parse_stream_entry only read the PID for stream-entry type 1 (a stream
in the PlayItem's own clip), returning PID 0 for every other type. The
Dolby Vision enhancement layer uses type 4 (verified on Wicked + Dune:
se_len=9 type=0x04 [00 10 15] -> PID 0x1015), so the EL fell through to
PID 0x0000 and was silently dropped by the demux/mux — Dolby Vision lost.
Now the PID offset is keyed off the entry type per the BD stream_entry()
layout: type 1 -> +2, type 2 -> +4, type 3/4 -> +3. The DV EL now
resolves to its real PID (0x1015) so it is demuxed and carried as a
stream through the PES layer to every writer (M2TS carries dual-PID DV
natively; the MKV writer's DV signaling is the format-specific piece).