` does `#include <pthread.h>`, and on Windows
   that header only exists because `target_export(w32-pthreads)` installs
   `pthread.h`/`sched.h` as `PUBLIC_HEADER` into `.deps/include/`.

Verified before pushing, on Linux, since this is a Linux sandbox: a
reconstruction of the exact failure — a stub `libobsConfig.cmake` containing
`find_dependency(w32-pthreads REQUIRED)`, reached through `libobs_DIR`, with
the package installed at `.deps/cmake/w32-pthreads/` — reproduces the CI
error without the `w32-pthreads_DIR` block and passes with it; and the
fallback find module was exercised separately by deleting that package, with
`find_package` resolving through MODULE mode to it instead. A full Linux
configure of this repo is unchanged (both blocks are inside `if(OS_WINDOWS)`,
and the upstream `find_dependency` is inside `if(MSVC)`, so macOS and Linux
are pure no-ops).

**Confirmed on the real runner.** The Windows job for `f27b1c0` completed
green, and its log body — not just its status — shows the whole chain:

```
-- w32-pthreads_DIR not set; libobsConfig.cmake's find_dependency(w32-pthreads
   REQUIRED) hits the same OBS_CMAKE_DESTINATION=cmake search-suffix problem as
   libobs itself, so pointing it directly at the from-source install:
   ...\.deps\cmake\w32-pthreads
-- libobs found (...\.deps\cmake\libobs) -- building OBS adapter module
   streamer-tools-camera.vcxproj -> ...\build\obs-adapter\Release\streamer-tools-camera.dll
100% tests passed out of 6
    Directory: ...\build\package\bin\64bit
-a----   3078656 livekit.dll
-a----  25008640 livekit_ffi.dll
-a----    136192 streamer-tools-camera.dll
```

Note which branch that log took: the `w32-pthreads_DIR` message means the
package config really was sitting at `.deps/cmake/w32-pthreads/` all along and
the fallback find module was never loaded. The export was never missing — only
unfindable. Linux and macOS were green in the same run, confirming the no-op.

The one piece of noise left in that log is the tolerated
`UI/obs-frontend-api/cmake_install.cmake` error, which now repeats once per
CMake re-configure because Visual Studio's `ZERO_CHECK` target re-runs the
bootstrap during the build. It is cosmetic and pre-dates this change, but it
makes the Windows log harder to read than it should be.