From 835cc990ad958708487d8f3b0faab7e88d2da590 Mon Sep 17 00:00:00 2001
From: Matthew Jackson <1085847+MattJackson@users.noreply.github.com>
Date: Fri, 26 Jun 2026 16:53:39 -0700
Subject: [PATCH] DVD vob_start absolute rebase + rc.5.3 audit fixes

- ifo.rs: rebase VTS title VOBS to absolute disc LBA (file_start_lba +
  vtstt_vobs); fixes DVD rips opening on the menu region instead of the
  movie (e.g. SOTL). Adds absolute-placement regression test.
- aacs/boil.rs: add mk_from_pk primitive (PK -> MK via MKB walk).
- dvdnav/: nav-VM command decoder + start-cell resolver seam, parked
  behind USE_NAV_RESOLVER (kept compiled, never executed).
- mux: FVI src.byte within-sector per spec; Unknown colour -> CICP
  unspecified (2,2,2,1); demux clear PCS -> NORMAL; ts.rs feed() base
  reset + boundary provenance fix.
- Assorted audit fixes (doc/comment/test accuracy) across the crate.
---
 CHANGELOG.md            |  17 +-
 src/aacs/boil.rs        | 110 ++++++++++-
 src/aacs/mod.rs         |   7 +-
 src/consts.rs           |   5 +-
 src/css/stevenson.rs    |   4 +-
 src/decrypt.rs          |  11 +-
 src/disc/dvd.rs         | 143 +++++++++++---
 src/disc/extract.rs     |   9 +-
 src/disc/patch.rs       |  24 +--
 src/drive/mod.rs        |   6 +-
 src/dvdnav/mod.rs       |  49 +++++
 src/dvdnav/vmcmd.rs     | 408 ++++++++++++++++++++++++++++++++++++++++
 src/error.rs            |   1 +
 src/ifo.rs              |  14 +-
 src/keysource.rs        |   6 +
 src/labels/mod.rs       |   7 +-
 src/lib.rs              |   1 +
 src/mux/codec/coding.rs |  15 +-
 src/mux/codec/h264.rs   |   3 +-
 src/mux/codec/hevc.rs   |   5 +-
 src/mux/demux_sink.rs   |   6 +-
 src/mux/fvi_sink.rs     |  16 +-
 src/mux/m2ts_mux/mod.rs |   5 +-
 src/mux/mkv.rs          |  54 +++++-
 src/mux/mkvstream.rs    |  92 ++++++---
 src/mux/resolve.rs      |  25 +++
 src/mux/ts.rs           |  95 +++++++++-
 src/mux/videomap.rs     |  15 ++
 src/pes.rs              |  21 +--
 src/unlock.rs           |  80 +++++++-
 tests/fvi_pipeline.rs   |  24 ++-
 31 files changed, 1149 insertions(+), 129 deletions(-)
 create mode 100644 src/dvdnav/mod.rs
 create mode 100644 src/dvdnav/vmcmd.rs

diff --git a/CHANGELOG.md b/CHANGELOG.md
index e54a7c6..daedc66 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,6 @@
 # Changelog
 
-## [1.0.0-rc.6] — UNRELEASED
+## [1.1.0-beta.1] — UNRELEASED
 
 ### Added
 
@@ -13,6 +13,21 @@
 
 ### Fixed
 
+- **DVD rips now start on the movie, not the disc menu.** A VTS title VOB's
+  start sector was read from the IFO as a VTS-relative pointer but used as an
+  absolute disc address, so a DVD title's read extents began `ifo_lba` sectors
+  too early — the rip opened on the disc's menu / VMGI region and only drifted
+  into the feature minutes later (Silence of the Lambs, for example, showed
+  several minutes of the main menu before the movie). The title VOB is now
+  rebased to its absolute on-disc location, so the rip begins at the first frame
+  of the feature. Aspect ratio and chapter timing were already correct; only the
+  starting sector was wrong. (Covered by a new absolute-placement regression
+  test.)
+- **Container metadata correctness.** Unknown colorimetry now emits the CICP
+  "unspecified" code point (2) consistently across the MKV track and the FVI
+  sidecar (previously 0); PGS subtitle wipes use the NORMAL composition state
+  rather than a full epoch reset; and FVI source-byte offsets are written
+  within-sector per the format spec.
 - **Multi-extent AACS alignment in `dir://` extraction.** The decrypted
   file-tree extractor anchored the AACS unit grid to the first extent only, so a
   file spanning multiple clip extents could mis-align and corrupt. Each extent
diff --git a/src/aacs/boil.rs b/src/aacs/boil.rs
index 27222fe..8aef997 100644
--- a/src/aacs/boil.rs
+++ b/src/aacs/boil.rs
@@ -15,11 +15,17 @@
 //!
 //! ```text
 //!   mk_from_dk(device_keys, mkb, vid)  →  MediaKey   (Km)
+//!   mk_from_pk(processing_keys, mkb)   →  MediaKey   (Km)
 //!   vuk_from_mk(MediaKey, Vid)         →  Vuk        (= AES-G(Km, VID))
 //!   uk_from_vuk(Vuk, enc_title_keys)   →  [UnitKey]  (decrypt_unit_key each)
 //! ```
+//!
+//! `mk_from_dk` and `mk_from_pk` are two entry points to the SAME Media Key:
+//! the device-key path walks the MKB's Media-Key-Variant chain, the
+//! processing-key path walks the MKB's Subset-Difference cvalue tables. Neither
+//! needs a VID (the VID enters at `vuk_from_mk`).
 
-use super::keys::{decrypt_unit_key, derive_vuk};
+use super::keys::{decrypt_unit_key, derive_media_key_from_pk, derive_vuk};
 use super::types::DeviceKey;
 use super::variants::{KEY_CORRECTION_DATA_PLACEHOLDER, derive_media_key_variant, walk_mkb};
 
@@ -111,6 +117,31 @@ pub fn mk_from_dk(
     }
 }
 
+/// Derive the Media Key (Km) from one or more Processing Keys and the disc MKB.
+///
+/// Wraps [`derive_media_key_from_pk`] — the Subset-Difference PK→MK walk: each
+/// processing key is validated (and tree-walked) against the MKB's cvalue tables
+/// (records `0x04`/`0x05`) until one yields the Media Key whose verify record
+/// (`0x81`/`0x86`) matches. Unlike [`mk_from_dk`] this path is reachable for
+/// real discs — a leaked/precomputed AACS Processing Key in the keydb resolves
+/// the Media Key directly. No VID is involved at this step; the VID enters at
+/// [`vuk_from_mk`].
+///
+/// Returns [`Error::AacsMkUnavailable`] (E7018) when no processing key resolves
+/// the MKB — the same terminal error as [`mk_from_dk`]; no numeric distinction
+/// is load-bearing at this boundary.
+///
+/// [`Error::AacsMkUnavailable`]: crate::error::Error::AacsMkUnavailable
+pub fn mk_from_pk(
+    processing_keys: &[[u8; 16]],
+    mkb: &[u8],
+) -> Result<MediaKey, crate::error::Error> {
+    match derive_media_key_from_pk(mkb, processing_keys) {
+        Some(km) => Ok(MediaKey(km)),
+        None => Err(crate::error::Error::AacsMkUnavailable),
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -197,4 +228,81 @@ mod tests {
         let e2 = mk_from_dk(&[dk], &mkb, Vid([0x09; 16]));
         assert!(matches!(e2, Err(crate::error::Error::AacsMkUnavailable)));
     }
+
+    /// Build a 4-byte MKB record header (type + 3-byte big-endian total length,
+    /// header included) and append `body`. Mirrors the MKB record framing the
+    /// parser expects; no crypto.
+    fn mkb_record(rec_type: u8, body: &[u8]) -> Vec<u8> {
+        let total = 4 + body.len();
+        let mut rec = Vec::with_capacity(total);
+        rec.push(rec_type);
+        rec.push(((total >> 16) & 0xFF) as u8);
+        rec.push(((total >> 8) & 0xFF) as u8);
+        rec.push((total & 0xFF) as u8);
+        rec.extend_from_slice(body);
+        rec
+    }
+
+    /// `mk_from_pk` resolves a planted Processing Key against a synthetic MKB and
+    /// drives the FULL boil chain PK → MK → VUK → UK. The MKB is built with the
+    /// same (pk, cv, mk_dv, uv) construction the production SD walk validates, so
+    /// this proves a PK entry yields real Unit Keys — not just an `Ok`.
+    #[test]
+    fn mk_from_pk_drives_full_chain_to_uks() {
+        let pk: [u8; 16] = [
+            0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77, 0x88, 0x99, 0xAA, 0xBB, 0xCC, 0xDD, 0xEE,
+            0xFF, 0x00,
+        ];
+        let mk: [u8; 16] = [
+            0xA0, 0xA1, 0xA2, 0xA3, 0xA4, 0xA5, 0xA6, 0xA7, 0xA8, 0xA9, 0xAA, 0xAB, 0xAC, 0xAD,
+            0xAE, 0xAF,
+        ];
+        let uv: [u8; 4] = [0x00, 0x00, 0x04, 0x00];
+
+        // cv = AES-E(pk, mk_raw), where mk_raw is mk with the last-4-bytes-uv XOR
+        // pre-undone, so the validate step XORs uv back in and recovers mk.
+        let mut mk_raw = mk;
+        for a in 0..4 {
+            mk_raw[12 + a] ^= uv[a];
+        }
+        let cv = aes_ecb_encrypt(&pk, &mk_raw);
+
+        // mk_dv = AES-E(mk, magic||pad): AES-D(mk, mk_dv) starts with the AACS
+        // verify sentinel.
+        let mut vd = [0x11u8; 16];
+        vd[..8].copy_from_slice(&[0x01, 0x23, 0x45, 0x67, 0x89, 0xAB, 0xCD, 0xEF]);
+        let mk_dv = aes_ecb_encrypt(&mk, &vd);
+
+        // Synthetic MKB: type/version (0x10), verify record (0x86 = mk_dv),
+        // one-entry SD index (0x04 = [u_mask_shift=0][uv]), one-entry cvalue
+        // table (0x05 = cv).
+        let mut sd = vec![0u8];
+        sd.extend_from_slice(&uv);
+        let mut mkb = Vec::new();
+        mkb.extend_from_slice(&mkb_record(0x10, &[0, 0, 0, 0x20, 0, 0, 0, 0x52]));
+        mkb.extend_from_slice(&mkb_record(0x86, &mk_dv));
+        mkb.extend_from_slice(&mkb_record(0x04, &sd));
+        mkb.extend_from_slice(&mkb_record(0x05, &cv));
+
+        // PK → MK.
+        let got_mk = mk_from_pk(std::slice::from_ref(&pk), &mkb).expect("planted PK resolves MK");
+        assert_eq!(got_mk, MediaKey(mk), "mk_from_pk recovers the planted MK");
+
+        // MK → VUK → UK over an encrypted title key.
+        let vid = Vid([0x42u8; 16]);
+        let plain_uk = [0x7Eu8; 16];
+        let vuk = vuk_from_mk(got_mk, vid);
+        let enc = aes_ecb_encrypt(&vuk.0, &plain_uk);
+        let uks = uk_from_vuk(vuk, std::slice::from_ref(&enc));
+        assert_eq!(uks.len(), 1);
+        assert_eq!(uks[0].key, plain_uk, "PK chain recovers the title key");
+
+        // A corrupt PK resolves nothing.
+        let mut bad = pk;
+        bad[0] ^= 0xFF;
+        assert!(matches!(
+            mk_from_pk(std::slice::from_ref(&bad), &mkb),
+            Err(crate::error::Error::AacsMkUnavailable)
+        ));
+    }
 }
diff --git a/src/aacs/mod.rs b/src/aacs/mod.rs
index 289d172..e8711af 100644
--- a/src/aacs/mod.rs
+++ b/src/aacs/mod.rs
@@ -24,7 +24,7 @@ pub mod types;
 pub mod variants;
 
 // Boil-down derivation primitives (thin newtypes + wrappers over the crypto).
-pub use boil::{MediaKey, UnitKey, Vid, Vuk, mk_from_dk, uk_from_vuk, vuk_from_mk};
+pub use boil::{MediaKey, UnitKey, Vid, Vuk, mk_from_dk, mk_from_pk, uk_from_vuk, vuk_from_mk};
 // Structured, English-free resolution trace.
 pub use trace::{KeyNode, KeyOutcome, KeyStep, ResolutionTrace, UnlockOutcome, UnlockStep};
 
