The ddts box declares both a channel count and a 16-bit speaker mask, and
a decoder may trust either. dts_channel_layout ended in a `_ => 0x0007`
catch-all describing five speakers (C + L/R + Ls/Rs), so for AMODE 6, 7,
and 10 through 15 the box contradicted the count DTS_AMODE_CH declared
alongside it — provoking a downmix or an outright decode error.
AMODE 6 (L + R + S) is the reachable case: its S is a single
centre-surround, not the Ls/Rs pair, so it is three channels and 0x0012,
not four and 0x0006. AMODE 13/14/15 do not occur on retail media, which
ships a 5.1 AMODE-9 core plus an extension substream.
Replace the catch-all with the full 16-entry ETSI TS 102 114 mask table.
Every entry is cross-checked against DTS_AMODE_CH by counting the
speakers its bits imply: sixteen independent constraints, all satisfied,
and that table is itself pinned to the per-AMODE channel counts in ETSI TS 102 114.
AMODE is a 6-bit field, so the reserved 16..=63 are reachable from a
malformed stream. The old `unwrap_or(6)` invented a channel count for
them that no mask could match; parse_dts now refuses those frames rather
than guessing a layout it cannot name.
One existing fixture placed the ext-sync pattern at f[4..8], which
incidentally set f[7]=0x25 → AMODE 20. That test is about where the
pattern sits, not about AMODE, so the frame is now spec-legal (AMODE 9,
48 kHz) with the pattern moved into the payload proper.
Matthew Jackson
f76688a0dc