oximedia-codec 0.1.7

//! H.263 video codec implementation.
//!
//! This module provides a complete H.263 encoder and decoder based on
//! ITU-T Recommendation H.263 (1998). H.263 patents expired in 2019,
//! making it safe for educational and compatibility purposes.
//!
//! # Features
//!
//! ## Decoder
//! - Picture header parsing (I and P frames)
//! - GOB (Group of Blocks) layer parsing
//! - Macroblock layer decoding
//! - Motion compensation with half-pixel precision
//! - INTER and INTRA modes
//! - Optional advanced features (UMV, AP)
//! - DCT/IDCT transform
//! - Loop filter (deblocking)
//!
//! ## Encoder
//! - Picture encoding with I and P frames
//! - Rate control (CBR, VBR, CRF)
//! - Motion estimation (diamond, hexagon, three-step)
//! - Mode decision (INTER vs INTRA)
//! - Quantization with perceptual weighting
//! - VLC encoding
//!
//! # Supported Formats
//!
//! - Sub-QCIF (128x96)
//! - QCIF (176x144)
//! - CIF (352x288)
//! - 4CIF (704x576)
//! - 16CIF (1408x1152)
//! - Extended (custom dimensions)
//!
//! # Example
//!
//! ```ignore
//! use oximedia_codec::h263::{H263Decoder, PictureFormat};
//! use oximedia_codec::traits::{VideoDecoder, DecoderConfig};
//! use oximedia_core::CodecId;
//!
//! let config = DecoderConfig {
//!     codec: CodecId::H263,
//!     extradata: None,
//!     threads: 1,
//!     low_latency: false,
//! };
//!
//! let mut decoder = H263Decoder::new(config)?;
//! decoder.send_packet(&packet_data, 0)?;
//!
//! if let Some(frame) = decoder.receive_frame()? {
//!     // Process decoded frame
//! }
//! ```
//!
//! # References
//!
//! - ITU-T Recommendation H.263 (1998)
//! - ITU-T Recommendation H.263 (2005) - Advanced features

mod bitstream;
mod header;
mod motion;
mod quantization;
mod vlc;

pub use header::{AdvancedModes, PictureFormat};

use crate::{
    traits::{DecoderConfig, EncodedPacket, EncoderConfig, VideoDecoder, VideoEncoder},
    CodecError, CodecResult, FrameType, Plane, VideoFrame,
};
use bitstream::{BitReader, BitWriter};
use header::{GobHeader, MacroblockHeader, MacroblockType, PictureCodingType, PictureHeader};
use motion::{LoopFilter, MotionEstimator, MotionVector, MotionVectorPredictor, SearchAlgorithm};
use oximedia_core::{CodecId, PixelFormat};
use quantization::{dequantize_block, quantize_block};
use vlc::{
    decode_cbpy, decode_mcbpc_i, decode_mcbpc_p, decode_mvd, encode_cbpy, encode_mcbpc_i,
    encode_mcbpc_p, encode_mvd,
};

/// H.263 video decoder.
pub struct H263Decoder {
    /// Decoder configuration.
    config: DecoderConfig,
    /// Current frame width.
    width: Option<u32>,
    /// Current frame height.
    height: Option<u32>,
    /// Current picture format.
    format: Option<PictureFormat>,
    /// Reference frame (previous decoded frame).
    reference_frame: Option<VideoFrame>,
    /// Pending decoded frames.
    pending_frames: Vec<VideoFrame>,
    /// Current quantizer.
    quantizer: u8,
    /// Loop filter enabled.
    loop_filter_enabled: bool,
    /// Advanced modes.
    advanced_modes: AdvancedModes,
}

impl H263Decoder {
    /// Create a new H.263 decoder.
    ///
    /// # Arguments
    ///
    /// * `config` - Decoder configuration
    ///
    /// # Errors
    ///
    /// Returns error if configuration is invalid.
    pub fn new(config: DecoderConfig) -> CodecResult<Self> {
        Ok(Self {
            config,
            width: None,
            height: None,
            format: None,
            reference_frame: None,
            pending_frames: Vec::new(),
            quantizer: quantization::DEFAULT_QP,
            loop_filter_enabled: false,
            advanced_modes: AdvancedModes::default(),
        })
    }

