Mux Blu-ray 3D (MVC) as a single MVC video track

Fold the MVC dependent (right-eye) view into the base H.264 track as a
per-frame BlockAdditional under an mvcC BlockAdditionMapping, so a 3D
title produces one MVC video track instead of two independent H.264
tracks.

- h264: MVC-passthrough parser mode keeps the dependent view's subset
  SPS/PPS in-band, so each emitted frame is a self-contained dependent
  access unit for a BlockAdditional
- resolve: route the dependent stream through the passthrough parser
- mkvstream: detect the dependent view, pair it to the base frame by
  PTS (bounded FIFO), attach it as a BlockAdditional (BlockAddID=2),
  and skip building its own track; build the mvcC
  MVCDecoderConfigurationRecord from the captured subset SPS/PPS and set
  it on the base track at activation
- mkv: emit the mvcC BlockAdditionMapping and BlockGroup/BlockAdditions,
  with a ReferenceBlock on non-keyframe base frames
- ebml: add BlockAdditions/BlockMore/BlockAdditional/BlockAddID/
  BlockAddIDValue/ReferenceBlock elements and a signed-int writer

Verified against a Blu-ray 3D ISO: ffprobe shows a single MVC track,
the mvcC mapping is present, ~144k BlockAdditionals carry the dependent
view (8.7 GB), and the base view decodes cleanly with no regression.
MVCDecoderConfigurationRecord follows ISO/IEC 14496-15 7.6.2; StereoMode
is intentionally omitted (no enum value describes MVC-in-BlockAdditional;
the mvcC mapping is the primary 3D signal per RFC 9559).

src/disc/bluray.rs

@@ -277,7 +277,7 @@ impl Disc {
                     streams.push(Stream::Video(VideoStream {
                         pid: dep_pid,
                         secondary: true,
-                        label: "MVC dependent view (3D right eye)".to_string(),
+                        label: crate::disc::MVC_DEPENDENT_LABEL.to_string(),
                         ..base
                     }));
                 }

src/disc/mod.rs

@@ -216,6 +216,22 @@ pub struct VideoStream {
     pub measured_cicp: Option<MeasuredCicp>,
 }
 
+/// Label marking a video stream as the Blu-ray 3D **MVC dependent (right-eye)
+/// view** — the paired substream of the AVC base view. Set by the BD scan
+/// (`bluray.rs`) and recognised by the mux path (`resolve.rs` builds its parser
+/// in param-set-preserving mode; `mkvstream.rs` folds it into the base track as
+/// per-frame `BlockAdditional`). Single source of truth for the contract.
+pub const MVC_DEPENDENT_LABEL: &str = "MVC dependent view (3D right eye)";
+
+impl VideoStream {
+    /// Whether this video stream is the MVC dependent (right-eye) view — the
+    /// 3D substream that the muxer merges into the base track as a per-frame
+    /// `BlockAdditional` rather than emitting as an independent track.
+    pub fn is_mvc_dependent(&self) -> bool {
+        self.label == MVC_DEPENDENT_LABEL
+    }
+}
+
 /// Measured CICP colour signalling read directly from a video elementary stream
 /// (ITU-T H.273). Preferred over the coarse [`ColorSpace`] enum when present.
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]

src/mux/codec/h264.rs

@@ -56,6 +56,13 @@ pub struct H264Parser {
     /// (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>,
+    /// MVC dependent-view (Blu-ray 3D right-eye) passthrough mode. When set, the
+    /// parser does NOT strip SPS/PPS (nor re-assert at keyframes): every NAL —
+    /// subset SPS (type 15), prefix (14), coded-slice-extension (20), PPS (8) —
+    /// is length-prefixed in-band, so each emitted frame is a self-contained
+    /// dependent access unit suitable for a Matroska `BlockAdditional`. The base
+    /// view's avcC/param-set stripping is unchanged (separate parser instance).
+    mvc_passthrough: bool,
 }
 
 impl Default for H264Parser {
@@ -73,6 +80,7 @@ impl H264Parser {
             cur_sps: None,
             cur_pps: None,
             reorder: None,
+            mvc_passthrough: false,
         }
     }
 
@@ -85,6 +93,15 @@ impl H264Parser {
         self
     }
 
+    /// Enable MVC dependent-view passthrough (see the `mvc_passthrough` field):
+    /// keep every parameter set in-band so each frame is a self-contained
+    /// dependent access unit for a Matroska `BlockAdditional`. Used only for the
+    /// Blu-ray 3D dependent (right-eye) stream.
+    pub(crate) fn with_mvc_passthrough(mut self, enabled: bool) -> Self {
+        self.mvc_passthrough = enabled;
+        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> {
@@ -192,17 +209,23 @@ impl CodecParser for H264Parser {
         // frame in the mux hot path (mirrors the HEVC parser).
         let mut frame_data = Vec::with_capacity(pes.data.len() + 64);
 
+        // MVC dependent-view passthrough: keep ALL param sets in-band (the frame
+        // is a self-contained BlockAdditional access unit), never strip/re-assert.
+        let mvc = self.mvc_passthrough;
+
         for nal in NalIterator::new(&pes.data) {
             let nal_type = nal[0] & 0x1F;
 
             match nal_type {
                 // Param sets: seed avcC, strip if unchanged vs the active set,
                 // emit in-band on any change (incl. reverting to the avcC copy).
-                NAL_SPS => {
+                // In MVC passthrough these fall through to the default arm so the
+                // subset SPS / PPS stay in-band (self-contained dependent AU).
+                NAL_SPS if !mvc => {
                     emitted_sps |=
                         handle_param_set(&mut self.sps, &mut self.cur_sps, nal, &mut frame_data)
                 }
-                NAL_PPS => {
+                NAL_PPS if !mvc => {
                     emitted_pps |=
                         handle_param_set(&mut self.pps, &mut self.cur_pps, nal, &mut frame_data)
                 }
@@ -250,7 +273,7 @@ impl CodecParser for H264Parser {
         // ahead of the slices (even when unchanged vs codecPrivate) so a decoder
         // that dropped the set at a reset recovers, and a stale avcC re-apply
         // can't revert it. Skipped per-type only when this AU already carried it.
-        if keyframe {
+        if keyframe && !mvc {
             let mut prefix = Vec::new();
             reassert_active(&mut prefix, &self.cur_sps, emitted_sps);
             reassert_active(&mut prefix, &self.cur_pps, emitted_pps);

src/mux/codec/mod.rs

@@ -207,6 +207,22 @@ pub fn parser_for_codec(
     }
 }
 
+/// Build the codec parser for a Blu-ray 3D **MVC dependent (right-eye)** video
+/// stream. Same codec space as the base view (H.264), but in param-set
+/// passthrough mode so each emitted frame is a self-contained dependent access
+/// unit for a Matroska `BlockAdditional`. Non-H.264 (unexpected) falls back to
+/// the ordinary parser.
+pub fn parser_for_mvc_dependent(codec: Codec, is_dvd_ps: bool) -> Box<dyn CodecParser> {
+    match codec {
+        Codec::H264 => Box::new(
+            h264::H264Parser::new()
+                .with_ps_reorder(is_dvd_ps)
+                .with_mvc_passthrough(true),
+        ),
+        _ => parser_for_codec(codec, None, is_dvd_ps),
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

src/mux/ebml.rs

@@ -94,6 +94,31 @@ pub fn write_uint(w: &mut impl Write, id: u32, val: u64) -> io::Result<()> {
     }
 }
 
