wip: rc6 VFR/DVD/CSS base (held for bulletproofing + split)

src/css/stevenson.rs

@@ -262,7 +262,20 @@ pub fn crack_title_key(sector: &[u8]) -> Option<[u8; 5]> {
 /// Inner body of [`crack_title_key`] — the actual AttackPattern search. Split
 /// out so the public entry point can wall-clock the whole attempt for the
 /// runaway guard without threading a timer through every return path.
-fn crack_title_key_inner(sector: &[u8]) -> Option<[u8; 5]> {
+/// AttackPattern crib: the predicted 10-byte plaintext at byte 0x80.
+///
+/// Scans the clear header `sec[0x00..0x80]` (never scrambled) for the longest
+/// run that repeats with a cycle length in 2..0x2F. If the run is long enough
+/// (`plen > 3` and at least two full cycles), the plaintext at 0x80 is taken to
+/// be that periodic run continuing forward. Returns `None` for an unscrambled
+/// sector or one with no usable run — such a sector can be neither cracked nor
+/// key-validated, only descrambled with an externally-cached key.
+///
+/// The header is untouched by `descramble_sector`, so the crib is identical
+/// before and after descramble: the decrypt path uses it as a per-sector
+/// "did the cached key descramble correctly?" oracle (the predicted plaintext
+/// must reappear at 0x80), and the cracker uses it as its known plaintext.
+pub(crate) fn attack_crib(sector: &[u8]) -> Option<[u8; 10]> {
     if sector.len() < SECTOR_SIZE || sector[FLAG_BYTE] & 0x30 == 0 {
         return None;
     }
@@ -285,14 +298,6 @@ fn crack_title_key_inner(sector: &[u8]) -> Option<[u8; 5]> {
 
     // Need at least a few repeated bytes and at least one full cycle.
     if best_plen > 3 && best_p > 0 && best_plen / best_p >= 2 {
-        let seed: [u8; 5] = [
-            sector[SEED_OFFSET],
-            sector[SEED_OFFSET + 1],
-            sector[SEED_OFFSET + 2],
-            sector[SEED_OFFSET + 3],
-            sector[SEED_OFFSET + 4],
-        ];
-
         // The known plaintext is the periodic run continuing past 0x80. The
         // crib starts at `0x80 - (best_plen/best_p)*best_p` and continues
         // through the encrypted region; the bytes at and after 0x80 are the
@@ -300,30 +305,40 @@ fn crack_title_key_inner(sector: &[u8]) -> Option<[u8; 5]> {
         let cycles = best_plen / best_p;
         let plain_start = 0x80 - cycles * best_p;
 
-        // The cipher is the 10 bytes at 0x80; the crib is their predicted
+        // Each predicted byte is the run sample one or more periods back:
-        // plaintext. The periodic run (period `best_p`) is known to continue
+        // `sec[plain_start + (i % best_p)]`. For in-run offsets
-        // through 0x80, so each predicted byte is the run sample one or more
-        // periods back: `sec[plain_start + (i % best_p)]`. For in-run offsets
         // (`plain_start + i < 0x80`) the run is exactly periodic, so this
         // equals `sec[plain_start + i]`; for offsets at/after 0x80 the raw
         // byte is ciphertext, so we MUST wrap within the period rather than
         // read it. (Reading `&sec[plain_start..+10]` directly — as before —
         // pulled ciphertext into the crib whenever the run covered fewer than
         // 10 bytes before 0x80, producing false-negative key recovery.)
-        let crypted = &sector[0x80..0x80 + 10];
         let mut plain = [0u8; 10];
         for (i, p) in plain.iter_mut().enumerate() {
             *p = sector[plain_start + (i % best_p)];
         }
+        Some(plain)
+    } else {
+        None
+    }
+}
 
+fn crack_title_key_inner(sector: &[u8]) -> Option<[u8; 5]> {
+    let plain = attack_crib(sector)?;
+    let seed: [u8; 5] = [
+        sector[SEED_OFFSET],
+        sector[SEED_OFFSET + 1],
+        sector[SEED_OFFSET + 2],
+        sector[SEED_OFFSET + 3],
+        sector[SEED_OFFSET + 4],
+    ];
+    let crypted = &sector[0x80..0x80 + 10];
     if let Some(key) = recover_title_key_from_plain(crypted, &plain, &seed) {
         // Verify against the same predicted plaintext.
         if descramble_matches(sector, &key, &plain) {
             return Some(key);
         }
     }
-    }
-
     None
 }
 

src/decrypt.rs

@@ -183,7 +183,7 @@ impl DecryptKeys {
 /// scrambled unit decrypted.
 pub fn decrypt_sectors(
     buf: &mut [u8],
-    keys: &DecryptKeys,
+    keys: &mut DecryptKeys,
     unit_key_idx: usize,
 ) -> Result<usize, crate::error::Error> {
     let dropped: usize = match keys {
@@ -351,8 +351,41 @@ pub fn decrypt_sectors(
             dropped_bytes.into_inner()
         }
         DecryptKeys::Css { title_key } => {
+            // CSS has no supplied key list: the ONLY source of a title key is
+            // cracking the data, and the key changes per VTS/VOB region. So
+            // `title_key` is a CACHE of the last crack, not a fixed disc key —
+            // applying it blindly across a region boundary descrambles with the
+            // wrong key (valid headers, garbage payload). Validate it on every
+            // scrambled sector and re-crack on a miss (libdvdcss's on-demand
+            // per-region rekey; the same validate-then-rekey shape the AACS arm
+            // above uses, but re-cracking instead of picking from a list).
+            //
+            // The clear header (<0x80) is never scrambled, so its periodic crib
+            // predicts the plaintext at 0x80. Descramble with the cached key; if
+            // the crib fails to reappear the key region changed (or the primed
+            // key was wrong) — restore the ciphertext, re-crack from this very
+            // sector, and descramble again. A crib-less sector (no periodic run)
+            // can be neither validated nor cracked, so it rides the cached key —
+            // correct, because it lives in the same region as the nearby crib
+            // sector that set the cache.
             for chunk in buf.chunks_mut(2048) {
+                if chunk.len() < 2048 || !css::is_scrambled(chunk) {
+                    continue;
+                }
+                let crib = css::stevenson::attack_crib(chunk);
+                let original: Option<Vec<u8>> = crib.as_ref().map(|_| chunk.to_vec());
                 css::lfsr::descramble_sector(title_key, chunk);
+                if let (Some(crib), Some(original)) = (crib, original) {
+                    if chunk[0x80..0x80 + 10] != crib[..] {
+                        // Cached key is stale for this region — restore the
+                        // ciphertext and crack this sector's own key.
+                        chunk.copy_from_slice(&original);
+                        if let Some(fresh) = css::stevenson::crack_title_key(chunk) {
+                            *title_key = fresh;
+                        }
+                        css::lfsr::descramble_sector(title_key, chunk);
+                    }
+                }
             }
             0
         }
@@ -381,11 +414,11 @@ mod tests {
         }
         let snapshot = unit.clone();
 
-        let keys = DecryptKeys::Aacs {
+        let mut keys = DecryptKeys::Aacs {
             unit_keys: vec![(0, [0xAB; 16])],
             read_data_key: None,
         };
-        decrypt_sectors(&mut unit, &keys, 0).unwrap();
+        decrypt_sectors(&mut unit, &mut keys, 0).unwrap();
         assert_eq!(
             unit, snapshot,
             "non-m2ts unit must be restored after failed decrypt"
@@ -424,7 +457,7 @@ mod tests {
     /// bytes byte-for-byte unchanged — no regression on real discs.
     #[test]
     fn aacs_clear_trailing_partial_is_tolerated_unchanged() {
-        let keys = DecryptKeys::Aacs {
+        let mut keys = DecryptKeys::Aacs {
             unit_keys: vec![(0, [0xAB; 16])],
             read_data_key: None,
         };
@@ -434,7 +467,7 @@ mod tests {
         let mut buf = unit;
         buf.extend_from_slice(&tail);
 
-        decrypt_sectors(&mut buf, &keys, 0).expect("clear trailing partial is Ok");
+        decrypt_sectors(&mut buf, &mut keys, 0).expect("clear trailing partial is Ok");
 
         assert_eq!(
             &buf[aacs::ALIGNED_UNIT_LEN..],
@@ -449,7 +482,7 @@ mod tests {
     /// corruption, so we must fail loud with `DecryptFailed`.
     #[test]
     fn aacs_scrambled_trailing_partial_is_rejected() {
-        let keys = DecryptKeys::Aacs {
+        let mut keys = DecryptKeys::Aacs {
             unit_keys: vec![(0, [0xAB; 16])],
             read_data_key: None,
         };
@@ -459,7 +492,7 @@ mod tests {
         let mut buf = unit;
         buf.extend_from_slice(&tail);
 
-        let err = decrypt_sectors(&mut buf, &keys, 0)
+        let err = decrypt_sectors(&mut buf, &mut keys, 0)
             .expect_err("scrambled trailing partial must be rejected");
         assert_eq!(
             err.code(),
@@ -471,12 +504,12 @@ mod tests {
     /// An empty buffer is a valid no-op (zero units), not an error.
     #[test]
     fn aacs_empty_buffer_is_ok() {
-        let keys = DecryptKeys::Aacs {
+        let mut keys = DecryptKeys::Aacs {
             unit_keys: vec![(0, [0xAB; 16])],
             read_data_key: None,
         };
         let mut buf: Vec<u8> = Vec::new();
-        assert!(decrypt_sectors(&mut buf, &keys, 0).is_ok());
+        assert!(decrypt_sectors(&mut buf, &mut keys, 0).is_ok());
     }
 
