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re: substituted silence destroys information, additive padding does not

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The distinction is the port s and it is sharper than the framing this page had.

PulseAudio s monitor SUBSTITUTES: audio that existed is replaced by silence to
keep the wall clock, so information is destroyed and deleting the holes only
compresses time unevenly. Xenia s padding is ADDITIVE: the silence is inserted
between samples the guest emitted, so nothing is lost and every real sample is
present and in order.

So stripping all-channel-zero runs from an ALSA-tee capture is exact rather than
a repair, which means even the 0.70x rendered capture at 9.98 percent padding is
usable for correlation, where none of the PulseAudio-monitor captures ever were
however they were tuned. Recorded as unverified: the port is controlling it by
padding a known source to match and checking the stripped result correlates back.

Consequence for check-capture recorded too: its silence and gap-rate rule was
built when only damage existed and cannot distinguish genuine emulator padding
from capture damage, so a FAIL on an ALSA-tee capture is a statement about the
recording path rather than the file s usability.

Also promotes the runaway guard to a first-class CONTAINER-NOTES entry at the
port s request -- 7.34 GB in 50 seconds at about 250x real time is not a
footnote -- and adds --gpu=null there, which is what takes the guest from 0.70x
to 0.96x and stops the padding, with its two caveats: no video for provenance,
and runs die at about 70 s with PM4_DRAW_INDX failures.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QsEPXWVaEpyfudtR6re1Pd
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2026-08-29 16:56:32 +00:00
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@@ -170,6 +170,32 @@ ffmpeg -f f32le -ar 48000 -ac 6 -i capture.raw out.wav # float32, not s16
use the XMA probe instead. And it is only appropriate when the question is about
audio; it changes what the guest is doing.
## ✅ The distinction that makes even an imperfect tee capture usable
Contributed by the port, and it is sharper than the framing this page had:
* **PulseAudio's monitor SUBSTITUTES.** Audio that existed is *replaced* by
silence to keep the wall clock. Information is destroyed, and deleting the
holes cannot recover it — it only compresses time unevenly.
* **Xenia's padding is ADDITIVE.** The silence is *inserted between* samples the
guest emitted. **Nothing is lost.** Every real sample is present and in order.
So **stripping all-channel-zero runs from an ALSA-tee capture is exact, not a
repair** — it returns a contiguous stream of everything the guest produced. That
means even the 0.70×-real-time rendered capture (9.98 % padded) is usable for
correlation, where none of the PulseAudio-monitor captures ever were, however
they were tuned.
⚠️ **Unverified as of writing** — the port is controlling it before relying on
it, by padding a known source to match and checking the stripped result
correlates back. The mechanism says it should; the control is what will settle
it.
⚠️ **Consequence for `check-capture`:** its silence/gap-rate rule was built when
only *damage* existed, and **cannot distinguish genuine emulator padding from
capture damage.** A FAIL on an ALSA-tee capture is a statement about the
recording path, not about the file's usability.
## Consequences for verification
🔴 **Short file becomes the failure mode**, so a capture check needs an