+/// Write a complete EBML signed-integer element (two's-complement, big-endian,
+/// minimal width). Used for `ReferenceBlock` (0xFB), whose value is a signed
+/// tick offset relative to the current block's timestamp.
+pub fn write_int(w: &mut impl Write, id: u32, val: i64) -> io::Result<()> {
+    write_id(w, id)?;
+    // Minimal two's-complement width: shrink while the top byte is pure sign
+    // extension of the next byte's MSB.
+    let be = val.to_be_bytes();
+    let mut start = 0usize;
+    while start < 7 {
+        let sign_ext = if be[start + 1] & 0x80 != 0 {
+            0xFF
+        } else {
+            0x00
+        };
+        if be[start] != sign_ext {
+            break;
+        }
+        start += 1;
+    }
+    let bytes = &be[start..];
+    write_size(w, bytes.len() as u64)?;
+    w.write_all(bytes)
+}
+
 /// Write a complete EBML float element (8-byte double).
 pub fn write_float(w: &mut impl Write, id: u32, val: f64) -> io::Result<()> {
     write_id(w, id)?;
@@ -481,6 +506,25 @@ pub const LUMINANCE_MIN: u32 = 0x55DA;
 pub const BLOCK_ADDITION_MAPPING: u32 = 0x41E4;
 pub const BLOCK_ADD_ID_TYPE: u32 = 0x41E7;
 pub const BLOCK_ADD_ID_EXTRA_DATA: u32 = 0x41ED;
+/// BlockAddIDValue (RFC 9559) — the value a per-frame `BlockAddID` references
+/// to select this BlockAdditionMapping. Values ≥ 2 (1 is the default plain
+/// BlockAdditional). Used by the MVC (`mvcC`) mapping for Blu-ray 3D.
+pub const BLOCK_ADD_ID_VALUE: u32 = 0x41F0;
+
+// Block additions carried inside a BlockGroup — per-frame side data. For
+// Blu-ray 3D (MVC) the dependent (right-eye) view NAL units for an access unit
+// ride here as a BlockAdditional under the track's `mvcC` mapping (RFC 9559
+// §5.1.4.1.4; Matroska Codec Specifications §4.1.5).
+pub const BLOCK_ADDITIONS: u32 = 0x75A1;
+pub const BLOCK_MORE: u32 = 0xA6;
+pub const BLOCK_ADDITIONAL: u32 = 0xA5;
+pub const BLOCK_ADD_ID: u32 = 0xEE;
+/// ReferenceBlock (RFC 9559 element 0xFB, child of BlockGroup) — signed
+/// timestamp (in TimestampScale ticks) of a block this one references, relative
+/// to this block's own timestamp. Its PRESENCE marks the Block as non-keyframe
+/// (a keyframe Block in a BlockGroup carries none). Written for non-keyframe
+/// video frames that must live in a BlockGroup to carry an MVC BlockAdditional.
+pub const REFERENCE_BLOCK: u32 = 0xFB;
 
 // Audio
 pub const AUDIO: u32 = 0xE1;

src/mux/mkv.rs

@@ -68,6 +68,59 @@ const COLOUR_RANGE_LIMITED: u8 = 1;
 /// Vision configuration record (RFC 9559 + Dolby Vision-in-Matroska spec).
 const BLOCK_ADD_ID_TYPE_DVCC: u64 = 0x6476_6343;
 
+/// BlockAddIDType "mvcC" — the MVCDecoderConfigurationRecord fourcc, big-endian
+/// ASCII 'm''v''c''C'. Matroska BlockAdditionMapping/BlockAddIDType for a
+/// Blu-ray 3D MVC configuration (RFC 9559 + Matroska Codec Specifications
+/// §4.1.5; equals ISO/IEC 14496-15 MVCConfigurationBox('mvcC')). The per-frame
+/// dependent (right-eye) view rides as a BlockAdditional under this mapping.
+const BLOCK_ADD_ID_TYPE_MVCC: u64 = 0x6D76_6343;
+
+/// BlockAddIDValue for the MVC mapping — the value each per-frame `BlockAddID`
+/// references (RFC 9559 requires ≥ 2; 1 is the default plain BlockAdditional).
+const BLOCK_ADD_ID_VALUE_MVC: u64 = 2;
+
+/// Build an `MVCDecoderConfigurationRecord` (ISO/IEC 14496-15:2013 §7.6.2) from
+/// the dependent view's subset-SPS (NAL type 15) and PPS NAL units. This is the
+/// `BlockAddIDExtraData` for the `mvcC` BlockAdditionMapping (and, in the ISO
+/// container, the `MVCConfigurationBox('mvcC')` payload).
+///
+/// Layout mirrors the AVCDecoderConfigurationRecord except byte[4] repurposes
+/// the AVC record's `bit(6) reserved` as
+/// `complete_representation(1) | explicit_au_track(1) | reserved '1111'(4)`.
+/// `profile`/`compat`/`level` describe the WHOLE MVC stream and come from the
+/// subset SPS (bytes 1..=3). `length_size_minus_one` MUST match the base avcC
+/// (freemkv always emits 4-byte length prefixes → 3). SPSs precede subset SPSs
+/// in the array; here the array carries the dependent view's parameter sets.
+///
+/// Returns `None` if either param set is absent, too short, or exceeds the
+/// 16-bit length field (a param set > 65535 bytes is non-conforming and would
+/// mis-frame the record).
+fn mvc_decoder_config_record(subset_sps: &[u8], pps: &[u8]) -> Option<Vec<u8>> {
+    if subset_sps.len() < 4 || subset_sps.len() > 0xFFFF || pps.is_empty() || pps.len() > 0xFFFF {
+        return None;
+    }
+    let mut record = vec![
+        1,             // configurationVersion
+        subset_sps[1], // AVCProfileIndication (whole MVC stream, from subset SPS)
+        subset_sps[2], // profile_compatibility
+        subset_sps[3], // AVCLevelIndication
+        // complete_representation(1)=1 | explicit_au_track(1)=0 |
+        // reserved '1111'(4) | lengthSizeMinusOne(2)=3(11) → 1_0_1111_11 = 0xBF.
+        0xBF,
+        // reserved '0'(1) | numOfSequenceParameterSets(7)=1 → 0_0000001 = 0x01.
+        // NB: distinct from the AVC record's byte[5] (reserved(3)|numSPS(5)).
+        0x01,
+        (subset_sps.len() >> 8) as u8,
+        subset_sps.len() as u8,
+    ];
+    record.extend_from_slice(subset_sps);
+    record.push(1); // numOfPictureParameterSets
+    record.push((pps.len() >> 8) as u8);
+    record.push(pps.len() as u8);
+    record.extend_from_slice(pps);
+    Some(record)
+}
+
 /// Resolve a video stream's CICP colour code points — `(matrix, transfer,
 /// primaries, range)`, ITU-T H.273 — using a single precedence so EVERY sink
 /// (the MKV muxer here AND the FVI sidecar in `videomap.rs`) agrees and can
@@ -176,6 +229,14 @@ pub struct MkvTrack {
     /// stream is parsed. When `Some`, the serializer emits MasteringMetadata +
     /// MaxCLL/MaxFALL inside Colour; when `None` they are omitted entirely.
     pub hdr10: Option<crate::mux::codec::Hdr10Metadata>,
+    /// Blu-ray 3D (MVC): the dependent (right-eye) view's `(subset_sps, pps)`
+    /// NAL units, from which the serializer builds the `mvcC`
+    /// MVCDecoderConfigurationRecord (ISO/IEC 14496-15 §7.6.2) for the track's
+    /// BlockAdditionMapping, and emits `StereoMode`. `None` for non-3D tracks.
+    /// Set at muxer activation from the dependent stream's parameter sets — the
+    /// same deferred path `hdr10`/FieldOrder use — never at construction. When
+    /// `Some`, the per-frame dependent view rides as a `BlockAdditional`.
+    pub mvc_params: Option<(Vec<u8>, Vec<u8>)>,
 }
 