@@ -35,6 +35,10 @@ pub use decrypt::{
     decrypt_unit_full, decrypt_unit_try_keys, is_aacs_scrambled, is_unit_aligned, ts_packet_total,
     ts_sync_count, unit_key_validates,
 };
+// `probe` is a reproduction-harness helper (see keys.rs), not part of the
+// documented 1.0 surface; keep it reachable but off the rendered docs so we
+// don't commit semver stability to test primitives.
+#[doc(hidden)]
 pub use keys::probe;
 pub use keys::{
     AacsVersion, ContentCert, MKB_20_CATEGORY_C, MKB_21_CATEGORY_C, MKB_TYPE_3_RECORDABLE,
@@ -97,5 +101,6 @@ mod tests {
         let _ = mkb_content_len(&[]);
         let _ = is_variant_mkb(&walk_mkb(&[]));
         let _ = disc_hash_hex(&disc_hash(b"x"));
+        let _ = mk_from_pk(&[[0u8; 16]], &[]);
     }
 }
diff --git a/src/consts.rs b/src/consts.rs
index 29e06d9..7437cc2 100644
--- a/src/consts.rs
+++ b/src/consts.rs
@@ -48,8 +48,9 @@ pub const BD_SOURCE_PACKET_BYTES: usize = TS_PACKET_BYTES + BD_TIMESTAMP_PREFIX_
 /// This is one registry used in two places that share the same value space:
 /// the MPEG-TS PMT `stream_type` (ISO/IEC 13818-1 Table 2-34) and the Blu-ray
 /// STN/CLPI `stream_coding_type` (BD-ROM Part 3). The standardized video codes
-/// (`0x02`, `0x1B`, `0x24`, `0xEA`) are ISO assignments; the `0x80..=0xA2`
-/// audio/graphics codes sit in the ISO user-private range and follow the
+/// (`0x02`, `0x1B`, `0x24`) are ISO assignments (ISO/IEC 13818-1 Table 2-34);
+/// `0xEA` (VC-1) is a BD-ROM convention in the ISO user-private range. The
+/// `0x80..=0xA2` audio/graphics codes also sit in the user-private range and follow the
 /// Blu-ray Disc Association / ATSC A/52 convention. Because every consumer
 /// reads or writes this single byte, the family is unprefixed — the scope is
 /// "any elementary stream freemkv parses or muxes".
diff --git a/src/css/stevenson.rs b/src/css/stevenson.rs
index 84798a8..63236bf 100644
--- a/src/css/stevenson.rs
+++ b/src/css/stevenson.rs
@@ -402,7 +402,7 @@ mod tests {
 
     #[test]
     fn crack_unscrambled_returns_none() {
-        let sector = vec![0u8; 2048];
+        let sector = vec![0u8; SECTOR_BYTES];
         assert!(crack_title_key(&sector).is_none());
     }
 
@@ -414,7 +414,7 @@ mod tests {
 
     #[test]
     fn recover_needs_min_plain() {
-        let sector = vec![0u8; 2048];
+        let sector = vec![0u8; SECTOR_BYTES];
         let short_plain = [0u8; 4];
         assert!(recover_title_key(&sector, &short_plain).is_none());
     }
diff --git a/src/decrypt.rs b/src/decrypt.rs
index 71673ca..7273ce7 100644
--- a/src/decrypt.rs
+++ b/src/decrypt.rs
@@ -373,9 +373,16 @@ pub fn decrypt_sectors(
                     continue;
                 }
                 let crib = css::stevenson::attack_crib(chunk);
-                let original: Option<Vec<u8>> = crib.as_ref().map(|_| chunk.to_vec());
+                // Snapshot the ciphertext into a stack buffer (chunk is exactly
+                // 2048 here — guaranteed by the `< 2048` continue above) only
+                // when there's a crib to validate against, so the common
+                // cache-hit path costs no per-sector heap allocation.
+                let mut original = [0u8; 2048];
+                if crib.is_some() {
+                    original.copy_from_slice(chunk);
+                }
                 css::lfsr::descramble_sector(title_key, chunk);
-                if let (Some(crib), Some(original)) = (crib, original) {
+                if let Some(crib) = crib {
                     if chunk[0x80..0x80 + 10] != crib[..] {
                         // Cached key is stale for this region — restore the
                         // ciphertext and crack this sector's own key.
diff --git a/src/disc/dvd.rs b/src/disc/dvd.rs
index 6476d6c..45fb48c 100644
--- a/src/disc/dvd.rs
+++ b/src/disc/dvd.rs
@@ -106,7 +106,7 @@ impl Disc {
                 })
                 .collect();
 
-            for dvd_title in &ts.titles {
+            for (vts_title_idx, dvd_title) in ts.titles.iter().enumerate() {
                 title_number += 1;
 
                 // Diagnostic dump (--log-level 3): per-cell category table +
@@ -114,13 +114,32 @@ impl Disc {
                 // per-cell IFO detail. No-op unless freemkv::diag is enabled.
                 crate::diag::dump_dvd_cells(ts.vts_number, title_number, dvd_title);
 
-                // Bug-4 leading-cell filter: drop any leading scene-index /
-                // interleaved-angle sub-block cells so the feature starts at the
-                // movie. Conservative — `feature_start_cell` only ever skips a
-                // prefix of secondary-block cells and never truncates a normal
-                // feature (category 0x00 on cell 0 → no-op). See
-                // `ifo::DvdTitle::feature_start_cell`.
-                let feature_start = dvd_title.feature_start_cell();
+                // Feature start cell. Prefer the DVD nav-VM resolver, which
+                // PARKED (#40, menu-at-start playback). The "menu at the start"
+                // symptom (e.g. SOTL) was a sector-mapping fault — the absolute
+                // VOB rebase in `ifo::parse_vts` (`vob_start_sector =
+                // file_start_lba + vtstt_vobs`) — NOT a navigation problem, so
+                // feature-start resolution is unnecessary for correct rips. The
+                // nav resolver + verified VM decoder (`dvdnav`) are kept compiled
+                // but deliberately bypassed; flip `USE_NAV_RESOLVER` to re-enable
+                // once the nav executor is finished. The fallback is the
+                // structural leading-cell filter (`feature_start_cell`), which
+                // drops leading scene-index / interleaved-angle sub-block cells
+                // and is a no-op for a normal feature (category 0x00 on cell 0).
+                // See `dvdnav::resolve_feature_start`.
+                const USE_NAV_RESOLVER: bool = false;
+                let feature_start = if USE_NAV_RESOLVER {
+                    crate::dvdnav::resolve_feature_start(
+                        reader,
+                        udf_fs,
+                        ts.vts_number as u16,
+                        (vts_title_idx + 1) as u16,
+                    )
+                    .unwrap_or_else(|| dvd_title.feature_start_cell())
+                } else {
+                    dvd_title.feature_start_cell()
+                }
+                .min(dvd_title.cells.len());
                 let dropped_secs: f64 = dvd_title.cells[..feature_start]
                     .iter()
                     .map(|c| c.duration_secs)
@@ -136,9 +155,9 @@ impl Disc {
                     );
                 }
 
-                // Build extents from cell sector ranges (absolute = vob_start + cell offset)
-                let extents: Vec<Extent> = dvd_title
-                    .feature_cells()
+                // Build extents from cell sector ranges (absolute = vob_start + cell offset),
+                // starting at the resolved feature-start cell.
+                let extents: Vec<Extent> = dvd_title.cells[feature_start..]
                     .iter()
                     .map(|cell| {
                         let start = ts.vob_start_sector.saturating_add(cell.first_sector);
@@ -553,8 +572,10 @@ mod tests {
         assert_eq!(titles.len(), 1);
         let t = &titles[0];
         assert_eq!(t.extents.len(), 1);
-        // absolute start = vob_start(1000) + first_sector(10) = 1010.
-        assert_eq!(t.extents[0].start_lba, 1010);
+        // absolute start = ifo_lba + vtstt_vobs(1000) + first_sector(10).
+        // The IFO file sits at PART_START(3000) + data_lba(6000) = 9000, so
+        // 9000 + 1000 + 10 = 10010.
+        assert_eq!(t.extents[0].start_lba, 10010);
         // inclusive: 109 - 10 + 1 = 100 sectors.
         assert_eq!(t.extents[0].sector_count, 100);
         // DVD sector = 2048 bytes.
@@ -607,12 +628,85 @@ mod tests {
         assert_eq!(titles.len(), 1);
         let t = &titles[0];
         assert_eq!(t.extents.len(), 1);
-        // Title VOBS (3640) + cell first_sector (0) = 3640 — NOT the menu 44.
+        // ifo_lba(9000) + vtstt_vobs(3640) + first_sector(0) = 12640 — built
+        // from the Title VOBS (0xC4), NOT the menu VOBS (0xC0). The IFO file is
+        // at PART_START(3000) + data_lba(6000) = 9000.
         assert_eq!(
+            t.extents[0].start_lba, 12640,
+            "extent must start at ifo_lba + vtstt_vobs (0xC4), not vtsm_vobs (0xC0)"
+        );
+        // Must not resolve from the menu VOBS (would be 9000 + 44 = 9044), nor
+        // use the raw IFO-relative vtstt_vobs (3640) without the absolute base.
+        assert_ne!(t.extents[0].start_lba, 9044, "must not use the menu VOBS");
+        assert_ne!(
             t.extents[0].start_lba, 3640,
-            "extent must start at vtstt_vobs (0xC4), not vtsm_vobs (0xC0)"
+            "must add the IFO's absolute disc LBA, not use the raw relative value"
+        );
+    }
+
+    /// ABSOLUTE-REBASE regression (THESILENCEOFTHELAMBS / Greenland fix):
+    /// `ifo::parse_vts` now sets `vob_start_sector = file_start_lba(IFO) +
+    /// vtstt_vobs`, so an extent's `start_lba` must equal the sum of THREE
+    /// independent terms — the IFO file's absolute on-disc LBA, the
+    /// IFO-relative `vtstt_vobs` (0xC4), and the cell's `first_sector` — none of
+    /// which may be dropped. The earlier code used the bare relative
+    /// `vtstt_vobs`, placing every extent `ifo_lba` sectors too early (the rip
+    /// opened in the VMGI/menu region before drifting into the movie). The
+    /// other tests fold two of the three terms together (zero cell offset, or
+    /// a single combined expectation); this one keeps all three distinct and
+    /// non-overlapping so a regression to ANY two-term combination is caught.
+    #[test]
+    fn scan_dvd_titles_extent_is_absolute_three_term_sum() {
+        let mut disc = MemDisc::new();
+        let vmg = build_vmg(&[(1, 1, 1)]);
+        // vtstt_vobs (Title VOBS, 0xC4) = 700; one cell first_sector = 33.
+        let vts = build_vts(700, 0x00, &[], &[], &[(33, 132)], false);
+        // IFO data at data_lba 6000 → absolute ifo_lba = PART_START(3000) + 6000.
+        let ifo_lba = PART_START + 6000; // 9000
+        let vtstt_vobs = 700u32;
+        let first_sector = 33u32;
+        let udf = build_video_ts_fs(
+            &mut disc,
+            &[
+                FileSpec {
+                    name: "VIDEO_TS.IFO".into(),
+                    icb_lba: 60,
+                    data_lba: 5000,
+                    contents: vmg,
+                },
+                FileSpec {
+                    name: "VTS_01_0.IFO".into(),
+                    icb_lba: 62,
+                    data_lba: 6000,
+                    contents: vts,
+                },
+            ],
+        );
+        let t = &Disc::scan_dvd_titles(&mut disc, &udf)[0];
+        assert_eq!(t.extents.len(), 1);
+        let got = t.extents[0].start_lba;
+        // The one correct answer: all three terms summed (9000 + 700 + 33).
+        assert_eq!(
+            got,
+            ifo_lba + vtstt_vobs + first_sector,
+            "extent start must be file_start_lba(IFO) + vtstt_vobs + cell.first_sector"
+        );
+        // Each wrong two-term combination must be rejected:
+        assert_ne!(
+            got,
+            vtstt_vobs + first_sector,
+            "must not use the bare relative vtstt_vobs (missing the IFO's absolute LBA)"
+        );
+        assert_ne!(
+            got,
+            ifo_lba + first_sector,
+            "must not drop vtstt_vobs (the Title VOBS pointer)"
+        );
+        assert_ne!(
+            got,
+            ifo_lba + vtstt_vobs,
+            "must not drop the cell's first_sector offset"
         );
-        assert_ne!(t.extents[0].start_lba, 44, "must not use the menu VOBS");
     }
 