     /// An exact multiple of the unit length has no trailing partial: behavior
@@ -484,14 +517,14 @@ mod tests {
     /// attempted. Two clear units must round-trip untouched and return `Ok`.
     #[test]
     fn aacs_exact_multiple_unchanged() {
-        let keys = DecryptKeys::Aacs {
+        let mut keys = DecryptKeys::Aacs {
             unit_keys: vec![(0, [0xAB; 16])],
             read_data_key: None,
         };
         let mut buf = clear_ts_region(aacs::ALIGNED_UNIT_LEN * 2);
         let snapshot = buf.clone();
 
-        decrypt_sectors(&mut buf, &keys, 0).expect("exact-multiple buffer is Ok");
+        decrypt_sectors(&mut buf, &mut keys, 0).expect("exact-multiple buffer is Ok");
 
         assert_eq!(
             buf, snapshot,
@@ -512,7 +545,7 @@ mod tests {
     fn none_keys_is_noop() {
         let mut buf: Vec<u8> = (0..4096u32).map(|i| (i % 256) as u8).collect();
         let snapshot = buf.clone();
-        decrypt_sectors(&mut buf, &DecryptKeys::None, 0).expect("None is always Ok");
+        decrypt_sectors(&mut buf, &mut DecryptKeys::None, 0).expect("None is always Ok");
         assert_eq!(buf, snapshot, "None must not touch the buffer");
     }
 
@@ -564,8 +597,8 @@ mod tests {
         let title_key = [0x42, 0x13, 0x37, 0xBE, 0xEF];
         let seed = [0xDE, 0xAD, 0xBE, 0xEF, 0x42];
         let (mut sector, plaintext) = make_css_sector(&title_key, &seed, 0xA5);
-        let keys = DecryptKeys::Css { title_key };
+        let mut keys = DecryptKeys::Css { title_key };
-        decrypt_sectors(&mut sector, &keys, 0).expect("CSS decrypt is Ok");
+        decrypt_sectors(&mut sector, &mut keys, 0).expect("CSS decrypt is Ok");
         assert_eq!(
             &sector[0x80..2048],
             &plaintext[0x80..2048],
@@ -594,8 +627,8 @@ mod tests {
         let (s1, p1) = make_css_sector(&title_key, &[0x66, 0x77, 0x88, 0x99, 0xAA], 0xC3);
         let mut buf = s0;
         buf.extend_from_slice(&s1);
-        let keys = DecryptKeys::Css { title_key };
+        let mut keys = DecryptKeys::Css { title_key };
-        decrypt_sectors(&mut buf, &keys, 0).expect("CSS multi-sector decrypt is Ok");
+        decrypt_sectors(&mut buf, &mut keys, 0).expect("CSS multi-sector decrypt is Ok");
         assert_eq!(
             &buf[0x80..2048],
             &p0[0x80..2048],
@@ -608,6 +641,94 @@ mod tests {
         );
     }
 
+    /// Build a CSS sector whose clear header ends in a periodic run that
+    /// continues into the encrypted region — the crackable shape `attack_crib`/
+    /// `crack_title_key` recover a key from (a constant body fill gives a
+    /// degenerate crib the cracker can't pin a unique key on). Returns
+    /// (scrambled_sector, plaintext_body).
+    fn make_crackable_css_sector(
+        title_key: &[u8; 5],
+        seed: &[u8; 5],
+        period: usize,
+    ) -> (Vec<u8>, Vec<u8>) {
+        let mut plaintext = vec![0u8; 2048];
+        plaintext[0x14] = 0x10; // scramble flag
+        // Periodic run from 0x59 (just above the seed) through 0x80 and on into
+        // the encrypted region; phase anchored to offset 0 so it is continuous
+        // across the 0x80 boundary.
+        let pat: Vec<u8> = (0..period)
+            .map(|k| (0xA0u8.wrapping_add(k as u8)) ^ 0x5A)
+            .collect();
+        for (i, b) in plaintext.iter_mut().enumerate().skip(0x59) {
+            *b = pat[i % period];
+        }
+        plaintext[0x54..0x59].copy_from_slice(seed); // seed sits below the run
+        let body = plaintext.clone();
+        css::lfsr::scramble_sector(title_key, &mut plaintext);
+        (plaintext, body)
+    }
+
+    /// CSS title keys are per-VTS/VOB region: a real disc holds DIFFERENT keys
+    /// for different regions and the only way to get each is to crack it. The
+    /// decrypt path must re-crack when the cached key stops descrambling (its
+    /// crib no longer reappears at 0x80) instead of blindly applying one key
+    /// across a region boundary — the bug that pixelated every freemkv DVD rip.
+    ///
+    /// Two sectors scrambled under DIFFERENT keys, cache primed to ONLY the
+    /// first (exactly what the one-shot scan crack leaves). Sector 0 validates +
+    /// descrambles with the cached key; sector 1's cached-key descramble fails
+    /// the crib, so the path re-cracks sector 1's own key and recovers its
+    /// plaintext. Before the fix (blind single-key apply) sector 1 was garbage.
+    ///
+    /// Grounding: the CSS arm's `attack_crib` → `chunk[0x80..] != crib` →
+    /// `crack_title_key` → `*title_key = fresh` rekey.
+    /// Mutation: drop the rekey branch (apply the cached key always) → sector 1's
+    /// body no longer matches its plaintext; this fails.
+    #[test]
+    fn css_rekeys_when_title_key_region_changes() {
+        let key_a = [0x42, 0x13, 0x37, 0xBE, 0xEF];
+        let key_b = [0x07, 0x5A, 0xC3, 0x10, 0x88]; // a DIFFERENT region's key
+        let (s0, p0) = make_crackable_css_sector(&key_a, &[0x11, 0x22, 0x33, 0x44, 0x55], 4);
+        let (s1, p1) = make_crackable_css_sector(&key_b, &[0x66, 0x77, 0x88, 0x99, 0xAA], 4);
+        // Precondition: each sector must be crackable on its own (the rekey
+        // depends on it). If this fails the fixture, not the path, is at fault.
+        assert_eq!(
+            crate::css::stevenson::crack_title_key(&s0),
+            Some(key_a),
+            "fixture s0 must crack to key_a standalone"
+        );
+        assert_eq!(
+            crate::css::stevenson::crack_title_key(&s1),
+            Some(key_b),
+            "fixture s1 must crack to key_b standalone"
+        );
+        let mut buf = s0;
+        buf.extend_from_slice(&s1);
+
+        // Cache primed to key_a only — exactly what the one-shot scan crack yields.
+        let mut keys = DecryptKeys::Css { title_key: key_a };
+        decrypt_sectors(&mut buf, &mut keys, 0).expect("CSS multi-region decrypt is Ok");
+
+        assert_eq!(
+            &buf[0x80..2048],
+            &p0[0x80..2048],
+            "region A sector descrambles with the cached (primed) key"
+        );
+        assert_eq!(
+            &buf[2048 + 0x80..4096],
+            &p1[0x80..2048],
+            "region B sector must descramble after the path re-cracks its own key"
+        );
+        // The cache must have advanced to region B's key.
+        match keys {
+            DecryptKeys::Css { title_key } => assert_eq!(
+                title_key, key_b,
+                "cache must hold region B's key after the rekey"
+            ),
+            _ => unreachable!(),
+        }
+    }
+
     /// The CSS path leaves UNSCRAMBLED sectors (flag clear) byte-for-byte
     /// untouched — descramble_sector early-returns on a zero flag. A clear
     /// sector mixed into the buffer must not be corrupted.
@@ -622,8 +743,8 @@ mod tests {
         let mut sector = vec![0x77u8; 2048];
         sector[0x14] = 0x00; // not scrambled
         let snapshot = sector.clone();
-        let keys = DecryptKeys::Css { title_key };
+        let mut keys = DecryptKeys::Css { title_key };
-        decrypt_sectors(&mut sector, &keys, 0).unwrap();
+        decrypt_sectors(&mut sector, &mut keys, 0).unwrap();
         assert_eq!(sector, snapshot, "clear CSS sector must be left untouched");
     }
 
@@ -636,8 +757,8 @@ mod tests {
     #[test]
     fn css_empty_buffer_is_ok() {
         let mut buf: Vec<u8> = Vec::new();
-        let keys = DecryptKeys::Css { title_key: [0; 5] };
+        let mut keys = DecryptKeys::Css { title_key: [0; 5] };
-        assert!(decrypt_sectors(&mut buf, &keys, 0).is_ok());
+        assert!(decrypt_sectors(&mut buf, &mut keys, 0).is_ok());
     }
 