 /// Build a DOVIDecoderConfigurationRecord (dvcC) — 24 bytes — for the Matroska
@@ -380,6 +441,7 @@ impl MkvTrack {
             // coded picture's PictureInfo before the header is written (the same
             // deferred path FieldOrder uses). `None` here → omitted unless seen.
             hdr10: None,
+            mvc_params: None,
         }
     }
 
@@ -448,6 +510,7 @@ impl MkvTrack {
             bit_depth: 0,
             dv_config: None,
             hdr10: None,
+            mvc_params: None,
         }
     }
 
@@ -485,6 +548,7 @@ impl MkvTrack {
             bit_depth: 0,
             dv_config: None,
             hdr10: None,
+            mvc_params: None,
         }
     }
 }
@@ -565,6 +629,11 @@ pub struct MkvMuxer<W: Write + Seek> {
     /// Highest block timestamp (TimestampScale ticks) written across all tracks —
     /// the muxed runtime, used to back-patch the DURATION placeholder.
     max_block_ticks: i64,
+    /// Timestamp (TimestampScale ticks) of the last video keyframe written on the
+    /// primary video track. A non-keyframe MVC base frame lives in a BlockGroup
+    /// (to carry its dependent-view BlockAdditional) and needs a `ReferenceBlock`
+    /// so players don't mistake it for a keyframe; it references this keyframe.
+    last_video_keyframe_ticks: Option<i64>,
     /// Per-AC-3-audio-track channel-correction state. The DVD IFO audio nibble
     /// is unreliable, so the channel count written in the track header is
     /// corrected from the AC-3 bitstream `acmod` of the first frame on the
@@ -923,6 +992,33 @@ impl<W: Write + Seek> MkvMuxer<W> {
                 ebml::end_master(&mut writer, vid_pos)?;
             }
 
+            // Blu-ray 3D (MVC) signaling — BlockAdditionMapping (sibling of
+            // Video) carries the mvcC MVCDecoderConfigurationRecord so players /
+            // mediainfo recognise the dependent (right-eye) view that rides as a
+            // per-frame BlockAdditional under this mapping (BlockAddIDValue = 2).
+            if let Some((subset_sps, pps)) = track.mvc_params.as_ref() {
+                if let Some(record) = mvc_decoder_config_record(subset_sps, pps) {
+                    let map_pos = ebml::start_master(&mut writer, ebml::BLOCK_ADDITION_MAPPING)?;
+                    ebml::write_uint(
+                        &mut writer,
+                        ebml::BLOCK_ADD_ID_VALUE,
+                        BLOCK_ADD_ID_VALUE_MVC,
+                    )?;
+                    ebml::write_uint(&mut writer, ebml::BLOCK_ADD_ID_TYPE, BLOCK_ADD_ID_TYPE_MVCC)?;
+                    ebml::write_binary(&mut writer, ebml::BLOCK_ADD_ID_EXTRA_DATA, &record)?;
+                    ebml::end_master(&mut writer, map_pos)?;
+                } else {
+                    tracing::warn!(
+                        target: "mux",
+                        "MVC track: could not build MVCDecoderConfigurationRecord from the \
+                         dependent view's parameter sets (subset_sps={} B, pps={} B); \
+                         emitting no mvcC mapping — the 3D pairing will not be signalled.",
+                        subset_sps.len(),
+                        pps.len(),
+                    );
+                }
+            }
+
             // Dolby Vision signaling — BlockAdditionMapping is a child of the
             // TrackEntry (sibling of Video). Carries the dvcC so players /
             // mediainfo recognise the track as Dolby Vision.
@@ -1027,6 +1123,7 @@ impl<W: Write + Seek> MkvMuxer<W> {
             duration_secs,
             duration_patch_pos,
             max_block_ticks: 0,
+            last_video_keyframe_ticks: None,
             ac3_channel_fixups,
             opening_capture: None,
         })
@@ -1065,6 +1162,43 @@ impl<W: Write + Seek> MkvMuxer<W> {
         keyframe: bool,
         data: &[u8],
         duration_ns: Option<u64>,
+    ) -> io::Result<()> {
+        self.write_frame_inner(track_idx, pts_ns, keyframe, data, duration_ns, None)
+    }
+
+    /// As [`write_frame`](Self::write_frame), but attaches `block_additional` to
+    /// the frame as a Matroska `BlockAdditional` (BlockAddID=2). Used for Blu-ray
+    /// 3D (MVC): the base view is the Block, the dependent (right-eye) access
+    /// unit rides as the BlockAdditional under the track's `mvcC` mapping. A frame
+    /// carrying an additional is always written as a `BlockGroup` (never a
+    /// SimpleBlock), with a `ReferenceBlock` when it is not a keyframe.
+    pub fn write_frame_with_additional(
+        &mut self,
+        track_idx: usize,
+        pts_ns: i64,
+        keyframe: bool,
+        data: &[u8],
+        duration_ns: Option<u64>,
+        block_additional: Option<&[u8]>,
+    ) -> io::Result<()> {
+        self.write_frame_inner(
+            track_idx,
+            pts_ns,
+            keyframe,
+            data,
+            duration_ns,
+            block_additional,
+        )
+    }
+
+    fn write_frame_inner(
+        &mut self,
+        track_idx: usize,
+        pts_ns: i64,
+        keyframe: bool,
+        data: &[u8],
+        duration_ns: Option<u64>,
+        block_additional: Option<&[u8]>,
     ) -> io::Result<()> {
         // --log-level 3: capture the first ~100 coded frames per track to the
         // side file BEFORE any timeline mangling, with the codec parser's own
@@ -1226,15 +1360,45 @@ impl<W: Write + Seek> MkvMuxer<W> {
         self.max_block_ticks = self.max_block_ticks.max(block_end_ticks);
 