     /// Multi-cell title: extents preserve cell order and each maps to its
@@ -648,9 +742,9 @@ mod tests {
         );
         let t = &Disc::scan_dvd_titles(&mut disc, &udf)[0];
         assert_eq!(t.extents.len(), 2);
-        assert_eq!(t.extents[0].start_lba, 500); // 500 + 0
+        assert_eq!(t.extents[0].start_lba, 9500); // ifo_lba(9000) + 500 + 0
         assert_eq!(t.extents[0].sector_count, 100);
-        assert_eq!(t.extents[1].start_lba, 700); // 500 + 200
+        assert_eq!(t.extents[1].start_lba, 9700); // ifo_lba(9000) + 500 + 200
         assert_eq!(t.extents[1].sector_count, 100);
         assert_eq!(t.size_bytes, 200 * 2048);
     }
@@ -1051,8 +1145,9 @@ mod tests {
         assert_eq!(titles[0].playlist, "VTS_01_1.VOB");
         assert_eq!(titles[1].playlist, "VTS_02_2.VOB");
         // Distinct vob_start → distinct extents.
-        assert_eq!(titles[0].extents[0].start_lba, 100);
-        assert_eq!(titles[1].extents[0].start_lba, 200);
+        // VTS_01 IFO @ PART_START(3000)+6000=9000; VTS_02 IFO @ 3000+7000=10000.
+        assert_eq!(titles[0].extents[0].start_lba, 9100); // 9000 + 100
+        assert_eq!(titles[1].extents[0].start_lba, 10200); // 10000 + 200
     }
 
     /// chapter_times from the IFO become Chapter entries with ordinal
@@ -1168,8 +1263,8 @@ mod tests {
         // The leading 0x90 cell is dropped: 2 feature extents, not 3.
         assert_eq!(t.extents.len(), 2, "leading angle sub-block cell dropped");
         // First extent starts at the feature cell (vob 1000 + 100), not at 1000+0.
-        assert_eq!(t.extents[0].start_lba, 1000 + 100);
-        assert_eq!(t.extents[1].start_lba, 1000 + 300);
+        assert_eq!(t.extents[0].start_lba, 9000 + 1000 + 100); // ifo_lba + vtstt + first
+        assert_eq!(t.extents[1].start_lba, 9000 + 1000 + 300);
         // Chapter times shift earlier by the dropped 5s. Program 0 was at the
         // dropped head (clamped to 0); program 1 was at cell 3 =
         // dur(cell0)+dur(cell1) = 5 + 59 = 64s, now 59s after the 5s shift.
@@ -1219,8 +1314,8 @@ mod tests {
         let t = &Disc::scan_dvd_titles(&mut disc, &udf)[0];
         // Nothing dropped: both cells become extents, starting at the very head.
         assert_eq!(t.extents.len(), 2);
-        assert_eq!(t.extents[0].start_lba, 1000); // 1000 + 0, head intact
-        assert_eq!(t.extents[1].start_lba, 1200);
+        assert_eq!(t.extents[0].start_lba, 9000 + 1000); // ifo_lba + vtstt + 0, head intact
+        assert_eq!(t.extents[1].start_lba, 9000 + 1200);
         // Chapter 0 stays at 0.0 (no shift).
         assert!((t.chapters[0].time_secs - 0.0).abs() < 0.01);
     }
diff --git a/src/disc/extract.rs b/src/disc/extract.rs
index 99a8516..9bddfea 100644
--- a/src/disc/extract.rs
+++ b/src/disc/extract.rs
@@ -234,9 +234,12 @@ impl Disc {
 
