When the host attaches to an already-running game it never saw the stream's
Initialize, so the render-hook assumes the device mix format and measures only
the sample rate from the render cadence -- which a jittery game can make wrong
(intermittent pitch shift). But during the measurement window the game is still
audible, so we have the same audio twice: the hook (pre-mix, unknown format) and
a process-loopback (post-mix, the known device format). Cross-correlating them
pins the true rate from ground truth.
- common/include/coop/audio_correlate.hpp: the pure correlator. Resample the hook
by each candidate standard rate up to the device rate and score how well it
aligns with the loopback across the window (drift-detecting). audio_correlation_test
recovers every rate (score ~1.0 vs ~0.01 for wrong ones), incl. 44100-vs-48000,
and rejects unrelated signals.
- Hook measurement tap: a host-set verify_capture ring flag makes the hook push a
still-being-measured (guessed) stream's raw pre-mix bytes WITHOUT silencing, so
the host can co-capture both signals (a silenced game's loopback is silent).
Inert by default -- the shipping no-echo path is untouched.
- host/src/audio/audio_format_verifier: co-captures hook + loopback and correlates,
feeding a correction into the existing override channel. Wired into AudioMirror's
measurement window (hidden in the gap loopback already covers, so exact streams
pay nothing). audio_verify_test drives it end-to-end against coop_mock_game.
Rate vs layout are coupled (correlating the waveform needs the right channel
de-interleaving), so this step assumes the hook layout matches the device (the
common stereo-on-stereo case); recovering a different channel count / bit depth
is step b.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Build coop_audio_validate, a tool that turns "the mirror audio sounds off"
into numbers. It plays a known sine (coop_tone, 44.1 kHz on a 48 kHz
endpoint -- the Godot/Brotato case), injects the hook as the host does, and
runs a fidelity analyzer (coop/tone_analysis.hpp: pitch error in cents,
SNR/THD, click + dropout counts), dumping a .wav to listen to. Modes:
--render drives the real AudioMirror and measures its rendered output;
--baseline/--selfcheck give the measurement floor; --listen <pid> records a
live coop_host's output; --wav analyzes a recording. Analyzer + WAV I/O are
unit-tested (tone_analysis_test) against synthesized defects.
Using it, the capture ring measures pristine (~68 dB, 0 gaps) while the
render path dropped to ~18 dB with gaps -- localizing a real defect in
AudioMirror::run_hooked: it re-primed (withheld the feed until ~30 ms had
rebuffered) on any partial fill (to_write < avail). A partial fill is normal
producer jitter, and withholding the feed drains the device, so a one-frame
ring dip became a full ~30 ms drop-out; on a jittery game it fired
constantly. Fix: feed whatever is available each tick and re-prime only on a
genuine starvation (device empty AND ring empty). The policy is factored
into a pure RenderPacer reused by run_hooked + run_loopback and proven by
render_pacer_test (the old policy withholds available data ~168x and drains
to one period from silence on a jittery schedule; the new one never
withholds).
ctest 17/17.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