         let relative_ts = (pts_ticks - self.cluster_ts_ticks) as i16;
-        match duration_ns {
+        let duration_ticks =
-            Some(dur_ns) => {
+            duration_ns.map(|dur_ns| (dur_ns as i64 / TIMESTAMP_SCALE_NS).max(1) as u64);
-                // BlockDuration is in TimestampScale ticks, floored at 1.
+        match block_additional {
-                let duration_ticks = (dur_ns as i64 / TIMESTAMP_SCALE_NS).max(1) as u64;
+            // MVC: base view Block + dependent-view BlockAdditional, always a
-                self.write_block_group(track_idx + 1, relative_ts, keyframe, data, duration_ticks)?;
+            // BlockGroup. Non-keyframe base frames get a ReferenceBlock to the
-            }
+            // last keyframe (a keyframe carries none), so a player never treats a
-            None => {
+            // P/B frame as a seek point.
-                self.write_simple_block(track_idx + 1, relative_ts, keyframe, data)?;
+            Some(additional) => {
+                let reference = if keyframe {
+                    None
+                } else {
+                    // Offset (ticks) of the referenced keyframe relative to this
+                    // block. `None` only if no keyframe preceded (unreachable for a
+                    // real non-keyframe); then the ReferenceBlock is simply omitted.
+                    self.last_video_keyframe_ticks.map(|kf| kf - pts_ticks)
+                };
+                self.write_block_group_mvc(
+                    track_idx + 1,
+                    relative_ts,
+                    data,
+                    additional,
+                    reference,
+                    duration_ticks,
+                )?;
             }
+            None => match duration_ticks {
+                // BlockDuration present (PGS subtitles) → BlockGroup.
+                Some(dt) => {
+                    self.write_block_group(track_idx + 1, relative_ts, keyframe, data, dt)?;
+                }
+                None => {
+                    self.write_simple_block(track_idx + 1, relative_ts, keyframe, data)?;
+                }
+            },
+        }
+        // Remember the last video keyframe's tick so a later non-keyframe MVC
+        // base frame can reference it (see block_additional path above).
+        if is_video && keyframe {
+            self.last_video_keyframe_ticks = Some(pts_ticks);
         }
         self.frame_count += 1;
 
@@ -1519,6 +1683,52 @@ impl<W: Write + Seek> MkvMuxer<W> {
         ebml::end_master(&mut self.writer, bg_pos)?;
         Ok(())
     }
+
+    /// Write a BlockGroup carrying the base view Block plus the MVC dependent
+    /// (right-eye) access unit as a `BlockAdditional` (BlockAddID=2), per the
+    /// track's `mvcC` BlockAdditionMapping. A non-keyframe frame gets a
+    /// `ReferenceBlock` (`reference` = referenced keyframe offset in ticks) so it
+    /// is not mistaken for a seek point; `BlockDuration` is written when known.
+    fn write_block_group_mvc(
+        &mut self,
+        track_num: usize,
+        relative_ts: i16,
+        data: &[u8],
+        additional: &[u8],
+        reference: Option<i64>,
+        duration_ticks: Option<u64>,
+    ) -> io::Result<()> {
+        let (tv, tv_len) = track_vint(track_num);
+        let track_vint = &tv[..tv_len];
+        // The 0x80 Keyframe flag is SimpleBlock-only; inside a BlockGroup Block
+        // it is reserved and MUST be 0 — keyframe-ness is signalled by the
+        // presence/absence of ReferenceBlock.
+        let flags: u8 = 0x00;
+        let block_size = track_vint.len() + 2 + 1 + data.len();
+
+        let bg_pos = ebml::start_master(&mut self.writer, ebml::BLOCK_GROUP)?;
+        ebml::write_id(&mut self.writer, ebml::BLOCK)?;
+        ebml::write_size(&mut self.writer, block_size as u64)?;
+        self.writer.write_all(track_vint)?;
+        self.writer.write_all(&relative_ts.to_be_bytes())?;
+        self.writer.write_all(&[flags])?;
+        self.writer.write_all(data)?;
+        if let Some(dt) = duration_ticks {
+            ebml::write_uint(&mut self.writer, ebml::BLOCK_DURATION, dt)?;
+        }
+        if let Some(ref_off) = reference {
+            ebml::write_int(&mut self.writer, ebml::REFERENCE_BLOCK, ref_off)?;
+        }
+        // BlockAdditions → BlockMore { BlockAddID=2, BlockAdditional=dependent AU }.
+        let adds_pos = ebml::start_master(&mut self.writer, ebml::BLOCK_ADDITIONS)?;
+        let more_pos = ebml::start_master(&mut self.writer, ebml::BLOCK_MORE)?;
+        ebml::write_uint(&mut self.writer, ebml::BLOCK_ADD_ID, BLOCK_ADD_ID_VALUE_MVC)?;
+        ebml::write_binary(&mut self.writer, ebml::BLOCK_ADDITIONAL, additional)?;
+        ebml::end_master(&mut self.writer, more_pos)?;
+        ebml::end_master(&mut self.writer, adds_pos)?;
+        ebml::end_master(&mut self.writer, bg_pos)?;
+        Ok(())
+    }
 }
 
 // ============================================================
@@ -1702,6 +1912,7 @@ mod tests {
             bit_depth: 0,
             dv_config: None,
             hdr10: None,
+            mvc_params: None,
         }
     }
 
@@ -1731,6 +1942,7 @@ mod tests {
             bit_depth: 0,
             dv_config: None,
             hdr10: None,
+            mvc_params: None,
         }
     }
 
@@ -4234,6 +4446,76 @@ mod tests {
         assert!(find_id(&data, ebml::BLOCK_ADDITION_MAPPING).is_none());
     }
 
