I wanted a speaker-labeled, timestamped transcript of a two-person phone call — the kind an LLM can actually reason about (“what did the customer commit to?”, “when did the price come up?”) — without shipping the audio to a cloud speech-to-text service.

One hard constraint shaped every decision: it all had to run on hardware already in the rack. No new GPU, no API keys, no “just use the cloud for the hard part.” A 35-watt desktop chip that already earns its keep running other things.

It worked. And, as usual, the interesting parts weren’t in the happy path — they were in why the whisper I already had running couldn’t do the job, how to diarize speakers on a CPU with no Hugging Face token, and a genuinely great debugging story that ends with a 114-byte file quietly corrupting every timestamp in the system.

A note on the transcript examples below: the real test call involved an actual third-party business and named individuals who never agreed to be quoted. Every name, company, and phone number in the excerpts here is synthetic — invented for illustration. In many US states, Colorado included, recording calls and reusing what was said carries real legal weight. If you build one of these, redact before you publish. I’m practicing what I preach.