Add MKV muxer and event system

- Add event.rs: structured event system for progress reporting
- Add mux/: MKV muxer pipeline (EBML writer, TS demuxer, stream assembly)
  - Codec parsers: H.264, HEVC, AC-3, DTS, TrueHD, PGS, VC-1
  - Lookahead buffer for codec private data extraction
  - Direct m2ts-to-MKV streaming without intermediate files

src/mux/codec/mod.rs

@@ -0,0 +1,88 @@
+//! Elementary stream codec parsers.
+//!
+//! Each parser takes PES packets and produces frames suitable for MKV muxing.
+//! Responsibilities:
+//! - Find frame boundaries
+//! - Extract codec initialization data (SPS/PPS, etc.)
+//! - Determine keyframe status
+//! - Convert PTS from 90kHz to nanoseconds
+
+pub mod ac3;
+pub mod h264;
+pub mod hevc;
+pub mod vc1;
+pub mod dts;
+pub mod truehd;
+pub mod pgs;
+
+use crate::disc::Codec;
+use super::ts::PesPacket;
+
+/// A single frame ready for MKV muxing.
+pub struct Frame {
+    /// Presentation timestamp in nanoseconds.
+    pub pts_ns: i64,
+    /// Whether this is a keyframe (used for cue points).
+    pub keyframe: bool,
+    /// Frame data (elementary stream bytes).
+    pub data: Vec<u8>,
+}
+
+/// Convert 90kHz PTS to nanoseconds.
+pub fn pts_to_ns(pts: i64) -> i64 {
+    pts * 100_000 / 9
+}
+
+/// Trait for codec-specific elementary stream parsers.
+pub trait CodecParser: Send {
+    /// Parse a PES packet into zero or more frames.
+    /// Most codecs: one PES = one frame.
+    /// Some (TrueHD): multiple access units per PES.
+    fn parse(&mut self, pes: &PesPacket) -> Vec<Frame>;
+
+    /// Get codec initialization data (e.g., SPS+PPS for H.264).
+    /// Returns None until enough data has been seen.
+    fn codec_private(&self) -> Option<Vec<u8>>;
+}
+
+/// Passthrough parser — treats each PES as one frame, no parsing.
+/// Used for codecs where PES = frame (AC3, DTS, PGS).
+pub struct PassthroughParser {
+    keyframe: bool,
+}
+
+impl PassthroughParser {
+    pub fn new(always_keyframe: bool) -> Self {
+        Self { keyframe: always_keyframe }
+    }
+}
+
+impl CodecParser for PassthroughParser {
+    fn parse(&mut self, pes: &PesPacket) -> Vec<Frame> {
+        let pts_ns = pes.pts.map(pts_to_ns).unwrap_or(0);
+        vec![Frame {
+            pts_ns,
+            keyframe: self.keyframe,
+            data: pes.data.clone(),
+        }]
+    }
+
+    fn codec_private(&self) -> Option<Vec<u8>> {
+        None
+    }
+}
+
+/// Create the appropriate parser for a codec.
+pub fn parser_for_codec(codec: Codec) -> Box<dyn CodecParser> {
+    match codec {
+        Codec::H264 => Box::new(h264::H264Parser::new()),
+        Codec::Hevc => Box::new(hevc::HevcParser::new()),
+        Codec::Vc1 => Box::new(vc1::Vc1Parser::new()),
+        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()),
+        Codec::Pgs => Box::new(pgs::PgsParser::new()),
+        Codec::Lpcm => Box::new(PassthroughParser::new(true)),
+        _ => Box::new(PassthroughParser::new(true)),
+    }
+}