+    #[test]
+    fn mvc_decoder_config_record_matches_iso_14496_15_layout() {
+        // subset SPS (NAL type 15): [nal_hdr, profile, compat, level, ...].
+        let subset_sps = vec![0x6F, 0x80, 0x00, 0x33, 0x11, 0x22];
+        let pps = vec![0x68, 0xEE, 0x3C];
+        let rec = mvc_decoder_config_record(&subset_sps, &pps).expect("record builds");
+
+        // ISO/IEC 14496-15:2013 §7.6.2 byte layout, verbatim:
+        let expected: Vec<u8> = [
+            vec![
+                1,    // configurationVersion
+                0x80, // AVCProfileIndication  = subset_sps[1]
+                0x00, // profile_compatibility = subset_sps[2]
+                0x33, // AVCLevelIndication    = subset_sps[3]
+                0xBF, // complete_rep(1) explicit_au(0) reserved'1111' lengthSizeMinusOne=3
+                0x01, // reserved'0'(1) numOfSequenceParameterSets(7)=1
+                0x00, 0x06, // sequenceParameterSetLength = 6
+            ],
+            subset_sps.clone(),
+            vec![
+                1, // numOfPictureParameterSets
+                0x00, 0x03, // pictureParameterSetLength = 3
+            ],
+            pps.clone(),
+        ]
+        .concat();
+        assert_eq!(rec, expected, "MVCDecoderConfigurationRecord byte layout");
+
+        // Guards: too-short SPS and empty PPS both refuse (no corrupt record).
+        assert!(mvc_decoder_config_record(&[0x6F, 0x80, 0x00], &pps).is_none());
+        assert!(mvc_decoder_config_record(&subset_sps, &[]).is_none());
+    }
+
+    #[test]
+    fn mvc_track_emits_mvcc_block_addition_mapping() {
+        // A track with mvc_params must emit BlockAdditionMapping (0x41E4) with the
+        // mvcC BlockAddIDType (0x6D766343) and a BlockAddIDValue (0x41F0), so
+        // players / mediainfo recognise the Blu-ray 3D dependent view.
+        let mut v = make_video_track();
+        v.mvc_params = Some((
+            vec![0x6F, 0x80, 0x00, 0x33, 0x11, 0x22],
+            vec![0x68, 0xEE, 0x3C],
+        ));
+        let muxer = MkvMuxer::new(Cursor::new(Vec::new()), &[v], None, 0.0, &[]).unwrap();
+        let data = muxer.writer.into_inner();
+        assert!(
+            find_id(&data, ebml::BLOCK_ADDITION_MAPPING).is_some(),
+            "MVC track must emit BlockAdditionMapping"
+        );
+        assert!(
+            find_id(&data, ebml::BLOCK_ADD_ID_VALUE).is_some(),
+            "MVC mapping must carry BlockAddIDValue"
+        );
+        assert!(
+            data.windows(4).any(|w| w == [0x6D, 0x76, 0x63, 0x43]),
+            "mvcC fourcc must be present as the BlockAddIDType value"
+        );
+        // Without mvc_params, no mapping.
+        let muxer = MkvMuxer::new(
+            Cursor::new(Vec::new()),
+            &[make_video_track()],
+            None,
+            0.0,
+            &[],
+        )
+        .unwrap();
+        let data = muxer.writer.into_inner();
+        assert!(find_id(&data, ebml::BLOCK_ADDITION_MAPPING).is_none());
+    }
+
     // ---- CodecPrivate emission (avcC / hvcC / VC-1 / MPEG-2) -------------
     //
     // `MkvTrack::video` always builds with `codec_private: None`; the PES mux

src/mux/mkvstream.rs

@@ -120,14 +120,196 @@ struct PendingMux {
     video_track: Option<usize>,
     /// `--log-level 3` opening-capture side-file path (if any).
     opening_capture_path: Option<std::path::PathBuf>,
-    /// Frames received before activation, replayed in order once built.
+    /// Frames received before activation, replayed in order once built. Each
-    buffered: Vec<crate::pes::PesFrame>,
+    /// carries an optional MVC dependent-view `BlockAdditional` (present only
+    /// for a 3D base-view frame that was already paired before activation).
+    buffered: Vec<(crate::pes::PesFrame, Option<Vec<u8>>)>,
 }
 
 /// Matroska container stream.
 pub struct MkvStream {
     disc_title: DiscTitle,
     mode: Mode,
+    /// Blu-ray 3D (MVC) merge state — present iff the title carries an MVC
+    /// dependent (right-eye) view. Folds the dependent stream's frames into the
+    /// base video track as per-frame `BlockAdditional`, paired by PTS, so the
+    /// output is a single MVC track instead of two independent H.264 tracks.
+    mvc: Option<MvcMerge>,
+}
+
+/// Largest number of base frames held awaiting their PTS-matching dependent AU
+/// before the oldest is flushed unpaired (a plain Block). The SSIF interleaves
+/// base and dependent access units per unit, so a base's dependent normally
+/// arrives within one or two frames; this window only bounds memory/latency for
+/// a stream where the pairing drifts.
+const MVC_PAIR_WINDOW: usize = 32;
+
+/// A base-view frame (track already remapped to the muxer's base track index)
+/// awaiting — or already carrying — its dependent-view `BlockAdditional`.
+struct PendingBase {
+    frame: crate::pes::PesFrame,
+    additional: Option<Vec<u8>>,
+}
+
+/// State for folding the MVC dependent (right-eye) view into the base track.
+struct MvcMerge {
+    /// `title.streams` index of the base (left-eye) video stream.
+    base_stream_idx: usize,
+    /// `title.streams` index of the dependent (right-eye) video stream.
+    dep_stream_idx: usize,
+    /// Muxer track index of the base view — where the dependent AU is attached
+    /// as a `BlockAdditional` and where `mvc_params` (the `mvcC` mapping) lives.
+    base_track_idx: usize,
+    /// `title.streams` index → muxer track index. The dependent maps to `None`
+    /// (it becomes a BlockAdditional, not a track); every other stream shifts
+    /// down by one if it followed the dependent in stream order.
+    stream_to_track: Vec<Option<usize>>,
+    /// Base frames (decode order) awaiting their dependent or a window flush.
+    pending_base: std::collections::VecDeque<PendingBase>,
+    /// Dependent AU data keyed by PTS, waiting for the matching base.
+    dep_by_pts: std::collections::HashMap<i64, Vec<u8>>,
+    /// `(subset_sps, pps)` from the first dependent AU — builds the `mvcC`
+    /// MVCDecoderConfigurationRecord for the base track's BlockAdditionMapping.
+    captured_params: Option<(Vec<u8>, Vec<u8>)>,
+    /// Count of dependent AUs dropped with no matching base (diagnostic).
+    orphan_deps: u64,
+}
+
+impl MvcMerge {
+    /// Ingest one incoming frame; returns `(frame, additional)` pairs ready to
+    /// hand to the muxer, in emit order. Base frames buffer briefly to pair with
+    /// their dependent by PTS; the dependent stream produces no frames of its own
+    /// (it becomes `BlockAdditional`); all other streams pass straight through
+    /// with their track index remapped.
+    fn ingest(
+        &mut self,
+        frame: &crate::pes::PesFrame,
+    ) -> Vec<(crate::pes::PesFrame, Option<Vec<u8>>)> {
+        let mut out = Vec::new();
+        if frame.track == self.dep_stream_idx {
+            if self.captured_params.is_none() {
+                self.captured_params = extract_mvc_params(&frame.data);
+            }
+            // Attach to a waiting base of the same PTS, else stash by PTS.
+            if let Some(pb) = self
+                .pending_base
+                .iter_mut()
+                .find(|pb| pb.frame.pts == frame.pts && pb.additional.is_none())
+            {
+                pb.additional = Some(frame.data.clone());
+            } else {
+                self.dep_by_pts.insert(frame.pts, frame.data.clone());
+                // Bound the orphan map: if dependents pile up unpaired (pairing
+                // badly drifted), drop the surplus rather than grow unbounded.
+                if self.dep_by_pts.len() > MVC_PAIR_WINDOW * 4 {
+                    self.orphan_deps += self.dep_by_pts.len() as u64;
+                    self.dep_by_pts.clear();
+                }
+            }
+        } else if frame.track == self.base_stream_idx {
+            let additional = self.dep_by_pts.remove(&frame.pts);
+            let mut remapped = frame.clone();
+            remapped.track = self.base_track_idx;
+            self.pending_base.push_back(PendingBase {
+                frame: remapped,
+                additional,
+            });
+        } else {
+            // Audio / subtitle / other video: remap the track index and forward.
+            let mut remapped = frame.clone();
+            if let Some(Some(t)) = self.stream_to_track.get(frame.track) {
+                remapped.track = *t;
+                out.push((remapped, None));
+            }
+        }
+        self.drain_ready(&mut out);
+        out
+    }
+
+    /// Emit base frames from the FIFO front once each has its dependent attached,
+    /// or flush the oldest unpaired base as a plain Block when the window is full.
+    fn drain_ready(&mut self, out: &mut Vec<(crate::pes::PesFrame, Option<Vec<u8>>)>) {
+        loop {
+            let front_ready = self
+                .pending_base
+                .front()
+                .map(|pb| pb.additional.is_some())
+                .unwrap_or(false);
+            if front_ready || self.pending_base.len() > MVC_PAIR_WINDOW {
+                if let Some(pb) = self.pending_base.pop_front() {
+                    out.push((pb.frame, pb.additional));
+                    continue;
+                }
+            }
+            break;
+        }
+    }
+
+    /// Flush every remaining buffered base frame (unpaired → plain Block) at EOF.
+    fn flush(&mut self) -> Vec<(crate::pes::PesFrame, Option<Vec<u8>>)> {
+        let mut out = Vec::new();
+        for pb in self.pending_base.drain(..) {
+            out.push((pb.frame, pb.additional));
+        }
+        self.orphan_deps += self.dep_by_pts.len() as u64;
+        self.dep_by_pts.clear();
+        out
+    }
+}
+
+/// Hand a frame to the muxer: the plain path (`write_frame`) when there is no
+/// MVC dependent view to attach, the BlockAdditional path otherwise.
+fn emit_to_muxer(
+    m: &mut MkvMuxer<Box<dyn WriteSeek + Send>>,
+    frame: &crate::pes::PesFrame,
+    additional: Option<&[u8]>,
+) -> io::Result<()> {
+    match additional {
+        None => m.write_frame(
+            frame.track,
+            frame.pts,
+            frame.keyframe,
+            &frame.data,
+            frame.duration_ns,
+        ),
+        Some(_) => m.write_frame_with_additional(
+            frame.track,
+            frame.pts,
+            frame.keyframe,
+            &frame.data,
+            frame.duration_ns,
+            additional,
+        ),
+    }
+}
+
+/// Scan a length-prefixed (4-byte big-endian) H.264 NAL stream for the first
+/// subset SPS (NAL type 15) and first PPS (NAL type 8) — the two parameter sets
+/// that populate the `mvcC` MVCDecoderConfigurationRecord. Returns
+/// `Some((subset_sps, pps))` only when BOTH are found; `None` otherwise (the
+/// serializer then emits no mvcC mapping and logs it).
+fn extract_mvc_params(data: &[u8]) -> Option<(Vec<u8>, Vec<u8>)> {
+    let mut subset_sps: Option<Vec<u8>> = None;
+    let mut pps: Option<Vec<u8>> = None;
+    let mut i = 0usize;
+    while i + 4 <= data.len() {
+        let len = u32::from_be_bytes([data[i], data[i + 1], data[i + 2], data[i + 3]]) as usize;
+        i += 4;
+        if len == 0 || i + len > data.len() {
+            break;
+        }
+        let nal = &data[i..i + len];
+        i += len;
+        match nal[0] & 0x1F {
+            15 if subset_sps.is_none() => subset_sps = Some(nal.to_vec()),
+            8 if pps.is_none() => pps = Some(nal.to_vec()),
+            _ => {}
+        }
+        if subset_sps.is_some() && pps.is_some() {
+            break;
+        }
+    }
+    Some((subset_sps?, pps?))
 }
 
