Parse resilient SACD images, decode DST, scan ISO releases into the local library, and keep explicit opens ephemeral.
Ship decoder notices across distribution formats and align DSD album filtering and version selection.
cx
Add random access for DSF, DFF, and SACD demuxers, replace live DoP/native sources without releasing ALSA, and expose seek through Qt, MPRIS, and the daemon API.
cx
Reported: a SACD image played as white noise with the music distorted behind
it, identically in all three DSD modes. That the three agreed was the clue —
DoP and native never touch the PCM filter, so the damage had to be upstream of
the delivery choice, in how the bits are pulled out of the image.
THE LAYOUT WAS DECIDED BACKWARDS. The first measurement converted twelve
seconds and looked at where the energy landed: block-per-channel put 23 % above
the audible band, byte-interleaved 0.2 %, and the reasoning was that real DSD64
must carry a large ultrasonic component. That argument does not hold for this
pipeline. DsdPcmConverter low-passes and decimates to 88.2 kHz, so it REMOVES
sigma-delta noise shaping by design — a correct decode has nothing above
24 kHz. The 23 % was aliased garbage from bits read out of order: the symptom
was being read as the proof. The ratio does not discriminate either, since
scrambled bits and shaped noise both put energy up high.
Re-measured with a statistic that can come out differently: decode with the
real converter, then ask whether the audible band has the shape of music and
whether the two channels are a stereo pair at all.
layout spectral flatness L/R correlation
BlockPerChannel 0.038 … 0.107 -0.17 … -0.06
ByteInterleaved 0.0036 … 0.0093 +0.24 … +0.48
Tracks 1, 4 and 13 of disc 1 and track 5 of disc 2. A negative correlation
between the channels of an orchestral recording is not a subtle hint, and a
spectrum ten to twenty times flatter is noise.
Two earlier instruments are recorded in the doc as non-discriminating rather
than deleted quietly: the energy ratio, and the variance of the raw stream's
64-bit local mean, which answers the same for clean and scrambled bits because
the local mean of a byte-level mix of two correlated channels is still roughly
the audio.
Also lands a real framing bug found on the way, which was NOT the cause: the
packet descriptors carry a frame_start bit that the reader ignored, and frames
begin 0, 672 or 1344 bytes into a track's payload depending on the track. With
byte interleaving an even offset is harmless, which is why it hid; an odd one
would swap the channels. FrameSync makes the reader hunt for the boundary, and
keeps the unsynced path so a probe can reproduce the broken stream.
cc
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 frontend-agnostic crate for DSD support. In-house DSF and DFF
demuxers (up to 5.1, DST rejected with a typed error), embedded ID3
tags and artwork via the id3 crate, a verbatim BSD port of Sebastian
Gesemann's dsd2pcm table engine plus a half-band decimation chain
(uniform 88.2 kHz output, ITU stereo downmix for multichannel), DoP
frame packing per the DoP 1.1 standard (marker alternation, 0x69
silence), and native DSD_U32 packing (BE/LE) for kernel-granted
devices. 20 tests over synthesized fixtures.
cc
vicrodh