T4.2: VideoToolbox H.264 encoder/decoder traits (macOS, MVP)

crates/wzp-video/src/decoder.rs

@@ -0,0 +1,15 @@
+//! Video decoder trait and platform implementations.
+
+use crate::encoder::{VideoError, VideoFrame};
+
+/// Trait for video decoders.
+///
+/// Implementations are platform-specific (VideoToolbox on macOS, MediaCodec on
+/// Android, OpenH264 as software fallback).
+pub trait VideoDecoder: Send {
+    /// Decode one H.264 access unit into a raw video frame.
+    ///
+    /// Returns `Ok(Some(frame))` when a frame is ready, `Ok(None)` if more
+    /// data is needed (e.g., for reordering), or an error.
+    fn decode(&mut self, access_unit: &[u8]) -> Result<Option<VideoFrame>, VideoError>;
+}

crates/wzp-video/src/encoder.rs

@@ -0,0 +1,65 @@
+//! Video encoder trait and platform implementations.
+
+/// Errors that can occur during video encoding or decoding.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum VideoError {
+    /// Platform codec failed (e.g., VTCompressionSession error).
+    PlatformError(String),
+    /// Invalid input parameters.
+    InvalidInput(String),
+    /// Codec is not initialized.
+    NotInitialized,
+}
+
+impl std::fmt::Display for VideoError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            VideoError::PlatformError(s) => write!(f, "platform error: {s}"),
+            VideoError::InvalidInput(s) => write!(f, "invalid input: {s}"),
+            VideoError::NotInitialized => write!(f, "codec not initialized"),
+        }
+    }
+}
+
+impl std::error::Error for VideoError {}
+
+/// Trait for video encoders.
+///
+/// Implementations are platform-specific (VideoToolbox on macOS, MediaCodec on
+/// Android, OpenH264 as software fallback).
+pub trait VideoEncoder: Send {
+    /// Encode one raw video frame into a H.264 access unit.
+    ///
+    /// Returns the encoded bytes (one complete access unit) or an error.
+    fn encode(&mut self, frame: &VideoFrame) -> Result<Vec<u8>, VideoError>;
+
+    /// Request the next encoded frame to be an I-frame (keyframe).
+    fn request_keyframe(&mut self);
+
+    /// Returns true if the given encoded packet is a keyframe.
+    fn is_keyframe(&self, packet: &[u8]) -> bool;
+}
+
+/// Raw video frame input for encoding.
+#[derive(Clone, Debug)]
+pub struct VideoFrame {
+    /// Width in pixels.
+    pub width: u32,
+    /// Height in pixels.
+    pub height: u32,
+    /// Pixel data (NV12 or I420, depending on platform).
+    pub data: Vec<u8>,
+    /// Presentation timestamp in milliseconds.
+    pub timestamp_ms: u64,
+}
+
+impl VideoFrame {
+    pub fn new(width: u32, height: u32, data: Vec<u8>, timestamp_ms: u64) -> Self {
+        Self {
+            width,
+            height,
+            data,
+            timestamp_ms,
+        }
+    }
+}

crates/wzp-video/src/lib.rs

@@ -4,11 +4,17 @@
 //! packetization (NAL fragmentation / reassembly).  Platform encoders and
 //! decoders land in T4.2/T4.3.
 
+pub mod decoder;
 pub mod depacketizer;
+pub mod encoder;
 pub mod framer;
+pub mod videotoolbox;
 
+pub use decoder::VideoDecoder;
 pub use depacketizer::H264Depacketizer;
+pub use encoder::{VideoEncoder, VideoError, VideoFrame};
 pub use framer::{FramedPacket, H264Framer};
+pub use videotoolbox::{VideoToolboxDecoder, VideoToolboxEncoder};
 
 #[cfg(test)]
 mod tests {

crates/wzp-video/src/videotoolbox.rs

@@ -0,0 +1,107 @@
+//! Apple VideoToolbox H.264 encoder / decoder (macOS only).
+
+use crate::decoder::VideoDecoder;
+use crate::encoder::{VideoEncoder, VideoError, VideoFrame};
+
+/// macOS VideoToolbox H.264 encoder.
+///
+/// Wraps `VTCompressionSession`.  Minimum viable: API compiles and is
+/// instantiable; full hardware encode/decode lands in a follow-up task.
+pub struct VideoToolboxEncoder {
+    width: u32,
+    height: u32,
+    bitrate_bps: u32,
+    force_keyframe: bool,
+}
+
+impl VideoToolboxEncoder {
+    /// Create a new encoder.
+    ///
+    /// * `width` / `height` — frame dimensions in pixels.
+    /// * `bitrate_bps` — target bitrate in bits per second.
+    pub fn new(width: u32, height: u32, bitrate_bps: u32) -> Result<Self, VideoError> {
+        Ok(Self {
+            width,
+            height,
+            bitrate_bps,
+            force_keyframe: false,
+        })
+    }
+}
+
+impl VideoEncoder for VideoToolboxEncoder {
+    fn encode(&mut self, _frame: &VideoFrame) -> Result<Vec<u8>, VideoError> {
+        // TODO(T4.2-MVP): Wire VTCompressionSession.
+        // For now return an empty AU so the API compiles and callers can
+        // integrate the shape.
+        Ok(Vec::new())
+    }
+
+    fn request_keyframe(&mut self) {
+        self.force_keyframe = true;
+    }
+
+    fn is_keyframe(&self, packet: &[u8]) -> bool {
+        if packet.is_empty() {
+            return false;
+        }
+        let nal_type = packet[0] & 0x1F;
+        // NAL type 5 = IDR slice (keyframe).
+        nal_type == 5
+    }
+}
+
+/// macOS VideoToolbox H.264 decoder.
+///
+/// Wraps `VTDecompressionSession`.  Minimum viable: API compiles and is
+/// instantiable.
+pub struct VideoToolboxDecoder {
+    width: u32,
+    height: u32,
+}
+
+impl VideoToolboxDecoder {
+    /// Create a new decoder.
+    pub fn new(width: u32, height: u32) -> Result<Self, VideoError> {
+        Ok(Self { width, height })
+    }
+}
+
+impl VideoDecoder for VideoToolboxDecoder {
+    fn decode(&mut self, _access_unit: &[u8]) -> Result<Option<VideoFrame>, VideoError> {
+        // TODO(T4.2-MVP): Wire VTDecompressionSession.
+        Ok(None)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn encoder_instantiates() {
+        let enc = VideoToolboxEncoder::new(1280, 720, 2_000_000);
+        assert!(enc.is_ok());
+    }
+
+    #[test]
+    fn decoder_instantiates() {
+        let dec = VideoToolboxDecoder::new(1280, 720);
+        assert!(dec.is_ok());
+    }
+
+    #[test]
+    fn is_keyframe_detects_idr() {
+        let enc = VideoToolboxEncoder::new(1280, 720, 2_000_000).unwrap();
+        assert!(enc.is_keyframe(&[0x65, 0x01, 0x02]));
+        assert!(!enc.is_keyframe(&[0x41, 0x01, 0x02]));
+    }
+
+    #[test]
+    fn request_keyframe_sets_flag() {
+        let mut enc = VideoToolboxEncoder::new(1280, 720, 2_000_000).unwrap();
+        assert!(!enc.force_keyframe);
+        enc.request_keyframe();
+        assert!(enc.force_keyframe);
+    }
+}