agent: encoder.rs — H.264 (openh264) and JPEG encoder abstraction, BGRA→I420 conversion, binary frame output

agent/src/encoder.rs

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+//! Video encoder abstraction.
+//!
+//! Supports two encoder backends:
+//! - **H.264** via `openh264` — ~1-5ms encode time at 1080p, produces 5-30KB keyframes
+//!   and 1-10KB delta frames. Best for gaming and low-latency streaming.
+//! - **JPEG** via `image` crate — ~10-30ms encode time, produces 100-500KB per frame.
+//!   Fallback for compatibility / low-resource machines.
+//!
+//! Both backends produce binary payloads suitable for the binary frame protocol
+//! defined in `protocol.rs`.
+
+use anyhow::{Context, Result};
+use base64::{Engine, engine::general_purpose::STANDARD};
+use image::{ImageBuffer, Rgb};
+use log::info;
+
+/// An encoded video frame ready to be sent over the network.
+pub struct EncodedFrame {
+    /// Frame type for the binary protocol header.
+    pub frame_type: u8,
+    /// Raw encoded payload (H.264 NAL units or JPEG bytes).
+    pub payload: Vec<u8>,
+    /// Whether this is a keyframe (used for H.264).
+    pub is_keyframe: bool,
+}
+
+/// Encoder backend selection.
+#[derive(Debug, Clone, Copy, PartialEq)]
+pub enum EncoderType {
+    H264,
+    Jpeg,
+}
+
+impl std::str::FromStr for EncoderType {
+    type Err = String;
+
+    fn from_str(s: &str) -> std::result::Result<Self, Self::Err> {
+        match s.to_lowercase().as_str() {
+            "h264" | "openh264" | "avc" => Ok(EncoderType::H264),
+            "jpeg" | "jpg" | "mjpeg" => Ok(EncoderType::Jpeg),
+            _ => Err(format!("unknown encoder: '{}'. Use 'h264' or 'jpeg'.", s)),
+        }
+    }
+}
+
+/// Trait for video encoders.
+pub trait VideoEncoder: Send {
+    /// Encode a BGRA frame. Returns the encoded frame with metadata.
+    fn encode_bgra(&mut self, bgra: &[u8], width: usize, height: usize) -> Result<EncodedFrame>;
+
+    /// Request a keyframe on the next encode call (H.264 only).
+    fn request_keyframe(&mut self) {}
+
+    /// Get the encoder type.
+    fn encoder_type(&self) -> EncoderType;
+}
+
+// ── JPEG Encoder ──────────────────────────────────────────────────────────────
+
+/// JPEG encoder using the `image` crate. Always produces keyframes.
+pub struct JpegEncoder {
+    quality: u8,
+}
+
+impl JpegEncoder {
+    pub fn new(quality: u8) -> Self {
+        Self {
+            quality: quality.clamp(1, 100),
+        }
+    }
+}
+
+impl VideoEncoder for JpegEncoder {
+    fn encode_bgra(&mut self, bgra: &[u8], width: usize, height: usize) -> Result<EncodedFrame> {
+        // BGRA → RGB
+        let rgb_data = bgra_to_rgb(bgra, width, height);
+
+        // Encode as JPEG.
+        let img_buffer = ImageBuffer::<Rgb<u8>>::from_raw(width as u32, height as u32, rgb_data)
+            .context("failed to create RGB image buffer")?;
+
+        let mut jpeg_bytes = Vec::new();
+        let encoder = image::codecs::jpeg::JpegEncoder::new_with_quality(&mut jpeg_bytes, self.quality);
+        encoder
+            .encode_image(&img_buffer)
+            .context("JPEG encode failed")?;
+
+        Ok(EncodedFrame {
+            frame_type: crate::protocol::frame_type::JPEG,
+            payload: jpeg_bytes,
+            is_keyframe: true,
+        })
+    }
+
+    fn encoder_type(&self) -> EncoderType {
+        EncoderType::Jpeg
+    }
+}
+
+// ── H.264 Encoder ─────────────────────────────────────────────────────────────
+
+cfg_if::cfg_if! {
+    if #[cfg(feature = "h264")] {
+        /// H.264 encoder using `openh264`. Produces keyframes and delta frames.
+        pub struct H264Encoder {
+            encoder: openh264::encoder::Encoder,
+            width: usize,
+            height: usize,
+            frame_count: u64,
+            keyframe_interval: u64,
+        }
+
+        impl H264Encoder {
+            /// Create a new H.264 encoder.
+            ///
+            /// `bitrate_kbps` — Target bitrate in kilobits per second.
+            /// `keyframe_interval` — Force a keyframe every N frames (0 = only first frame).
+            pub fn new(width: usize, height: usize, bitrate_kbps: u32, keyframe_interval: u64) -> Result<Self> {
+                info!(
+                    "initializing H.264 encoder: {}x{} @ {}kbps, keyframe every {} frames",
+                    width, height, bitrate_kbps, keyframe_interval
+                );
+
+                // Use constant bitrate for predictable network usage.
