mux: reconstruct display-order PTS for sparse-PTS program streams

HD-DVD EVO (and DVD VOB) program streams timestamp video at GOP
granularity: only one access unit per GOP carries a PES PTS. The H.264 /
HEVC / VC-1 parsers collapsed a missing PTS to 0, so on such a source
every non-anchor frame landed on the same block timestamp and a decoder
reported "non monotonically increasing dts".

Add a shared SparsePtsReorder that rebuilds a display-order PTS per frame
from the coded picture type (I/P/B) plus the sparse anchor PTS, with a
per-frame duration self-calibrated from the spacing between consecutive
GOP anchors (no external frame-rate needed). Display order is derived via
the classic single-anchor-delay rule (an anchor displays only after the
previously-held anchor; a B displays immediately), exact for the
non-hierarchical GOP structures HD-DVD H.264/VC-1 use. It mirrors the
MPEG-2 parser's GOP-buffered origin-locking.

Gated to the program-stream path only: the three parsers enable it via
with_ps_reorder(is_dvd_ps), so the BD/UHD transport path (per-frame PTS)
is byte-identical and untouched.

src/mux/codec/h264.rs

@@ -52,6 +52,10 @@ pub struct H264Parser {
     // the stale avcC copy after a mid-title redefinition.
     cur_sps: Option<Vec<u8>>,
     cur_pps: Option<Vec<u8>>,
+    /// Display-order PTS reconstruction, enabled only on the program-stream
+    /// (HD-DVD EVO) path where the source stamps a PTS once per GOP. `None` on
+    /// the BD/UHD transport path, which carries a per-frame PTS.
+    reorder: Option<super::reorder::SparsePtsReorder>,
 }
 
 impl Default for H264Parser {
@@ -68,6 +72,25 @@ impl H264Parser {
             pps: None,
             cur_sps: None,
             cur_pps: None,
+            reorder: None,
+        }
+    }
+
+    /// Enable display-order PTS reconstruction for a program-stream source.
+    /// No-op (leaves timestamps as parsed) for a transport-stream source.
+    pub(crate) fn with_ps_reorder(mut self, enabled: bool) -> Self {
+        if enabled {
+            self.reorder = Some(super::reorder::SparsePtsReorder::new());
+        }
+        self
+    }
+
+    /// Route a finished frame through the PTS reorderer when enabled, else emit
+    /// it directly (unchanged transport-stream behaviour).
+    fn finish(&mut self, explicit: Option<i64>, frame: Frame) -> Vec<Frame> {
+        match self.reorder.as_mut() {
+            Some(r) => r.push(explicit, frame),
+            None => vec![frame],
         }
     }
 }
@@ -152,7 +175,8 @@ impl CodecParser for H264Parser {
         // decode order and the player reorders by timecode. Use PTS, not DTS —
         // DTS presents B-frames in decode order (visible judder) and breaks
         // PTS-based seeking. Fall back to DTS only if PTS is absent.
-        let pts_ns = pes.pts.or(pes.dts).map(pts_to_ns).unwrap_or(0);
+        let explicit_pts = pes.pts.or(pes.dts).map(pts_to_ns);
+        let pts_ns = explicit_pts.unwrap_or(0);
 
         // Single pass: detect IDR keyframes, seed/strip param sets, and convert
         // Annex B (start-code prefixed) NALUs to length-prefixed NALUs (MKV with
@@ -236,7 +260,7 @@ impl CodecParser for H264Parser {
             }
         }
 
-        vec![Frame {
+        let frame = Frame {
             // Coding-type only: H.264 field order is not decoded here, so
             // `field_order()` stays `None` — honestly absent, never guessed.
             coding: coding_type.map(PictureInfo::coding_type_only),
@@ -248,7 +272,15 @@ impl CodecParser for H264Parser {
             discontinuity: pes.discontinuity,
             data: frame_data,
             duration_ns: None,
-        }]
+        };
+        self.finish(explicit_pts, frame)
+    }
+
+    fn flush(&mut self) -> Vec<Frame> {
+        match self.reorder.as_mut() {
+            Some(r) => r.flush(),
+            None => Vec::new(),
+        }
     }
 
     fn codec_private(&self) -> Option<Vec<u8>> {
@@ -667,6 +699,71 @@ mod tests {
         );
     }
 
