AUDIO-VERIFICATION.md section 1 calls transcode fidelity the question P4 actually
raised, needing neither an engine nor a device, and gives it in four lines of
shell. Nothing implemented it: verify-video-audio deliberately declines, saying a
difference RMS without alignment is meaningless. So the P4/P7 gate has rested on
level and non-silence and the fidelity claim has never been made.
tools/port/verify-transcode-fidelity now exists and is committed WITHOUT a
verdict, deliberately.
Four ways the measurement lies, each reproduced here rather than reasoned about.
Indexing with a negative lag wraps to the end of the array in Python, so the
difference was the transcode subtracted from an unrelated part of the source --
reported 7 dB LOUDER than the source, the same catastrophic-looking number the
doc warns of. My regex for the recorded -af truncated the fold to its FL half,
folding the source to a left-only signal: the doc names that trap, I reached it
through a parsing bug, and the matrix contains runs of spaces so it cannot be
tokenised on whitespace. -ss before -i is a container-level jump and on this WMA
Pro source returned 4.6 s for a 4.0 s request while the Ogg side returned 4.0 s,
so the windows covered different stretches of the movie, best correlation 0.172 --
this one is NOT in the doc and is indistinguishable from the alignment trap that
is. And the single-resolution search returned +2413 against a window of +-2400,
its own boundary rather than a peak, the same family as the Decoder's period
estimator returning its search floor.
Why no verdict: best alignment is corr 0.763 on S00A and 0.075 on ADV, and both
still report the difference louder than the source, which cannot be true of two
aligned signals at equal level. The remaining fault is on my side. A tool printing
'not faithful' in that state would put a false defect on the exporter. It now
distinguishes 'could not align' from 'not faithful', two failures I conflated
twice before separating them.
Filed for the human as a proposal, not an edit: section 1 should carry the
imprecise-seek trap as a fourth entry.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01N7FiFFFwbvG2uxdcEh8HyF
c7ebab1624