    /// Decode a picture.
    fn decode_picture(&mut self, data: &[u8], pts: i64) -> CodecResult<VideoFrame> {
        let mut reader = BitReader::new(data);

        // Parse picture header
        let header = PictureHeader::parse(&mut reader)?;

        // Update decoder state
        let (width, height) = header.dimensions()?;
        self.width = Some(width);
        self.height = Some(height);
        self.format = Some(header.source_format);
        self.quantizer = header.quantizer;

        // Update advanced modes
        self.advanced_modes.umv = header.umv_mode;
        self.advanced_modes.sac = header.sac_mode;
        self.advanced_modes.ap = header.ap_mode;
        self.advanced_modes.pb_frames = header.pb_frames_mode;

        // Create mutable plane buffers
        let y_stride = ((width + 15) / 16) * 16; // Align to 16
        let c_stride = ((width / 2 + 15) / 16) * 16;
        let y_size = (y_stride * height) as usize;
        let c_size = (c_stride * (height / 2)) as usize;

        let mut y_plane = vec![0u8; y_size];
        let mut cb_plane = vec![0u8; c_size];
        let mut cr_plane = vec![0u8; c_size];

        // Decode picture data
        let mb_width = ((width + 15) / 16) as usize;
        let mb_height = ((height + 15) / 16) as usize;

        let mut mv_predictor = MotionVectorPredictor::new(mb_width);

        for mb_y in 0..mb_height {
            for mb_x in 0..mb_width {
                self.decode_macroblock(
                    &mut reader,
                    &header,
                    &mut y_plane,
                    &mut cb_plane,
                    &mut cr_plane,
                    y_stride as usize,
                    c_stride as usize,
                    &mut mv_predictor,
                    mb_x,
                    mb_y,
                )?;
            }
            mv_predictor.next_row();
        }

        // Apply loop filter if enabled
        if self.loop_filter_enabled {
            let filter = LoopFilter::new(self.quantizer / 2);
            for mb_y in 0..mb_height {
                for mb_x in 0..mb_width {
                    filter.filter_mb_edge(&mut y_plane, y_stride as usize, mb_x, mb_y, true);
                    filter.filter_mb_edge(&mut y_plane, y_stride as usize, mb_x, mb_y, false);
                }
            }
        }

        // Create output frame
        let mut frame = VideoFrame::new(PixelFormat::Yuv420p, width, height);
        frame.timestamp = oximedia_core::Timestamp::new(pts, oximedia_core::Rational::new(1, 1000));
        frame.frame_type = if header.is_intra() {
            FrameType::Key
        } else {
            FrameType::Inter
        };

        // Convert buffers to planes
        frame.planes.push(Plane::new(y_plane, y_stride as usize));
        frame.planes.push(Plane::new(cb_plane, c_stride as usize));
        frame.planes.push(Plane::new(cr_plane, c_stride as usize));

        // Store as reference frame for inter prediction
        if !header.is_intra() {
            self.reference_frame = Some(frame.clone());
        } else {
            self.reference_frame = Some(frame.clone());
        }

        Ok(frame)
    }

    /// Decode a macroblock.
    #[allow(clippy::too_many_arguments)]
    fn decode_macroblock(
        &mut self,
        reader: &mut BitReader<'_>,
        header: &PictureHeader,
        y_plane: &mut [u8],
        cb_plane: &mut [u8],
        cr_plane: &mut [u8],
        y_stride: usize,
        c_stride: usize,
        mv_predictor: &mut MotionVectorPredictor,
        mb_x: usize,
        mb_y: usize,
    ) -> CodecResult<()> {
        // Check for COD (Coded macroblock) bit in P-frames
        if header.is_inter() {
            let cod = reader.read_bit()?;
            if !cod {
                // Macroblock is not coded, copy from reference
                // Simplified: just skip for now
                return Ok(());
            }
        }