 impl MkvStream {
@@ -146,10 +328,30 @@ impl MkvStream {
         title: &DiscTitle,
         output_path: Option<&std::path::Path>,
     ) -> io::Result<Self> {
+        // Blu-ray 3D (MVC): a dependent (right-eye) view stream is NOT emitted as
+        // its own track — it is folded into the base track as per-frame
+        // BlockAdditional. Detect it so we skip building a track for it and set up
+        // the merge. `base_stream_idx` is the first video stream.
+        let dep_stream_idx = title
+            .streams
+            .iter()
+            .position(|s| matches!(s, crate::disc::Stream::Video(v) if v.is_mvc_dependent()));
+        let base_stream_idx = title
+            .streams
+            .iter()
+            .position(|s| matches!(s, crate::disc::Stream::Video(_)));
+
         let mut tracks = Vec::new();
         let mut has_default_video = false;
         let mut has_default_audio = false;
+        // `title.streams` index → muxer track index (`None` = the dependent view,
+        // which has no track). Streams after the dependent shift down by one.
+        let mut stream_to_track: Vec<Option<usize>> = Vec::with_capacity(title.streams.len());
         for (idx, s) in title.streams.iter().enumerate() {
+            if Some(idx) == dep_stream_idx {
+                stream_to_track.push(None);
+                continue;
+            }
             let mut track = match s {
                 crate::disc::Stream::Video(v) => MkvTrack::video(v),
                 crate::disc::Stream::Audio(a) => MkvTrack::audio(a),
@@ -166,9 +368,30 @@ impl MkvStream {
             if let Some(cp) = title.codec_privates.get(idx).and_then(|c| c.as_ref()) {
                 track.codec_private = Some(cp.clone());
             }
+            stream_to_track.push(Some(tracks.len()));
             tracks.push(track);
         }
 
+        // Assemble the MVC merge when a dependent view is present and paired with
+        // a base video track.
+        let mvc = match (dep_stream_idx, base_stream_idx) {
+            (Some(dep_stream_idx), Some(base_stream_idx)) => {
+                let base_track_idx =
+                    stream_to_track[base_stream_idx].expect("base video stream always has a track");
+                Some(MvcMerge {
+                    base_stream_idx,
+                    dep_stream_idx,
+                    base_track_idx,
+                    stream_to_track,
+                    pending_base: std::collections::VecDeque::new(),
+                    dep_by_pts: std::collections::HashMap::new(),
+                    captured_params: None,
+                    orphan_deps: 0,
+                })
+            }
+            _ => None,
+        };
+
         // Defer muxer construction (and the TrackEntry dump) until the first
         // coded picture arrives, so the primary video track's FieldOrder is set
         // from the parser's MEASURED value before the header is written — never
@@ -177,6 +400,7 @@ impl MkvStream {
 