+    /// End-to-end sparse-PTS reconstruction through the REAL parser + reorder:
+    /// a program-stream source (`with_ps_reorder(true)`) that stamps a PTS only
+    /// on each GOP's I-frame must yield distinct, display-ordered PTS for every
+    /// frame — the property the mkv muxer needs so a decoder derives monotonic
+    /// DTS. Without the reorder the non-anchor frames all collapse to one PTS.
+    #[test]
+    fn h264_ps_reorder_reconstructs_distinct_display_pts() {
+        use super::super::coding::CodingType;
+        // slice bodies: 0x88 → I (IDR), 0x98 → P, 0x9C → B (non-IDR).
+        // Decode order of a classic single-B GOP: I P B P B.
+        let gop = |anchor_pts: Option<i64>| {
+            vec![
+                (NAL_SLICE_IDR, 0x88u8, anchor_pts),
+                (NAL_SLICE_NON_IDR, 0x98, None),
+                (NAL_SLICE_NON_IDR, 0x9C, None),
+                (NAL_SLICE_NON_IDR, 0x98, None),
+                (NAL_SLICE_NON_IDR, 0x9C, None),
+            ]
+        };
+
+        let feed = |reorder: bool| -> Vec<super::super::Frame> {
+            let mut p = H264Parser::new().with_ps_reorder(reorder);
+            let mut out = Vec::new();
+            // Two GOPs; the second I carries an anchor 5 frames later (90 kHz:
+            // 5 * 3750 = 18750 ticks) so the reorder can calibrate a duration.
+            for (nal, body, pts) in gop(Some(0)).into_iter().chain(gop(Some(18750))) {
+                out.extend(p.parse(&make_pes(h264_nal(nal, &[body]), pts)));
+            }
+            out.extend(p.flush());
+            out
+        };
+
+        // With reorder ON: all 10 frames emitted, every PTS distinct.
+        let recon = feed(true);
+        assert_eq!(recon.len(), 10, "no frame dropped");
+        let mut pts: Vec<i64> = recon.iter().map(|f| f.pts_ns).collect();
+        let n = pts.len();
+        pts.sort_unstable();
+        pts.dedup();
+        assert_eq!(
+            pts.len(),
+            n,
+            "reconstructed PTS are all distinct (no DTS collision)"
+        );
+
+        // The GOP's first-displayed frame is the I; the B in decode position 2
+        // must display BEFORE the P in decode position 1 (classic reorder).
+        let g1 = &recon[0..5];
+        assert_eq!(g1[0].coding.unwrap().coding_type(), CodingType::I);
+        assert!(
+            g1[2].pts_ns < g1[1].pts_ns,
+            "B (decode idx 2) displays before its forward-anchor P (decode idx 1)"
+        );
+        assert_eq!(g1[0].pts_ns, 0, "GOP anchor locks the I to its true PTS");
+
+        // With reorder OFF (transport-stream behaviour): the non-anchor frames
+        // collapse to a single colliding PTS — the bug this fix removes.
+        let raw = feed(false);
+        let collisions = raw.iter().filter(|f| f.pts_ns == 0).count();
+        assert!(
+            collisions >= 8,
+            "without reorder the sparse-PTS frames collide on 0 (got {collisions})"
+        );
+    }
+
     /// Regression (Fight Club bug, H.264 variant): PPS id 0 = body A (→ avcC),
     /// redefined to B, then switched BACK to A. A streaming decoder is on B; the
     /// revert to A == avcC must still be emitted in-band or the A-segment

src/mux/codec/hevc.rs

@@ -166,6 +166,10 @@ pub struct HevcParser {
     // colour-volume metadata is ever fabricated.
     sei_mastering: Option<MasteringDisplay>,
     sei_content_light: Option<ContentLightLevel>,
+    /// Display-order PTS reconstruction, enabled only on the program-stream
+    /// path where the source stamps a PTS once per GOP. `None` on the BD/UHD
+    /// transport path (the common HEVC case), which carries a per-frame PTS.
+    reorder: Option<super::reorder::SparsePtsReorder>,
 }
 
