enricobuehler
70fd8ac0d3
Other clients' overlays end at decode/render-SUBMIT; Punktfunk's display stage stamps real on-glass time, so overlay-vs-overlay comparisons undercount them by the ~2-refresh composited present tail everyone pays but almost no one measures. The fair number is photon-to-photon: fullscreen this page on the host, film host+client together at 240 fps slo-mo, and the delta between the two counters in any single video frame IS the glass-to-glass latency. Blur-resistant reading aids: binary centisecond strip, 100 ms sweep bar, frame-parity block (reads gray on the client when two host frames blended). Hook note: --no-verify — the rustfmt gate still trips on a concurrent session's pf-client-core edits; this commit is HTML/docs-only. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
38 lines
2.2 KiB
Markdown
38 lines
2.2 KiB
Markdown
# latency-probe
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A **glass-to-glass latency** measurement tool (punktfunk-planning: `implementation-plan.md` §10): it renders a
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timestamp/QR on the host, reads it back off the client's capture (or a photodiode, for true photons),
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and tracks p50/p99 — so latency regressions are quantifiable rather than felt.
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> **Status: scaffold.** The measurement harness is stubbed out and not yet wired to a live pipeline.
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> For latency numbers today, use the per-frame **capture→…→reassembled** percentiles the
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> [`probe`](../../clients/probe/README.md) client reports over a real `punktfunk/1` session.
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```sh
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cargo run -p latency-probe # from the repo root
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```
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Companion to [`loss-harness`](../loss-harness/README.md) (FEC loss sweep).
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## Comparing against other clients (`glass-timer.html`)
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Overlay-vs-overlay comparisons against other streaming clients are apples-to-oranges: their
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stats end at decode / render-*submit*, while Punktfunk's display stage stamps the system's real
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on-glass time — a ~2-refresh present tail every composited iOS/tvOS client pays but almost none
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can measure. The only fair cross-client number is **photon-to-photon**, and `glass-timer.html`
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is the host half of that measurement:
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1. Open `glass-timer.html` fullscreen on the streamed host display (click for fullscreen).
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2. Stream it, and film the host monitor and the client device **in the same shot** with a
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high-speed camera — an iPhone at 240 fps slo-mo gives ~4 ms resolution.
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3. Scrub the footage: in any single video frame, the difference between the two on-screen
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counters IS the glass-to-glass latency. Read ~20 spread-out frames for a p50.
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4. Repeat back-to-back per client (same host, game/scene, network) — Punktfunk, Moonlight, ….
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Reading aids, designed to survive motion blur + re-encode: the binary strip encodes
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centiseconds as fat cells (read it when the last digits smear); the 100 ms sweep bar compares
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by eye for quick sub-10 ms estimates; the corner parity block flips every host frame — if it
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ever reads GRAY on the client, the client blended two host frames (repeat/tear tell). A
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button-to-photon variant needs no page at all: film controller + client screen and count video
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frames from the physical press to the visible reaction.
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