The diagnostic hashed IFO contents but not where they came from, so a
content difference could not be told apart from a path resolving to a
different place. It now prints file_start_lba and file_extents next to the
hash.
That measurement is what inverted this investigation: both a CSS disc and
its decrypted copy resolve VIDEO_TS.IFO to the same extent, and only one
sector of the fourteen differs — by exactly a descrambled payload with the
scrambling-control bits cleared. So the decrypted copy holds the correct
bytes, and an iso:// scan of a CSS disc is parsing a still-scrambled IFO
sector, because scan_iso opens a plain FileSectorSource.
Two opt-in dumps, driven by FMKV_IMAGE, that narrow where a decrypted DVD
image loses titles:
dump_title_sets_for_an_image reports what survives parse_vmg. On one disc
the CSS image yields 13 title sets and 38 titles; its decrypted copy
yields 8 and 10. Sets 8, 9, 10, 12 and 13 are dropped outright, set 11
parses but returns no titles at all, and set 7 returns 3 of 5.
dump_vts_ifo_reads_for_an_image reads every VTS IFO and hashes the
CONTENT. All thirteen are byte-identical across the two images, so
parse_vts is handed the same bytes and the same TT_SRPT info and still
fails on one of them — the divergence is in what it reads from the READER
afterwards, which is file_start_lba and the PGCIT.
An earlier version of the second dump compared only length and magic and
so wrongly reported the images as identical; it hashes the bytes now.
parse_vmg skipped any title set whose parse failed, with no log and no
counter. A real disc enumerated 38 titles from one image and 10 from
another, and the 28 discarded failures were invisible — the symptom read
as a scan difference rather than as dropped reads, which is most of why
it took so long to localise.
Behaviour is unchanged: a disc may legitimately carry placeholder TT_SRPT
entries, so one failure is still not fatal. It now warns per skip with the
title set and the error, and once at the end with kept-versus-declared.
Also adds an opt-in diagnostic that reads every VTS IFO from an image, to
separate a read failure from a parse failure. It reports all 13 sets
reading identically from both a CSS image and its decrypted copy, which is
what proves the 38-to-10 loss is downstream of these reads.
dvd_placement_invariant_on_a_real_folder checks, per title set, the sum
ifo.rs relies on: file_start_lba(VTS_nn_0.IFO) + vtstt_vobs must land on
VTS_nn_1.VOB. It reports all 13 sets correct on a real DVD folder, which
is what excluded placement as the cause.
dump_titles_for_an_image prints every title a scan produces with the
numbers canonical_title_order sorts on. It is what showed the real shape:
the same disc scans to 38 titles as a CSS image and 10 once decrypted,
with identical capacity and a byte-complete image.
Both are #[ignore]d and read their target from the environment, so they
cost the gate nothing and are there for whoever picks the defect up.
The zero-frame check ran before the seam gate, and its error is
classified as a skippable nav stub — so a title the plan dropped
ENTIRELY was reported as an empty stub and an all-titles rip would omit
a real feature and finish the rest at exit 0. The seam case is decided
first now, with a code that is not skippable.
The demux sink read a frame's track kind out of the FILTERED slot, which
is empty for a class the export drops. On an audio:// or sub:// export
the video track was therefore called non-video and handed the permissive
crossing rule — the same defect round 4 fixed for a Dolby Vision layer,
reintroduced one file over. Video tracks are now recorded before the kind
filter, beside the primary-video reference that exists for this reason.
Its frame counter counted frames PLACED, not written, while its name and
doc claimed otherwise. Renamed and documented for what it is, including
that it cannot see a single lost track among many.
Placement: files in a subdirectory of VIDEO_TS were never given data.
They were declared at full size with no extents, so they appeared in the
tree and read as nothing. The same folder under BDMV was always placed
correctly. And the duplicate title-set guard keyed on the constraint maps,
so an IFO declaring no offsets inserted nothing and a colliding second IFO
went undetected — it keys on the groups seen now.
Display for SeamPlanDroppedMost and ShortImageRead discarded their
payloads, and four new variants were missing from the code-uniqueness
test.
The cap was added without a test. Its companion — a modest oversize is
honoured as a gap — already existed, so this pins the other side: an
offset past the ceiling is refused rather than grown into, which is what
keeps a rewritten IFO from planning a multi-terabyte image.
Users keep discs as extracted folders — a DVD VIDEO_TS or a Blu-ray BDMV,
usually a backup that is already decrypted. dir:// could only ever be a
destination, so those folders could be produced and never read back.
Everything above the sector layer wants a UdfFs over a SectorSource, and
every UdfFs read re-reads the ICB off that source at call time, so a
folder has to present itself as sectors. It does: dirimage plans a block
layout over the real files, encodes a UDF 1.02 filesystem for the
metadata, and serves data straight from disk. read_filesystem then parses
it exactly as it parses a disc, so nothing above changes — and the
iso:// arm of input() is now shared rather than duplicated, so dir://
inherits its decrypt gates, title selection and stream pruning.
The encoder is validated by more than its own reader: macOS mounts the
synthesized image and the mounted files compare byte-identical to the
originals. A round-trip through our own parser could not have shown that
— the tag CRC seeds at zero, and a wrong seed would satisfy us and no
real driver.
DVD placement is not free packing: a VTS IFO records where its title
VOBS begins relative to itself, so the VOB has to land exactly there.
Unsatisfiable marks fail loudly rather than misplace the file. 3D folders
are refused for now: the scanner detects SSIF and the planner cannot
alias its extents yet, so accepting them would produce quiet nonsense.
Left for later: metadata capture, HD-DVD, FMTS, encrypted folders.
Matthew Jackson