Adds an ISO 9660 walk (no mounting, no privileges) and a Scarlet Book parser
for the stereo audio area, plus the `DsdDemuxer` adapter that lets every DSD
delivery the player already has — PCM, DoP, native — play a disc image.
The parser exists because the previous account of this format, written in this
repo, was WRONG: it said the per-sector header was a fixed 8 bytes, derived
from looking at one sector. Every structure below was re-derived by a CENSUS —
3 066 893 sectors across both of the owner's Rheingold discs, zero exceptions —
and each claim is falsifiable rather than asserted:
- byte 0 carries packet_count = (b>>5)&7 and frame_info_count = (b>>2)&7,
so the header is 1 + pc*2 + fic*3 and takes the values 5, 8 or 10;
- packet descriptors are BIG-endian, and the length field is ELEVEN bits,
not the twelve every published layout shows. The first descriptor on both
discs is 0x181B, whose low twelve bits are 2075 — larger than the sector
it lives in. With eleven bits it is 27, and 5 + 27 + 2016 = 2048;
- the proof of the whole decoding is the sum rule
`header + SUM(packet lengths) == 2048`, which the parser CHECKS on every
sector rather than trusting;
- the area is uncompressed, proven from the data and not from a flag: the
audio-packet bytes divide by 9408 (one uncompressed DSD64 stereo frame)
exactly — 350 495 frames on Disc 1, 306 696 on Disc 2. DST is
variable-length; those could not be integers.
Track geometry comes from SACDTRL1/TRL2, tied together by an identity that
holds for 44 of 44 tracks: start_lsn == area_start + start_time * 350. The
ISO 9660 extents mirror SACDTRL1 byte for byte, so the one-sector overlap
between consecutive tracks is the disc's own accounting, not a bug to fix.
The channel layout inside a frame was the last unknown, and three statistical
probes could not settle it — they were measuring the DSD noise floor. What
settled it was physics: converted with the real filter, block-per-channel puts
23 % of its energy above the audible band while byte-interleaving puts 0.2 %
there. A correctly decoded 1-bit stream MUST carry that rising noise floor,
and no filter puts it back once scrambling has folded it away.
Also in this commit, from the same measurements: `2C_TAREA.2CH` on Disc 1 is
recorded in FOUR extents, so `IsoImage::find` REFUSES a multi-extent file
rather than returning its first quarter as if it were the whole thing.
cc
New crate `qbz-disc`: table of contents and raw audio sectors through the
kernel's own cdrom ioctls. No libcdio — not because libcdio is worse (it is
better at RIPPING than this will ever be) but because this path PLAYS a clean
disc, and for that the kernel interface is enough while a native library would
have to be built into Flatpak, Snap and AppImage. Both need the same --device
permission in a sandbox; only one needs the library shipped.
Every claim below was measured on the owner's USB drive with Tool — Fear
Inoculum BEFORE a line of this crate existed, so the design answers evidence
rather than the other way round:
- the TOC reads back 7 audio tracks, lead-out at LSN 356568, and the track
lengths match the record exactly (10:21, 11:52, 12:44, 13:37, 10:05, 4:48,
15:44 — 79:11 total);
- CDROMREADAUDIO over 20 frames from LSN 4000 returned 47 040 bytes, 99 %
non-zero samples, peak 14559: real audio, not silence;
- the drive hands back LITTLE-endian samples. Neighbouring-sample deltas
average 73.5 read as LE against 20 971 read as BE, a 285x margin, so the
bytes go straight into a little-endian WAV with no swap. That is one
drive, so `looks_byte_swapped` keeps the test available as a diagnostic
instead of an article of faith;
- the disc's MCN is all zeros, which is why identity is a digest over the
track table and not the catalogue number.
What this is NOT is accurate extraction: no overlap synchronisation, no cache
modelling, no jitter verification. On a clean disc that is fine for playback,
and an unreadable sector surfaces as an ERROR rather than a hole full of
zeros — silence that pretends to be audio is the one outcome a bit-perfect
player must never produce.
`/dev/sr0` is nowhere in the code: drives are enumerated, because a box can
have several and /dev/cdrom is a symlink that may point at any of them. Data
tracks of a mixed-mode disc are skipped by their control bits.
`CdRef` is the typed reference (`cdda:/dev/sr0#285735+70833`) with ONE parser,
not prefix tests copied around — the scattered version is a known failure mode
here and cost a whole session on 2026-08-20.
11 tests, several asserting against that real table of contents.
cc
vicrodh