     // ── AACS unit-key index selection ──────────────────────────────────────
@@ -653,12 +774,12 @@ mod tests {
     /// fails.
     #[test]
     fn aacs_out_of_range_unit_key_idx_errors() {
-        let keys = DecryptKeys::Aacs {
+        let mut keys = DecryptKeys::Aacs {
             unit_keys: vec![(0, [0xAB; 16])],
             read_data_key: None,
         };
         let mut buf = clear_ts_region(aacs::ALIGNED_UNIT_LEN);
-        let err = decrypt_sectors(&mut buf, &keys, 5)
+        let err = decrypt_sectors(&mut buf, &mut keys, 5)
             .expect_err("unit_key_idx 5 is out of range for a 1-key list");
         assert_eq!(
             err.code(),
@@ -673,12 +794,12 @@ mod tests {
     /// Mutation: defaulting to [0u8;16] on None would proceed; this fails.
     #[test]
     fn aacs_empty_unit_keys_errors() {
-        let keys = DecryptKeys::Aacs {
+        let mut keys = DecryptKeys::Aacs {
             unit_keys: vec![],
             read_data_key: None,
         };
         let mut buf = clear_ts_region(aacs::ALIGNED_UNIT_LEN);
-        let err = decrypt_sectors(&mut buf, &keys, 0).expect_err("empty unit_keys must error");
+        let err = decrypt_sectors(&mut buf, &mut keys, 0).expect_err("empty unit_keys must error");
         assert_eq!(err.code(), crate::error::Error::DecryptFailed.code());
     }
 
@@ -751,14 +872,14 @@ mod tests {
             "encrypted unit must look scrambled before decrypt"
         );
 
-        let keys = DecryptKeys::Aacs {
+        let mut keys = DecryptKeys::Aacs {
             unit_keys: vec![(0, key0), (1, key1)], // two CPS units
             read_data_key: None,
         };
 
         // Call with the default hint (idx 0) — the fix must fall back to key1.
         let mut buf = unit;
-        decrypt_sectors(&mut buf, &keys, 0).expect("multi-CPS decrypt must succeed");
+        decrypt_sectors(&mut buf, &mut keys, 0).expect("multi-CPS decrypt must succeed");
 
         assert!(
             !aacs::is_aacs_scrambled(&buf),
@@ -785,12 +906,12 @@ mod tests {
         let mut unit = clear_ts_unit();
         aacs_encrypt_unit_for_test(&mut unit, &key);
 
-        let keys = DecryptKeys::Aacs {
+        let mut keys = DecryptKeys::Aacs {
             unit_keys: vec![(0, key)],
             read_data_key: None,
         };
         let mut buf = unit;
-        decrypt_sectors(&mut buf, &keys, 0).expect("single-key disc must decrypt");
+        decrypt_sectors(&mut buf, &mut keys, 0).expect("single-key disc must decrypt");
         assert!(
             !aacs::is_aacs_scrambled(&buf),
             "single-key disc: TS syncs must be restored"
@@ -829,13 +950,13 @@ mod tests {
             "encrypted unit must look scrambled going in"
         );
 
-        let keys = DecryptKeys::Aacs {
+        let mut keys = DecryptKeys::Aacs {
             unit_keys: vec![(0, wrong_key)],
             read_data_key: None,
         };
         let mut buf = unit;
-        let dropped =
+        let dropped = decrypt_sectors(&mut buf, &mut keys, 0)
-            decrypt_sectors(&mut buf, &keys, 0).expect("undecryptable unit is not a hard error");
+            .expect("undecryptable unit is not a hard error");
 
         assert_eq!(
             dropped,
@@ -872,11 +993,11 @@ mod tests {
         buf.extend_from_slice(&unit_a);
         buf.extend_from_slice(&unit_b);
 
-        let keys = DecryptKeys::Aacs {
+        let mut keys = DecryptKeys::Aacs {
             unit_keys: vec![(0, key)],
             read_data_key: None,
         };
-        let dropped = decrypt_sectors(&mut buf, &keys, 0).expect("partial decrypt is Ok");
+        let dropped = decrypt_sectors(&mut buf, &mut keys, 0).expect("partial decrypt is Ok");
 
         assert_eq!(
             dropped,
@@ -901,12 +1022,12 @@ mod tests {
         let key = [0x77u8; 16];
         let mut unit = clear_ts_unit();
         aacs_encrypt_unit_for_test(&mut unit, &key);
-        let keys = DecryptKeys::Aacs {
+        let mut keys = DecryptKeys::Aacs {
             unit_keys: vec![(0, key)],
             read_data_key: None,
         };
         let mut buf = unit;
-        let dropped = decrypt_sectors(&mut buf, &keys, 0).expect("clean decrypt");
+        let dropped = decrypt_sectors(&mut buf, &mut keys, 0).expect("clean decrypt");
         assert_eq!(dropped, 0, "a fully-decrypted buffer must report no loss");
     }
 

src/diag.rs

@@ -148,14 +148,15 @@ pub fn dvd_cell_row(idx: usize, cell: &crate::ifo::DvdCell, dropped: bool) -> St
         "keep(plain-feature)"
     };
     format!(
-        "tag=dvd.cell idx={idx} cat=0x{:02X} type={} block_mode={} block_type={} \
+        "tag=dvd.cell idx={idx} cat=0x{:02X} block_mode={} block_type={} \
-seamless={} ilv={} plain={} first={} last={} dur={:.1}s {}",
+seamless={} ilv={} stc={} angle={} plain={} first={} last={} dur={:.1}s {}",
         cell.category,
-        c.cell_type,
         c.block_mode,
         c.block_type,
         c.seamless_play as u8,
         c.interleaved as u8,
+        c.stc_discontinuity as u8,
+        c.seamless_angle as u8,
         c.is_plain_feature() as u8,
         cell.first_sector,
         cell.last_sector,
@@ -726,23 +727,25 @@ mod tests {
         };
         let row = dvd_cell_row(0, &plain, false);
         assert!(row.contains("cat=0x00"), "{row}");
-        assert!(row.contains("type=0"), "{row}");
+        assert!(row.contains("block_mode=0"), "{row}");
         assert!(row.contains("first=100"), "{row}");
         assert!(row.contains("last=199"), "{row}");
         assert!(row.contains("dur=12.5s"), "{row}");
         assert!(row.contains("keep(plain-feature)"), "{row}");
         assert!(!row.contains("DROP"), "{row}");
 
-        // 0x80 = middle-of-angle-block (cell_type=2), shown dropped.
+        // 0x90 = in-block cell of an angle block (block_mode=2, block_type=1),
+        // shown dropped as a leading secondary piece.
         let sec = crate::ifo::DvdCell {
             first_sector: 0,
             last_sector: 9,
-            category: 0x80,
+            category: 0x90,
             duration_secs: 1.0,
         };
         let row = dvd_cell_row(0, &sec, true);
-        assert!(row.contains("cat=0x80"), "{row}");
+        assert!(row.contains("cat=0x90"), "{row}");
-        assert!(row.contains("type=2"), "{row}");
+        assert!(row.contains("block_mode=2"), "{row}");
+        assert!(row.contains("block_type=1"), "{row}");
         assert!(row.contains("DROP(leading-secondary-block-piece)"), "{row}");
     }
 }

src/disc/dvd.rs

@@ -1098,14 +1098,14 @@ mod tests {
     }
 
     /// End-to-end bug-4 fix: a feature PGC that opens with a leading
-    /// interleaved-angle sub-block cell (category 0x80 = middle-of-angle-block)
+    /// interleaved-angle sub-block cell (category 0x90 = in-block cell of an
-    /// must have that cell DROPPED from the muxed extents, so the rip starts at
+    /// angle block) must have that cell DROPPED from the muxed extents, so the
-    /// the real feature. Chapters shift earlier by the dropped duration.
+    /// rip starts at the real feature. Chapters shift earlier by the dropped duration.
     #[test]
     fn scan_dvd_titles_drops_leading_scene_index_cell() {
         let mut disc = MemDisc::new();
         let vmg = build_vmg(&[(2, 1, 1)]);
-        // Cell 0: leading scene-index/angle sub-block (cat 0x80), 5s, sectors 0..9.
+        // Cell 0: leading scene-index/angle sub-block (cat 0x90), 5s, sectors 0..9.
         // Cell 1: feature start (cat 0x00), 59s, sectors 100..199.
         // Cell 2: feature (cat 0x00), 59s, sectors 300..399.
         // Programs: prog0 → cell 1 (feature start), prog1 → cell 3.
@@ -1113,7 +1113,7 @@ mod tests {
             1000,
             0x00,
             &[
-                (0, 9, 0x80, 0x05),
+                (0, 9, 0x90, 0x05),
                 (100, 199, 0x00, 0x59),
                 (300, 399, 0x00, 0x59),
             ],
@@ -1137,7 +1137,7 @@ mod tests {
             ],
         );
         let t = &Disc::scan_dvd_titles(&mut disc, &udf)[0];
-        // The leading 0x80 cell is dropped: 2 feature extents, not 3.
+        // 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);

src/ifo.rs

@@ -58,12 +58,12 @@ pub struct DvdTitle {
 pub struct DvdCell {
     pub first_sector: u32,
     pub last_sector: u32,
-    /// Raw cell-category byte at `cell_playback + 0` (DVD-Video spec).
+    /// Raw cell-category byte at `cell_playback + 0` (libdvdread layout).
-    /// Packs cell_type (bits 7-6), block_mode (bits 5-4), block_type
+    /// Packs block_mode (bits 7-6), block_type (bits 5-4), seamless_play
-    /// (bits 3-2), seamless_play (bit 1), interleaved (bit 0). Carried so
+    /// (bit 3), interleaved (bit 2), stc_discontinuity (bit 1),
-    /// the extent builder can recognise non-feature leading cells
+    /// seamless_angle (bit 0). Carried so the extent builder can recognise
-    /// (scene-index / interleaved angle sub-blocks) and the diagnostic dump
+    /// non-feature leading cells (interleaved angle sub-blocks) and the
-    /// can show why a cell was kept or dropped.
+    /// diagnostic dump can show why a cell was kept or dropped.
     pub category: u8,
     /// Per-cell playback duration in seconds (BCD time at `cell_playback + 4`).
     /// Used by the diagnostic dump and the conservative leading-cell filter
@@ -72,51 +72,54 @@ pub struct DvdCell {
 }
 