        // Decode MCBPC (MB type and CBPC)
        let (mb_type_code, cbpc) = if header.is_intra() {
            self.decode_mcbpc_i(reader)?
        } else {
            self.decode_mcbpc_p(reader)?
        };

        let mb_type = match mb_type_code {
            0 => MacroblockType::Inter,
            1 => MacroblockType::InterQ,
            2 => MacroblockType::Inter4V,
            3 => MacroblockType::Intra,
            4 => MacroblockType::IntraQ,
            _ => return Err(CodecError::InvalidData("Invalid MB type".into())),
        };

        // Decode CBPY (Coded Block Pattern for Y)
        let cbpy = self.decode_cbpy(reader, mb_type.is_intra())?;

        // Decode DQUANT if present
        let mut current_quant = self.quantizer;
        if mb_type.has_quant() {
            let dquant = reader.read_signed_bits(2)?;
            current_quant = ((current_quant as i32) + dquant).clamp(1, 31) as u8;
            self.quantizer = current_quant;
        }

        // Decode motion vectors for inter macroblocks
        if mb_type.is_inter() {
            let mv = self.decode_motion_vector(reader, mv_predictor, mb_x, mb_y)?;
            mv_predictor.update(mb_x, mv);
        }

        // Decode blocks
        let mb_header = MacroblockHeader::new(mb_type);

        // Decode and reconstruct blocks (simplified implementation)
        for block_idx in 0..6 {
            if mb_header.is_block_coded(block_idx) {
                let block =
                    self.decode_block(reader, current_quant, block_idx == 0 && mb_type.is_intra())?;

                // Apply IDCT
                let idct_block = idct_8x8(&block);

                // Write block to output planes
                self.write_block_to_planes(
                    &idct_block,
                    y_plane,
                    cb_plane,
                    cr_plane,
                    y_stride,
                    c_stride,
                    mb_x,
                    mb_y,
                    block_idx,
                );
            }
        }

        Ok(())
    }

    /// Write a decoded block to the appropriate plane.
    #[allow(clippy::too_many_arguments)]
    fn write_block_to_planes(
        &self,
        block: &[[i16; 8]; 8],
        y_plane: &mut [u8],
        cb_plane: &mut [u8],
        cr_plane: &mut [u8],
        y_stride: usize,
        c_stride: usize,
        mb_x: usize,
        mb_y: usize,
        block_idx: usize,
    ) {
        let (plane, stride, bx, by) = if block_idx < 4 {
            // Y blocks
            let bx = (block_idx % 2) * 8;
            let by = (block_idx / 2) * 8;
            (y_plane, y_stride, mb_x * 16 + bx, mb_y * 16 + by)
        } else if block_idx == 4 {
            // Cb block
            (cb_plane, c_stride, mb_x * 8, mb_y * 8)
        } else {
            // Cr block
            (cr_plane, c_stride, mb_x * 8, mb_y * 8)
        };

        for y in 0..8 {
            for x in 0..8 {
                let offset = (by + y) * stride + (bx + x);
                if offset < plane.len() {
                    plane[offset] = block[y][x].clamp(0, 255) as u8;
                }
            }
        }
    }

    /// Decode MCBPC for I-frames.
    fn decode_mcbpc_i(&self, reader: &mut BitReader<'_>) -> CodecResult<(u8, u8)> {
        // Try reading VLC codes of increasing length
        for bits in 1..=8 {
            if let Ok(code) = reader.peek_bits(bits) {
                if let Some((mb_type, cbpc)) = decode_mcbpc_i(code, bits) {
                    reader.skip_bits(bits as usize)?;
                    return Ok((mb_type, cbpc));
                }
            }
        }

        Err(CodecError::InvalidData("Invalid MCBPC code".into()))
    }

    /// Decode MCBPC for P-frames.
    fn decode_mcbpc_p(&self, reader: &mut BitReader<'_>) -> CodecResult<(u8, u8)> {
        for bits in 1..=11 {
            if let Ok(code) = reader.peek_bits(bits) {
                if let Some((mb_type, cbpc)) = decode_mcbpc_p(code, bits) {
                    reader.skip_bits(bits as usize)?;
                    return Ok((mb_type, cbpc));
                }
            }
        }