             // Acquire (rather than Relaxed) on these per-file delta loads:
             // `extract_tree` drives `dec` single-threaded so there is no race
-            // today, but Acquire costs nothing on x86 and gives a happens-
-            // before edge if file extraction is ever parallelised, so the
-            // delta can never read a torn/stale counter across iterations.
+            // today, and Acquire costs nothing on x86. Note this is only half
+            // the synchronisation: the paired counter store
+            // (sector/decrypting.rs `fetch_add`) is Relaxed, so an Acquire
+            // load alone does NOT yet establish a happens-before edge. Before
+            // file extraction is parallelised, upgrade that store to Release
+            // (or stronger) so the delta cannot read a stale counter.
             let before_loss = decrypt_loss.load(Ordering::Acquire);
             let (mut fr, halted) =
                 extract_one_file(&mut dec, dest, pf, total_bytes, &mut done_bytes, opts)?;
diff --git a/src/disc/patch.rs b/src/disc/patch.rs
index 0d69cad..0f23858 100644
--- a/src/disc/patch.rs
+++ b/src/disc/patch.rs
@@ -825,12 +825,12 @@ pub(super) fn handle_read_success<R: SectorSource + ?Sized>(
         state.stall_start = (state.now)();
         state.bytes_good_last = bytes_good_now;
     }
-    if (state.now)().duration_since(state.stall_start) > std::time::Duration::from_secs(STALL_SECS)
-    {
+    let stall_elapsed = (state.now)().duration_since(state.stall_start);
+    if stall_elapsed > std::time::Duration::from_secs(STALL_SECS) {
         tracing::warn!(
             target: "freemkv::disc",
             phase = "patch_stall",
-            elapsed_secs = (state.now)().duration_since(state.stall_start).as_secs(),
+            elapsed_secs = stall_elapsed.as_secs(),
             bytes_good = bytes_good_now,
             bytes_good_start = state.bytes_good_start,
             "Patch stalled - no recovery for {}s, exiting pass",
@@ -1107,13 +1107,12 @@ pub(super) fn handle_read_failure<R: SectorSource + ?Sized>(
                 state.stall_start = (state.now)();
                 state.bytes_good_last = bytes_good_now;
             }
-            if (state.now)().duration_since(state.stall_start)
-                > std::time::Duration::from_secs(STALL_SECS)
-            {
+            let stall_elapsed = (state.now)().duration_since(state.stall_start);
+            if stall_elapsed > std::time::Duration::from_secs(STALL_SECS) {
                 tracing::warn!(
                     target: "freemkv::disc",
                     phase = "patch_stall",
-                    elapsed_secs = (state.now)().duration_since(state.stall_start).as_secs(),
+                    elapsed_secs = stall_elapsed.as_secs(),
                     bytes_good = bytes_good_now,
                     bytes_good_start = state.bytes_good_start,
                     "Patch stalled (NOT_READY path) - no recovery for {}s, exiting pass",
@@ -1193,12 +1192,12 @@ pub(super) fn handle_read_failure<R: SectorSource + ?Sized>(
         state.stall_start = (state.now)();
         state.bytes_good_last = bytes_good_now;
     }
-    if (state.now)().duration_since(state.stall_start) > std::time::Duration::from_secs(STALL_SECS)
-    {
+    let stall_elapsed = (state.now)().duration_since(state.stall_start);
+    if stall_elapsed > std::time::Duration::from_secs(STALL_SECS) {
         tracing::warn!(
             target: "freemkv::disc",
             phase = "patch_stall",
-            elapsed_secs = (state.now)().duration_since(state.stall_start).as_secs(),
+            elapsed_secs = stall_elapsed.as_secs(),
             consecutive_failures = state.consecutive_failures,
             bytes_good = bytes_good_now,
             bytes_good_start = state.bytes_good_start,
@@ -1472,13 +1471,14 @@ pub(super) fn check_range_watchdog(
         state.range_bytes_good = bytes_good_now;
         state.range_start = (state.now)();
     }
-    if (state.now)().duration_since(state.range_start).as_secs() >= frame.range_budget_secs {
+    let range_elapsed = (state.now)().duration_since(state.range_start);
+    if range_elapsed.as_secs() >= frame.range_budget_secs {
         tracing::warn!(
             target: "freemkv::disc",
             phase = "patch_range_stall",
             range_lba = frame.range_pos / 2048,
             range_sectors = frame.range_sectors,
-            elapsed_secs = (state.now)().duration_since(state.range_start).as_secs(),
+            elapsed_secs = range_elapsed.as_secs(),
             budget_secs = frame.range_budget_secs,
             bytes_recovered = state.range_bytes_good.saturating_sub(state.bytes_good_before),
             "Range stalled - moving to next range"
diff --git a/src/drive/mod.rs b/src/drive/mod.rs
index b460bb3..16fcf1c 100644
--- a/src/drive/mod.rs
+++ b/src/drive/mod.rs
@@ -433,8 +433,12 @@ impl Drive {
                 }
                 Ok(())
             }
-            // No unlocker matched: not an error — fall through to OEM route.
+            // No unlocker matched, or one matched but only hit a capability
+            // failure (not firmware-unlockable / no OEM VID): not an error —
+            // fall through to the OEM host-cert route.
             Ok(None) => Ok(()),
+            // A genuine transport fault during unlock (UnlockError::Scsi)
+            // propagates here and aborts init — the bus is dead.
             Err(e) => Err(e),
         };
         tracing::info!(
diff --git a/src/dvdnav/mod.rs b/src/dvdnav/mod.rs
new file mode 100644
index 0000000..84961e0
--- /dev/null
+++ b/src/dvdnav/mod.rs
@@ -0,0 +1,49 @@
+//! DVD-Video navigation — read-only resolver for the **main-feature start
+//! point** (issue #40). Mirrors what a DVD player's nav VM resolves: First-Play
+//! → menu "Play" → title dispatch → the first cell of the feature, so the rip
+//! starts at the movie rather than at raw cell 0 (e.g. skipping a leading
+//! logo/warning segment when the disc's own navigation does).
+//!
+//! Byte layout follows the DVD-Video specification (VMGI/VTSI headers,
+//! PGC/cell tables, PCI/HLI button packets); the VM command decoder is
+//! verified against libdvdnav's decoder.
+//!
+//! Current contents: [`vmcmd`] — the VM command decoder (proven against the
+//! SOTL/Greenland test discs). The IFO/PCI parsing and the navigation executor
+//! that resolves the start cell build on top of this.
+
+pub mod vmcmd;
+
+use crate::sector::SectorSource;
+
+/// Resolve the feature title's **true start cell** (0-based index into the
+/// title PGC's cell list) by following the disc's own navigation — First-Play →
+/// menu "Play" → title dispatch — the way a player reaches the movie. This is
+/// what lets the rip begin at the feature instead of at raw cell 0 when the
+/// disc's nav enters the title past a leading logo/warning segment (e.g. a
+/// disc whose "Play" resolves to a later cell than cell 0).
+///
+/// Returns `None` when navigation cannot be resolved, so the caller falls back
+/// to the structural leading-cell filter (today's behaviour, ≈ cell 0 / 0:00).
+///
+/// TODO(#40): the IFO/PCI parsing + nav executor (built on [`vmcmd`]) land
+/// incrementally. Until the executor is complete this returns `None`, so wiring
+/// it in is behaviour-neutral; improvements to the resolver take effect here
+/// without touching the call site.
+pub fn resolve_feature_start(
+    reader: &mut dyn SectorSource,
+    udf: &crate::udf::UdfFs,
+    vtsn: u16,
+    vts_ttn: u16,
+) -> Option<usize> {
+    // `reader`/`udf` are the seam inputs the nav executor will consume to read
+    // VIDEO_TS.IFO + the VTS IFOs/menu VOBs. Reserved until that lands.
+    let _ = (reader, udf);
+    tracing::trace!(
+        target: "freemkv::dvdnav",
+        vtsn,
+        vts_ttn,
+        "nav start-cell resolver: unresolved — caller falls back to leading-cell filter"
+    );
+    None
+}
diff --git a/src/dvdnav/vmcmd.rs b/src/dvdnav/vmcmd.rs
new file mode 100644
index 0000000..713a15e
--- /dev/null
+++ b/src/dvdnav/vmcmd.rs
@@ -0,0 +1,408 @@
+//! DVD-Video VM command decoder.
+//!
+//! An 8-byte navigation command as found in PGC command tables (pre/post/cell)
+//! and PCI button info. Decoded per the DVD-Video VM instruction set and
+//! verified against libdvdnav's command decoder.
+//!
+//! Bit model: the 8 bytes are a big-endian 64-bit word. `byte0` bits 7-5 are the
+//! command **type**; for type 1, `byte0` bit 4 selects Link (0) vs Jump (1), and
+//! `byte1` bits 3-0 are the sub-command. Compare predicates live in `byte1`
+//! bits 6-4 with the operands in bytes 2-5.
+//!
+//! This module is pure decode + a register model — no I/O, no English (numeric
+//! semantics only), matching libfreemkv conventions. The navigation *executor*
+//! and IFO/PCI parsing build on top of this.
+
+/// A decoded navigation instruction. Only the variants freemkv's start-point
+/// resolver needs are modelled explicitly; everything else is [`Instr::Other`].
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum Instr {
+    Nop,
+    /// Stop executing the current command list (resume cell playback).
+    Break,
+    /// Goto command line within the same list (1-based).
+    Goto {
+        line: u8,
+    },
+    /// Leave the current domain.
+    Exit,
+    /// Jump to a VMG title (1-based TT_SRPT index).
+    JumpTt {
+        ttn: u8,
+    },
+    /// Jump to a title within the current VTS (1-based VTS title index).
+    JumpVtsTt {
+        ttn: u8,
+    },
+    /// Jump to a part-of-title (chapter) within a VTS title.
+    JumpVtsPtt {
+        ttn: u8,
+        pttn: u16,
+    },
+    /// Jump to the First-Play PGC.
+    JumpSsFp,
+    /// Jump to a Video-Manager menu (`menu` = menu id).
+    JumpSsVmgm {
+        menu: u8,
+    },
+    /// Jump to a Video-Title-Set menu.
+    JumpSsVtsm {
+        vts: u8,
+        ttn: u8,
+        menu: u8,
+    },
+    /// Jump to a specific VMGM menu PGC.
+    JumpSsVmgmPgc {
+        pgcn: u16,
+    },
+    /// Call a sub-domain (raw retained; resume handled by the executor).
+    CallSs {
+        sub: u8,
+    },
+    /// Link to a PGC number within the current domain.
+    LinkPgcn {
+        pgcn: u16,
+    },
+    /// Link to a part-of-title within the current PGC's title.
+    LinkPttn {
+        pttn: u16,
+    },
+    /// Link to a program number within the current PGC (1-based).
+    LinkPgn {
+        pgn: u8,
+    },
+    /// Link to a cell number within the current PGC (1-based).
+    LinkCn {
+        cn: u8,
+    },
+    /// A link "subset" op (LinkTopCell/NextPG/RSM/…); `sub` is the raw code.
+    LinkSub {
+        sub: u8,
+    },
+    /// Set a GPRM. `op` is the set-op code (1=mov, 3=add, …); value is immediate
+    /// (`imm`) when `immediate`, else the contents of register `src`.
+    SetGprm {
+        reg: u8,
+        op: u8,
+        immediate: bool,
+        imm: u16,
+        src: u8,
+    },
+    /// Set a system parameter / unmodelled set — executor may ignore.
+    SetSystem,
+    /// Anything not individually modelled (kept as raw bytes).
+    Other([u8; 8]),
+}
+
+/// A compare predicate carried by a command (`byte1` bits 6-4). `None` = always.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct Compare {
+    /// Compare op: 1=&,2===,3=!=,4=>=,5=>,6=<=,7=<.
+    pub op: u8,
+    /// Left register index (GPRM 0-15, SPRM 128+).
+    pub lhs_reg: u8,
+    /// Right side: immediate when `immediate`, else register `rhs_reg`.
+    pub immediate: bool,
+    pub imm: u16,
+    pub rhs_reg: u8,
+}
+
+/// A fully decoded command: its predicate (if any) and the instruction.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct Command {
+    pub compare: Option<Compare>,
+    pub instr: Instr,
+}
+
+// Command types — `byte0` bits 7-5.
+const TYPE_SPECIAL: u8 = 0;
+const TYPE_LINK_JUMP: u8 = 1;
+const TYPE_SET_SYSTEM: u8 = 2;
+const TYPE_SET_GPRM: u8 = 3;
+
+// Special (type 0) sub-commands — `byte1` bits 3-0.
+const SP_GOTO: u8 = 1;
+const SP_BREAK: u8 = 2;
+
+// Jump/Call (type 1, direct=1) sub-commands.
+const JP_EXIT: u8 = 1;
+const JP_JUMP_TT: u8 = 2;
+const JP_JUMP_VTS_TT: u8 = 3;
+const JP_JUMP_VTS_PTT: u8 = 5;
+const JP_JUMP_SS: u8 = 6;
+const JP_CALL_SS: u8 = 8;
+
+// Link (type 1, direct=0) sub-commands. NOTE: sub-op 0 is NOP/no-link and 1 is
+// the LinkSub form (libdvdnav `decoder.c` `eval_link_instruction`).
+const LK_SUB: u8 = 1;
+const LK_PGCN: u8 = 4;
+const LK_PTTN: u8 = 5;
+const LK_PGN: u8 = 6;
+const LK_CN: u8 = 7;
+
+// JumpSS sub-domain selector — `byte5` bits 7-6.
+const SS_FP: u8 = 0;
+const SS_VMGM_MENU: u8 = 1;
+const SS_VTSM: u8 = 2;
+
+// Operand field widths (spec-defined bit counts).
+const MASK_TTN: u8 = 0x7F; // 7-bit title number
+const MASK_PGN: u8 = 0x7F; // 7-bit program number
+const MASK_LINKOP: u8 = 0x1F; // 5-bit link sub-op
+const MASK_REG: u8 = 0x0F; // 4-bit GPRM index
+const MASK_MENU: u8 = 0x0F; // 4-bit menu id
+const MASK_PTTN: u16 = 0x03FF; // 10-bit part-of-title
+const MASK_PGCN: u16 = 0x7FFF; // 15-bit PGC number
+
+#[inline]
+fn be16(b: &[u8; 8], o: usize) -> u16 {
+    ((b[o] as u16) << 8) | b[o + 1] as u16
+}
+
+// Compare-operand layouts ("if_version"s) per libdvdnav `decoder.c`. The op
+// nibble is always `byte1` bits 6-4; the immediate flag is `byte1` bit 7. The
+// operand *offsets* differ by command family.
+//
+// v1 (special + link): lhs reg = b[3]; rhs imm = bytes4-5 / rhs reg = b[4].
+// v2 (jump + system-set): lhs reg = b[6]; rhs reg = b[7] (registers only).
+// v3 (set-GPRM): lhs reg = b[2]; rhs imm = bytes6-7 / rhs reg = b[6].
+fn if_v1(b: &[u8; 8]) -> Option<Compare> {
+    let op = (b[1] >> 4) & 7;
+    (op != 0).then(|| Compare {
+        op,
+        lhs_reg: b[3],
+        immediate: b[1] >> 7 != 0,
+        imm: be16(b, 4),
+        rhs_reg: b[4],
+    })
+}
+fn if_v2(b: &[u8; 8]) -> Option<Compare> {
+    let op = (b[1] >> 4) & 7;
+    (op != 0).then(|| Compare {
+        op,
+        lhs_reg: b[6],
+        immediate: false,
+        imm: 0,
+        rhs_reg: b[7],
+    })
+}
+fn if_v3(b: &[u8; 8]) -> Option<Compare> {
+    let op = (b[1] >> 4) & 7;
+    (op != 0).then(|| Compare {
+        op,
+        lhs_reg: b[2],
+        immediate: b[1] >> 7 != 0,
+        imm: be16(b, 6),
+        rhs_reg: b[6],
+    })
+}
+
+/// Decode an 8-byte VM command.
+pub fn decode(b: &[u8; 8]) -> Command {
+    let typ = b[0] >> 5;
+    let direct = (b[0] >> 4) & 1;
+    let setop = b[0] & 0x0F;
+    let cmd = b[1] & 0x0F;
+
+    // Compare predicate, with the operand layout for this command family
+    // (libdvdnav `decoder.c` `vm_eval_command` type dispatch).
+    let compare = match (typ, direct) {
+        (TYPE_SPECIAL, _) => if_v1(b),
+        (TYPE_LINK_JUMP, 1) => if_v2(b), // jump
+        (TYPE_LINK_JUMP, 0) => if_v1(b), // link
+        (TYPE_SET_SYSTEM, _) => if_v2(b),
+        (TYPE_SET_GPRM, _) => if_v3(b),
+        _ => None, // 4/5/6 compound — not needed by the resolver
+    };
+
+    // JumpSS sub-domain selector lives in byte5 bits 7-6.
+    let ss_sel = b[5] >> 6;
+
+    let instr = match typ {
+        TYPE_LINK_JUMP if direct == 1 => match cmd {
+            JP_EXIT => Instr::Exit,
+            JP_JUMP_TT => Instr::JumpTt {
+                ttn: b[5] & MASK_TTN,
+            },
+            JP_JUMP_VTS_TT => Instr::JumpVtsTt {
+                ttn: b[5] & MASK_TTN,
+            },
+            JP_JUMP_VTS_PTT => Instr::JumpVtsPtt {
+                ttn: b[5] & MASK_TTN,
+                pttn: be16(b, 2) & MASK_PTTN,
+            },
+            JP_JUMP_SS => match ss_sel {
+                SS_FP => Instr::JumpSsFp,
+                SS_VMGM_MENU => Instr::JumpSsVmgm {
+                    menu: b[5] & MASK_MENU,
+                },
+                SS_VTSM => Instr::JumpSsVtsm {
+                    vts: b[4],
+                    ttn: b[3],
+                    menu: b[5] & MASK_MENU,
+                },
+                _ => Instr::JumpSsVmgmPgc {
+                    pgcn: be16(b, 2) & MASK_PGCN,
+                },
+            },
+            JP_CALL_SS => Instr::CallSs { sub: ss_sel },
+            _ => Instr::Nop,
+        },
+        TYPE_LINK_JUMP => match cmd {
+            // direct == 0 (link). sub-op 0 = NOP/no-link.
+            LK_SUB => Instr::LinkSub {
+                sub: b[7] & MASK_LINKOP,
+            },
+            LK_PGCN => Instr::LinkPgcn {
+                pgcn: be16(b, 6) & MASK_PGCN,
+            },
+            LK_PTTN => Instr::LinkPttn {
+                pttn: be16(b, 6) & MASK_PTTN,
+            },
+            LK_PGN => Instr::LinkPgn {
+                pgn: b[7] & MASK_PGN,
+            },
+            LK_CN => Instr::LinkCn { cn: b[7] },
+            _ => Instr::Nop,
+        },
+        TYPE_SPECIAL => match cmd {
+            SP_GOTO => Instr::Goto { line: b[7] },
+            SP_BREAK => Instr::Break,
+            _ => Instr::Nop,
+        },
+        TYPE_SET_GPRM => Instr::SetGprm {
+            reg: b[3] & MASK_REG,
+            op: setop,
+            immediate: direct != 0,
+            imm: be16(b, 4),
+            src: b[5],
+        },
+        TYPE_SET_SYSTEM => Instr::SetSystem,
+        _ => Instr::Other(*b),
+    };
+
+    Command { compare, instr }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn h(s: &str) -> [u8; 8] {
+        let v: Vec<u8> = (0..8)
+            .map(|i| u8::from_str_radix(&s[i * 2..i * 2 + 2], 16).unwrap())
+            .collect();
+        v.try_into().unwrap()
+    }
+
+    // KATs taken from the real SOTL / Greenland discs (decoded in the PoC).
+    #[test]
+    fn greenland_first_play_is_jumptt_1() {
+        let c = decode(&h("3002000000010000"));
+        assert_eq!(c.instr, Instr::JumpTt { ttn: 1 });
+        assert!(c.compare.is_none());
+    }
+
+    #[test]
+    fn sotl_first_play_is_jumpss_vtsm_root() {
+        // 30 06 ... byte5=0x83 -> sub 2 (VTSM), vts=byte4=1, menu=byte5&0xF=3 (root)
+        let c = decode(&h("3006000101830000"));
+        assert_eq!(
+            c.instr,
+            Instr::JumpSsVtsm {
+                vts: 1,
+                ttn: 1,
+                menu: 3
+            }
+        );
+    }
+
+    #[test]
+    fn sotl_title_dispatch_is_conditional_linkpgn_2() {
+        // 20 a6 ... CmpLink: if GPRM0 == 2 -> LinkPGN 2  (cell 2 = the 5:02 start)
+        let c = decode(&h("20a6000000020002"));
+        assert_eq!(c.instr, Instr::LinkPgn { pgn: 2 });
+        let cmp = c.compare.expect("conditional");
+        assert_eq!(cmp.op, 2); // ==
+        assert_eq!(cmp.lhs_reg, 0); // GPRM0
+        assert!(cmp.immediate);
+        assert_eq!(cmp.imm, 2);
+    }
+
+    #[test]
+    fn sotl_root_button_is_linkpgcn_37() {
+        assert_eq!(
+            decode(&h("2004000000000025")).instr,
+            Instr::LinkPgcn { pgcn: 37 }
+        );
+    }
+
+    #[test]
+    fn greenland_scene_button_is_linkpgn() {
+        assert_eq!(
+            decode(&h("2006000000001401")).instr,
+            Instr::LinkPgn { pgn: 1 }
+        );
+    }
+
+    #[test]
+    fn jumpvts_ptt_decodes_ttn_and_pttn() {
+        // synthetic: 30 05 | ptt(bytes2-3)=0x0002 | ttn(byte5)=1
+        let c = decode(&h("3005000200010000"));
+        assert_eq!(c.instr, Instr::JumpVtsPtt { ttn: 1, pttn: 2 });
+    }
+
+    #[test]
+    fn setgprm_immediate_mov() {
+        // SOTL First-Play pre[0]: 71 00 | reg=byte3=6 | imm(bytes4-5)=0x03e8 -> g6 = 1000
+        match decode(&h("7100000603e80000")).instr {
+            Instr::SetGprm {
+                reg,
+                op,
+                immediate,
+                imm,
+                ..
+            } => {
+                assert_eq!(reg, 6);
+                assert_eq!(op, 1); // mov
+                assert!(immediate);
+                assert_eq!(imm, 1000);
+            }
+            other => panic!("expected SetGprm, got {other:?}"),
+        }
+    }
+
+    // Regression for the libdvdnav cross-check: link sub-op 0 = NOP, 1 = LinkSub.
+    #[test]
+    fn link_subop_zero_is_nop_one_is_linksub() {
+        assert_eq!(decode(&h("2000000000000000")).instr, Instr::Nop);
+        assert_eq!(
+            decode(&h("2001000000000010")).instr,
+            Instr::LinkSub { sub: 0x10 }
+        );
+    }
+
+    // if_version_1 register compare: rhs register is byte4 (not byte5).
+    #[test]
+    fn link_register_compare_rhs_is_byte4() {
+        // 20 26: link, cmp=EQ(2), dircmp=0(register) ; cmd=6 LinkPGN
+        let c = decode(&h("2026000304000002"));
+        assert_eq!(c.instr, Instr::LinkPgn { pgn: 2 });
+        let cmp = c.compare.expect("conditional");
+        assert!(!cmp.immediate);
+        assert_eq!(cmp.lhs_reg, 3);
+        assert_eq!(cmp.rhs_reg, 4);
+    }
+
+    // if_version_2 jump compare: both operands are registers in byte6 / byte7.
+    #[test]
+    fn jump_compare_uses_bytes6_and_7() {
+        // 30 22: jump, cmp=EQ(2) ; cmd=2 JumpTT ttn=byte5=5
+        let c = decode(&h("3022000000050607"));
+        assert_eq!(c.instr, Instr::JumpTt { ttn: 5 });
+        let cmp = c.compare.expect("conditional");
+        assert!(!cmp.immediate);
+        assert_eq!(cmp.lhs_reg, 6);
+        assert_eq!(cmp.rhs_reg, 7);
+    }
+}
diff --git a/src/error.rs b/src/error.rs
index 002a4cb..a206a5b 100644
--- a/src/error.rs
+++ b/src/error.rs
@@ -1199,6 +1199,7 @@ mod tests {
             E_NO_DISC_KEY,
             E_CSS_KEY_MISSING,
             E_AACS_NO_HOST_CERT,
+            E_AACS_BUS_KEY_UNAVAILABLE,
             E_KEYDB_CONNECT,
             E_KEYDB_HTTP,
             E_KEYDB_INVALID,
diff --git a/src/ifo.rs b/src/ifo.rs
index 341d454..589ae4b 100644
--- a/src/ifo.rs
+++ b/src/ifo.rs
@@ -440,7 +440,19 @@ fn parse_vts(
     // to the feature and shifted every cell extent back by
     // `vtstt_vobs - vtsm_vobs` sectors, so the rip opened on the parental
     // prompt instead of the movie. The title content lives at `vtstt_vobs`.
-    let vob_start_sector = be_u32(&vts_data, VTSTT_VOBS_OFFSET)?;
+    //
+    // `vtstt_vobs` is a sector address **relative to the start of this VTS_xx_0.IFO
+    // file**, not an absolute disc LBA. The cell `first_sector`/`last_sector`
+    // values are in turn relative to `vtstt_vobs`. To turn them into the absolute
+    // disc LBAs the reader needs, add the IFO file's own on-disc location (from
+    // the UDF FS). Without this rebase every extent started `ifo_lba` sectors too
+    // early — for THESILENCEOFTHELAMBS the feature began at LBA 126 (the VMGI /
+    // VIDEO_TS.VOB main-menu region) instead of 132886 (VTS_03_1.VOB), so the
+    // first ~4.5 min of muxed video was the disc's main menu before the stream
+    // drifted into the movie.
+    let vtstt_vobs = be_u32(&vts_data, VTSTT_VOBS_OFFSET)?;
+    let ifo_lba = udf.file_start_lba(reader, &path)?;
+    let vob_start_sector = ifo_lba.saturating_add(vtstt_vobs);
 
