Add Syphon output sink (macOS, opt-in)

[ktamas77]

Adds a third Output 2 sink alongside NDI and FFmpeg: a macOS-only Syphon server that publishes captured Web frames as a Syphon source via node-syphon. Other macOS apps on the same machine — Resolume, OBS (with the Syphon plugin), VDMX, TouchDesigner, MadMapper — can then consume the video locally without going through the NDI encoder + network stack.

Why add a Syphon sink

For local same-Mac pipelines into VJ/streaming software, Syphon is the right primitive:

	Syphon	NDI
Transport	Shared GPU surface (IOSurface + Mach ports)	CPU readback → SpeedHQ encode → socket → decode
Localhost latency	<5 ms	1–3 frames
CPU cost	~0%	NDI's encoder isn't free at high frame rates
Reach	Same Mac only	Network-wide, cross-platform

NDI keeps doing what it does best (cross-machine routing). This just gives macOS users a much faster local option.

Cross-platform philosophy: opt-in only, no impact elsewhere

I'm aware the project values tri-platform parity. This PR is structured so it cleanly degrades on Windows and Linux:

• node-syphon is in optionalDependencies, not dependencies — npm install skips it cleanly on Win/Linux.
• A runtime support.syphon flag is true only on macOS and only when the dep loaded — gated by process.platform === "darwin" plus a try/require.
• The new "Syphon" UI row is rendered only when support.syphon is true (v-show="… && support.syphon"), so the control window on Win/Linux is byte-identical to before.
• valid() (main process) and the renderer-side mirror only count cfg.s as a valid Output 2 sub-sink when Syphon is actually available — so a YAML config imported on an unsupported host with Output2SinkSyphonEnabled: true is correctly flagged invalid rather than silently dropping every frame.

A natural counterpart on Windows is Spout, which has the same role and is also wrapped by some Node bindings. Happy to look at adding Spout in a follow-up PR if you'd like; I kept this PR macOS-only to keep the surface small and reviewable, and because Syphon is what I have a working setup for.

Implementation details

• New config field s / Output2SinkSyphonEnabled, parallel to n (NDI) and m (FFmpeg).
• vingester-browser-worker.js: try-requires SyphonMetalServer once at module load on darwin; creates one server per worker named after the browser title; publishes each captured frame's BGRA buffer via publishImageData (wrapped as Uint8ClampedArray — that's what node-syphon requires); disposes in stop(). The publish happens before the existing NDI in-place BGRA→BGRX mutation so Syphon receives the original alpha-preserving frame.
• vingester-main.js: detects node-syphon availability and exposes support.syphon to the renderer via the existing support IPC handle; logs Syphon availability at startup alongside NDI/FFmpeg.
• vingester-control.html: new SINK row with a YES/NO toggle, gated on support.syphon.
• The existing cfg.N master toggle still gates the entire Output 2 block; Syphon is just one of three checkbox-level sub-sinks underneath it.
• An inline comment in the worker explains why FFmpeg is intentionally excluded from the BGRA endianness normalization (it gets a JPEG from nativeImage.toJPEG() and handles pixel format itself).

Diff size

File	+/−
package.json	+5 −1
vingester-main.js	+12 −1
vingester-browser.js	+14 −1
vingester-browser-worker.js	+56 −6
vingester-control.js	+1 −1
vingester-control.html	+12
Total	+100 −10

License

node-syphon is GPL-3.0+, compatible with Vingester's GPL-3.0-only.

Verified locally

• macOS 26.4 / Apple Silicon: cfg.s=true flows from YAML → main → worker; node-syphon loads inside the Electron 18 renderer; SyphonMetalServer constructs with the correct name and a real info.v002.Syphon.<UUID> identifier; frames publish at the configured FPS without errors; clean shutdown on stop.
• Receiver-app smoke: works as a Syphon source for typical receivers on the same machine.
• Bundling: node_modules/node-syphon/** is asarUnpacked so syphon.node and Syphon.framework (universal2) are both extracted next to the runtime.

Known follow-ups (not in this PR)

• A symmetric per-frame error rate-limit for all three sinks (NDI / FFmpeg / Syphon currently each log.error per failed frame, which can flood at 30+ fps if a sink gets stuck). This is a pre-existing pattern; happy to send a separate PR if you'd like it.
• A Windows Spout equivalent for cross-platform parity.