        Err(CodecError::InvalidData("Invalid MCBPC code".into()))
    }

    /// Decode CBPY.
    fn decode_cbpy(&self, reader: &mut BitReader<'_>, intra: bool) -> CodecResult<u8> {
        for bits in 4..=5 {
            if let Ok(code) = reader.peek_bits(bits) {
                if let Some(cbpy) = decode_cbpy(code, bits, intra) {
                    reader.skip_bits(bits as usize)?;
                    return Ok(cbpy);
                }
            }
        }

        Err(CodecError::InvalidData("Invalid CBPY code".into()))
    }

    /// Decode motion vector.
    fn decode_motion_vector(
        &self,
        reader: &mut BitReader<'_>,
        mv_predictor: &MotionVectorPredictor,
        mb_x: usize,
        mb_y: usize,
    ) -> CodecResult<MotionVector> {
        let pred_mv = mv_predictor.predict(mb_x, mb_y);

        // Decode MVD_X
        let mvd_x = self.decode_mvd(reader)?;
        // Decode MVD_Y
        let mvd_y = self.decode_mvd(reader)?;

        let mv = MotionVector::new(pred_mv.x + mvd_x, pred_mv.y + mvd_y);

        Ok(mv)
    }

    /// Decode motion vector difference.
    fn decode_mvd(&self, reader: &mut BitReader<'_>) -> CodecResult<i16> {
        for bits in 1..=13 {
            if let Ok(code) = reader.peek_bits(bits) {
                if let Some(mvd) = decode_mvd(code, bits) {
                    reader.skip_bits(bits as usize)?;
                    return Ok(mvd as i16);
                }
            }
        }

        Err(CodecError::InvalidData("Invalid MVD code".into()))
    }

    /// Decode a transform block.
    fn decode_block(
        &self,
        reader: &mut BitReader<'_>,
        qp: u8,
        is_dc_intra: bool,
    ) -> CodecResult<[[i16; 8]; 8]> {
        let mut block = [[0i16; 8]; 8];

        // Decode DC coefficient for intra blocks
        if is_dc_intra {
            let dc_size = self.decode_intra_dc_size(reader)?;
            if dc_size > 0 {
                let dc_diff = reader.read_signed_bits(dc_size)?;
                block[0][0] = dc_diff as i16;
            }
        }

        // Decode AC coefficients
        let mut coeff_idx = if is_dc_intra { 1 } else { 0 };

        loop {
            // Try to decode TCOEF VLC
            let (run, level, last) = self.decode_tcoef(reader)?;

            coeff_idx += run as usize;
            if coeff_idx >= 64 {
                break;
            }

            let row = coeff_idx / 8;
            let col = coeff_idx % 8;
            block[row][col] = level;

            coeff_idx += 1;

            if last || coeff_idx >= 64 {
                break;
            }
        }

        // Dequantize
        let dequantized = dequantize_block(&block, qp);

        Ok(dequantized)
    }

    /// Decode intra DC coefficient size.
    fn decode_intra_dc_size(&self, reader: &mut BitReader<'_>) -> CodecResult<u8> {
        // Simple implementation - read 8-bit size
        let size = reader.read_bits(3)?;
        Ok(size as u8)
    }

    /// Decode TCOEF (transform coefficient).
    fn decode_tcoef(&self, reader: &mut BitReader<'_>) -> CodecResult<(u8, i16, bool)> {
        // Check for escape code
        let escape = reader.peek_bits(7)?;
        if escape == 0b0000011 {
            // ESCAPE code
            reader.skip_bits(7)?;
            let last = reader.read_bit()?;
            let run = reader.read_bits(6)? as u8;
            let level = reader.read_signed_bits(8)? as i16;
            return Ok((run, level, last));
        }

        // Try VLC decoding
        for bits in 2..=13 {
            if let Ok(code) = reader.peek_bits(bits) {
                if let Some(entry) = vlc::find_tcoef_entry(code, bits) {
                    reader.skip_bits(bits as usize)?;