 /// Decoded view of a cell-category byte (`cell_playback + 0`), per the
-/// DVD-Video spec `cell_playback_information` layout.
+/// DVD-Video spec / libdvdread `cell_playback_t` layout. Byte-0 bitfields,
+/// MSB-first: `block_mode`(7-6), `block_type`(5-4), `seamless_play`(3),
+/// `interleaved`(2), `stc_discontinuity`(1), `seamless_angle`(0). (The real
+/// `cell_type` is a karaoke-only field in byte 1, not used here.)
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub struct CellCategory {
-    /// bits 7-6: 0=normal, 1=first cell of angle block, 2=middle, 3=last.
+    /// bits 7-6: 0=not in block, 1=first cell of block, 2=in block, 3=last cell.
-    pub cell_type: u8,
-    /// bits 5-4: 0=not in block, 1=first cell of block, 2=in block, 3=last.
     pub block_mode: u8,
-    /// bits 3-2: 0=not part of a block, 1=angle block.
+    /// bits 5-4: 0=not part of a block, 1=angle block.
     pub block_type: u8,
-    /// bit 1: seamless playback (STC continuous).
+    /// bit 3: seamless playback (STC continuous).
     pub seamless_play: bool,
-    /// bit 0: interleaved (multi-angle / seamless-branch interleave).
+    /// bit 2: interleaved (multi-angle / seamless-branch interleave).
     pub interleaved: bool,
+    /// bit 1: STC discontinuity at the start of this cell.
+    pub stc_discontinuity: bool,
+    /// bit 0: seamless angle change.
+    pub seamless_angle: bool,
 }
 
 impl CellCategory {
-    /// Decode the raw `cell_playback + 0` byte.
+    /// Decode the raw `cell_playback + 0` byte (libdvdread `read_cell_playback`).
     pub fn decode(raw: u8) -> Self {
         CellCategory {
-            cell_type: (raw >> 6) & 0x03,
+            block_mode: (raw >> 6) & 0x03,
-            block_mode: (raw >> 4) & 0x03,
+            block_type: (raw >> 4) & 0x03,
-            block_type: (raw >> 2) & 0x03,
+            seamless_play: (raw & 0x08) != 0,
-            seamless_play: (raw & 0x02) != 0,
+            interleaved: (raw & 0x04) != 0,
-            interleaved: (raw & 0x01) != 0,
+            stc_discontinuity: (raw & 0x02) != 0,
+            seamless_angle: (raw & 0x01) != 0,
         }
     }
 
-    /// A plain feature cell: not part of any angle/interleave block. Every
+    /// A plain feature cell: not part of any angle/interleave block. Every cell
-    /// cell of a normal single-angle feature decodes to this (`category`
+    /// of a normal single-angle feature decodes to this (`block_mode` and
-    /// byte `0x00`, or `0x00` in every block field with only the
+    /// `block_type` both 0, only the seamless/interleaved flags possibly set).
-    /// seamless/interleaved flags possibly set). Such a cell is NEVER
+    /// Such a cell is NEVER dropped by the leading-cell filter.
-    /// dropped by the leading-cell filter.
     pub fn is_plain_feature(&self) -> bool {
-        self.cell_type == 0 && self.block_mode == 0 && self.block_type == 0
+        self.block_mode == 0 && self.block_type == 0
     }
 
-    /// Marks a non-first piece of an angle / interleaved block: a "middle" or
+    /// Marks a non-first piece of an angle block: an "in-block" or "last of
-    /// "last" cell of an angle block (`cell_type ∈ {2,3}`), or an
+    /// block" cell (`block_mode ∈ {2,3}`) of an angle block (`block_type==1`).
-    /// in-block / last-of-block cell (`block_mode ∈ {2,3}`). Concatenating
+    /// Concatenating these back-to-back with the first angle duplicates content
-    /// these back-to-back with the first angle duplicates content at the head
+    /// at the head of the feature. Conservative: the FIRST cell of a block
-    /// of the feature. Conservative: the FIRST cell of a block
+    /// (`block_mode==1`) is NOT flagged — it is the angle we keep.
-    /// (`cell_type==1` / `block_mode==1`) is NOT flagged — it is the angle we
-    /// keep.
     pub fn is_secondary_block_piece(&self) -> bool {
-        matches!(self.cell_type, 2 | 3) || matches!(self.block_mode, 2 | 3)
+        self.block_type == 1 && matches!(self.block_mode, 2 | 3)
     }
 }
 
@@ -567,7 +570,7 @@ fn parse_audio_attr(data: &[u8], offset: usize) -> Result<DvdAudioAttr> {
         _ => Codec::Unknown(coding_mode),
     };
 
-    let sample_rate_flag = (b0 >> 3) & 0x03;
+    let sample_rate_flag = (b1 >> 4) & 0x03; // sample_frequency: byte 1 bits 5-4 (libdvdread audio_attr_t)
     let sample_rate = match sample_rate_flag {
         0 => 48000,
         1 => 96000,
@@ -1174,11 +1177,11 @@ mod tests {
     #[test]
     fn audio_attr_dts() {
         let mut data = vec![0u8; 16];
-        // DTS (coding=6), 96kHz (rate=1), 2 channels (stored as 1)
+        // DTS (coding=6), 96kHz (rate=1, byte1 bits 5-4), 2 channels (stored as 1)
-        // b0: bits 7-5=110(DTS), bits 4-3=01(96k) => 0b110_01_000 = 0xC8
+        // b0: bits 7-5=110(DTS) => 0b110_00000 = 0xC0
-        data[0] = 0xC8;
+        data[0] = 0xC0;
-        // b1: bits 2-0=001 (channels-1=1) => 0x01
+        // b1: bits 5-4=01(96k), bits 2-0=001(channels-1=1) => 0b00_01_0_001 = 0x11
-        data[1] = 0x01;
+        data[1] = 0x11;
         data[2] = b'f';
         data[3] = b'r';
 
@@ -1546,13 +1549,13 @@ mod tests {
         }
     }
 
-    /// CellCategory decodes the spec bitfields: cell_type (7-6), block_mode
+    /// CellCategory decodes the libdvdread byte-0 bitfields: block_mode (7-6),
-    /// (5-4), block_type (3-2), seamless (1), interleaved (0).
+    /// block_type (5-4), seamless_play (3), interleaved (2),
+    /// stc_discontinuity (1), seamless_angle (0).
     #[test]
     fn cell_category_decode_bits() {
         // 0x00 → plain feature, nothing set.
         let c = CellCategory::decode(0x00);
-        assert_eq!(c.cell_type, 0);
         assert_eq!(c.block_mode, 0);
         assert_eq!(c.block_type, 0);
         assert!(!c.seamless_play);
@@ -1560,27 +1563,29 @@ mod tests {
         assert!(c.is_plain_feature());
         assert!(!c.is_secondary_block_piece());
 
-        // cell_type=1 (first of angle block), block_mode=1 (first of block):
+        // block_mode=1 (first cell of block), block_type=1 (angle block):
-        // 0b01_01_00_0_0 = 0x50. This is the angle we KEEP — not secondary.
+        // 0b01_01_0000 = 0x50. This is the angle we KEEP — not secondary.
-        let c = CellCategory::decode(0b01_01_00_00);
+        let c = CellCategory::decode(0b01_01_0000);
-        assert_eq!(c.cell_type, 1);
         assert_eq!(c.block_mode, 1);
+        assert_eq!(c.block_type, 1);
         assert!(!c.is_plain_feature());
         assert!(!c.is_secondary_block_piece());
 
-        // cell_type=2 (middle of angle block): 0b10_00_00_00 = 0x80 → secondary.
+        // block_mode=2 (in block) / 3 (last of block) of an angle block
-        assert!(CellCategory::decode(0b10_00_00_00).is_secondary_block_piece());
+        // (block_type=1) → secondary.
-        // cell_type=3 (last of angle block) → secondary.
+        assert!(CellCategory::decode(0b10_01_0000).is_secondary_block_piece());
-        assert!(CellCategory::decode(0b11_00_00_00).is_secondary_block_piece());
+        assert!(CellCategory::decode(0b11_01_0000).is_secondary_block_piece());
-        // block_mode=2 (in block) → secondary; block_mode=3 (last of block) → secondary.
+        // First cell of the block (block_mode=1) is NEVER secondary.
-        assert!(CellCategory::decode(0b00_10_00_00).is_secondary_block_piece());
+        assert!(!CellCategory::decode(0b01_01_0000).is_secondary_block_piece());
-        assert!(CellCategory::decode(0b00_11_00_00).is_secondary_block_piece());
 