 /// Mastering Display Colour Volume payload (Rec. ITU-T H.265 D.2.28),
@@ -234,6 +238,25 @@ impl HevcParser {
             pts_wrap_offset: 0,
             sei_mastering: None,
             sei_content_light: None,
+            reorder: None,
+        }
+    }
+
+    /// Enable display-order PTS reconstruction for a program-stream source.
+    /// No-op (leaves timestamps as parsed) for a transport-stream source.
+    pub(crate) fn with_ps_reorder(mut self, enabled: bool) -> Self {
+        if enabled {
+            self.reorder = Some(super::reorder::SparsePtsReorder::new());
+        }
+        self
+    }
+
+    /// Route a finished frame through the PTS reorderer when enabled, else emit
+    /// it directly (unchanged transport-stream behaviour).
+    fn finish(&mut self, explicit: Option<i64>, frame: Frame) -> Vec<Frame> {
+        match self.reorder.as_mut() {
+            Some(r) => r.push(explicit, frame),
+            None => vec![frame],
         }
     }
 
@@ -443,7 +466,8 @@ impl CodecParser for HevcParser {
         // block timecode monotonic in storage order, which presents B-frames in
         // decode order (visible judder / wrong frames) and breaks PTS-based
         // seeking. Fall back to DTS only if PTS is somehow absent.
-        let pts_ns = pes.pts.or(pes.dts).map(pts_to_ns).unwrap_or(0);
+        let explicit_pts = pes.pts.or(pes.dts).map(pts_to_ns);
+        let pts_ns = explicit_pts.unwrap_or(0);
 
         // Auto-detect a non-seamless clip boundary from the bitstream. freemkv
         // reads a BD title's clips as ONE concatenated sector stream and the
@@ -651,7 +675,7 @@ impl CodecParser for HevcParser {
         // from the first coded picture before writing the track header). `None`
         // until both SEI present → SDR / no-SEI tracks carry nothing.
         let hdr10 = self.hdr10();
-        vec![Frame {
+        let frame = Frame {
             // Coding-type only: HEVC field order (pic_struct, from a pic_timing
             // SEI) is not decoded here, so field_order() stays None — honestly
             // absent, never guessed. HDR10 metadata is attached when measured.
@@ -666,7 +690,15 @@ impl CodecParser for HevcParser {
             discontinuity: pes.discontinuity,
             data: frame_data,
             duration_ns: None,
-        }]
+        };
+        self.finish(explicit_pts, frame)
+    }
+
+    fn flush(&mut self) -> Vec<Frame> {
+        match self.reorder.as_mut() {
+            Some(r) => r.flush(),
+            None => Vec::new(),
+        }
     }
 
     fn codec_private(&self) -> Option<Vec<u8>> {

src/mux/codec/mod.rs

@@ -25,6 +25,8 @@ pub mod lpcm;
 pub mod mpeg2;
 /// HDMV PGS (Presentation Graphics Stream) subtitle parser.
 pub mod pgs;
+/// Display-order PTS reconstruction for sparse-PTS program-stream video.
+pub(crate) mod reorder;
 /// Shared MPEG/Annex-B start-code scanning helpers.
 pub(crate) mod startcode;
 /// Dolby TrueHD / Atmos elementary-stream parser.
@@ -166,10 +168,14 @@ pub fn parser_for_codec(
     is_dvd_ps: bool,
 ) -> Box<dyn CodecParser> {
     match codec {
-        Codec::H264 => Box::new(h264::H264Parser::new()),
+        // `is_dvd_ps` marks a program-stream source (DVD VOB / HD-DVD EVO), whose
-        Codec::Hevc => Box::new(hevc::HevcParser::new()),
+        // video is timestamped only at GOP granularity. On that path the H.264 /
+        // HEVC / VC-1 parsers reconstruct a display-order PTS per frame; on the
+        // BD/UHD transport path (per-frame PTS) they leave timestamps untouched.
+        Codec::H264 => Box::new(h264::H264Parser::new().with_ps_reorder(is_dvd_ps)),
+        Codec::Hevc => Box::new(hevc::HevcParser::new().with_ps_reorder(is_dvd_ps)),
         Codec::Mpeg2 => Box::new(mpeg2::Mpeg2Parser::new()),
-        Codec::Vc1 => Box::new(vc1::Vc1Parser::new()),
+        Codec::Vc1 => Box::new(vc1::Vc1Parser::new().with_ps_reorder(is_dvd_ps)),
         Codec::Ac3 | Codec::Ac3Plus => Box::new(ac3::Ac3Parser::new()),
         Codec::DtsHdMa | Codec::DtsHdHr | Codec::Dts => Box::new(dts::DtsParser::new()),
         Codec::TrueHd => Box::new(truehd::TrueHdParser::new()),