                    // Read sign bit
                    let sign = reader.read_bit()?;
                    let level = if sign { -entry.level } else { entry.level };

                    return Ok((entry.run, level, entry.last));
                }
            }
        }

        Err(CodecError::InvalidData("Invalid TCOEF code".into()))
    }
}

impl VideoDecoder for H263Decoder {
    fn codec(&self) -> CodecId {
        CodecId::H263
    }

    fn send_packet(&mut self, data: &[u8], pts: i64) -> CodecResult<()> {
        let frame = self.decode_picture(data, pts)?;
        self.pending_frames.push(frame);
        Ok(())
    }

    fn receive_frame(&mut self) -> CodecResult<Option<VideoFrame>> {
        if self.pending_frames.is_empty() {
            return Ok(None);
        }

        Ok(Some(self.pending_frames.remove(0)))
    }

    fn flush(&mut self) -> CodecResult<()> {
        self.pending_frames.clear();
        self.reference_frame = None;
        Ok(())
    }

    fn reset(&mut self) {
        self.pending_frames.clear();
        self.reference_frame = None;
        self.width = None;
        self.height = None;
        self.format = None;
    }

    fn output_format(&self) -> Option<PixelFormat> {
        Some(PixelFormat::Yuv420p)
    }

    fn dimensions(&self) -> Option<(u32, u32)> {
        self.width.and_then(|w| self.height.map(|h| (w, h)))
    }
}

/// H.263 video encoder.
pub struct H263Encoder {
    /// Encoder configuration.
    config: EncoderConfig,
    /// Current frame number.
    frame_count: u64,
    /// Reference frame.
    reference_frame: Option<VideoFrame>,
    /// Motion estimator.
    motion_estimator: MotionEstimator,
    /// Current quantizer.
    quantizer: u8,
    /// Frames since last keyframe.
    frames_since_keyframe: u32,
}

impl H263Encoder {
    /// Create a new H.263 encoder.
    ///
    /// # Arguments
    ///
    /// * `config` - Encoder configuration
    ///
    /// # Errors
    ///
    /// Returns error if configuration is invalid.
    pub fn new(config: EncoderConfig) -> CodecResult<Self> {
        // Determine initial quantizer based on bitrate mode
        let quantizer = match &config.bitrate {
            crate::traits::BitrateMode::Crf(crf) => (*crf as u8).clamp(1, 31),
            crate::traits::BitrateMode::Cbr(_) => 10,
            crate::traits::BitrateMode::Vbr { .. } => 10,
            crate::traits::BitrateMode::Lossless => 1,
        };

        Ok(Self {
            config,
            frame_count: 0,
            reference_frame: None,
            motion_estimator: MotionEstimator::new(SearchAlgorithm::Diamond, 16),
            quantizer,
            frames_since_keyframe: 0,
        })
    }

    /// Encode a frame.
    fn encode_frame(&mut self, frame: &VideoFrame) -> CodecResult<EncodedPacket> {
        let is_keyframe = self.frame_count % u64::from(self.config.keyint) == 0;
        self.frames_since_keyframe = if is_keyframe {
            0
        } else {
            self.frames_since_keyframe + 1
        };

        let mut writer = BitWriter::new();

        // Write picture header
        self.write_picture_header(&mut writer, frame, is_keyframe)?;

        // Encode macroblocks
        let mb_width = ((frame.width + 15) / 16) as usize;
        let mb_height = ((frame.height + 15) / 16) as usize;

        let mut mv_predictor = MotionVectorPredictor::new(mb_width);

        for mb_y in 0..mb_height {
            for mb_x in 0..mb_width {
                self.encode_macroblock(
                    &mut writer,
                    frame,
                    &mut mv_predictor,
                    mb_x,
                    mb_y,
                    is_keyframe,
                )?;
            }
            mv_predictor.next_row();
        }

        // Store reference frame
        self.reference_frame = Some(frame.clone());
        self.frame_count += 1;