     // Video attributes at offset 0x200 (2 bytes)
     let video = parse_video_attr(&vts_data)?;
diff --git a/src/keysource.rs b/src/keysource.rs
index 841ebd2..1378b74 100644
--- a/src/keysource.rs
+++ b/src/keysource.rs
@@ -100,6 +100,12 @@ pub struct DiscInputsCtx<'a> {
 impl<'a> DiscInputsCtx<'a> {
     /// Build a context over `inputs`, parsing the encrypted title keys at the
     /// stride for AACS major `version_u8` (1 = V10, else V20/V21).
+    ///
+    /// A present-but-malformed `unit_key_ro` (truncated / wrong magic / wrong
+    /// stride) parses to an empty key set, so a later [`Self::enc_title_keys`]
+    /// returns `Ok(&[])` indistinguishably from a disc that legitimately has no
+    /// title keys — the parse failure is swallowed here, not surfaced as an
+    /// error.
     pub fn new(inputs: &'a DiscInputs, version_u8: u8) -> Self {
         use crate::aacs::{AacsVersion, parse_unit_key_ro};
         let enc_keys = if inputs.unit_key_ro.is_empty() {
diff --git a/src/labels/mod.rs b/src/labels/mod.rs
index f3ac45e..38e614e 100644
--- a/src/labels/mod.rs
+++ b/src/labels/mod.rs
@@ -1124,9 +1124,10 @@ mod registry_tests {
             // and as a marker for "these parsers exist."
             let _ = (name, detect, parse);
         }
-        // The loop above touches every registry entry; iterating a non-empty
-        // fixed-size array is the assertion (a `.is_empty()` check would be
-        // const-folded). The test fails to compile if the tuple shape changes.
+        // The loop above touches every registry entry. The non-empty
+        // invariant is covered separately by `parsers_registry_order_locked`,
+        // whose assert_eq! on the expected order fails if PARSERS is empty.
+        // This test fails to compile if the tuple shape changes.
     }
 }
 
diff --git a/src/lib.rs b/src/lib.rs
index d60067f..038c71b 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -93,6 +93,7 @@ pub mod decrypt;
 pub mod diag;
 pub mod disc;
 pub mod drive;
+pub mod dvdnav;
 pub mod error;
 pub mod event;
 pub mod halt;
diff --git a/src/mux/codec/coding.rs b/src/mux/codec/coding.rs
index 1600b91..9abc396 100644
--- a/src/mux/codec/coding.rs
+++ b/src/mux/codec/coding.rs
@@ -181,8 +181,13 @@ impl PictureInfo {
         match self.detail {
             CodingDetail::Mpeg2(m) => {
                 if !m.frame_picture {
-                    // A single field picture is inherently interlaced; the
-                    // top_field_first bit names which field this picture is.
+                    // A single field picture is inherently interlaced. Which
+                    // field it actually codes is given by picture_structure
+                    // (top/bottom), not by top_field_first — §6.3.10 constrains
+                    // top_field_first to 0 for field pictures, so it is not the
+                    // spec source here. picture_structure is not retained on
+                    // this carrier, so top_field_first is used only as the lone
+                    // field hint available (best-effort, not spec-derived).
                     Some(if m.top_field_first {
                         FieldOrder::Tff
                     } else {
@@ -203,8 +208,10 @@ impl PictureInfo {
     /// Number of field-display periods this picture occupies — the basis for
     /// soft-telecine (2:3 pulldown) timing. MPEG-2 (ISO/IEC 13818-2 §6.3.10,
     /// ffmpeg `nb_fields = repeat_pict + 2`): a field picture occupies 1 field,
-    /// a normal frame 2, a `repeat_first_field` frame 3 (or 4/6 in a progressive
-    /// sequence). Codecs without pulldown signalling report the normal 2 fields.
+    /// a normal frame 2, a `repeat_first_field` progressive-frame 3 (or 4/6 in a
+    /// progressive sequence); an rff bit on a non-progressive interlaced frame is
+    /// spec-forbidden (§6.3.10) and is treated as 2. Codecs without pulldown
+    /// signalling report the normal 2 fields.
     pub fn nb_fields(&self) -> u8 {
         match self.detail {
             CodingDetail::Mpeg2(m) => {
diff --git a/src/mux/codec/h264.rs b/src/mux/codec/h264.rs
index 8f7bb00..83d5763 100644
--- a/src/mux/codec/h264.rs
+++ b/src/mux/codec/h264.rs
@@ -325,7 +325,8 @@ impl CodecParser for H264Parser {
 }
 
 /// Parse `(chroma_format_idc, bit_depth_luma_minus8, bit_depth_chroma_minus8)` from
-/// a High-Profile SPS NAL (profile_idc ∈ {100, 110, 122, 144}).
+/// a High-Profile SPS NAL (profile_idc ∈ `HIGH_PROFILES` — the 14 chroma/bit-depth
+/// extended profiles `codec_private` invokes this for).
 ///
 /// SPS RBSP layout (ITU-T H.264 §7.3.2.1.1) up to the fields we need:
 ///   byte 0        NAL header (already known to be type 7)
diff --git a/src/mux/codec/hevc.rs b/src/mux/codec/hevc.rs
index a1c2a49..91ac64d 100644
--- a/src/mux/codec/hevc.rs
+++ b/src/mux/codec/hevc.rs
@@ -56,10 +56,7 @@ fn hevc_num_extra_slice_header_bits(pps_nal: &[u8]) -> Option<u32> {
     br.read_ue()?; // pps_pic_parameter_set_id
     br.read_ue()?; // pps_seq_parameter_set_id
     br.skip_bits(2)?; // dependent_slice_segments_enabled_flag, output_flag_present_flag
-    let mut n = 0u32;
-    for _ in 0..3 {
-        n = (n << 1) | br.read_bit()?;
-    }
+    let n = br.read_bits(3)?;
     Some(n)
 }
 
diff --git a/src/mux/demux_sink.rs b/src/mux/demux_sink.rs
index 91d28cf..42cb9e5 100644
--- a/src/mux/demux_sink.rs
+++ b/src/mux/demux_sink.rs
@@ -273,8 +273,8 @@ const SUP_HEADER_LEN: usize = SUP_MAGIC.len() + 4 + 4;
 const SEG_PCS: u8 = 0x16;
 /// PGS segment type: END of display set.
 const SEG_END: u8 = 0x80;
-/// PCS `composition_state` value: Epoch Start (a fresh display).
-const PCS_COMPOSITION_STATE_EPOCH_START: u8 = 0x80;
+/// PCS `composition_state` value: Normal (an update to the current epoch).
+const PCS_COMPOSITION_STATE_NORMAL: u8 = 0x00;
 /// PGS segment header on the wire (inside `frame.data`): type(1) + size(2 BE).
 const PGS_SEG_HEADER_LEN: usize = 3;
 /// Byte offset of `width`/`height` within a PCS segment (after type+size).
@@ -346,7 +346,7 @@ impl PgsSupWriter {
             PCS_FRAME_RATE,
             0x00,
             0x00, // composition_number
-            PCS_COMPOSITION_STATE_EPOCH_START,
+            PCS_COMPOSITION_STATE_NORMAL,
             0x00, // palette_update_flag
             0x00, // palette_id
             PCS_NO_OBJECTS,
diff --git a/src/mux/fvi_sink.rs b/src/mux/fvi_sink.rs
index 1c1ed30..cca0b6b 100644
--- a/src/mux/fvi_sink.rs
+++ b/src/mux/fvi_sink.rs
@@ -82,8 +82,16 @@ fn write_fvi_record(w: &mut dyn Write, r: &PictureRecord) -> io::Result<()> {
     // `src` is REQUIRED by the record schema (Appendix A); when provenance is
     // absent the member is still emitted as null — a reader treats null as
     // "position unknown".
+    //
+    // Per `docs/FVI_FORMAT.md` §9, `src.byte` is the offset of the AU's first
+    // byte WITHIN its `sector` (not the absolute source offset). `SourcePos.byte`
+    // is the absolute offset, so reduce it modulo the sector size; `sector`
+    // already carries the whole-sector count.
     let src = match r.source {
-        Some(s) => serde_json::json!({ "sector": s.sector, "byte": s.byte }),
+        Some(s) => serde_json::json!({
+            "sector": s.sector,
+            "byte": s.byte % u64::from(FVI_SECTOR_SIZE),
+        }),
         None => serde_json::Value::Null,
     };
 
