oxideav-webp 0.0.11

Pure-Rust WebP image codec for oxideav — RIFF VP8 lossy + VP8L lossless + VP8X extended + ALPH + animation decode, plus VP8 lossy and VP8L lossless single-frame encode
Documentation

oxideav-webp

Pure-Rust WebP image codec and container — RIFF/WEBP simple (lossy VP8 + lossless VP8L) + extended (VP8X with ALPH, ICCP, EXIF, XMP ) + animated (ANIM/ANMF) decode, plus single-frame encode on both the VP8 lossy and VP8L lossless paths. Zero C dependencies.

VP8 lossy decoding and encoding both go through oxideav-vp8 (also pure-Rust). VP8L lossless is a self-contained implementation of Google's Huffman + LZ77 + colour-cache + four-transform bitstream in this crate.

Part of the oxideav framework but usable standalone.

Installation

[dependencies]
oxideav-core = "0.1"
oxideav-codec = "0.1"
oxideav-container = "0.1"
oxideav-webp = "0.0"

Standalone use (no oxideav-core)

Image-library consumers that just want to turn a .webp byte buffer into RGBA pixels — no framework, no codec registry, no trait objects — can depend on this crate with the default registry feature off:

[dependencies]
oxideav-webp = { version = "0.0", default-features = false }

That drops the oxideav-core dependency entirely (and cascades the same off-switch through to oxideav-vp8) and exposes the free-standing decode/encode entry points:

use oxideav_webp::{decode_webp, WebpImage, WebpError};

let img: WebpImage = decode_webp(&bytes)?;
for frame in &img.frames {
    // frame.rgba is `Vec<u8>` of length width * height * 4
}
# Ok::<_, WebpError>(())

WebpImage / WebpFrame / WebpFileMetadata already use std-primitive fields (Vec<u8> RGBA, u32 dimensions). WebpError covers InvalidData / Unsupported / Eof / NeedMore and From-converts from oxideav_vp8::Vp8Error so the VP8 lossy path composes through cleanly. Encoder entry points (encode_vp8l_argb / encode_vp8l_argb_with, build_animated_webp) likewise stay available without oxideav-core. Turning the registry feature back on adds the Decoder / Encoder / Demuxer trait implementations + the register helpers + the WebpDecoder streaming type so the crate plugs into the framework registry as before.

Quick use

.webp files carry one or many frames, so the typical path is: open the file as a container, pull packets, decode them. Output is always PixelFormat::Rgba regardless of whether the source chunk was VP8 (lossy YUV → RGB) or VP8L (native RGBA).

use oxideav_codec::CodecRegistry;
use oxideav_container::ContainerRegistry;
use oxideav_core::Frame;

let mut codecs = CodecRegistry::new();
let mut containers = ContainerRegistry::new();
oxideav_webp::register(&mut codecs, &mut containers);

let input: Box<dyn oxideav_container::ReadSeek> = Box::new(
    std::io::Cursor::new(std::fs::read("image.webp")?),
);
let mut dmx = containers.open("webp", input)?;
let stream = &dmx.streams()[0];
let mut dec = oxideav_webp::decoder::WebpDecoder::new(
    stream.params.width.unwrap_or(0),
    stream.params.height.unwrap_or(0),
);

loop {
    match dmx.next_packet() {
        Ok(pkt) => {
            oxideav_codec::Decoder::send_packet(&mut dec, &pkt)?;
            while let Ok(Frame::Video(vf)) = oxideav_codec::Decoder::receive_frame(&mut dec) {
                // vf.format == PixelFormat::Rgba
                // vf.planes[0].data holds width*height*4 bytes, row-major.
            }
        }
        Err(oxideav_core::Error::Eof) => break,
        Err(e) => return Err(e.into()),
    }
}
# Ok::<(), Box<dyn std::error::Error>>(())

For a one-shot decode of an in-memory buffer, skip the registry dance:

let bytes = std::fs::read("image.webp")?;
let img = oxideav_webp::decode_webp(&bytes)?;
for frame in &img.frames {
    // frame.rgba has width*height*4 bytes; frame.duration_ms is the
    // ANMF per-frame delay (0 for still images).
}
# Ok::<(), Box<dyn std::error::Error>>(())