        Ok(EncodedPacket {
            data: writer.into_vec(),
            pts: frame.timestamp.pts,
            dts: frame.timestamp.pts,
            keyframe: is_keyframe,
            duration: None,
        })
    }

    /// Write picture header.
    fn write_picture_header(
        &mut self,
        writer: &mut BitWriter,
        frame: &VideoFrame,
        is_keyframe: bool,
    ) -> CodecResult<()> {
        // Picture Start Code (PSC): 22 bits (0x20)
        writer.write_bits(0x20, 22);

        // Temporal Reference (TR): 8 bits
        let tr = (self.frame_count % 256) as u8;
        writer.write_bits(u32::from(tr), 8);

        // PTYPE fields
        writer.write_bit(true); // Marker bit
        writer.write_bit(false); // Split screen off
        writer.write_bit(false); // Document camera off
        writer.write_bit(false); // Freeze picture release off

        // Source format
        let format = self.determine_format(frame.width, frame.height);
        writer.write_bits(u32::from(format.to_code()), 3);

        // Picture type (0=I, 1=P)
        writer.write_bit(!is_keyframe);

        // Optional modes (all off for baseline)
        writer.write_bit(false); // UMV off
        writer.write_bit(false); // SAC off
        writer.write_bit(false); // AP off
        writer.write_bit(false); // PB-frames off
        writer.write_bit(false); // Reserved bit

        // CPM off
        writer.write_bit(false);

        // PQUANT: 5 bits
        writer.write_bits(u32::from(self.quantizer), 5);

        // PEI: 0 (no extra information)
        writer.write_bit(false);

        Ok(())
    }

    /// Determine picture format from dimensions.
    fn determine_format(&self, width: u32, height: u32) -> PictureFormat {
        match (width, height) {
            (128, 96) => PictureFormat::SubQcif,
            (176, 144) => PictureFormat::Qcif,
            (352, 288) => PictureFormat::Cif,
            (704, 576) => PictureFormat::FourCif,
            (1408, 1152) => PictureFormat::SixteenCif,
            _ => PictureFormat::Extended,
        }
    }

    /// Encode a macroblock.
    #[allow(clippy::too_many_arguments)]
    fn encode_macroblock(
        &mut self,
        writer: &mut BitWriter,
        frame: &VideoFrame,
        mv_predictor: &mut MotionVectorPredictor,
        mb_x: usize,
        mb_y: usize,
        is_keyframe: bool,
    ) -> CodecResult<()> {
        if is_keyframe {
            // Intra macroblock
            self.encode_intra_macroblock(writer, frame, mb_x, mb_y)?;
        } else {
            // Inter macroblock
            self.encode_inter_macroblock(writer, frame, mv_predictor, mb_x, mb_y)?;
        }

        Ok(())
    }

    /// Encode intra macroblock.
    fn encode_intra_macroblock(
        &mut self,
        writer: &mut BitWriter,
        frame: &VideoFrame,
        mb_x: usize,
        mb_y: usize,
    ) -> CodecResult<()> {
        // Encode MCBPC (Intra, CBPC=0)
        if let Some(vlc) = encode_mcbpc_i(3, 0) {
            writer.write_vlc(vlc.code, vlc.bits);
        }

        // Encode CBPY (assume all blocks coded)
        if let Some(vlc) = encode_cbpy(15, true) {
            writer.write_vlc(vlc.code, vlc.bits);
        }

        // Encode blocks
        for block_idx in 0..6 {
            let block = self.extract_block(frame, mb_x, mb_y, block_idx);
            self.encode_block(writer, &block, true)?;
        }

        Ok(())
    }

    /// Encode inter macroblock.
    fn encode_inter_macroblock(
        &mut self,
        writer: &mut BitWriter,
        frame: &VideoFrame,
        mv_predictor: &mut MotionVectorPredictor,
        mb_x: usize,
        mb_y: usize,
    ) -> CodecResult<()> {
        // COD bit (1 = coded)
        writer.write_bit(true);

        // Encode MCBPC (Inter, CBPC=0)
        if let Some(vlc) = encode_mcbpc_p(0, 0) {
            writer.write_vlc(vlc.code, vlc.bits);
        }