@@ -355,8 +363,9 @@ mod tests {
         let dir = tempdir();
         let path = dir.join("movie.fvi");
         let mut sink = FviSink::create(&path, &mpeg2_title(), "iso://m.iso".into(), 1).unwrap();
-        // Video frame on track 0 → indexed.
-        sink.write(&vframe(0, Some(i_pic()), Some(SourcePos::at_byte(2048))))
+        // Video frame on track 0 → indexed. Offset 2148 = sector 1, byte 100
+        // within that sector (exercises the within-sector `src.byte`, §9).
+        sink.write(&vframe(0, Some(i_pic()), Some(SourcePos::at_byte(2148))))
             .unwrap();
         // Audio frame on a non-video track → ignored.
         sink.write(&vframe(7, None, Some(SourcePos::at_byte(9999))))
@@ -387,6 +396,7 @@ mod tests {
         assert_eq!(rec["nb_fields"], 2);
         assert_eq!(rec["pts"], 0);
         assert_eq!(rec["src"]["sector"], 1);
+        assert_eq!(rec["src"]["byte"], 100); // 2148 % 2048 → within-sector (§9)
         assert!(rec.get("dts").is_none(), "no DTS on a frame → omitted");
         assert!(
             rec.get("gop").is_none(),
diff --git a/src/mux/m2ts_mux/mod.rs b/src/mux/m2ts_mux/mod.rs
index d13a41d..72fe861 100644
--- a/src/mux/m2ts_mux/mod.rs
+++ b/src/mux/m2ts_mux/mod.rs
@@ -254,7 +254,10 @@ impl<W: Write> M2tsMux<W> {
         // step — e.g. a leading audio frame ahead of the first video keyframe),
         // which still floors to 0 per the documented behavior.
         let delta = raw_90k.wrapping_sub(base) & 0x1_FFFF_FFFF;
-        if delta > (1 << 32) { 0 } else { delta }
+        // Signed 33-bit: the sign bit is bit 32 (value 2^32), so the entire
+        // upper half [2^32, 2^33) is negative (frame before base) and floors
+        // to 0. delta == 2^32 is the most-negative value (-2^32), hence `>=`.
+        if delta >= (1 << 32) { 0 } else { delta }
     }
 
     /// Emit one PES payload as a chain of TS packets on `pid`. If `pcr`
diff --git a/src/mux/mkv.rs b/src/mux/mkv.rs
index b27d41e..b14e070 100644
--- a/src/mux/mkv.rs
+++ b/src/mux/mkv.rs
@@ -28,6 +28,9 @@ const CICP_PRIMARIES_BT470BG: u8 = 5;
 const CICP_PRIMARIES_BT601_525: u8 = 6;
 /// ColourPrimaries = 9 (BT.2020 / BT.2100) — ITU-T H.273 Table 2.
 const CICP_PRIMARIES_BT2020: u8 = 9;
+/// ColourPrimaries = 2 ("unspecified" — colorimetry unknown) — ITU-T H.273
+/// Table 2.
+const CICP_PRIMARIES_UNSPECIFIED: u8 = 2;
 
 /// TransferCharacteristics = 1 (BT.709) — ITU-T H.273 Table 3.
 const CICP_TRANSFER_BT709: u8 = 1;
@@ -41,6 +44,9 @@ const CICP_TRANSFER_PQ: u8 = 16;
 /// TransferCharacteristics = 18 (ARIB STD-B67 / Hybrid Log-Gamma) — ITU-T H.273
 /// Table 3.
 const CICP_TRANSFER_HLG: u8 = 18;
+/// TransferCharacteristics = 2 ("unspecified" — transfer unknown) — ITU-T H.273
+/// Table 3.
+const CICP_TRANSFER_UNSPECIFIED: u8 = 2;
 
 /// MatrixCoefficients = 1 (BT.709) — ITU-T H.273 Table 4.
 const CICP_MATRIX_BT709: u8 = 1;
@@ -50,6 +56,8 @@ const CICP_MATRIX_BT470BG: u8 = 5;
 const CICP_MATRIX_BT601_525: u8 = 6;
 /// MatrixCoefficients = 9 (BT.2020 non-constant luminance) — ITU-T H.273 Table 4.
 const CICP_MATRIX_BT2020NC: u8 = 9;
+/// MatrixCoefficients = 2 ("unspecified" — matrix unknown) — ITU-T H.273 Table 4.
+const CICP_MATRIX_UNSPECIFIED: u8 = 2;
 
 /// Matroska Colour/Range = 1 (broadcast / studio-swing "limited" range). RFC
 /// 9559 Range element. (0 = unspecified, 2 = full.)
@@ -104,7 +112,16 @@ pub(crate) fn cicp_for_video(v: &VideoStream) -> (u8, u8, u8, u8) {
             CICP_PRIMARIES_BT601_525,
             COLOUR_RANGE_LIMITED,
         ),
-        ColorSpace::Unknown => (0, 0, 0, 0),
+        // Unknown colorimetry → CICP "unspecified" (code point 2) for matrix,
+        // transfer, and primaries, with limited range (the disc norm). Both the
+        // MKV sink and the FVI sidecar emit 2 so the two sinks of one title
+        // agree (matches `Colour::from_color_space`'s Unknown mapping).
+        ColorSpace::Unknown => (
+            CICP_MATRIX_UNSPECIFIED,
+            CICP_TRANSFER_UNSPECIFIED,
+            CICP_PRIMARIES_UNSPECIFIED,
+            COLOUR_RANGE_LIMITED,
+        ),
     };
     // Override the transfer for HDR signalled by the HdrFormat (the coarse enum
     // can't express PQ/HLG). Only applies on the enum fallback; a measured CICP
@@ -1549,6 +1566,41 @@ mod tests {
         );
     }
 
+    /// Unknown colorimetry with no measured CICP and no HDR must emit CICP
+    /// "unspecified" (code point 2) for matrix/transfer/primaries — never 0 — so
+    /// the MKV sink agrees with the FVI sidecar (`Colour::from_color_space`).
+    #[test]
+    fn unknown_color_space_emits_unspecified_cicp() {
+        let v = VideoStream {
+            pid: 0xE0,
+            codec: Codec::Hevc,
+            resolution: Resolution::R1080p,
+            frame_rate: crate::disc::FrameRate::F24,
+            hdr: HdrFormat::Sdr,
+            color_space: ColorSpace::Unknown,
+            display_aspect: None,
+            secondary: false,
+            label: String::new(),
+            measured_cicp: None,
+        };
+        let t = MkvTrack::video(&v);
+        assert_eq!(
+            (
+                t.colour_matrix,
+                t.colour_transfer,
+                t.colour_primaries,
+                t.colour_range
+            ),
+            (
+                CICP_MATRIX_UNSPECIFIED,
+                CICP_TRANSFER_UNSPECIFIED,
+                CICP_PRIMARIES_UNSPECIFIED,
+                COLOUR_RANGE_LIMITED
+            ),
+            "Unknown colorimetry must emit CICP 'unspecified' (2), not 0"
+        );
+    }
+
     /// Helper: search for a 4-byte big-endian EBML ID in a byte slice.
     fn find_id(data: &[u8], id: u32) -> Option<usize> {
         let bytes = id.to_be_bytes();
diff --git a/src/mux/mkvstream.rs b/src/mux/mkvstream.rs
index 9b57b92..971e84c 100644
--- a/src/mux/mkvstream.rs
+++ b/src/mux/mkvstream.rs
@@ -101,8 +101,12 @@ enum WriteMode {
     /// Header written; muxing live. Boxed (MkvMuxer is large) to keep the enum
     /// small (clippy::large_enum_variant).
     Active(Box<MkvMuxer<Box<dyn WriteSeek + Send>>>),
-    /// Transient placeholder held only across the Pending → Active swap; never
-    /// observed by `read` / `write` / `finish`.
+    /// Sentinel held in `self.mode` while the muxer is being built (across the
+    /// Pending → Active swap). It is also the terminal state left behind after
+    /// `finish()` swaps the muxer out, and the degraded state left behind if
+    /// `activate()` fails partway (the first error still surfaces via `?`). In
+    /// that terminal state a subsequent `write()` no-ops (`Ok(())`) and `finish()`
+    /// does not re-finalize.
     Building,
 }
 
@@ -188,7 +192,11 @@ impl MkvStream {
     /// available), then write the header and replay buffered frames. A no-op if
     /// not pending. The muxer only ever muxes the track it is given — this routes
     /// the parser's measured value onto that track first.
-    fn activate(&mut self, coding: Option<crate::mux::codec::PictureInfo>) -> io::Result<()> {
+    fn activate(
+        &mut self,
+        coding: Option<crate::mux::codec::PictureInfo>,
+        video_picture_seen: bool,
+    ) -> io::Result<()> {
         let mut pending = match std::mem::replace(&mut self.mode, Mode::Write(WriteMode::Building))
         {
             Mode::Write(WriteMode::Pending(p)) => p,
@@ -199,7 +207,7 @@ impl MkvStream {
             }
         };
         if let Some(vt) = pending.video_track {
-            apply_coding_to_track(&mut pending.tracks[vt], coding);
+            apply_coding_to_track(&mut pending.tracks[vt], coding, video_picture_seen);
         }
         // --log-level 3: dump the FINAL TrackEntry metadata (field order set).
         for (i, track) in pending.tracks.iter().enumerate() {
@@ -240,12 +248,20 @@ impl MkvStream {
 /// Set a video track's `FieldOrder` from the MEASURED coding of the first coded
 /// picture — the parser's value, the first time, never a guess.
 ///
-/// A progressive track has no field order (left UNDETERMINED — expected). An
-/// INTERLACED track that reaches here with no measured field order is a
+/// A progressive track — or a progressive picture on an interlaced-flagged track
+/// — has no field order (left UNDETERMINED — expected). An INTERLACED track that
+/// reaches here WITH a video picture but no measured field order is a
 /// parser/source gap (MPEG-2 carries `top_field_first` on every interlaced
 /// picture, so it should never be missing): LOG it loudly so the source can be
 /// debugged, and leave UNDETERMINED — a muxer never fabricates a source fact.
-fn apply_coding_to_track(track: &mut MkvTrack, coding: Option<crate::mux::codec::PictureInfo>) {
+/// `video_picture_seen == false` (an empty title finalized with no frames, or a
+/// cap-triggered build that never saw the video frame) is NOT a defect — the
+/// missing coding is expected there, so log it quietly.
+fn apply_coding_to_track(
+    track: &mut MkvTrack,
+    coding: Option<crate::mux::codec::PictureInfo>,
+    video_picture_seen: bool,
+) {
     // HDR10 static metadata measured from the bitstream (HEVC SEI). Applied for
     // ANY track type that carries it (independent of interlace): the first coded
     // picture's PictureInfo holds it once both HDR10 SEI messages were seen.
@@ -260,17 +276,32 @@ fn apply_coding_to_track(track: &mut MkvTrack, coding: Option<crate::mux::codec:
     match coding.and_then(|c| c.field_order()) {
         Some(FieldOrder::Tff) => track.field_order = ebml::FIELD_ORDER_TFF,
         Some(FieldOrder::Bff) => track.field_order = ebml::FIELD_ORDER_BFF,
-        other => {
+        // A progressive picture on an interlaced-flagged track carries no field
+        // order. Leave UNDETERMINED (not a guess) — there is no parser gap here.
+        Some(FieldOrder::Progressive) => {
+            track.field_order = ebml::FIELD_ORDER_UNDETERMINED;
+        }
+        None if video_picture_seen => {
             tracing::warn!(
                 target: "mux",
-                "interlaced video track reached the muxer with NO measured field order \
-                 (field_order={:?}, coding_present={}); writing FieldOrder=UNDETERMINED \
-                 — NOT a guess. Debug why the source/parser did not set top_field_first.",
-                other,
+                "interlaced video track had a video picture but NO usable field order \
+                 (coding_present={}); writing FieldOrder=UNDETERMINED — NOT a guess. \
+                 Debug why the source/parser did not set top_field_first.",
                 coding.is_some(),
             );
             track.field_order = ebml::FIELD_ORDER_UNDETERMINED;
         }
+        None => {
+            // No video picture was ever measured (empty title finalized with no
+            // frames, or a cap-triggered build before the first video frame).
+            // Coding is legitimately absent, not a parser defect — log quietly.
+            tracing::debug!(
+                target: "mux",
+                "interlaced video track activated with no video picture \
+                 (empty/buffered-only title); writing FieldOrder=UNDETERMINED.",
+            );
+            track.field_order = ebml::FIELD_ORDER_UNDETERMINED;
+        }
     }
 }
 
