Fox 2026-06-05: "the web page for zebra spaces seems noticeably slower
after enabling transcribe… even the tones for entering and leaving are
showing up way way later even on the host side."
Root cause: ONNX Runtime via transformers.js was running on the main
thread, blocking JS for 1–3 seconds per chunk. Join/leave chimes,
button clicks, scroll, EVERY UI gesture queues behind it.
Two changes:
1. Move Whisper to a dedicated module Web Worker. The worker imports
transformers.js + loads the whisper-tiny.en pipeline ONCE; each
chunk is transferred (zero-copy) via postMessage, processed in
isolation from the UI thread, and the resulting text is posted
back. Main thread is free during inference now — UI stays
responsive. Worker is created on first toggle ON; same ~40MB
model download still happens, just off-thread.
2. Global "inflight gate" on the main thread side. Only one
transcribe request can be in flight at a time. If a new chunk
arrives while busy, DROP it (don't queue). Counter is logged
every ~30s so we can see worker saturation. With N speakers all
talking at once, dropping is correct — stale chunks from 10s ago
aren't worth transcribing.
Combined with the RMS silence gate in the capture worklet, the result
is: silent chunks never even reach the main thread, busy chunks are
processed sequentially by the worker, and the UI never blocks.
Phase 4 (deferred): switch to WebGPU backend for ONNX where supported
— roughly 2-5× faster than WASM on capable devices. transformers.js
v3 supports this with `{ device: 'webgpu' }` in pipeline opts.
Russell Ballestrini
9b91c726e5