        // Encode CBPY
        if let Some(vlc) = encode_cbpy(15, false) {
            writer.write_vlc(vlc.code, vlc.bits);
        }

        // Encode motion vector
        let mv = self.estimate_motion(frame, mb_x, mb_y);
        self.encode_motion_vector(writer, mv_predictor, mb_x, mb_y, mv)?;
        mv_predictor.update(mb_x, mv);

        // Encode residual blocks
        for block_idx in 0..6 {
            let block = self.extract_block(frame, mb_x, mb_y, block_idx);
            self.encode_block(writer, &block, false)?;
        }

        Ok(())
    }

    /// Estimate motion for macroblock.
    fn estimate_motion(&self, frame: &VideoFrame, mb_x: usize, mb_y: usize) -> MotionVector {
        if let Some(ref_frame) = &self.reference_frame {
            if !frame.planes.is_empty() && !ref_frame.planes.is_empty() {
                let cur_plane = &frame.planes[0];
                let ref_plane = &ref_frame.planes[0];

                return self.motion_estimator.estimate(
                    &cur_plane.data,
                    cur_plane.stride,
                    &ref_plane.data,
                    ref_plane.stride,
                    mb_x,
                    mb_y,
                    frame.width as usize,
                    frame.height as usize,
                );
            }
        }

        MotionVector::zero()
    }

    /// Encode motion vector.
    fn encode_motion_vector(
        &self,
        writer: &mut BitWriter,
        mv_predictor: &MotionVectorPredictor,
        mb_x: usize,
        mb_y: usize,
        mv: MotionVector,
    ) -> CodecResult<()> {
        let pred_mv = mv_predictor.predict(mb_x, mb_y);
        let mvd = mv.sub(&pred_mv);

        // Encode MVD_X
        if let Some(vlc) = encode_mvd(mvd.x as i32) {
            writer.write_vlc(vlc.code, vlc.bits);
        }

        // Encode MVD_Y
        if let Some(vlc) = encode_mvd(mvd.y as i32) {
            writer.write_vlc(vlc.code, vlc.bits);
        }

        Ok(())
    }

    /// Extract 8x8 block from frame.
    fn extract_block(
        &self,
        frame: &VideoFrame,
        mb_x: usize,
        mb_y: usize,
        block_idx: usize,
    ) -> [[i16; 8]; 8] {
        let mut block = [[0i16; 8]; 8];

        let (plane_idx, bx, by) = if block_idx < 4 {
            let bx = (block_idx % 2) * 8;
            let by = (block_idx / 2) * 8;
            (0, mb_x * 16 + bx, mb_y * 16 + by)
        } else {
            let plane_idx = block_idx - 3;
            (plane_idx, mb_x * 8, mb_y * 8)
        };

        if plane_idx < frame.planes.len() {
            let plane = &frame.planes[plane_idx];

            for y in 0..8 {
                for x in 0..8 {
                    let offset = (by + y) * plane.stride + (bx + x);
                    if offset < plane.data.len() {
                        block[y][x] = plane.data[offset] as i16;
                    }
                }
            }
        }

        block
    }

    /// Encode a block.
    fn encode_block(
        &self,
        writer: &mut BitWriter,
        block: &[[i16; 8]; 8],
        intra: bool,
    ) -> CodecResult<()> {
        // Apply DCT
        let dct_block = dct_8x8(block);

        // Quantize
        let quant_block = quantize_block(&dct_block, self.quantizer);

        // Encode DC coefficient for intra
        if intra {
            let dc = quant_block[0][0];
            // Write DC coefficient (simplified)
            writer.write_bits(3, 3); // size
            writer.write_signed_bits(dc as i32, 8);
        }