-        // seamless (bit1) + interleaved (bit0) on an otherwise-plain cell must
+        // The low flags (seamless_play bit3, interleaved bit2, stc bit1,
-        // NOT make it secondary — they don't mark non-feature content.
+        // seamless_angle bit0) on an otherwise-plain cell must NOT make it
-        let c = CellCategory::decode(0b00_00_00_11);
+        // secondary — they don't mark non-feature content.
+        let c = CellCategory::decode(0b0000_1111);
         assert!(c.seamless_play);
         assert!(c.interleaved);
+        assert!(c.stc_discontinuity);
+        assert!(c.seamless_angle);
         assert!(c.is_plain_feature());
         assert!(!c.is_secondary_block_piece());
     }
@@ -1614,8 +1619,8 @@ mod tests {
             chapters: 2,
             duration_secs: 100.0,
             cells: vec![
-                cell(0, 9, 0b10_00_00_00),   // middle of angle block → drop
+                cell(0, 9, 0b10_01_0000),   // in-block cell of angle block → drop
-                cell(10, 19, 0b00_11_00_00), // last of block → drop
+                cell(10, 19, 0b11_01_0000), // last cell of angle block → drop
                 cell(20, 119, 0x00),        // feature starts here
                 cell(120, 219, 0x00),
             ],
@@ -1637,7 +1642,7 @@ mod tests {
         let t = DvdTitle {
             chapters: 1,
             duration_secs: 100.0,
-            cells: vec![cell(0, 9, 0b10_00_00_00), cell(10, 19, 0b11_00_00_00)],
+            cells: vec![cell(0, 9, 0b10_01_0000), cell(10, 19, 0b11_01_0000)],
             chapter_times: vec![0.0],
             palette: None,
         };
@@ -1669,8 +1674,8 @@ mod tests {
         pgc[0xE8] = 0x00;
         pgc[0xE9] = 0xEA;
         pgc.resize(0xEA + 48, 0);
-        // Cell 0: category byte = 0x80 (middle of angle block), 5s BCD.
+        // Cell 0: category byte = 0x90 (in-block cell of angle block), 5s BCD.
-        pgc[0xEA] = 0x80;
+        pgc[0xEA] = 0x90;
         pgc[0xEA + 6] = 0x05;
         pgc[0xEA + 8..0xEA + 12].copy_from_slice(&10u32.to_be_bytes());
         // Cell 1: category 0x00 (plain feature), 7s BCD.
@@ -1678,7 +1683,7 @@ mod tests {
         pgc[0xEA + 24 + 6] = 0x07;
         pgc[0xEA + 24 + 8..0xEA + 24 + 12].copy_from_slice(&20u32.to_be_bytes());
         let title = parse_pgc(&pgc, 0, 2).unwrap();
-        assert_eq!(title.cells[0].category, 0x80);
+        assert_eq!(title.cells[0].category, 0x90);
         assert!((title.cells[0].duration_secs - 5.0).abs() < 0.01);
         assert_eq!(title.cells[1].category, 0x00);
         assert!((title.cells[1].duration_secs - 7.0).abs() < 0.01);

src/mux/codec/mpeg2.rs

@@ -101,32 +101,39 @@ pub struct Mpeg2Parser {
     /// `(absolute ES offset of a PES's first byte, PTS in ns)` for every PES
     /// that carried a timestamp, in ascending offset order.
     pts_marks: VecDeque<(u64, i64)>,
-    /// Per-frame presentation interval (ns), derived from the sequence header
+    /// Full-frame presentation interval (ns) at the sequence-header display rate
-    /// frame rate. DVD stamps a PTS only ~once per VOBU (every ~0.5 s), so
+    /// (`1/frame_rate`). The field period is half this. Per-frame durations are
-    /// frames between marks must be timed by `temporal_reference` × this
+    /// `nb_fields × field_period`, so 2:3-telecined frames alternate 2- and
-    /// interval. 0 until a sequence header with a valid frame rate is seen.
+    /// 3-field durations. 0 until a sequence header with a valid frame rate.
     frame_duration_ns: i64,
-    /// Cumulative count of coded pictures emitted in all GOPs before the
+    /// `progressive_sequence` from the sequence extension — selects the
-    /// current one. `temporal_reference` is GOP-relative (display order within
+    /// `nb_fields` rules for `repeat_first_field` pictures.
-    /// the GOP); adding this base makes a whole-stream display index.
+    progressive_sequence: bool,
-    gop_base: u64,
+    /// Pictures of the current GOP, buffered in DECODE order until the GOP
-    /// Coded pictures emitted in the current GOP so far (folded into
+    /// completes (the next GOP/sequence header). Held so each frame's PTS can be
-    /// `gop_base` at the next GOP boundary).
+    /// the display-order prefix-sum of field durations — exact for 2:3 pulldown
-    gop_count: u64,
+    /// without ever reordering emitted blocks (B-frames keep decode order; only
-    /// Display index of the last frame that carried an explicit PES PTS, used
+    /// their PTS is lower).
-    /// to anchor interpolated timestamps to the real disc timeline (so video
+    gop_buf: Vec<BufferedPicture>,
-    /// stays in sync with the PES-timestamped audio tracks).
+    /// Total field-display periods of all frames already emitted, in display
-    anchor_index: Option<u64>,
+    /// order — the running base for each new frame's display time.
-    /// PTS (ns) of the anchor frame.
+    emitted_fields: u64,
-    anchor_pts: i64,
+    /// PTS (ns) that display-field 0 of the whole stream maps to. Re-locked from
-    /// Frames emitted before the first PES PTS anchor is known, held with their
+    /// each GOP's first PES PTS so video stays in sync with the PES-timestamped
-    /// display index. A DVD title can open with a still-frame/first-play
+    /// audio. None until the first PES timestamp is seen.
-    /// sequence whose PTS lands a few frames in; buffering until the anchor lets
+    origin_pts_ns: Option<i64>,
-    /// those leading frames take the disc's real timeline instead of a 0 base.
+}
-    pending: Vec<(u64, Frame)>,
+
-    /// Accumulated `data.len()` of frames currently in `pending`. Bounds the
+/// One coded picture buffered awaiting its GOP's completion (see `gop_buf`).
-    /// pre-anchor hold by BYTES, not just frame count (see [`MAX_PENDING_BYTES`]).
+struct BufferedPicture {
-    pending_bytes: usize,
+    /// `temporal_reference` — display order within the GOP.
+    tr: u64,
+    /// Field-display periods this picture occupies (`picture_nb_fields`).
+    nb_fields: u8,
+    /// This picture's own PES PTS (ns), if its access unit carried one.
+    explicit_pts: Option<i64>,
+    /// The emitted frame (PTS + duration filled in at GOP flush).
+    frame: Frame,
 }
 
 impl Default for Mpeg2Parser {
@@ -144,12 +151,10 @@ impl Mpeg2Parser {
             base_offset: 0,
             pts_marks: VecDeque::new(),
             frame_duration_ns: 0,
-            gop_base: 0,
+            progressive_sequence: false,
-            gop_count: 0,
+            gop_buf: Vec::new(),
-            anchor_index: None,
+            emitted_fields: 0,
-            anchor_pts: 0,
+            origin_pts_ns: None,
-            pending: Vec::new(),
-            pending_bytes: 0,
         }
     }
 
@@ -174,22 +179,6 @@ impl Mpeg2Parser {
         parse_aspect_ratio(hdr)
     }
 
-    /// The PTS (ns) to assign to an access unit whose first relevant byte is at
-    /// absolute ES offset `target`: the most recent PES timestamp at or before
-    /// that offset (the PES that contains the access unit's start). Falls back
-    /// to 0 when no timestamp has been seen yet.
-    fn pts_for(&self, target: u64) -> i64 {
-        let mut best = 0;
-        for &(off, pts) in &self.pts_marks {
-            if off <= target {
-                best = pts;
-            } else {
-                break;
-            }
-        }
-        best
-    }
-
     /// Drain every complete access unit from `buf`, returning one Frame each.
     /// When `force` is true (EOF flush, or buffer-cap backstop) the trailing
     /// in-progress access unit is emitted even without a following boundary.
@@ -247,12 +236,12 @@ impl Mpeg2Parser {
             } else {
                 0
             };
-            let pic_abs = self.base_offset + pic as u64;
             let end_abs = self.base_offset + end as u64;
             let data = self.buf[..end].to_vec();
 
             // Phase 2 — mutate self.
             if let Some(h) = hdr {
+                self.progressive_sequence = parse_progressive_sequence(&h);
                 self.seq_header = Some(h);
                 if let Some((num, den)) = self.frame_rate() {
                     if num > 0 {
@@ -260,11 +249,7 @@ impl Mpeg2Parser {
                     }
                 }
             }
-            if gop_boundary && self.gop_count > 0 {
+            let nb_fields = picture_nb_fields(&data, self.progressive_sequence);
-                self.gop_base += self.gop_count;
-                self.gop_count = 0;
-            }
-            let display_index = self.gop_base + tr;
 
             // An explicit PES PTS for this access unit, if any. By the mark-drain
             // invariant the front mark's offset is >= this AU's start, so a front
@@ -275,71 +260,29 @@ impl Mpeg2Parser {
                 .filter(|&&(off, _)| off < end_abs)
                 .map(|&(_, p)| p);
 
