33bb50e80d
The Decoder made this the gate on S00A and that was the right order: ADV plays itself on boot and can be captured with --gpu=null at 0.96x real time, but S00A starts ~4.5 s after (A) on a save slot, which needs a driven run, which needs screens, which rules out --gpu=null. So S00A is necessarily the 0.70x rendered route with ~10% additive padding, and is only worth a boot if stripping is exact. It is. A real music+SFX bed -- 137.37 s, carrying 454 genuine zero runs of its own -- had 1149 holes inserted at 8.37/s to +9.9% length, matching the observed ALSA profile, then was stripped and correlated in the low band: original vs itself r 1.000 lag 0.0 s margin +0.141 ceiling PADDED vs original r 0.436 lag -12.2 s margin +0.006 destroyed STRIPPED vs original r 1.000 lag 0.0 s margin +0.142 recovered stripped vs orig-also-stripped r 1.000 margin +0.143 Two things worth reading off that. Padding at that profile destroys correlation completely -- r 0.436 in the known-absent regime -- which independently confirms on a file whose contents I control that the earlier captures were unusable for the reason claimed and not for some other one. And recovery does NOT require stripping both sides: the stripped capture matches the UNSTRIPPED source at the ceiling, so the port's reference assets never need touching. `tools/port/strip-padding` implements it, and its header leads with when the operation is vandalism rather than with what it does: PulseAudio's monitor SUBSTITUTES silence and deleting those holes repairs nothing, while Xenia's ALSA writer PADS and removing that is exact. Running it on the wrong artefact would look like it worked. Its output is byte-identical to the control's own stripping, so the tool and the experiment are one operation rather than two implementations that agree. Not licensed by this: stripping removes genuine silence too and cannot tell them apart. Here the genuine runs total 0.71 s in 137 s and cost nothing measurable; on material that is mostly silence they would. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01N7FiFFFwbvG2uxdcEh8HyF
68 lines
3.2 KiB
Bash
Executable File
68 lines
3.2 KiB
Bash
Executable File
#!/usr/bin/env bash
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# Remove driver-inserted silence from a capture, exactly.
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#
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# tools/port/strip-padding in.wav out.wav
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#
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# WHEN THIS IS VALID, AND WHEN IT IS VANDALISM. The distinction is the whole
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# tool and getting it backwards destroys the artefact:
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#
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# * PulseAudio's monitor SUBSTITUTES silence. It advances on a wall clock and
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# replaces audio that existed when the producer was late. Information is
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# gone; deleting the holes compresses time unevenly and repairs nothing.
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# DO NOT RUN THIS ON A MONITOR CAPTURE.
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# * Xenia's ALSA writer PADS. It inserts silence between samples the guest
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# emitted when its ring is empty (`alsa_audio_driver.cc:359`). Nothing is
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# lost and nothing is overwritten, so removing the padding is EXACT -- it
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# hands back the contiguous stream the guest produced.
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#
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# CONTROLLED, not argued. A real music+SFX bed (137.37 s, with 454 zero runs of
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# its own) had 1 149 holes inserted at 8.37/s to +9.9 % length, matching the
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# observed ALSA profile, then was stripped:
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#
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# original vs itself r 1.000 lag 0.0 s margin +0.141 [ceiling]
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# PADDED vs original r 0.436 lag -12.2 s margin +0.006 [destroyed]
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# STRIPPED vs original r 1.000 lag 0.0 s margin +0.142 [recovered]
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#
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# Frame counts: original 6 593 984, stripped 6 559 880, and the original stripped
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# of its own genuine zero runs 6 560 044 -- a difference of 164 frames, 3.4 ms in
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# 137 s, from inserted holes abutting genuine ones and merging.
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#
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# ⚠️ It removes GENUINE silence too, and cannot tell the two apart -- that is why
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# the reference above is the unstripped original: recovery does not depend on
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# stripping both sides. On this material the genuine runs total 0.71 s in 137 s
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# and cost nothing measurable. On material that is mostly silence they would.
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set -euo pipefail
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in="${1:?usage: strip-padding IN.wav OUT.wav}"; out="${2:?usage: strip-padding IN.wav OUT.wav}"
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python3 - "$in" "$out" <<'PYEOF'
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import array, struct, sys, wave
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src, dst = sys.argv[1], sys.argv[2]
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w = wave.open(src); ch = w.getnchannels(); rate = w.getframerate()
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if w.getsampwidth() != 2:
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print("strip-padding: 16-bit PCM only (got %d-bit)" % (w.getsampwidth()*8)); raise SystemExit(2)
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n = w.getnframes(); a = array.array('h'); a.frombytes(w.readframes(n)); w.close()
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MIN = max(1, rate // 1000) # a gap is a run, not a sample
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sil = bytearray(n)
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for f in range(n):
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b = f * ch
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if not any(a[b+c] for c in range(ch)): sil[f] = 1
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keep = array.array('h'); f = 0; removed = 0; holes = 0
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while f < n:
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s = f
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if sil[f]:
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while f < n and sil[f]: f += 1
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if f - s < MIN: keep.extend(a[s*ch:f*ch])
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else: removed += f - s; holes += 1
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else:
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while f < n and not sil[f]: f += 1
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keep.extend(a[s*ch:f*ch])
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k = len(keep) // ch
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o = wave.open(dst + ".partial", "wb") # temp name, renamed on completion
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o.setnchannels(ch); o.setsampwidth(2); o.setframerate(rate)
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o.writeframes(keep.tobytes()); o.close()
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import os; os.replace(dst + ".partial", dst)
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print("%s: %d frames (%.3f s) -> %s: %d frames (%.3f s)"
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% (src, n, n/rate, dst, k, k/rate))
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print(" removed %d run(s) totalling %.3f s (%.2f %% of the input)"
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% (holes, removed/rate, 100.0*removed/n))
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PYEOF
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