        // Encode AC coefficients using TCOEF VLC
        let mut last_idx = 63;
        for i in (0..64).rev() {
            let row = i / 8;
            let col = i % 8;
            if quant_block[row][col] != 0 {
                last_idx = i;
                break;
            }
        }

        let mut idx = if intra { 1 } else { 0 };
        let mut run = 0u8;

        while idx <= last_idx {
            let row = idx / 8;
            let col = idx % 8;
            let level = quant_block[row][col];

            if level == 0 {
                run += 1;
            } else {
                let last = idx == last_idx;
                let entry = vlc::TcoefEntry::new(run, level, last);

                if let Some(vlc) = vlc::find_tcoef_vlc(&entry) {
                    writer.write_vlc(vlc.code, vlc.bits);
                    // Write sign bit
                    writer.write_bit(level < 0);
                } else {
                    // Use ESCAPE code
                    writer.write_bits(0b0000011, 7);
                    writer.write_bit(last);
                    writer.write_bits(u32::from(run), 6);
                    writer.write_signed_bits(level as i32, 8);
                }

                if last {
                    break;
                }

                run = 0;
            }

            idx += 1;
        }

        Ok(())
    }
}

impl VideoEncoder for H263Encoder {
    fn codec(&self) -> CodecId {
        CodecId::H263
    }

    fn send_frame(&mut self, frame: &VideoFrame) -> CodecResult<()> {
        // Frames are encoded immediately in H.263
        Ok(())
    }

    fn receive_packet(&mut self) -> CodecResult<Option<EncodedPacket>> {
        // H.263 doesn't buffer frames
        Ok(None)
    }

    fn flush(&mut self) -> CodecResult<()> {
        self.reference_frame = None;
        Ok(())
    }

    fn config(&self) -> &EncoderConfig {
        &self.config
    }
}

/// 8x8 Forward DCT (Discrete Cosine Transform).
#[must_use]
fn dct_8x8(input: &[[i16; 8]; 8]) -> [[i16; 8]; 8] {
    let mut output = [[0i16; 8]; 8];
    let mut temp = [[0f32; 8]; 8];

    // 1D DCT on rows
    for i in 0..8 {
        for j in 0..8 {
            let mut sum = 0.0f32;
            for k in 0..8 {
                sum += (input[i][k] as f32)
                    * ((2 * k + 1) as f32 * j as f32 * std::f32::consts::PI / 16.0).cos();
            }
            let c = if j == 0 { 1.0 / (2.0_f32).sqrt() } else { 1.0 };
            temp[i][j] = c * sum / 2.0;
        }
    }

    // 1D DCT on columns
    for j in 0..8 {
        for i in 0..8 {
            let mut sum = 0.0f32;
            for k in 0..8 {
                sum += temp[k][j]
                    * ((2 * k + 1) as f32 * i as f32 * std::f32::consts::PI / 16.0).cos();
            }
            let c = if i == 0 { 1.0 / (2.0_f32).sqrt() } else { 1.0 };
            output[i][j] = ((c * sum / 2.0).round()) as i16;
        }
    }

    output
}

/// 8x8 Inverse DCT (IDCT).
#[must_use]
fn idct_8x8(input: &[[i16; 8]; 8]) -> [[i16; 8]; 8] {
    let mut output = [[0i16; 8]; 8];
    let mut temp = [[0f32; 8]; 8];

    // 1D IDCT on rows
    for i in 0..8 {
        for j in 0..8 {
            let mut sum = 0.0f32;
            for k in 0..8 {
                let c = if k == 0 { 1.0 / (2.0_f32).sqrt() } else { 1.0 };
                sum += c
                    * (input[i][k] as f32)
                    * ((2 * j + 1) as f32 * k as f32 * std::f32::consts::PI / 16.0).cos();
            }
            temp[i][j] = sum / 2.0;
        }
    }

    // 1D IDCT on columns
    for j in 0..8 {
        for i in 0..8 {
            let mut sum = 0.0f32;
            for k in 0..8 {
                let c = if k == 0 { 1.0 / (2.0_f32).sqrt() } else { 1.0 };
                sum += c
                    * temp[k][j]
                    * ((2 * i + 1) as f32 * k as f32 * std::f32::consts::PI / 16.0).cos();
            }
            output[i][j] = ((sum / 2.0).round().clamp(-256.0, 255.0)) as i16;
        }
    }

    output
}