Encoder — VP8L (lossless, RGBA / RGB in)

use oxideav_core::{CodecId, CodecParameters, PixelFormat};

let mut params = CodecParameters::video(CodecId::new(oxideav_webp::CODEC_ID_VP8L));
params.width = Some(w);
params.height = Some(h);
params.pixel_format = Some(PixelFormat::Rgba); // or PixelFormat::Rgb24
let mut enc = codecs.make_encoder(&params)?;
enc.send_frame(&Frame::Video(frame))?;
let pkt = enc.receive_packet()?; // complete .webp file

The registered webp_vp8l encoder accepts two input pixel formats:

  • Rgba — the historical default. Fully-opaque frames use the simple RIFF/WEBP/VP8L layout; frames with any transparent pixel switch to the extended RIFF/WEBP/VP8X + VP8L layout so the VP8X header advertises the alpha flag (required by any spec-compliant reader).
  • Rgb24 — three bytes per pixel, no alpha. Useful when the upstream is a JPEG decode or a PNG-without-alpha decode (the common case on the image crate side). The conversion to the encoder's internal ARGB pixel buffer streams through the input three bytes at a time — no intermediate Rgba byte buffer is materialised, so re-encoding an RGB image to WebP costs only the encoder's own working memory, not a full 4-byte expansion. Always emits the simple layout (Rgb24 is implicitly opaque). Closes #7.

If you need a bare VP8L bitstream (for embedding in another container, say), call oxideav_webp::encode_vp8l_argb directly — that entry point still returns the header-to-data bytes with no RIFF wrapper.

Encoder — VP8 (lossy)

let mut params = CodecParameters::video(CodecId::new(oxideav_webp::CODEC_ID_VP8));
params.width = Some(w);
params.height = Some(h);
// One of: Yuv420P, Yuva420P, Rgba, Rgb24
params.pixel_format = Some(PixelFormat::Yuv420P);
let mut enc = codecs.make_encoder(&params)?;
enc.send_frame(&Frame::Video(frame))?;
let pkt = enc.receive_packet()?; // complete .webp file

Four input pixel formats are accepted:

  • Yuv420P — the native VP8 input. Emits the simple RIFF/WEBP/VP8 layout.
  • Yuva420P — Yuv420P with a side full-resolution alpha plane. The YUV planes feed straight into the keyframe (no RGB roundtrip) and the alpha plane goes straight into a VP8L-compressed ALPH sidecar. Emits the extended RIFF/WEBP/VP8X + ALPH + VP8 layout with the VP8X ALPHA flag set.
  • Rgba — converts RGB to YUV 4:2:0 (BT.601 limited range) for the VP8 keyframe and compresses the alpha plane into an ALPH sidecar chunk. Emits the extended RIFF/WEBP/VP8X + ALPH + VP8 layout with the VP8X ALPHA flag set.
  • Rgb24 — RGB without alpha. Streams the RGB→YUV conversion three bytes at a time without ever building a Rgba byte buffer (issue #7), and emits the simple RIFF/WEBP/VP8 layout.

Yuva420P is the natural input shape if you already have a YUV-with-alpha frame from a video decoder. It avoids the YUV→RGB→YUV roundtrip the Rgba path goes through.

Quality control: the VP8 lossy encoder exposes two equivalent factory entry points for picking a target compression level —

  • encoder_vp8::make_encoder_with_quality(&params, quality) — takes a libwebp-style quality: f32 in 0.0..=100.0 (higher = better quality / larger file; the libwebp default is 75.0).
  • encoder_vp8::make_encoder_with_qindex(&params, qindex) — takes the underlying VP8 qindex in 0..=127 (lower = better) for callers that already speak the libvpx scale.

The quality → qindex mapping is the linear inversion qindex = round((100 - quality) * 1.27), so the API surface lines up with libwebp but the perceptual behaviour does not: libwebp also adjusts its quantizer matrices, AC/DC deltas, and segment-level QP based on quality, none of which we currently do. Round-2 work would tune the quantizer matrix and segment QPs to track libwebp's perceptual targets at matching quality values.