@@ -427,7 +458,7 @@ impl crate::pes::Stream for MkvStream {
             // Pass the trigger frame's coding only when it IS the video frame; a
             // cap-triggered build never saw the video frame, so nothing measured
             // is passed (apply_coding_to_track then logs + leaves UNDETERMINED).
-            self.activate(if use_coding { frame.coding } else { None })?;
+            self.activate(if use_coding { frame.coding } else { None }, use_coding)?;
             if let Mode::Write(WriteMode::Active(m)) = &mut self.mode {
                 return m.write_frame(
                     frame.track,
@@ -450,7 +481,10 @@ impl crate::pes::Stream for MkvStream {
         // A title that produced no frames (or only buffered ones) is still
         // finalized into a valid MKV: activate now with no measured coding.
         if matches!(self.mode, Mode::Write(WriteMode::Pending(_))) {
-            self.activate(None)?;
+            // No video picture was ever measured for this title (it produced no
+            // frames, or only buffered non-video ones): coding is legitimately
+            // absent, not a parser defect — `video_picture_seen=false`.
+            self.activate(None, false)?;
         }
         if let Mode::Write(WriteMode::Active(m)) =
             std::mem::replace(&mut self.mode, Mode::Write(WriteMode::Building))
@@ -923,7 +957,7 @@ mod tests {
 
         // MEASURED bottom-field-first → BFF (6). The red-flag fix.
         let mut t = interlaced_track();
-        apply_coding_to_track(&mut t, Some(pic(false, false)));
+        apply_coding_to_track(&mut t, Some(pic(false, false)), true);
         assert_eq!(
             t.field_order,
             ebml::FIELD_ORDER_BFF,
@@ -932,27 +966,37 @@ mod tests {
 
         // MEASURED top-field-first → TFF (1).
         let mut t = interlaced_track();
-        apply_coding_to_track(&mut t, Some(pic(true, false)));
+        apply_coding_to_track(&mut t, Some(pic(true, false)), true);
         assert_eq!(
             t.field_order,
             ebml::FIELD_ORDER_TFF,
             "measured TFF → FieldOrder=1"
         );
 
-        // Interlaced track, NO measured coding → UNDETERMINED (logged loudly,
-        // never faked).
+        // Interlaced track, a video picture but NO usable field order →
+        // UNDETERMINED (logged loudly, never faked).
         let mut t = interlaced_track();
-        apply_coding_to_track(&mut t, None);
+        apply_coding_to_track(&mut t, None, true);
         assert_eq!(
             t.field_order,
             ebml::FIELD_ORDER_UNDETERMINED,
             "no measured value → UNDETERMINED, never a guess"
         );
 
+        // Interlaced track activated with NO video picture (empty/buffered-only
+        // title) → UNDETERMINED, logged quietly (not a parser defect).
+        let mut t = interlaced_track();
+        apply_coding_to_track(&mut t, None, false);
+        assert_eq!(
+            t.field_order,
+            ebml::FIELD_ORDER_UNDETERMINED,
+            "empty title → UNDETERMINED, never a guess"
+        );
+
         // Progressive picture on an interlaced-flagged track → UNDETERMINED (no
         // field order applies; not faked to TFF/BFF).
         let mut t = interlaced_track();
-        apply_coding_to_track(&mut t, Some(pic(true, true)));
+        apply_coding_to_track(&mut t, Some(pic(true, true)), true);
         assert_eq!(t.field_order, ebml::FIELD_ORDER_UNDETERMINED);
 
         // A PROGRESSIVE track is never touched — field order stays UNDETERMINED.
@@ -969,7 +1013,7 @@ mod tests {
             measured_cicp: None,
         });
         assert!(!prog.interlaced);
-        apply_coding_to_track(&mut prog, Some(pic(false, false)));
+        apply_coding_to_track(&mut prog, Some(pic(false, false)), true);
         assert_eq!(prog.field_order, ebml::FIELD_ORDER_UNDETERMINED);
     }
 
@@ -1011,18 +1055,18 @@ mod tests {
         let mut t = make();
         assert!(t.hdr10.is_none(), "fresh track has no HDR10");
         let pic = PictureInfo::coding_type_only(CodingType::I).with_hdr10(Some(h));
-        apply_coding_to_track(&mut t, Some(pic));
+        apply_coding_to_track(&mut t, Some(pic), true);
         assert_eq!(t.hdr10, Some(h), "measured HDR10 must reach the track");
 
         // Picture without HDR10 → track stays None (never fabricated).
         let mut t = make();
         let pic = PictureInfo::coding_type_only(CodingType::I);
-        apply_coding_to_track(&mut t, Some(pic));
+        apply_coding_to_track(&mut t, Some(pic), true);
         assert!(t.hdr10.is_none(), "no measured HDR10 → track stays None");
 
         // No coding at all → None.
         let mut t = make();
-        apply_coding_to_track(&mut t, None);
+        apply_coding_to_track(&mut t, None, true);
         assert!(t.hdr10.is_none());
     }
 
diff --git a/src/mux/resolve.rs b/src/mux/resolve.rs
index 2b76064..92695ea 100644
--- a/src/mux/resolve.rs
+++ b/src/mux/resolve.rs
@@ -12,6 +12,7 @@
 //! | network:// | Yes (listen) | Yes (connect) | host:port (required) |
 //! | stdio:// | Yes (stdin) | Yes (stdout) | empty |
 //! | null:// | -- | Yes | empty |
+//! | demux:// | -- | Yes | directory path (required) — per-track ES demux |
 //! | fvi://  | -- | Yes | file path (required) — per-picture video index |
 //!
 //! Bare paths without a scheme are rejected.
@@ -920,6 +921,30 @@ mod tests {
             !parse_url("dir://x").is_disc_source(),
             "dir:// is a sink, never a disc source"
         );
+        // fvi:// parses to Fvi with the raw remainder as the path, and is a
+        // sink (never a disc source) — parallel to the demux:// coverage above.
+        match parse_url("fvi://out/movie.fvi") {
+            StreamUrl::Fvi { path } => {
+                assert_eq!(path, PathBuf::from("out/movie.fvi"));
+            }
+            other => panic!("fvi:// must parse to Fvi, got {other:?}"),
+        }
+        assert_eq!(parse_url("fvi://x").scheme(), "fvi");
+        assert_eq!(parse_url("fvi://x/y.fvi").path_str(), "x/y.fvi");
+        assert!(
+            !parse_url("fvi://x").is_disc_source(),
+            "fvi:// is a sink, never a disc source"
+        );
+    }
+
+    /// `fvi://` is output-only: `input()` rejects it with StreamWriteOnly
+    /// (E9001 → Unsupported), mirroring `null://` / `demux://`.
+    #[test]
+    fn input_fvi_url_is_write_only() {
+        assert_eq!(
+            input_err_kind("fvi://out/movie.fvi"),
+            std::io::ErrorKind::Unsupported
+        );
     }
 
     /// `dir://` is output-only: `input()` rejects it (StreamWriteOnly →
diff --git a/src/mux/ts.rs b/src/mux/ts.rs
index e0937fa..e0bbd1b 100644
--- a/src/mux/ts.rs
+++ b/src/mux/ts.rs
@@ -229,6 +229,12 @@ impl TsDemuxer {
     /// `data` in place. Zero-copy on the bulk path; one 192-byte copy
     /// on the boundary.
     pub fn feed(&mut self, data: &[u8]) -> Vec<PesPacket> {
+        // A plain feed carries no provenance. Reset any base a prior
+        // `feed_at` left behind so mixing the two entry points is safe:
+        // after this call no `SourcePos` is stamped, and the stale running
+        // base can't leak a wrong offset into the boundary packet.
+        self.feed_base = 0;
+        self.has_base = false;
         self.feed_inner(data)
     }
 
@@ -263,15 +269,20 @@ impl TsDemuxer {
                 self.remainder.extend_from_slice(data);
                 return completed;
             }
+            // Capture the remainder length before clearing — it's how many of
+            // the boundary packet's bytes lived in the PREVIOUS feed buffer,
+            // and `feed_base` currently points at the FIRST byte of THIS buffer.
+            let rem_len = self.remainder.len();
             let mut boundary = [0u8; BD_SOURCE_PACKET_BYTES];
-            boundary[..self.remainder.len()].copy_from_slice(&self.remainder);
-            boundary[self.remainder.len()..].copy_from_slice(&data[..need]);
+            boundary[..rem_len].copy_from_slice(&self.remainder);
+            boundary[rem_len..].copy_from_slice(&data[..need]);
             self.remainder.clear();
-            // The boundary packet began in the PREVIOUS feed buffer; stamp it
-            // with the offset just before this buffer (its first bytes' base).
-            let src = self
-                .has_base
-                .then(|| crate::pes::SourcePos::at_byte(self.feed_base.saturating_sub(1)));
+            // The boundary packet's first byte sat `rem_len` bytes before the
+            // current feed_base (in the previous buffer). Stamp it there — not
+            // at `feed_base - 1`, which would be wrong by `rem_len - 1` bytes.
+            let src = self.has_base.then(|| {
+                crate::pes::SourcePos::at_byte(self.feed_base.saturating_sub(rem_len as u64))
+            });
             self.process_packet(&boundary, src, &mut completed);
             offset = need;
         }
@@ -931,6 +942,76 @@ mod tests {
         assert!(result.is_empty());
     }
 
+    /// A boundary packet (one split across two feeds) must be stamped with the
+    /// source offset of its FIRST byte, which sat `remainder.len()` bytes before
+    /// the current feed's base — not at `feed_base - 1`. We feed two 192-byte
+    /// packets via `feed_at`, splitting mid-second-packet so the second packet
+    /// is reassembled at the boundary, and assert its provenance lands exactly
+    /// on its first byte.
+    #[test]
+    fn boundary_packet_source_is_first_byte_not_base_minus_one() {
+        let pid = 0x1011;
+        let base: u64 = 20480; // sector-aligned (10 × 2048)
+        let mut demux = TsDemuxer::new(&[pid]);
+
+        let pkt0 = ts_payload_packet(pid, true, 0, &pes_start(b"AAAA"));
+        let pkt1 = ts_payload_packet(pid, true, 1, &pes_start(b"BBBB"));
+        let mut full = pkt0;
+        full.extend_from_slice(&pkt1);
+
+        // Split mid-pkt1 → pkt1 is reassembled from a 100-byte remainder + the
+        // next feed's head. pkt1's first byte is at absolute offset base + 192.
+        let split = BD_SOURCE_PACKET_BYTES + 100;
+        let out1 = demux.feed_at(base, &full[..split]);
+        assert!(out1.is_empty(), "pkt0's PES is still open");
+
+        // Second feed carries the rest; data[0] is at absolute base + split.
+        let out2 = demux.feed_at(base + split as u64, &full[split..]);
+        // pkt1 (PUSI) flushes pkt0's "AAAA" PES, stamped at pkt0's first byte.
+        assert_eq!(out2.len(), 1, "pkt0's PES completes when pkt1 starts");
+        assert_eq!(
+            out2[0].source.map(|s| s.byte),
+            Some(base),
+            "AAAA PES provenance is pkt0's first byte"
+        );
+
+        // Flush emits pkt1's "BBBB" PES — its source is the boundary stamp.
+        let out3 = demux.flush();
+        assert_eq!(out3.len(), 1, "pkt1's PES flushes out");
+        assert_eq!(
+            out3[0].source.map(|s| s.byte),
+            Some(base + BD_SOURCE_PACKET_BYTES as u64),
+            "boundary packet provenance must be its first byte (base + 192), \
+             not feed_base - 1"
+        );
+    }
+
+    /// Owner decision #7: a plain `feed()` must reset/ignore any base a prior
+    /// `feed_at()` left behind, so mixing the two is safe. After a `feed_at`
+    /// primes a base, the next plain `feed` must stamp `None` on PES packets it
+    /// begins.
+    #[test]
+    fn plain_feed_resets_prior_feed_at_base() {
+        let pid = 0x1011;
+        let mut demux = TsDemuxer::new(&[pid]);
+
+        // Prime a base via feed_at; pkt0's PES stays open.
+        let out1 = demux.feed_at(20480, &ts_payload_packet(pid, true, 0, &pes_start(b"AAAA")));
+        assert!(out1.is_empty());
+
+        // Plain feed must clear the base. pkt1 (PUSI) flushes "AAAA" (which was
+        // stamped during feed_at) and starts "BBBB" with NO provenance.
+        let out2 = demux.feed(&ts_payload_packet(pid, true, 1, &pes_start(b"BBBB")));
+        assert_eq!(out2.len(), 1, "AAAA completes");
+
+        let out3 = demux.flush();
+        assert_eq!(out3.len(), 1, "BBBB flushes");
+        assert_eq!(
+            out3[0].source, None,
+            "PES begun by a plain feed must carry no source after a prior feed_at"
+        );
+    }
+
     // ── scan_streams PMT parsing ──────────────────────────────────────────
 