-            let duration_ns = (self.frame_duration_ns > 0).then_some(self.frame_duration_ns as u64);
+            // A GOP boundary means the buffered run is a COMPLETE GOP (all its
-            let mut frame = Frame {
+            // pictures display before the next GOP's), so flush it before
+            // starting the new one. `temporal_reference` resets to 0 at the
+            // boundary, keeping each GOP's display order self-contained.
+            if gop_boundary && !self.gop_buf.is_empty() {
+                self.flush_gop(&mut out);
+            }
+            self.gop_buf.push(BufferedPicture {
+                tr,
+                nb_fields,
+                explicit_pts: explicit,
+                frame: Frame {
                     pts_ns: 0,
                     keyframe,
                     data,
-                duration_ns,
+                    duration_ns: None,
-            };
-
-            if self.frame_duration_ns > 0 {
-                // Reconstruct from display order; anchor to the real PES PTS so
-                // video stays in sync with the PES-timestamped audio.
-                match explicit {
-                    Some(p) => {
-                        self.anchor_index = Some(display_index);
-                        self.anchor_pts = p;
-                        // Backfill any leading frames held before the anchor was
-                        // known (still-frame / first-play opening): give each the
-                        // disc's real timeline relative to this anchor.
-                        for (di, mut held) in self.pending.drain(..) {
-                            held.pts_ns =
-                                p + (di as i64 - display_index as i64) * self.frame_duration_ns;
-                            out.push(held);
-                        }
-                        self.pending_bytes = 0;
-                        frame.pts_ns = p;
-                        out.push(frame);
-                    }
-                    None => match self.anchor_index {
-                        Some(ai) => {
-                            frame.pts_ns = self.anchor_pts
-                                + (display_index as i64 - ai as i64) * self.frame_duration_ns;
-                            out.push(frame);
-                        }
-                        None if self.pending.len() < MAX_PENDING_FRAMES
-                            && self.pending_bytes < MAX_PENDING_BYTES =>
-                        {
-                            // No anchor yet — hold so leading frames get the
-                            // disc's real timeline once the first PTS arrives,
-                            // not a 0 base.
-                            self.pending_bytes += frame.data.len();
-                            self.pending.push((display_index, frame));
-                        }
-                        None => {
-                            // Hold cap (count OR bytes) reached without a PTS
-                            // anchor ever arriving. Release everything held so
-                            // far on the 0-base timeline rather than growing the
-                            // buffer unbounded, then emit this frame the same way.
-                            for (di, mut held) in self.pending.drain(..) {
-                                held.pts_ns = di as i64 * self.frame_duration_ns;
-                                out.push(held);
-                            }
-                            self.pending_bytes = 0;
-                            frame.pts_ns = display_index as i64 * self.frame_duration_ns;
-                            out.push(frame);
-                        }
                 },
+            });
+            // Safety cap: a stream with no GOP/sequence boundaries would buffer
+            // unbounded. Force-flush a pathologically long run as its own GOP.
+            if self.gop_buf.len() >= MAX_PENDING_FRAMES {
+                self.flush_gop(&mut out);
             }
-            } else {
-                // No frame rate yet (no sequence header) — fall back to the
-                // nearest preceding PES timestamp.
-                frame.pts_ns = self.pts_for(pic_abs);
-                out.push(frame);
-            }
-
-            self.gop_count += 1;
             self.buf.drain(..end);
             self.base_offset = end_abs;
             // Drop PTS marks fully consumed by the emitted AU; keep the mark at
@@ -352,8 +295,64 @@ impl Mpeg2Parser {
                 }
             }
         }
+        // EOF: emit the final (possibly incomplete) GOP so nothing is dropped.
+        if force {
+            self.flush_gop(&mut out);
+        }
         out
     }
+
+    /// Emit the buffered GOP. Each frame's PTS is the display-order prefix-sum of
+    /// field durations from the timeline origin; its block duration is its own
+    /// `nb_fields × field_period`. Frames are emitted in DECODE (buffer) order —
+    /// B-frames keep their position with a correctly LOWER PTS, never reordered
+    /// (reordering emitted blocks is what corrupts the picture). The origin is
+    /// (re-)locked to the GOP's PES PTS; because that is a *presentation*
+    /// timestamp, backing out the carrying frame's display-field offset keeps the
+    /// timeline continuous and monotonic across GOP boundaries.
+    fn flush_gop(&mut self, out: &mut Vec<Frame>) {
+        let n = self.gop_buf.len();
+        if n == 0 {
+            return;
+        }
+        let field_period = self.frame_duration_ns / 2;
+        if field_period <= 0 {
+            // No sequence header / frame rate yet (malformed lead-in): emit in
+            // decode order off each AU's own PES PTS, with no field timing.
+            for bp in self.gop_buf.drain(..) {
+                let mut f = bp.frame;
+                f.pts_ns = bp.explicit_pts.unwrap_or(0);
+                out.push(f);
+            }
+            return;
+        }
+        // Fields displayed BEFORE each picture within this GOP: order indices by
+        // temporal_reference (display order) and prefix-sum `nb_fields`.
+        let mut order: Vec<usize> = (0..n).collect();
+        order.sort_by_key(|&i| self.gop_buf[i].tr);
+        let mut cum_before = vec![0u64; n];
+        let mut running = 0u64;
+        for &i in &order {
+            cum_before[i] = running;
+            running += self.gop_buf[i].nb_fields as u64;
+        }
+        let gop_fields = running;
+        let base = self.emitted_fields;
+        // (Re-)lock the timeline origin to the GOP's PES PTS.
+        for &i in &order {
+            if let Some(p) = self.gop_buf[i].explicit_pts {
+                self.origin_pts_ns = Some(p - field_period * (base + cum_before[i]) as i64);
+                break;
+            }
+        }
+        let origin = self.origin_pts_ns.unwrap_or(0);
+        for (i, mut bp) in self.gop_buf.drain(..).enumerate() {
+            bp.frame.pts_ns = origin + field_period * (base + cum_before[i]) as i64;
+            bp.frame.duration_ns = Some(bp.nb_fields as u64 * field_period as u64);
+            out.push(bp.frame);
+        }
+        self.emitted_fields += gop_fields;
+    }
 }
 
 impl CodecParser for Mpeg2Parser {
@@ -374,23 +373,9 @@ impl CodecParser for Mpeg2Parser {
     }
 
     fn flush(&mut self) -> Vec<Frame> {
-        let mut out = self.drain_complete_aus(true);
+        // drain_complete_aus(true) force-completes the trailing access unit and
-        // EOF: if no PES ever supplied a PTS/DTS, `self.pending` still holds the
+        // flushes the final GOP, so nothing is left buffered at EOF.
-        // frames buffered while waiting for an anchor (the opening keyframe +
+        self.drain_complete_aus(true)
-        // first ~20s). Without this they'd be silently dropped — a 100%-recovery
-        // violation. Emit each with the same 0-base fallback the no-anchor
-        // overflow arm uses (`display_index * frame_duration_ns`), ordered by
-        // display_index so presentation order is preserved.
-        if !self.pending.is_empty() {
-            let mut held: Vec<(u64, Frame)> = self.pending.drain(..).collect();
-            held.sort_by_key(|(di, _)| *di);
-            for (di, mut frame) in held {
-                frame.pts_ns = di as i64 * self.frame_duration_ns;
-                out.push(frame);
-            }
-            self.pending_bytes = 0;
-        }
-        out
     }
 
     fn codec_private(&self) -> Option<Vec<u8>> {
@@ -493,11 +478,145 @@ fn parse_aspect_ratio(hdr: &[u8]) -> Option<(u8, u8)> {
     Some(ASPECT_RATIOS[ar_code])
 }
 
+/// Number of field-display periods a coded picture occupies, from its picture
+/// coding extension (`00 00 01 B5`, ext-id `1000`), per ISO/IEC 13818-2 §6.3.10
+/// and ffmpeg `mpeg_field_start` (`nb_fields = repeat_pict + 2`). This is what
+/// times soft-telecined (2:3 pulldown) DVD video correctly: a
+/// `repeat_first_field` frame occupies 3 fields, a normal frame 2, so honoring
+/// it spreads the ~23.976 coded frames across the 29.97 display span with no
+/// gap (the "play, pause, play" judder). `progressive_sequence` comes from the
+/// sequence extension. Returns 2 (a normal frame) when no picture coding
+/// extension is present.
+fn picture_nb_fields(au: &[u8], progressive_sequence: bool) -> u8 {
+    let mut search = 0;
+    while let Some(q) = find_code(au, search, SEQ_EXT_CODE) {
+        search = q + 4;
+        // The picture coding extension is the B5 whose ext-id nibble is 1000.
+        if au.get(q + 4).map(|b| b >> 4) != Some(0b1000) {
+            continue;
+        }
+        // Extension bytes e2..=e4 = au[q+6 ..= q+8].
+        let (Some(&e2), Some(&e3), Some(&e4)) = (au.get(q + 6), au.get(q + 7), au.get(q + 8))
+        else {
+            break;
+        };
+        // picture_structure (e2 bits 1-0): 11 = frame picture. A field picture
+        // (01/10) occupies a single field; two combine into one frame upstream.
+        if e2 & 0x03 != 0b11 {
+            return 1;
+        }
+        let tff = (e3 >> 7) & 1;
+        let rff = (e3 >> 1) & 1;
+        let progressive_frame = (e4 >> 7) & 1;
+        let repeat_pict = if rff == 0 {
+            0
+        } else if progressive_sequence {
+            if tff == 1 { 4 } else { 2 }
+        } else if progressive_frame == 1 {
+            1
+        } else {
+            0
+        };
+        return repeat_pict + 2;
+    }
+    2
+}
+
+/// Read `progressive_sequence` from a captured sequence header's sequence
+/// extension (`00 00 01 B5`, ext-id `0001`). False when absent (MPEG-1 / no
+/// extension) — the interlaced default. Bit layout after the start code:
+/// ext-id(4) profile_and_level(8) **progressive_sequence(1)** … so it is bit 3
+/// of the second extension byte (`hdr[q+5]`).
+fn parse_progressive_sequence(hdr: &[u8]) -> bool {
+    let mut search = 0;
+    while let Some(q) = find_code(hdr, search, SEQ_EXT_CODE) {
+        search = q + 4;
+        if hdr.get(q + 4).map(|b| b >> 4) != Some(0b0001) {
+            continue;
+        }
+        return hdr.get(q + 5).map(|&b| (b >> 3) & 1 == 1).unwrap_or(false);
+    }
+    false
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
     use crate::mux::ts::PesPacket;
 