         Ok(Self {
             disc_title: title.clone(),
+            mvc,
             mode: Mode::Write(WriteMode::Pending(Box::new(PendingMux {
                 writer,
                 tracks,
@@ -209,6 +433,24 @@ impl MkvStream {
         if let Some(vt) = pending.video_track {
             apply_coding_to_track(&mut pending.tracks[vt], coding, video_picture_seen);
         }
+        // Blu-ray 3D: set the base video track's `mvc_params` from the dependent
+        // view's captured subset-SPS/PPS BEFORE the header is written, so the
+        // TrackEntry carries the `mvcC` BlockAdditionMapping. Captured from the
+        // first dependent AU (which arrives right after the first base AU in the
+        // SSIF), so it is available by the time the first base frame activates.
+        if let Some(mvc) = &self.mvc {
+            if let Some(params) = &mvc.captured_params {
+                if let Some(t) = pending.tracks.get_mut(mvc.base_track_idx) {
+                    t.mvc_params = Some(params.clone());
+                }
+            } else {
+                tracing::warn!(
+                    target: "mux",
+                    "MVC: no dependent-view subset-SPS/PPS captured before activation; \
+                     the base track will carry no mvcC mapping (3D not signalled)."
+                );
+            }
+        }
         // --log-level 3: dump the FINAL TrackEntry metadata (field order set).
         for (i, track) in pending.tracks.iter().enumerate() {
             crate::diag::dump_mkv_track((i + 1) as u64, track);
@@ -223,18 +465,72 @@ impl MkvStream {
         if let Some(path) = &pending.opening_capture_path {
             muxer.set_opening_capture(crate::diag::OpeningCapture::new(path, pending.tracks.len()));
         }
-        for f in pending.buffered.drain(..) {
+        for (f, additional) in pending.buffered.drain(..) {
-            muxer.write_frame(f.track, f.pts, f.keyframe, &f.data, f.duration_ns)?;
+            muxer.write_frame_with_additional(
+                f.track,
+                f.pts,
+                f.keyframe,
+                &f.data,
+                f.duration_ns,
+                additional.as_deref(),
+            )?;
         }
         self.mode = Mode::Write(WriteMode::Active(Box::new(muxer)));
         Ok(())
     }
 
+    /// Emit one frame (track index already muxer-relative) with an optional MVC
+    /// dependent-view `BlockAdditional`, honouring the deferred-activation
+    /// machinery: the first video frame triggers muxer construction (its coding
+    /// sets FieldOrder); earlier frames buffer. `additional` is `None` for every
+    /// non-3D frame and for the 3D base frames that had no paired dependent.
+    fn emit(&mut self, frame: &crate::pes::PesFrame, additional: Option<&[u8]>) -> io::Result<()> {
+        match &mut self.mode {
+            Mode::Read(_) => return Err(crate::error::Error::StreamReadOnly.into()),
+            Mode::Write(WriteMode::Active(m)) => {
+                return emit_to_muxer(m, frame, additional);
+            }
+            Mode::Write(WriteMode::Building) => return Ok(()),
+            Mode::Write(WriteMode::Pending(_)) => {}
+        }
+        // Pending: the first video frame (or the safety cap) triggers muxer
+        // construction; that frame's coding sets the field order. Other frames
+        // buffer until then.
+        let (activate_now, use_coding) = match &self.mode {
+            Mode::Write(WriteMode::Pending(p)) => {
+                let is_video = match p.video_track {
+                    Some(vt) => frame.track == vt,
+                    // No video track: nothing to wait for — build on frame one.
+                    None => true,
+                };
+                (is_video || p.buffered.len() >= MAX_PENDING_FRAMES, is_video)
+            }
+            _ => unreachable!("guarded above"),
+        };
+        if activate_now {
+            // Pass the trigger frame's coding only when it IS the video frame; a
+            // cap-triggered build never saw the video frame, so nothing measured
+            // is passed (apply_coding_to_track then logs + leaves UNDETERMINED).
+            self.activate(if use_coding { frame.coding } else { None }, use_coding)?;
+            if let Mode::Write(WriteMode::Active(m)) = &mut self.mode {
+                return emit_to_muxer(m, frame, additional);
+            }
+            Ok(())
+        } else {
+            if let Mode::Write(WriteMode::Pending(p)) = &mut self.mode {
+                p.buffered
+                    .push((frame.clone(), additional.map(|a| a.to_vec())));
+            }
+            Ok(())
+        }
+    }
+
     /// Open an MKV file for reading → PES frames.
     pub fn open(mut reader: impl Read + Send + 'static) -> io::Result<Self> {
         let (disc_title, codec_privates, ts_scale_ns) = parse_mkv_header(&mut reader)?;
         Ok(Self {
             disc_title,
+            mvc: None,
             mode: Mode::Read(ReadState {
                 reader: Box::new(reader),
                 cluster_ts_ticks: 0,
@@ -425,59 +721,40 @@ impl crate::pes::Stream for MkvStream {
     }
 
     fn write(&mut self, frame: &crate::pes::PesFrame) -> io::Result<()> {
-        // Fast paths.
+        if matches!(self.mode, Mode::Read(_)) {
-        match &mut self.mode {
+            return Err(crate::error::Error::StreamReadOnly.into());
-            Mode::Read(_) => return Err(crate::error::Error::StreamReadOnly.into()),
-            Mode::Write(WriteMode::Active(m)) => {
-                return m.write_frame(
-                    frame.track,
-                    frame.pts,
-                    frame.keyframe,
-                    &frame.data,
-                    frame.duration_ns,
-                );
-            }
-            Mode::Write(WriteMode::Building) => return Ok(()),
-            Mode::Write(WriteMode::Pending(_)) => {}
         }
-        // Pending: the first video frame (or the safety cap) triggers muxer
+        // Non-3D fast path: emit the frame directly, no clone, no buffering.
-        // construction; that frame's coding sets the field order. Other frames
+        if self.mvc.is_none() {
-        // buffer until then.
+            return self.emit(frame, None);
-        let (activate_now, use_coding) = match &self.mode {
-            Mode::Write(WriteMode::Pending(p)) => {
-                let is_video = match p.video_track {
-                    Some(vt) => frame.track == vt,
-                    // No video track: nothing to wait for — build on frame one.
-                    None => true,
-                };
-                (is_video || p.buffered.len() >= MAX_PENDING_FRAMES, is_video)
-            }
-            _ => unreachable!("guarded above"),
-        };
-        if activate_now {
-            // Pass the trigger frame's coding only when it IS the video frame; a
-            // cap-triggered build never saw the video frame, so nothing measured
-            // is passed (apply_coding_to_track then logs + leaves UNDETERMINED).
-            self.activate(if use_coding { frame.coding } else { None }, use_coding)?;
-            if let Mode::Write(WriteMode::Active(m)) = &mut self.mode {
-                return m.write_frame(
-                    frame.track,
-                    frame.pts,
-                    frame.keyframe,
-                    &frame.data,
-                    frame.duration_ns,
-                );
-            }
-            Ok(())
-        } else {
-            if let Mode::Write(WriteMode::Pending(p)) = &mut self.mode {
-                p.buffered.push(frame.clone());
-            }
-            Ok(())
         }
+        // Blu-ray 3D: run the frame through the MVC merge, which remaps track
+        // indices, folds the dependent view into the base as BlockAdditional
+        // (paired by PTS), and yields 0+ frames ready to emit. `ingest` returns
+        // owned pairs so the `self.mvc` borrow is released before `emit`.
+        let emits = self.mvc.as_mut().unwrap().ingest(frame);
+        for (f, additional) in emits {
+            self.emit(&f, additional.as_deref())?;
+        }
+        Ok(())
     }
 
     fn finish(&mut self) -> io::Result<()> {
+        // Blu-ray 3D: flush any base frames still awaiting a dependent (emitted
+        // unpaired as plain Blocks) before finalizing.
+        if let Some(mvc) = self.mvc.as_mut() {
+            let tail = mvc.flush();
+            let orphans = mvc.orphan_deps;
+            if orphans > 0 {
+                tracing::debug!(
+                    target: "mux",
+                    "MVC: {orphans} dependent-view access units had no matching base frame (dropped)"
+                );
+            }
+            for (f, additional) in tail {
+                self.emit(&f, additional.as_deref())?;
+            }
+        }
         // A title that produced no frames (or only buffered ones) is still
         // finalized into a valid MKV: activate now with no measured coding.
         if matches!(self.mode, Mode::Write(WriteMode::Pending(_))) {
@@ -916,6 +1193,107 @@ mod tests {
     use crate::pes::Stream as _;
     use std::io::Cursor;
 
