{
  "frozenAt": "2026-11-14T21:08:03.113250+00:00",
  "dateSeoul": "2026-11-15",
  "keyword": "m4a to midi",
  "status": "FROZEN_BEFORE_OUTPUT",
  "mode": 2,
  "sampleRate": 44100,
  "monoRule": "Arithmetic channel average, nearest integer PCM16, then common0.5 gain and nearest integer; no normalization/denoising/parameter tuning",
  "gain": 0.5,
  "activeSeconds": 5,
  "zeroTailSeconds": 0.5,
  "sourceWindows": [
    {
      "id": "guitar15",
      "source": "guitar",
      "start": 15,
      "end": 20
    },
    {
      "id": "piano36",
      "source": "piano",
      "start": 36,
      "end": 41
    },
    {
      "id": "piano61",
      "source": "piano",
      "start": 61,
      "end": 66
    }
  ],
  "selectionRule": "Three windows fixed before codec outputs or converter results; previously archived human performances reused and explicitly disclosed, not new independent performers or an iPhone capture. No best-case selection.",
  "sourcePolicy": "Existing verified GuitarSet1.1.0 and Vienna4x22 CC BY4.0 originals; controlled exported codec files, not genuine iOS Voice Memo files",
  "audioMinusPianoMidiSeconds": -0.63375,
  "codecPaths": [
    {
      "id": "raw",
      "kind": "Original mono PCM16 WAV baseline"
    },
    {
      "id": "aac",
      "kind": "AAC128kbps M4A, decoded with existing FFmpeg to monoPCM16 WAV"
    },
    {
      "id": "alac",
      "kind": "ALAC M4A, decoded with same FFmpeg to monoPCM16 WAV"
    }
  ],
  "matching": {
    "pitch": "Exact integer MIDI pitch",
    "onsetToleranceSeconds": 0.05,
    "algorithm": "Reference onset order then pitch; nearest unused exact-pitch output; no fitted global shift, octave credit or widened tolerance",
    "headlineReference": "Only new annotated attacks within original5s crop; carried-in notes retained separately for context, not attacks",
    "offset": "Duration and ending errors of actual matched pairs reported separately; acoustic pedal decay not hardware key duration"
  },
  "runtimeScope": "Offline Node exact production detector after local FFmpeg decoding. Does NOT validate native Chrome M4A decoder, actual UI downloads, mobile browser, private file handling or rankings.",
  "browserRequired": "12actual UI attempts: each3clip x AAC M4A, same AAC-decoded WAV, ALAC M4A, same ALAC-decoded WAV; actual downloaded MIDI independently parsed, never relabel offline as browser. Browser differences trigger explicit analysis.",
  "noveltyBoundary": "Competitor audiotomidiconverter.com/m4a-to-midi already measures seven encodings and bit-identical outputs; no claim codec/hash comparison itself is unique. Only new useful annotated-human-performance findings can count after proper top10 and own-intent review.",
  "sourceConfounders": [
    "Same archived recordings, not3independent participants",
    "Guitar per-string annotation timing/pitch-rounding uncertainty",
    "Piano inherited fixed timing calibration, not refitted; hardware key duration differs from acoustic sustain",
    "Carried-in held notes and real overlapping notes remain contextual, monophonic detector not promoted to polyphony"
  ]
}