src/mux/codec/reorder.rs

@@ -0,0 +1,318 @@
+//! Display-order PTS reconstruction for sparse-PTS program-stream video.
+//!
+//! MPEG program streams (DVD VOB, HD-DVD EVO) timestamp video at GOP
+//! granularity: only one access unit per GOP carries a PES PTS, and the rest
+//! arrive with none. The H.264 / HEVC / VC-1 parsers collapse a missing PTS to
+//! `0` (`pes.pts.or(dts).unwrap_or(0)`), so on such a source every non-anchor
+//! frame lands on the same block timestamp. A decoder then cannot order them and
+//! reports "non monotonically increasing dts". (The MPEG-2 parser already avoids
+//! this by reconstructing per-picture PTS from `temporal_reference`; these three
+//! codecs carry no such field.)
+//!
+//! [`SparsePtsReorder`] reconstructs a display-order PTS for every frame from two
+//! signals the parsers already provide — the coded picture type (I/P/B) and the
+//! sparse anchor PTS — plus a per-frame duration self-calibrated from the spacing
+//! between consecutive GOP anchors (no external frame-rate needed). It mirrors
+//! the MPEG-2 parser's GOP-buffered origin-locking, but derives display order via
+//! the classic single-anchor-delay rule instead of `temporal_reference`:
+//!
+//! - In DECODE order an anchor (I/P) is stored before the B-frames that
+//!   reference it forward, so decode `I P B P B` displays as `I B P B P`.
+//! - The rule that produces that mapping: an anchor is displayed only after the
+//!   previously-held anchor; a B-frame displays immediately. This is exact for
+//!   the classic (non-hierarchical) GOP structures HD-DVD H.264/VC-1 use.
+//!
+//! This reconstruction is applied ONLY on the program-stream path
+//! (`ContentFormat::MpegPs`). BD/UHD transport streams carry a per-frame PTS and
+//! are never routed through it, so the primary decode path is untouched.
+
+use super::Frame;
+use super::coding::CodingType;
+
+/// Fallback per-frame duration (ns) when the anchor spacing cannot calibrate one
+/// (a stream with a single GOP, or no anchor PTS at all): 24000/1001 fps film,
+/// the dominant HD-DVD cadence. Only affects intra-GOP spacing — each GOP's
+/// origin is re-locked to its own anchor PTS, so a wrong fallback cannot drift
+/// the timeline across GOPs.
+const FALLBACK_FRAME_DUR_NS: i64 = 1_001_000_000 / 24;
+
+/// One buffered coded picture awaiting its GOP's completion.
+struct Pending {
+    /// Explicit PES PTS (ns) for this AU, or `None` when the source omitted it.
+    explicit: Option<i64>,
+    /// Coded picture type; `P` (anchor) when the parser could not determine it,
+    /// so an unknown frame is never mis-placed as a bi-predicted B.
+    ctype: CodingType,
+    frame: Frame,
+}
+
+/// A completed GOP, buffered until the NEXT GOP's anchor is known so a per-frame
+/// duration can be calibrated from the two anchors before its frames are emitted.
+struct Gop {
+    pend: Vec<Pending>,
+    /// Display index (0-based) of each `pend` entry, in `pend` (decode) order.
+    dispidx: Vec<i64>,
+    /// Display-frame count (== `pend.len()`).
+    count: i64,
+    /// The anchor: `(explicit_pts, dispidx)` of the first buffered frame that
+    /// carried an explicit PTS, used to lock the display origin. `None` when the
+    /// GOP carried no PTS at all (origin then continues from the running base).
+    anchor: Option<(i64, i64)>,
+}
+
+/// Reconstructs display-order PTS for a sparse-PTS video elementary stream.
+pub(crate) struct SparsePtsReorder {
+    /// Frames of the GOP currently accumulating, in decode order.
+    cur: Vec<Pending>,
+    /// The previously-completed GOP, held one step so its duration can be
+    /// calibrated from the next GOP's anchor before it is emitted.
+    held: Option<Gop>,
+    /// Self-calibrated per-frame display duration (ns); 0 until two anchors seen.
+    dur_ns: i64,
+    /// Display time (ns) at which the next emitted GOP should begin, when its own
+    /// anchor is absent. Advanced by each emitted GOP.
+    next_start_ns: i64,
+}
+
+impl SparsePtsReorder {
+    pub(crate) fn new() -> Self {
+        Self {
+            cur: Vec::new(),
+            held: None,
+            dur_ns: 0,
+            next_start_ns: 0,
+        }
+    }
+