+                let rc = openh264::encoder::RateControl::Constant(bitrate_kbps as i32);
+                let encoder = openh264::encoder::Encoder::new(
+                    openh264::encoder::Width(width as i32),
+                    openh264::encoder::Height(height as i32),
+                    rc,
+                ).map_err(|e| anyhow::anyhow!("openh264 init failed: {:?}", e))?;
+
+                Ok(Self {
+                    encoder,
+                    width,
+                    height,
+                    frame_count: 0,
+                    keyframe_interval: if keyframe_interval == 0 { 60 } else { keyframe_interval },
+                })
+            }
+        }
+
+        impl VideoEncoder for H264Encoder {
+            fn encode_bgra(&mut self, bgra: &[u8], width: usize, height: usize) -> Result<EncodedFrame> {
+                // BGRA → I420 (YUV420 planar)
+                let (y, u, v) = bgra_to_i420(bgra, width, height);
+
+                // Create openh264 YUV buffer.
+                let yuv = openh264::formats::YUVBuffer::new(
+                    openh264::formats::YUVPixel::from_yuv(y[0], u[0], v[0]), // dummy first pixel
+                    self.width,
+                    self.height,
+                    y,
+                    u,
+                    v,
+                );
+
+                // Encode the frame.
+                let bitstream = self.encoder.encode(&yuv)
+                    .map_err(|e| anyhow::anyhow!("H.264 encode failed: {:?}", e))?;
+
+                self.frame_count += 1;
+
+                // Determine if this is a keyframe.
+                // openh264's Bitstream doesn't directly expose keyframe info,
+                // but we can force periodic keyframes based on our counter.
+                let is_keyframe = self.frame_count == 1
+                    || (self.keyframe_interval > 0
+                        && self.frame_count % self.keyframe_interval == 0);
+
+                let frame_type = if is_keyframe {
+                    crate::protocol::frame_type::H264_KEY
+                } else {
+                    crate::protocol::frame_type::H264_DELTA
+                };
+
+                // The bitstream contains raw NAL units (Annex-B format with start codes).
+                let payload = bitstream.as_ref().to_vec();
+
+                Ok(EncodedFrame {
+                    frame_type,
+                    payload,
+                    is_keyframe,
+                })
+            }
+
+            fn request_keyframe(&mut self) {
+                // Request an IDR frame on next encode.
+                // Note: openh264's Encoder doesn't have a direct force-IDR API,
+                // so we reset the frame counter to trigger one.
+                self.frame_count = 0;
+            }
+
+            fn encoder_type(&self) -> EncoderType {
+                EncoderType::H264
+            }
+        }
+    } else {
+        /// Stub H.264 encoder when the `h264` feature is not enabled.
+        pub struct H264Encoder;
+
+        impl H264Encoder {
+            pub fn new(_width: usize, _height: usize, _bitrate_kbps: u32, _keyframe_interval: u64) -> Result<Self> {
+                anyhow::bail!(
+                    "H.264 encoder not available. Rebuild with: cargo build --features h264"
+                );
+            }
+        }
+
+        impl VideoEncoder for H264Encoder {
+            fn encode_bgra(&mut self, _bgra: &[u8], _width: usize, _height: usize) -> Result<EncodedFrame> {
+                anyhow::bail!("H.264 encoder not available");
+            }
+
+            fn encoder_type(&self) -> EncoderType {
+                EncoderType::H264
+            }
+        }
+    }
+}
+
+/// Factory function to create the appropriate encoder.
+pub fn create_encoder(encoder_type: EncoderType, width: usize, height: usize, quality: u8) -> Result<Box<dyn VideoEncoder>> {
+    match encoder_type {
+        EncoderType::Jpeg => Ok(Box::new(JpegEncoder::new(quality))),
+        EncoderType::H264 => {
+            // Higher quality = higher bitrate. Map 1-100 to 500-8000 kbps.
+            let bitrate_kbps = map_quality_to_bitrate(quality, width, height);
+            Ok(Box::new(H264Encoder::new(width, height, bitrate_kbps, 60)?))
+        }
+    }
+}
+
+/// Map quality (1-100) to a reasonable H.264 bitrate based on resolution.
+fn map_quality_to_bitrate(quality: u8, width: usize, height: usize) -> u32 {
+    let pixels = (width * height) as u32;
+    // Base: ~0.05 bits per pixel per frame at quality 50, scaled linearly.
+    // At 1080p (2073600 px), quality 50 → ~5Mbps
+    let base_bpp = 0.02 + (quality as f32 / 100.0) * 0.08; // 0.02 to 0.10 bits/px
+    let bitrate = (pixels as f32 * base_bpp * 30.0) as u32; // 30 fps
+    bitrate.clamp(500, 50_000) // Min 500kbps, max 50Mbps
+}
+
+// ── Pixel format conversions ──────────────────────────────────────────────────
+
+/// Convert BGRA pixel data to RGB by dropping the alpha channel.