Scope

Encoder scope (current):

  • VP8L lossless from Rgba or Rgb24 (single frame). Emits subtract-green + colour (G↔R/B decorrelation) + tile-based predictor
    • colour-indexing (palette) transforms plus a tunable colour cache. The default encode_vp8l_argb entry point runs a 32-trial RDO sweep over every combination of the four optional transforms × four colour-cache widths ({off, 6, 8, 10} bits) and keeps the smallest encoded variant. Each trial also tries meta-Huffman per-tile grouping at K = 1 / 2 / 4 / 8 (gated by image pixel count) and picks the byte-smallest. Predictor pool covers all 14 RFC 9649 §4.1 modes per 16-pixel tile. Optional near-lossless preprocessing (libwebp-compatible 0..=100 knob) collapses near-identical pixels into longer LZ77 runs / richer cache hits. Callers that want a fixed configuration call encode_vp8l_argb_with directly. Encoder ≈ 90 % libwebp parity on natural fixtures (lossless ratio within ~30 % of cwebp on the workspace corpus); residual gap is multi-pass LZ77 (cost-modelled match selection), the entropy-image transform, and finer predictor-tile-size adaptation.
  • VP8 lossy from Yuv420P, Yuva420P, Rgba, or Rgb24 (single frame). For Yuva420P and Rgba the alpha plane is emitted as a VP8L-compressed ALPH chunk inside the extended (VP8X) container; Yuva420P skips the YUV→RGB→YUV roundtrip the Rgba path forces. Rgb24 streams the RGB→YUV conversion without a Rgba alloc (issue #7). Per-segment quantiser deltas (RFC 6386 §10)
    • per-segment loop-filter deltas (§15.2) are wired in based on a source-luma variance classifier, so smooth / textured regions get finer / coarser quant + softer / stronger deblocking respectively. Per-frequency AC/DC quantiser deltas (y_dc_delta / y2_dc_delta / y2_ac_delta / uv_dc_delta / uv_ac_delta) are exposed via encoder_vp8::Vp8FreqDeltas plus the matching factory entry points make_encoder_with_qindex_and_freq_deltas / make_encoder_with_quality_and_freq_deltas so callers can bias bits toward a specific frequency band (defaults to all-zero, which reproduces the prior bitstream byte-for-byte). Default qindex from oxideav-vp8 is used unless the caller selects a specific one via encoder_vp8::make_encoder_with_qindex (VP8 qindex 0..=127, lower = better) or the libwebp-style encoder_vp8::make_encoder_with_quality (0.0..=100.0, higher = better). Encoder ≈ 80 % libwebp parity on natural fixtures; residual gap is a quality-driven quantizer matrix.
  • VP8X extended header is emitted automatically whenever the output carries an ALPH sidecar or optional ICC / EXIF / XMP metadata via the riff::WebpMetadata helper.
  • Animated WebP encode via [build_animated_webp] / [build_animated_webp_with_options] — emits a VP8X + ANIM + ANMF...ANMF file from a slice of AnimFrames with per-frame durations, x/y offsets, blend, and disposal flags. Per-frame AnimFrameMode::Auto runs both VP8L and VP8+ALPH encoders and picks whichever sub-chunk is byte-smaller — animations can mix lossless and lossy frames, matching libwebp's WebPAnimEncoderAdd behaviour. All four blend × dispose-to-background combinations round-trip through the in-crate decoder.

Decoder scope:

  • VP8 simple lossy (through oxideav-vp8), VP8L lossless, VP8X extended with ALPH (raw / filtered / VP8L-compressed alpha plane), and ANIM/ANMF animation with per-frame disposal + blend modes composited onto an internal RGBA canvas.
  • ICCP / EXIF / XMP chunks are surfaced on WebpImage::metadata (a WebpFileMetadata struct with optional icc / exif / xmp byte vectors). For metadata-only access without decoding any pixels, call oxideav_webp::extract_metadata on the file bytes directly.
  • Default output pixel format is Rgba. For single-frame VP8+ALPH input, WebpDecoder::new_yuva420p(w, h) (or set_prefer_yuva420p(true) after construction) flips the output to a 4-plane Yuva420P frame — skipping the YUV→RGB conversion
    • alpha overlay the default path runs. VP8L and animated files always stay on the RGBA path (cross-frame composite needs a unified pixel format).

Codec / container IDs

  • Codec: "webp_vp8l" (VP8L encoder + standalone VP8L decoder); accepted input pixel formats Rgba, Rgb24. Decoded output is always Rgba.
  • Codec: "webp_vp8" (VP8 lossy encoder path); accepted input pixel formats Yuv420P, