Key Matcher

Key detection runs Krumhansl-Schmuckler profiles over chroma from a single FFT pass (Camelot code included for DJ use). The transposition distance is the smallest semitone shift that moves the detected root onto your target root, always within plus or minus six semitones, so loops are never lugged an octave away. Shifting prefers the rubberband filter with formant preservation (vocals keep their timbre); when the FFmpeg build has no rubberband it falls back to the asetrate resample chain, which shifts formants along — fine for samples, audible on vocals. The result is re-analyzed after shifting and the detected key of the output is reported next to the target, so the match is verified end to end. Note that transposition moves pitch but cannot change modality: matching a minor loop to a major key aligns the tonics and warns instead of pretending.