oxideav-h265

Pure-Rust H.265 / HEVC (ITU-T H.265 | ISO/IEC 23008-2) bitstream parser for oxideav. The pixel-reconstruction pipeline is not yet implemented — this crate currently decodes parameter sets and slice headers but refuses to produce frames.

Part of the oxideav framework but usable standalone. Zero C dependencies, no FFI, no *-sys crates.

Installation

[dependencies]
oxideav-core = "0.0"
oxideav-codec = "0.0"
oxideav-h265 = "0.0"

Parse support

• NAL framing — Annex B byte-stream (0x000001 / 0x00000001 start codes) and length-prefixed (HVCC / MP4 hvc1 / hev1), including emulation-prevention byte removal.

• Parameter sets — VPS, SPS, PPS fully parsed. Out of range field values (bit depths, RPS counts, tile dimensions, picture size) are rejected with Error::InvalidData.

• Slice segment header — parsed through byte_alignment() for first-segment IDR I-slices under:

  • 4:2:0 / 4:2:2 / 4:4:4 chroma (no separate_colour_plane),
  • no multi-tile and no wavefront entry points,
  • no slice-header extension payload.

  For those slices the parsed header exposes slice_sao_luma_flag, slice_sao_chroma_flag, slice_qp_delta, derived SliceQpY, and a byte-aligned slice_data_bit_offset that marks where the CTU entropy payload begins. Other slice shapes (P/B, non-IDR, tiles, wavefronts) parse the leading portion of the header (type, POC, PPS id, RPS index) and then stop — is_full_i_slice reports false and CTU decode refuses as below.

• HEVCDecoderConfigurationRecord (hvcC) — used to populate VPS/SPS/PPS from MP4 / ISOBMFF extradata and to select the length-prefix size.

• CABAC init kernel (§9.3.4.2.1) — the (pStateIdx, valMps) derivation from an 8-bit initValue byte plus SliceQpY, with a unit-tested exemplar table (split_cu_flag). The rest of the context tables and the arithmetic decode engine itself are not yet written.

Decode support

No pixel decode yet. Calling Decoder::receive_frame on an HevcDecoder always returns Error::Unsupported("hevc CTU decode not yet implemented").

The decoder does run every step described in Parse support above on incoming packets, so tests can verify that a real ffmpeg-generated IDR I-slice reaches the CTU-decode boundary with correctly derived SliceQpY and byte-aligned slice_data() offset before refusing.

Missing to produce frames

• CABAC arithmetic decode engine (ivlCurrRange / ivlOffset / renorm, §9.3.4.3) and the full per-syntax context tables (~50 tables from §9.3.4.2.X).
• Coding-quadtree traversal (CTU → CU recursion, §7.3.8.4 / §7.3.8.5).
• Intra prediction — planar, DC, and the 33 angular modes (§8.4.4.2).
• Inverse transform pipeline — 4×4 DST-VII plus 4/8/16/32 DCT-II inverse (§8.6.4), dequantisation (§8.6.3).
• In-loop filters — deblocking (§8.7.2) and Sample Adaptive Offset (§8.7.3).
• Decoded Picture Buffer / reference picture set management for inter-coded slices.

No HEVC encoder. No scalable / multiview / 3D extensions (SHVC, MV-HEVC, 3D-HEVC).

Usage

Registering the codec surfaces the parser + the graceful Unsupported error so the codec registry behaves correctly when an HEVC stream is encountered:

use oxideav_codec::CodecRegistry;
let mut codecs = CodecRegistry::new();
oxideav_h265::register(&mut codecs);

Parsing parameter sets directly without going through the registry:

use oxideav_h265::nal::{iter_annex_b, extract_rbsp, NalUnitType};
use oxideav_h265::sps::parse_sps;

let bytes: &[u8] = /* Annex B stream */;
for nal in iter_annex_b(bytes) {
    if nal.header.nal_unit_type == NalUnitType::Sps {
        let rbsp = extract_rbsp(nal.payload());
        let sps = parse_sps(&rbsp)?;
        println!(
            "{}x{} {}-bit",
            sps.cropped_width(),
            sps.cropped_height(),
            sps.bit_depth_y(),
        );
    }
}
# Ok::<(), oxideav_core::Error>(())

License

MIT — see LICENSE.