+    /// Build a picture coding extension (`00 00 01 B5`, ext-id 1000) carrying the
+    /// given pulldown flags, for `picture_nb_fields` tests.
+    fn pic_coding_ext(tff: u8, rff: u8, progressive_frame: u8, frame_picture: bool) -> Vec<u8> {
+        let e0 = 0x80; // ext-id 1000, f_code high nibble 0
+        let e1 = 0x00;
+        let e2 = if frame_picture { 0x03 } else { 0x01 }; // picture_structure bits 1-0
+        let e3 = (tff << 7) | (rff << 1);
+        let e4 = progressive_frame << 7;
+        vec![0x00, 0x00, 0x01, SEQ_EXT_CODE, e0, e1, e2, e3, e4]
+    }
+
+    #[test]
+    fn nb_fields_normal_frame_is_two() {
+        assert_eq!(picture_nb_fields(&pic_coding_ext(0, 0, 0, true), false), 2);
+    }
+
+    #[test]
+    fn nb_fields_telecine_repeat_field_is_three() {
+        // NTSC 2:3 soft telecine: interlaced sequence, progressive frame, rff=1.
+        assert_eq!(picture_nb_fields(&pic_coding_ext(0, 1, 1, true), false), 3);
+    }
+
+    #[test]
+    fn nb_fields_field_picture_is_one() {
+        assert_eq!(picture_nb_fields(&pic_coding_ext(0, 0, 0, false), false), 1);
+    }
+
+    #[test]
+    fn nb_fields_progressive_seq_rff_tff_is_six() {
+        assert_eq!(picture_nb_fields(&pic_coding_ext(1, 1, 0, true), true), 6);
+    }
+
+    #[test]
+    fn nb_fields_progressive_seq_rff_no_tff_is_four() {
+        assert_eq!(picture_nb_fields(&pic_coding_ext(0, 1, 0, true), true), 4);
+    }
+
+    #[test]
+    fn nb_fields_no_picture_ext_defaults_two() {
+        // A picture header with no coding extension → assume a normal 2-field frame.
+        assert_eq!(picture_nb_fields(&[0, 0, 1, 0x00, 0, 0], false), 2);
+    }
+
+    #[test]
+    fn progressive_sequence_parsed_from_seq_ext() {
+        // Sequence extension: 00 00 01 B5, e0 ext-id 0001 (0x1_), e1 bit3 = progressive_sequence.
+        assert!(parse_progressive_sequence(&[
+            0,
+            0,
+            1,
+            SEQ_EXT_CODE,
+            0x10,
+            0x08
+        ]));
+        assert!(!parse_progressive_sequence(&[
+            0,
+            0,
+            1,
+            SEQ_EXT_CODE,
+            0x10,
+            0x00
+        ]));
+        // No sequence extension at all → interlaced default (false).
+        assert!(!parse_progressive_sequence(&[
+            0,
+            0,
+            1,
+            SEQ_HEADER_CODE,
+            0,
+            0
+        ]));
+    }
+
     fn make_pes(data: Vec<u8>, pts: Option<i64>) -> PesPacket {
         PesPacket {
             pid: 0x1011,
@@ -651,9 +770,11 @@ mod tests {
     }
 
     #[test]
-    fn two_pictures_emit_two_frames_at_the_boundary() {
+    fn two_pictures_in_one_gop_emit_both_on_flush() {
-        // pic1's frame is emitted as soon as pic2's start code is seen; pic2 on
+        // Two pictures with no GOP/sequence boundary between them are ONE GOP.
-        // flush. Each frame contains exactly its own picture.
+        // The VFR timeline needs the whole GOP (a P-frame's PTS depends on its
+        // later B-frames), so they buffer until the GOP closes / EOF, then emit
+        // in DECODE order, each containing exactly its own picture.
         let mut parser = Mpeg2Parser::new();
 
         let mut pic1 = make_picture_header(PICTURE_TYPE_I);
@@ -664,17 +785,13 @@ mod tests {
         let mut stream = pic1.clone();
         stream.extend_from_slice(&pic2);
 
-        let mut frames = parser.parse(&make_pes(stream, Some(0)));
+        let frames = parser.parse(&make_pes(stream, Some(0)));
-        assert_eq!(
+        assert!(frames.is_empty(), "same GOP — buffered until flush");
-            frames.len(),
+
-            1,
+        let frames = parser.flush();
-            "first picture emitted at second's boundary"
+        assert_eq!(frames.len(), 2);
-        );
         assert_eq!(frames[0].data, pic1);
         assert!(frames[0].keyframe);
-
-        frames.extend(parser.flush());
-        assert_eq!(frames.len(), 2);
         assert_eq!(frames[1].data, pic2);
         assert!(!frames[1].keyframe);
     }
@@ -703,23 +820,24 @@ mod tests {
 
     #[test]
     fn each_picture_gets_the_pts_of_the_pes_that_began_it() {
+        // With no sequence header (no frame rate) the parser falls back to each
+        // AU's own PES PTS. Both pictures are one GOP → emitted on flush in
+        // decode order, each carrying the PTS of the PES that began it.
         let mut parser = Mpeg2Parser::new();
 
-        // PES 1: pic1 (PTS 90000) + start of pic2's bytes carried later.
         let mut pic1 = make_picture_header(PICTURE_TYPE_I);
         pic1.extend_from_slice(&vec![0x11; 50]);
         let frames1 = parser.parse(&make_pes(pic1, Some(90000)));
-        assert!(frames1.is_empty(), "pic1 awaits pic2's boundary");
+        assert!(frames1.is_empty(), "buffered until flush");
 
-        // PES 2: pic2 (PTS 180000).
         let mut pic2 = make_picture_header(2);
         pic2.extend_from_slice(&vec![0x22; 50]);
-        let mut frames = parser.parse(&make_pes(pic2, Some(180000)));
+        let frames2 = parser.parse(&make_pes(pic2, Some(180000)));
-        assert_eq!(frames.len(), 1, "pic1 emitted when pic2 starts");
+        assert!(frames2.is_empty(), "same GOP — still buffered");
-        assert_eq!(frames[0].pts_ns, 1_000_000_000, "pic1 → PTS 90000");
 
-        frames.extend(parser.flush());
+        let frames = parser.flush();
         assert_eq!(frames.len(), 2);
+        assert_eq!(frames[0].pts_ns, 1_000_000_000, "pic1 → PTS 90000");
         assert_eq!(frames[1].pts_ns, 2_000_000_000, "pic2 → PTS 180000");
     }
 
@@ -761,6 +879,89 @@ mod tests {
         assert_eq!(frames[0].duration_ns, Some(40_000_000));
     }
 
+    /// A frame-picture AU with a picture coding extension carrying pulldown
+    /// flags (progressive_frame=1, so rff=1 → 3 fields), for VFR timing tests.
+    fn make_pulldown_picture(coding_type: u8, tr: u16, rff: u8) -> Vec<u8> {
+        let mut au = make_picture_header_tr(coding_type, tr);
+        // 00 00 01 B5 | e0 ext-id 1000 | e1 | e2 frame-pic | e3 rff<<1 | e4 prog_frame
+        au.extend_from_slice(&[
+            0x00,
+            0x00,
+            0x01,
+            SEQ_EXT_CODE,
+            0x80,
+            0x00,
+            0x03,
+            rff << 1,
+            0x80,
+        ]);
+        au.extend_from_slice(&[0xAA; 16]);
+        au
+    }
+
+    #[test]
+    fn telecine_pts_accumulates_by_field_durations_not_a_fixed_grid() {
+        // NTSC film, frame_rate_code 4 = 29.97 → field_period ≈ 16.683 ms. A 2:3
+        // frame (rff=1) occupies 3 fields, a 2:2 frame 2 fields. PTS must
+        // accumulate by ACTUAL field durations so the next frame starts exactly
+        // when this one ends — closing the fixed-29.97-grid gap that judders.
+        let mut p = Mpeg2Parser::new();
+        let field = 1_000_000_000i64 * 1001 / 30000 / 2;
+
+        let mut a = make_seq_header(720, 480, 2, 4);
+        a.extend_from_slice(&gop());
+        a.extend(make_pulldown_picture(1, 0, 1)); // I tr0, 3 fields, PES anchor 0
+        a.extend(make_pulldown_picture(2, 1, 0)); // P tr1, 2 fields
+        let mut frames = p.parse(&make_pes(a, Some(0)));
+        frames.extend(p.flush());
+
+        assert_eq!(frames.len(), 2);
+        assert_eq!(frames[0].pts_ns, 0, "I anchored to PES PTS 0");
+        assert_eq!(
+            frames[0].duration_ns,
+            Some(3 * field as u64),
+            "I = 3 fields"
+        );
+        assert_eq!(
+            frames[1].pts_ns,
+            3 * field,
+            "P starts exactly at I-end (3 fields), not the 1/29.97 grid"
+        );
+        assert_eq!(
+            frames[1].duration_ns,
+            Some(2 * field as u64),
+            "P = 2 fields"
+        );
+        assert!(frames[1].pts_ns > frames[0].pts_ns, "strictly monotonic");
+    }
+
+    #[test]
+    fn b_frames_emit_in_decode_order_with_lower_display_pts() {
+        // Decode order I(tr0) P(tr2) B(tr1): emitted in DECODE order, but the
+        // B-frame carries a LOWER (earlier) display PTS than the P that precedes
+        // it in the stream — never reordered (reordering corrupts the picture).
+        let mut p = Mpeg2Parser::new();
+        let field = 1_000_000_000i64 * 1001 / 30000 / 2;
+
+        let mut a = make_seq_header(720, 480, 2, 4);
+        a.extend_from_slice(&gop());
+        a.extend(make_pulldown_picture(1, 0, 0)); // I tr0 (displays 1st), PES anchor 0
+        a.extend(make_pulldown_picture(2, 2, 0)); // P tr2 (displays 3rd)
+        a.extend(make_pulldown_picture(3, 1, 0)); // B tr1 (displays 2nd)
+        let mut frames = p.parse(&make_pes(a, Some(0)));
+        frames.extend(p.flush());
+
+        assert_eq!(frames.len(), 3);
+        assert!(frames[0].keyframe, "decode order preserved: I first");
+        assert_eq!(frames[0].pts_ns, 0, "I (tr0) displays 1st");
+        assert_eq!(frames[1].pts_ns, 4 * field, "P (tr2) displays 3rd");
+        assert_eq!(frames[2].pts_ns, 2 * field, "B (tr1) displays 2nd");
+        assert!(
+            frames[2].pts_ns < frames[1].pts_ns,
+            "B emitted AFTER P (decode order) but displays BEFORE it (lower PTS)"
+        );
+    }
+
     #[test]
     fn temporal_reference_resets_each_gop_via_gop_base() {
         // Across a GOP boundary, temporal_reference restarts at 0 but the
@@ -973,9 +1174,10 @@ mod tests {
         let mut a = make_seq_header(1920, 1080, 3, 4);
         a.extend_from_slice(&make_picture_header(PICTURE_TYPE_I));
         a.extend_from_slice(&[0xAA; 20]);
-        a.extend_from_slice(&gop()); // boundary → AU A emits
+        a.extend_from_slice(&gop()); // trailing GOP header starts the next GOP
-        let fa = parser.parse(&make_pes(a, Some(0)));
+        let _fa = parser.parse(&make_pes(a, Some(0)));
-        assert_eq!(fa.len(), 1);
+        // Header A is captured during parse (codec_private) even though its GOP
+        // only emits once header B's picture closes it / on flush.
         assert_eq!(parser.resolution(), Some((1920, 1080)));
 
         // AU B: a NEW 720x480 seq header + I picture. Its extension/header must
@@ -1062,11 +1264,12 @@ mod tests {
         // > MAX_AU_BUFFER of slice bytes with no following picture/seq/GOP.
         data.extend(std::iter::repeat_n(0xAA, MAX_AU_BUFFER + 1024));
         let frames = parser.parse(&make_pes(data, Some(0)));
-        assert_eq!(
+        assert!(
-            frames.len(),
+            frames.is_empty(),
-            1,
+            "over-cap AU is force-COMPLETED (bounded) but buffered in its GOP"
-            "over-cap AU force-flushed rather than buffered"
         );
+        let frames = parser.flush();
+        assert_eq!(frames.len(), 1, "force-flushed at EOF, not dropped");
         assert!(frames[0].keyframe);
     }
 

src/mux/ebml.rs

@@ -435,17 +435,18 @@ pub const FIELD_ORDER: u32 = 0x9D;
 // FlagInterlaced values: 1 = interlaced, 2 = progressive (0 = undetermined).
 pub const INTERLACED_INTERLACED: u64 = 1;
 pub const INTERLACED_PROGRESSIVE: u64 = 2;
-// FieldOrder values (Matroska): 0/2 = top-field-first, 1/9 = bottom-field-first.
+// FieldOrder values (Matroska / RFC 9559, element 0x9D): 1 = top-field-first,
-// NTSC DVD (480i), PAL DVD (576i) and HD (1080i) are all emitted top-field-first
+// 6 = bottom-field-first, 2 = undetermined, 0 = progressive. NTSC DVD (480i),
-// — the muxer hardcodes TFF for every interlaced DVD/HD source (DV is the only
+// PAL DVD (576i) and HD (1080i) are all emitted top-field-first — the muxer
-// common BFF source and freemkv does not produce it). 0xFF is our sentinel for
+// hardcodes TFF for every interlaced DVD/HD source (DV is the only common BFF
+// source and freemkv does not produce it). 0xFF is our sentinel for
 // "undetermined / omit".
-pub const FIELD_ORDER_TFF: u8 = 2;
+pub const FIELD_ORDER_TFF: u8 = 1;
 // Bottom-field-first. Retained for completeness/round-trip tests; the muxer
 // emits TFF for all DVD/HD interlaced content (DV is the only common BFF
 // source and freemkv does not produce it).
 #[allow(dead_code)]
-pub const FIELD_ORDER_BFF: u8 = 9;
+pub const FIELD_ORDER_BFF: u8 = 6;
 pub const FIELD_ORDER_UNDETERMINED: u8 = 0xFF;
 pub const DISPLAY_WIDTH: u32 = 0x54B0;
 pub const DISPLAY_HEIGHT: u32 = 0x54BA;

src/sector/decrypting.rs

@@ -149,7 +149,7 @@ impl<S: SectorSource> SectorSource for DecryptingSectorSource<S> {
         // count is bytes of scrambled units no key could decrypt — silent
         // decrypt loss the TS assembler will drop. Tally it so the mux loss
         // accounting (and the abort gate) can see partial decrypt failure.
-        let dropped = decrypt_sectors(&mut buf[..n], &self.keys, self.unit_key_idx)?;
+        let dropped = decrypt_sectors(&mut buf[..n], &mut self.keys, self.unit_key_idx)?;
         if dropped > 0 {
             self.decrypt_dropped
                 .fetch_add(dropped as u64, Ordering::Relaxed);

tests/pass_n_patch_fix.rs

@@ -31,13 +31,13 @@ fn decrypt_sectors_with_aacs_keys_works() {
     aacs::decrypt_unit(&mut unit, &unit_key); // decrypt_unit is idempotent on already-encrypted data
 
     // Now we have encrypted data - create DecryptKeys with actual keys
-    let keys = DecryptKeys::Aacs {
+    let mut keys = DecryptKeys::Aacs {
         unit_keys: vec![(0u32, unit_key)],
         read_data_key: None,
     };
 
     // decrypt_sectors should handle this without error
-    let result = libfreemkv::decrypt::decrypt_sectors(&mut unit, &keys, 0);
+    let result = libfreemkv::decrypt::decrypt_sectors(&mut unit, &mut keys, 0);
 
     assert!(
         result.is_ok(),
@@ -50,8 +50,8 @@ fn decrypt_sectors_with_aacs_keys_works() {
 fn decrypt_sectors_with_none_keys_is_noop() {
     let mut sector = vec![0x42u8; 2048];
 
-    let keys = DecryptKeys::None;
+    let mut keys = DecryptKeys::None;
-    let result = libfreemkv::decrypt::decrypt_sectors(&mut sector, &keys, 0);
+    let result = libfreemkv::decrypt::decrypt_sectors(&mut sector, &mut keys, 0);
 
     assert!(result.is_ok());
     assert_eq!(
@@ -70,10 +70,10 @@ fn decrypt_sectors_with_css_keys_works() {
     sector[0x14] |= 0x30;
 
     let title_key: [u8; 5] = [0x42, 0x13, 0x37, 0xBE, 0xEF]; // Not used - defined later
-    let keys = DecryptKeys::Css { title_key };
+    let mut keys = DecryptKeys::Css { title_key };
 
     // Descramble (CSS uses same operation for encrypt/decrypt)
-    libfreemkv::decrypt::decrypt_sectors(&mut sector, &keys, 0).unwrap();
+    libfreemkv::decrypt::decrypt_sectors(&mut sector, &mut keys, 0).unwrap();
 
     // Flag should be cleared
     assert_eq!(sector[0x14] & 0x30, 0x00, "CSS flag should be cleared");