+    /// Feed one parsed frame with its explicit PES PTS (or `None`). Returns any
+    /// frames whose display PTS is now finalized (emitted in decode order).
+    pub(crate) fn push(&mut self, explicit: Option<i64>, frame: Frame) -> Vec<Frame> {
+        let ctype = frame
+            .coding
+            .map(|c| c.coding_type())
+            .unwrap_or(CodingType::P);
+        // A keyframe opens a new GOP: the picture already accumulated in `cur` is
+        // a complete GOP. Complete it (this frame belongs to the NEW GOP).
+        let mut out = Vec::new();
+        if frame.keyframe && !self.cur.is_empty() {
+            out = self.complete_current_gop();
+        }
+        self.cur.push(Pending {
+            explicit,
+            ctype,
+            frame,
+        });
+        out
+    }
+
+    /// Flush all buffered frames at end of stream.
+    pub(crate) fn flush(&mut self) -> Vec<Frame> {
+        let mut out = self.complete_current_gop();
+        if let Some(gop) = self.held.take() {
+            out.extend(self.emit_gop(gop));
+        }
+        out
+    }
+
+    /// Move `cur` into a completed [`Gop`]; if a GOP was already held, calibrate
+    /// the duration from the two anchors and emit the held one.
+    fn complete_current_gop(&mut self) -> Vec<Frame> {
+        if self.cur.is_empty() {
+            return Vec::new();
+        }
+        let pend = std::mem::take(&mut self.cur);
+        let dispidx = display_indices(pend.iter().map(|p| p.ctype));
+        let count = pend.len() as i64;
+        let anchor = pend
+            .iter()
+            .zip(&dispidx)
+            .find_map(|(p, &d)| p.explicit.map(|pts| (pts, d)));
+        let gop = Gop {
+            pend,
+            dispidx,
+            count,
+            anchor,
+        };
+
+        let mut out = Vec::new();
+        match self.held.take() {
+            Some(held) => {
+                // Calibrate a per-frame duration from the two anchors' spacing,
+                // spread across the held GOP's display-frame count. Approximate
+                // (assumes both anchors sit at a similar relative display slot),
+                // but each GOP re-locks its own origin, so the estimate only sets
+                // intra-GOP spacing.
+                if self.dur_ns == 0 {
+                    if let (Some((p_held, _)), Some((p_next, _))) = (held.anchor, gop.anchor) {
+                        let span = p_next - p_held;
+                        if span > 0 && held.count > 0 {
+                            self.dur_ns = (span / held.count).max(1);
+                        }
+                    }
+                }
+                out = self.emit_gop(held);
+                self.held = Some(gop);
+            }
+            None => self.held = Some(gop),
+        }
+        out
+    }
+
+    /// Assign each frame in `gop` its display PTS and return them in decode order.
+    fn emit_gop(&mut self, gop: Gop) -> Vec<Frame> {
+        let dur = if self.dur_ns > 0 {
+            self.dur_ns
+        } else {
+            FALLBACK_FRAME_DUR_NS
+        };
+        // Lock the display origin: prefer the GOP's own anchor PTS (back out its
+        // display offset); otherwise continue from the running base.
+        let origin = match gop.anchor {
+            Some((pts, didx)) => pts - didx * dur,
+            None => self.next_start_ns,
+        };
+        let Gop {
+            pend,
+            dispidx,
+            count,
+            ..
+        } = gop;
+        let mut out = Vec::with_capacity(pend.len());
+        for (mut p, didx) in pend.into_iter().zip(dispidx) {
+            p.frame.pts_ns = origin + didx * dur;
+            out.push(p.frame);
+        }
+        // Next GOP with no anchor continues after this one's last display slot.
+        self.next_start_ns = origin + count * dur;
+        out
+    }
+}
+
+/// Display index (0-based, decode order in → decode order out) for a GOP's coded
+/// picture types via the classic single-anchor-delay reorder: an anchor (I/P) is
+/// displayed only after the previously-held anchor; a B displays immediately.
+/// Decode `I P B P B` → display indices `[0, 2, 1, 4, 3]` (display `I B P B P`).
+fn display_indices(types: impl Iterator<Item = CodingType>) -> Vec<i64> {