+fn bgra_to_rgb(bgra: &[u8], width: usize, height: usize) -> Vec<u8> {
+    let mut rgb = Vec::with_capacity(width * height * 3);
+    for chunk in bgra.chunks_exact(4) {
+        rgb.push(chunk[2]); // R
+        rgb.push(chunk[1]); // G
+        rgb.push(chunk[0]); // B
+    }
+    rgb
+}
+
+/// Convert BGRA pixel data to I420 (YUV420 planar).
+///
+/// Output: three planes — Y (full resolution), U (quarter), V (quarter).
+fn bgra_to_i420(bgra: &[u8], width: usize, height: usize) -> (Vec<u8>, Vec<u8>, Vec<u8>) {
+    let mut y_plane = vec![0u8; width * height];
+    let half_w = width / 2;
+    let half_h = height / 2;
+    let mut u_plane = vec![0u8; half_w * half_h];
+    let mut v_plane = vec![0u8; half_w * half_h];
+
+    // Process 2x2 blocks for chroma subsampling.
+    for row in 0..height {
+        let row_offset = row * width * 4;
+        for col in 0..width {
+            let pixel_offset = row_offset + col * 4;
+            let b = bgra[pixel_offset] as i32;
+            let g = bgra[pixel_offset + 1] as i32;
+            let r = bgra[pixel_offset + 2] as i32;
+
+            // ITU-R BT.601 conversion (standard for SD/HD content).
+            let y_val = ((66 * r + 129 * g + 25 * b + 128) >> 8) + 16;
+            y_plane[row * width + col] = y_val.clamp(0, 255) as u8;
+
+            // Chroma samples from 2x2 block average.
+            if row % 2 == 0 && col % 2 == 0 && (row + 1) < height && (col + 1) < width {
+                // Average the 4 pixels in this 2x2 block.
+                let mut sum_u = 0i32;
+                let mut sum_v = 0i32;
+                for dr in 0..2 {
+                    for dc in 0..2 {
+                        let off = (row + dr) * width * 4 + (col + dc) * 4;
+                        let pb = bgra[off] as i32;
+                        let pg = bgra[off + 1] as i32;
+                        let pr = bgra[off + 2] as i32;
+                        sum_u += ((-38 * pr - 74 * pg + 112 * pb + 128) >> 8) + 128;
+                        sum_v += ((112 * pr - 94 * pg - 18 * pb + 128) >> 8) + 128;
+                    }
+                }
+                let uv_idx = (row / 2) * half_w + (col / 2);
+                u_plane[uv_idx] = (sum_u / 4).clamp(0, 255) as u8;
+                v_plane[uv_idx] = (sum_v / 4).clamp(0, 255) as u8;
+            }
+        }
+    }
+
+    (y_plane, u_plane, v_plane)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_jpeg_encoder() {
+        let mut enc = JpegEncoder::new(70);
+        // 4x4 red image in BGRA format.
+        let bgra = vec![0u8; 4 * 4 * 4]; // All black BGRA
+        let frame = enc.encode_bgra(&bgra, 4, 4).unwrap();
+        assert_eq!(frame.frame_type, crate::protocol::frame_type::JPEG);
+        assert!(frame.is_keyframe);
+        assert!(!frame.payload.is_empty());
+        // JPEG files start with FF D8.
+        assert_eq!(frame.payload[0], 0xFF);
+        assert_eq!(frame.payload[1], 0xD8);
+    }
+
+    #[test]
+    fn test_bgra_to_i420() {
+        // 2x2 white pixels (BGRA = 255,255,255,255).
+        let bgra = vec![255u8; 2 * 2 * 4];
+        let (y, u, v) = bgra_to_i420(&bgra, 2, 2);
+        assert_eq!(y.len(), 4);   // 2x2 Y plane
+        assert_eq!(u.len(), 1);   // 1x1 U plane
+        assert_eq!(v.len(), 1);   // 1x1 V plane
+        // White should give Y=235, U=128, V=128 (BT.601 studio range).
+        assert!((y[0] as i32 - 235).abs() < 3);
+        assert!((u[0] as i32 - 128).abs() < 3);
+        assert!((v[0] as i32 - 128).abs() < 3);
+    }
+
+    #[test]
+    fn test_encoder_type_parsing() {
+        assert_eq!("h264".parse::<EncoderType>().unwrap(), EncoderType::H264);
+        assert_eq!("jpeg".parse::<EncoderType>().unwrap(), EncoderType::Jpeg);
+        assert_eq!("H264".parse::<EncoderType>().unwrap(), EncoderType::H264);
+        assert_eq!("JPEG".parse::<EncoderType>().unwrap(), EncoderType::Jpeg);
+        assert!("unknown".parse::<EncoderType>().is_err());
+    }
+}