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codec: crack wide-NN blocks (1X NN / 2X NN); loud events now fully decode

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When NN exceeds 0xFC, the codec extends to 12-bit NN by using the
low nibble of the TYPE byte as the high nibble of NN:

    1X NN  →  nibble-delta block, NN = (X << 8) | NN_byte
    2X NN  →  int8-delta block, same NN encoding

Walker and decode_waveform_v2 now handle both narrow (X=0) and wide
(X != 0) forms uniformly.

Discovered while investigating why SP0/SS0/SV0/event-b walkers stopped
mid-event.  SP0 segment 12 (V continuation, cycle 3) starts with
"11 90" — high nibble of byte 0 = 1 (= nibble-delta block type), low
nibble = 1 plus byte 1 = 0x90 → NN = 0x190 = 400 nibble deltas in
202 bytes.  Walker was rejecting "11" as a non-tag.

Sample count went from 47,364 to 72,972 verified byte-exact:

  event-a:  9984 (full)        was 9984 (full)
  event-b:  6912 (full)        was   738
  event-c:  3840 (full)        was 3840 (full)
  event-d:  3840 (full)        was 3840 (full)
  JQ0:      9984 (full)        was 9984 (full)
  V70:      9984 (full)        was 9984 (full)
  SP0:      9984 (full)        was 5122
  SS0:      9222 (-7 tail)     was 1758
  SV0:      9222 (-7 tail)     was 2114

7 of 9 fixtures now decode end-to-end across all 3 geo channels.
The 2 remaining (SS0, SV0) are missing only 1-7 tail samples per
channel — minor walker edge case at the very end.

74 tests pass (was 71).
This commit is contained in:
Claude
2026-05-16 03:29:13 +00:00
committed by serversdown
parent 85f4bcfe86
commit 0466bb4f44
4 changed files with 77 additions and 28 deletions
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minimateplus/waveform_codec.py
+18 -2
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@@ -196,8 +196,20 @@ def walk_body(body: bytes, start: Optional[int] = None) -> List[WaveformBlock]:
t1 = body[i + 1]
if t0 == 0x10 and t1 % 4 == 0 and 0 < t1 <= 0xFC:
length = t1 // 2 + 2
elif (t0 & 0xF0) == 0x10 and (t0 & 0x0F) != 0 and t1 % 4 == 0:
# Wide-NN nibble block: ``1X NN`` where X is the high nibble of a
# 12-bit NN value. NN = ((t0 & 0x0F) << 8) | t1. Block length
# = NN/2 + 2 bytes (NN nibble deltas, same as ``10 NN`` semantics
# but with NN > 0xFC). Confirmed 2026-05-11 in SP0 segment 12
# where V continuation uses ``11 90`` = NN=0x190=400.
wide_nn = ((t0 & 0x0F) << 8) | t1
length = wide_nn // 2 + 2
elif t0 == 0x20 and t1 % 4 == 0 and 0 < t1 <= 0xFC:
length = t1 + 2
elif (t0 & 0xF0) == 0x20 and (t0 & 0x0F) != 0 and t1 % 4 == 0:
# Wide-NN int8 block: ``2X NN`` extends NN to 12 bits the same way.
wide_nn = ((t0 & 0x0F) << 8) | t1
length = wide_nn + 2
elif t0 == 0x00 and t1 % 4 == 0:
length = 2
elif t0 == 0x30 and t1 % 4 == 0 and 0 < t1 <= 0x10:
@@ -395,12 +407,16 @@ def decode_waveform_v2(body: bytes) -> Optional[dict]:
cur = anchor
for bi in range(block_start, block_end):
blk = blocks[bi]
if blk.tag_hi == 0x10:
if (blk.tag_hi & 0xF0) == 0x10:
# Both ``10 NN`` (NN ≤ 0xFC) and wide-NN ``1X NN`` (X != 0)
# are nibble-delta streams. The walker has already used the
# right length; here we just iterate the payload bytes.
for byte in blk.data:
for nib in ((byte >> 4) & 0xF, byte & 0xF):
cur += _s4(nib)
out[channel].append(cur)
elif blk.tag_hi == 0x20:
elif (blk.tag_hi & 0xF0) == 0x20:
# ``20 NN`` and wide ``2X NN`` both carry int8 deltas.
for byte in blk.data:
cur += _i8(byte)
out[channel].append(cur)