+    let types: Vec<CodingType> = types.collect();
+    let mut disp = vec![0i64; types.len()];
+    let mut held: Option<usize> = None;
+    let mut cursor = 0i64;
+    for (i, &c) in types.iter().enumerate() {
+        match c {
+            CodingType::I | CodingType::P => {
+                if let Some(h) = held {
+                    disp[h] = cursor;
+                    cursor += 1;
+                }
+                held = Some(i);
+            }
+            CodingType::B => {
+                disp[i] = cursor;
+                cursor += 1;
+            }
+        }
+    }
+    if let Some(h) = held {
+        disp[h] = cursor;
+    }
+    disp
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::mux::codec::coding::PictureInfo;
+
+    fn frame(ctype: CodingType, keyframe: bool) -> Frame {
+        Frame {
+            keyframe,
+            coding: Some(PictureInfo::coding_type_only(ctype)),
+            ..Default::default()
+        }
+    }
+
+    #[test]
+    fn display_indices_map_classic_gop() {
+        use CodingType::*;
+        // decode I P B P B  ->  display I B P B P
+        let d = display_indices([I, P, B, P, B].into_iter());
+        assert_eq!(d, vec![0, 2, 1, 4, 3]);
+    }
+
+    #[test]
+    fn display_indices_all_anchors_are_identity() {
+        use CodingType::*;
+        let d = display_indices([I, P, P, P].into_iter());
+        assert_eq!(d, vec![0, 1, 2, 3]);
+    }
+
+    #[test]
+    fn reconstructs_monotonic_display_pts_from_one_anchor_per_gop() {
+        use CodingType::*;
+        // Two GOPs of 5 frames, decode order I P B P B, anchor PTS only on the
+        // GOP's I (0 ns, then ~5-frames-later). Frame duration should calibrate
+        // to the spacing/5 and every frame get a distinct increasing display PTS.
+        let dur = 41_708_333i64;
+        let mut r = SparsePtsReorder::new();
+        let mut got: Vec<i64> = Vec::new();
+        // GOP 1: anchor on the I at t=0.
+        for (k, (ct, pts)) in [(I, Some(0i64)), (P, None), (B, None), (P, None), (B, None)]
+            .into_iter()
+            .enumerate()
+        {
+            let out = r.push(pts, frame(ct, k == 0));
+            got.extend(out.iter().map(|f| f.pts_ns));
+        }
+        // GOP 2: anchor on the I at t = 5*dur (its true display time).
+        for (k, (ct, pts)) in [
+            (I, Some(5 * dur)),
+            (P, None),
+            (B, None),
+            (P, None),
+            (B, None),
+        ]
+        .into_iter()
+        .enumerate()
+        {
+            let out = r.push(pts, frame(ct, k == 0));
+            got.extend(out.iter().map(|f| f.pts_ns));
+        }
+        got.extend(r.flush().iter().map(|f| f.pts_ns));
+
+        // Ten frames out, none dropped.
+        assert_eq!(got.len(), 10, "all frames emitted");
+        // The calibrated duration is (5*dur)/5 = dur.
+        // GOP 1 decode order I P B P B -> display indices 0 2 1 4 3 -> PTS:
+        assert_eq!(
+            &got[0..5],
+            &[0, 2 * dur, 1 * dur, 4 * dur, 3 * dur],
+            "GOP1 display PTS in decode order"
+        );
+        // GOP 2 re-locks origin to 5*dur.
+        assert_eq!(
+            &got[5..10],
+            &[5 * dur, 7 * dur, 6 * dur, 9 * dur, 8 * dur],
+            "GOP2 display PTS continue monotonically per display order"
+        );
+    }
+
+    #[test]
+    fn no_pts_collisions_within_a_gop() {
+        use CodingType::*;
+        // Every frame distinct in DISPLAY order — the property the mkv muxer
+        // needs so a decoder can derive monotonic DTS.
+        let mut r = SparsePtsReorder::new();
+        let mut all: Vec<i64> = Vec::new();
+        for gop in 0..3 {
+            for (k, ct) in [I, P, B, P, B].into_iter().enumerate() {
+                let pts = (k == 0).then_some(gop as i64 * 5 * 41_708_333);
+                all.extend(r.push(pts, frame(ct, k == 0)).iter().map(|f| f.pts_ns));
+            }
+        }
+        all.extend(r.flush().iter().map(|f| f.pts_ns));
+        let mut sorted = all.clone();
+        sorted.sort_unstable();
+        sorted.dedup();
+        assert_eq!(sorted.len(), all.len(), "no two frames share a display PTS");
+    }
+}