+    /// Length-prefix (4-byte big-endian) each NAL, as the H.264 parser emits.
+    fn lp(nals: &[&[u8]]) -> Vec<u8> {
+        let mut v = Vec::new();
+        for n in nals {
+            v.extend_from_slice(&(n.len() as u32).to_be_bytes());
+            v.extend_from_slice(n);
+        }
+        v
+    }
+
+    fn mvc_frame(track: usize, pts: i64, keyframe: bool, data: Vec<u8>) -> crate::pes::PesFrame {
+        crate::pes::PesFrame {
+            track,
+            pts,
+            keyframe,
+            data,
+            duration_ns: None,
+            source: None,
+            coding: None,
+        }
+    }
+
+    // A subset SPS (NAL type 15), a PPS (type 8), and a coded-slice-extension
+    // (type 20) — the shape of a dependent-view access unit.
+    const SUBSET_SPS: [u8; 5] = [0x6F, 0x80, 0x00, 0x33, 0xAA]; // 0x6F & 0x1F = 15
+    const DEP_PPS: [u8; 3] = [0x68, 0xEE, 0x3C]; // 0x68 & 0x1F = 8
+    const DEP_SLICE: [u8; 3] = [0x74, 0x11, 0x22]; // 0x74 & 0x1F = 20
+
+    #[test]
+    fn extract_mvc_params_finds_subset_sps_and_pps() {
+        let data = lp(&[&SUBSET_SPS, &DEP_PPS, &DEP_SLICE]);
+        let (s, p) = extract_mvc_params(&data).expect("both param sets present");
+        assert_eq!(s, SUBSET_SPS, "subset SPS (NAL 15) captured verbatim");
+        assert_eq!(p, DEP_PPS, "PPS (NAL 8) captured verbatim");
+        // Missing PPS → None (the serializer then emits no mvcC mapping).
+        assert!(extract_mvc_params(&lp(&[&SUBSET_SPS, &DEP_SLICE])).is_none());
+        // Missing subset SPS → None.
+        assert!(extract_mvc_params(&lp(&[&DEP_PPS, &DEP_SLICE])).is_none());
+    }
+
+    fn empty_merge() -> MvcMerge {
+        MvcMerge {
+            base_stream_idx: 0,
+            dep_stream_idx: 2,
+            base_track_idx: 0,
+            stream_to_track: vec![Some(0), Some(1), None],
+            pending_base: std::collections::VecDeque::new(),
+            dep_by_pts: std::collections::HashMap::new(),
+            captured_params: None,
+            orphan_deps: 0,
+        }
+    }
+
+    #[test]
+    fn mvc_merge_pairs_base_and_dependent_by_pts() {
+        let mut m = empty_merge();
+        let dep = lp(&[&SUBSET_SPS, &DEP_PPS, &DEP_SLICE]);
+
+        // Base arrives first (SSIF order): buffered, nothing emitted yet.
+        let e = m.ingest(&mvc_frame(0, 100, true, lp(&[&[0x65, 1, 2]])));
+        assert!(e.is_empty(), "base held until its dependent arrives");
+
+        // Dependent arrives → base is emitted, remapped to the base track, with
+        // the dependent AU as its BlockAdditional; params are captured.
+        let e = m.ingest(&mvc_frame(2, 100, false, dep.clone()));
+        assert_eq!(e.len(), 1, "the paired base frame is emitted");
+        assert_eq!(e[0].0.track, 0, "remapped to the base muxer track");
+        assert_eq!(
+            e[0].1.as_deref(),
+            Some(dep.as_slice()),
+            "dependent attached"
+        );
+        assert!(m.captured_params.is_some(), "mvcC params captured");
+
+        // Audio passes straight through (remapped, no additional).
+        let e = m.ingest(&mvc_frame(1, 100, true, vec![0xAA]));
+        assert_eq!(e.len(), 1);
+        assert_eq!(e[0].0.track, 1);
+        assert!(e[0].1.is_none());
+
+        // Dependent-before-base (reordered) also pairs.
+        let dep2 = lp(&[&DEP_SLICE]);
+        assert!(m.ingest(&mvc_frame(2, 200, false, dep2.clone())).is_empty());
+        let e = m.ingest(&mvc_frame(0, 200, false, lp(&[&[0x61, 3, 4]])));
+        assert_eq!(e.len(), 1);
+        assert_eq!(e[0].1.as_deref(), Some(dep2.as_slice()));
+    }
+
+    #[test]
+    fn mvc_merge_flushes_unpaired_base_at_eof() {
+        let mut m = empty_merge();
+        // Base with no dependent ever → held, then flushed unpaired at EOF.
+        assert!(
+            m.ingest(&mvc_frame(0, 10, true, vec![0, 0, 0, 1]))
+                .is_empty()
+        );
+        let tail = m.flush();
+        assert_eq!(tail.len(), 1, "unpaired base still emitted");
+        assert!(tail[0].1.is_none(), "no BlockAdditional when unpaired");
+    }
+
     #[test]
     fn apply_coding_to_track_sets_measured_field_order_never_guesses() {
         use crate::disc::{Codec, ColorSpace, FrameRate, HdrFormat, Resolution, VideoStream};

src/mux/resolve.rs

@@ -575,7 +575,17 @@ fn build_demux_state(title: &DiscTitle, format: ContentFormat) -> DemuxState {
         pids.push(pid);
         pid_to_track.push((pid, idx));
         let is_dvd_ps = matches!(format, ContentFormat::MpegPs);
-        parsers.push((pid, super::codec::parser_for_codec(codec, None, is_dvd_ps)));
+        // The Blu-ray 3D MVC dependent (right-eye) view uses a param-set-
+        // passthrough H.264 parser so each frame is a self-contained dependent
+        // access unit for a BlockAdditional; every other stream uses the
+        // ordinary parser for its codec.
+        let parser = match s {
+            crate::disc::Stream::Video(v) if v.is_mvc_dependent() => {
+                super::codec::parser_for_mvc_dependent(codec, is_dvd_ps)
+            }
+            _ => super::codec::parser_for_codec(codec, None, is_dvd_ps),
+        };
+        parsers.push((pid, parser));
     }
     let (ts, ps) = match format {
         ContentFormat::MpegPs => (None, Some(super::ps::PsDemuxer::new())),