     /// Wrap a 188-byte TS packet body in a 192-byte BD-TS packet
diff --git a/src/mux/videomap.rs b/src/mux/videomap.rs
index e121e98..733ccf0 100644
--- a/src/mux/videomap.rs
+++ b/src/mux/videomap.rs
@@ -551,6 +551,21 @@ mod tests {
             },
             "measured CICP must override the coarse color_space enum"
         );
+
+        // Unknown colorimetry, SDR, no measured CICP → all code points map to
+        // "unspecified" (2), matching `from_color_space(Unknown)`. Both sinks of
+        // one title must emit 2, never 0.
+        let c = Colour::from_video(&mk(HdrFormat::Sdr, ColorSpace::Unknown, None));
+        assert_eq!(
+            c,
+            Colour {
+                primaries: 2,
+                transfer: 2,
+                matrix: 2,
+                full_range: false,
+            },
+            "Unknown colorimetry must emit CICP 'unspecified' (2), not 0"
+        );
     }
 
     #[test]
diff --git a/src/pes.rs b/src/pes.rs
index a502f86..102658e 100644
--- a/src/pes.rs
+++ b/src/pes.rs
@@ -107,20 +107,17 @@ impl PesFrame {
     /// truncated `.pes` data would be accepted as a graceful end.
     pub fn deserialize(r: &mut dyn std::io::Read) -> std::io::Result<Option<Self>> {
         // Probe one byte first to distinguish clean EOF from a truncated
-        // header.
+        // header. Loop on EINTR so back-to-back signals don't fail a
+        // recoverable read — symmetric with read_exact's internal retry
+        // on the rest of the header and the data below.
         let mut first = [0u8; 1];
-        match r.read(&mut first) {
-            Ok(0) => return Ok(None), // clean EOF, no frame started
-            Ok(_) => {}
-            Err(e) if e.kind() == std::io::ErrorKind::Interrupted => {
-                // Retry-once on EINTR before committing to the header read.
-                match r.read(&mut first) {
-                    Ok(0) => return Ok(None),
-                    Ok(_) => {}
-                    Err(e) => return Err(e),
-                }
+        loop {
+            match r.read(&mut first) {
+                Ok(0) => return Ok(None), // clean EOF, no frame started
+                Ok(_) => break,
+                Err(e) if e.kind() == std::io::ErrorKind::Interrupted => continue,
+                Err(e) => return Err(e),
             }
-            Err(e) => return Err(e),
         }
 
         let mut header = [0u8; 22]; // 1 + 8 + 1 + 8 + 4
diff --git a/src/unlock.rs b/src/unlock.rs
index 0114d1d..8a7174c 100644
--- a/src/unlock.rs
+++ b/src/unlock.rs
@@ -104,11 +104,17 @@ pub fn register_unlocker(u: Box<dyn Unlocker>) {
 ///   * `Ok(Some((name, vid)))` — a registered unlocker matched, put the drive
 ///     into extended mode, and returned the OEM Volume ID. The caller stashes
 ///     the VID for the handshake phase and need not run the cert handshake.
-///   * `Ok(None)` — no unlocker matched, OR the matching unlocker failed
-///     ([`UnlockError`], logged). Either way the drive is usable in stock mode
-///     and the caller falls through to the in-tree cert handshake. Folding an
-///     unlock failure into `Ok(None)` keeps drive `init()` infallible — a drive
-///     that simply isn't firmware-unlockable must not fail init.
+///   * `Ok(None)` — no unlocker matched, OR the matching unlocker reported a
+///     *capability* failure ([`UnlockError::FirmwareNotUnlockable`],
+///     [`UnlockError::VidUnavailable`], or a cert-auth outcome — all logged).
+///     Either way the drive is usable in stock mode and the caller falls
+///     through to the in-tree cert handshake. Folding a capability failure into
+///     `Ok(None)` keeps drive `init()` infallible — a drive that simply isn't
+///     firmware-unlockable must not fail init.
+///   * `Err(_)` — the matching unlocker hit a genuine SCSI/transport fault
+///     ([`UnlockError::Scsi`]). The bus is broken, not merely unsupported, so
+///     this propagates and aborts init rather than silently falling through to
+///     a cert handshake that would also fail.
 pub(crate) fn route_unlock(
     scsi: &mut dyn ScsiTransport,
     id: &DriveId,
@@ -124,10 +130,29 @@ pub(crate) fn route_unlock(
             let name = u.name().to_string();
             match u.unlock(scsi, id) {
                 Ok(vid) => return Ok(Some((name, vid))),
+                // A genuine SCSI/transport fault is not "this drive can't be
+                // unlocked" — the bus is broken. Propagate so init() aborts
+                // instead of falling through to a cert handshake that will
+                // also fail on the same dead transport. The numeric code from
+                // the originating error is logged; the returned error is the
+                // canonical transport-error variant.
+                Err(UnlockError::Scsi(code)) => {
+                    tracing::error!(
+                        target: "freemkv::unlock",
+                        unlocker = %name,
+                        code,
+                        "unlocker hit a transport fault during unlock; aborting init"
+                    );
+                    return Err(crate::error::Error::ScsiError {
+                        opcode: 0,
+                        status: 0,
+                        sense: None,
+                    });
+                }
+                // A firmware unlocker that can't unlock / has no OEM VID:
+                // fall through to the cert handshake. Debug-only structured
+                // log (variant identifiers, no English prose).
                 Err(e) => {
-                    // A firmware unlocker that can't unlock / has no OEM VID:
-                    // fall through to the cert handshake. Debug-only structured
-                    // log (variant identifiers, no English prose).
                     tracing::warn!(
                         target: "freemkv::unlock",
                         unlocker = %name,
@@ -228,6 +253,10 @@ mod tests {
         /// `None` → `unlock` yields `Err(UnlockError::VidUnavailable)` so
         /// `route_unlock` falls through to the cert handshake.
         vid: Option<[u8; 16]>,
+        /// When `Some(code)`, `unlock` yields `Err(UnlockError::Scsi(code))`
+        /// (a transport fault) instead of consulting `vid`, so `route_unlock`
+        /// propagates an error and aborts init.
+        scsi_err: Option<u16>,
         /// Records whether set_max_read_speed was invoked.
         speed_ran: Arc<AtomicBool>,
     }
@@ -238,6 +267,7 @@ mod tests {
                 ran,
                 // Default: a successful unlock returning an all-zero VID.
                 vid: Some([0u8; 16]),
+                scsi_err: None,
                 speed_ran: Arc::new(AtomicBool::new(false)),
             }
         }
@@ -245,6 +275,10 @@ mod tests {
             self.vid = vid;
             self
         }
+        fn with_scsi_err(mut self, code: u16) -> Self {
+            self.scsi_err = Some(code);
+            self
+        }
         fn with_speed(mut self, speed_ran: Arc<AtomicBool>) -> Self {
             self.speed_ran = speed_ran;
             self
@@ -263,6 +297,9 @@ mod tests {
             _id: &DriveId,
         ) -> std::result::Result<Vid, UnlockError> {
             self.ran.store(true, Ordering::SeqCst);
+            if let Some(code) = self.scsi_err {
+                return Err(UnlockError::Scsi(code));
+            }
             match self.vid {
                 Some(v) => Ok(Vid(v)),
                 None => Err(UnlockError::VidUnavailable),
@@ -359,6 +396,33 @@ mod tests {
         assert!(got.is_none(), "no match → cert fallback");
     }
 
+    /// A matching unlocker that hits a genuine transport fault
+    /// (`UnlockError::Scsi`) makes `route_unlock` PROPAGATE an `Err` rather
+    /// than fold to `Ok(None)`: a dead bus must abort init, not silently fall
+    /// through to a cert handshake that would also fail. Capability failures
+    /// (`VidUnavailable` etc.) still fold to `Ok(None)` — proven by the sibling
+    /// routing tests; this one pins the transport-fault exception.
+    #[test]
+    fn route_unlock_propagates_scsi_transport_fault() {
+        let mut scsi = NoopTransport;
+
+        register_unlocker(Box::new(
+            FakeUnlocker::new("SCSIVNDR", Arc::new(AtomicBool::new(false)))
+                .with_scsi_err(crate::error::E_SCSI_ERROR),
+        ));
+
+        let got = route_unlock(&mut scsi, &fake_id("SCSIVNDR"));
+        assert!(
+            got.is_err(),
+            "a transport fault during unlock aborts init (propagates Err)"
+        );
+        assert_eq!(
+            got.unwrap_err().code(),
+            crate::error::E_SCSI_ERROR,
+            "propagated error is the canonical transport-error code"
+        );
+    }
+
     /// `unlocker_set_max_read_speed` consults the FIRST matching unlocker's
     /// `set_max_read_speed`. A matching unlocker is invoked; a non-match is a
     /// safe no-op (nothing invoked, `Ok(())`).
diff --git a/tests/fvi_pipeline.rs b/tests/fvi_pipeline.rs
index c6f3c31..6039176 100644
--- a/tests/fvi_pipeline.rs
+++ b/tests/fvi_pipeline.rs
@@ -160,7 +160,7 @@ fn two_gop_image() -> Vec<u8> {
     data[..a.len()].copy_from_slice(&a);
 
     let mut b = ps_pack_header();
-    b.extend_from_slice(&video_pes(&gop_es(), 3003)); // ~0.1s later
+    b.extend_from_slice(&video_pes(&gop_es(), 3003)); // one frame (~33 ms) later at 29.97 fps (3003/90000 s)
     let off = 3 * 2048;
     data[off..off + b.len()].copy_from_slice(&b);
 
@@ -276,13 +276,21 @@ fn fvi_sink_indexes_real_mpeg2_pipeline_output() {
         vec![0, 3],
         "stamped src sectors must reach the .fvi in arrival order; got {src_sectors:?}"
     );
-    // For each stamped record, sector == byte / 2048 (SourcePos::at_byte). The
-    // byte offset is exact (here 14 into each region, just past the pack
-    // header), so it is NOT sector-aligned — provenance is byte-exact.
+    // Per FVI_FORMAT.md §9, `src.byte` is the offset of the AU's first byte
+    // WITHIN its 2048-byte `src.sector`, so it is always < 2048. The two
+    // stamped sources sit 14 bytes into their sector (just past the pack
+    // header), so the within-sector byte is exact (14) — provenance is
+    // byte-exact, carried unchanged from demux.
     for r in &records {
-        if let (Some(sector), Some(byte)) = (r["src"]["sector"].as_u64(), r["src"]["byte"].as_u64())
-        {
-            assert_eq!(sector, byte / 2048, "src.sector must equal src.byte / 2048");
+        if let Some(byte) = r["src"]["byte"].as_u64() {
+            assert!(
+                byte < 2048,
+                "src.byte is a within-sector offset (§9), must be < 2048; got {byte}"
+            );
+            assert_eq!(
+                byte, 14,
+                "stamped src.byte is 14 (just past the pack header)"
+            );
         }
     }
 
@@ -338,7 +346,7 @@ fn fvi_sink_indexes_non_mpeg2_frames_codec_agnostically() {
     assert_eq!(recs[0]["type"], "I");
     assert_eq!(recs[0]["pts"], 1234);
     assert_eq!(recs[0]["src"]["sector"], 4); // 8192 / 2048
-    assert_eq!(recs[0]["src"]["byte"], 8192);
+    assert_eq!(recs[0]["src"]["byte"], 0); // 8192 is sector-aligned → within-sector offset 0 (§9)
     assert!(
         recs[0].get("field_order").is_none() && recs[0].get("nb_fields").is_none(),
         "coding-absent record omits field_order/nb_fields"