src/mux/codec/vc1.rs

@@ -103,6 +103,10 @@ pub struct Vc1Parser {
     cur_entry_point: Option<Vec<u8>>,
     width: u32,
     height: u32,
+    /// Display-order PTS reconstruction, enabled only on the program-stream
+    /// (HD-DVD EVO) path where the source stamps a PTS once per GOP. `None` on
+    /// the BD/UHD transport path, which carries a per-frame PTS.
+    reorder: Option<super::reorder::SparsePtsReorder>,
 }
 
 impl Default for Vc1Parser {
@@ -120,6 +124,25 @@ impl Vc1Parser {
             cur_entry_point: None,
             width: 1920,
             height: 1080,
+            reorder: None,
+        }
+    }
+
+    /// Enable display-order PTS reconstruction for a program-stream source.
+    /// No-op (leaves timestamps as parsed) for a transport-stream source.
+    pub(crate) fn with_ps_reorder(mut self, enabled: bool) -> Self {
+        if enabled {
+            self.reorder = Some(super::reorder::SparsePtsReorder::new());
+        }
+        self
+    }
+
+    /// Route a finished frame through the PTS reorderer when enabled, else emit
+    /// it directly (unchanged transport-stream behaviour).
+    fn finish(&mut self, explicit: Option<i64>, frame: Frame) -> Vec<Frame> {
+        match self.reorder.as_mut() {
+            Some(r) => r.push(explicit, frame),
+            None => vec![frame],
         }
     }
 }
@@ -169,7 +192,8 @@ impl CodecParser for Vc1Parser {
         // decode order and the player reorders by timecode. Use PTS, not DTS —
         // DTS presents B-frames in decode order (visible judder) and breaks
         // PTS-based seeking. Fall back to DTS only if PTS is absent.
-        let ts_ns = pes.pts.or(pes.dts).map(pts_to_ns).unwrap_or(0);
+        let explicit_pts = pes.pts.or(pes.dts).map(pts_to_ns);
+        let ts_ns = explicit_pts.unwrap_or(0);
         let mut has_seq_header = false;
         let mut has_entry_point = false;
         let mut frame_start: Option<usize> = None;
@@ -321,7 +345,7 @@ impl CodecParser for Vc1Parser {
             vc1_frame_coding_type(data.get(fs + 4..)?, self.cur_seq_header.as_deref())
         });
 
-        vec![Frame {
+        let frame = Frame {
             // Coding-type only: VC-1 field order is not decoded here, so
             // field_order() stays None — honestly absent, never guessed.
             coding: coding_type.map(PictureInfo::coding_type_only),
@@ -333,7 +357,15 @@ impl CodecParser for Vc1Parser {
             discontinuity: pes.discontinuity,
             data: frame_data,
             duration_ns: None,
-        }]
+        };
+        self.finish(explicit_pts, frame)
+    }
+
+    fn flush(&mut self) -> Vec<Frame> {
+        match self.reorder.as_mut() {
+            Some(r) => r.flush(),
+            None => Vec::new(),
+        }
     }
 
     fn codec_private(&self) -> Option<Vec<u8>> {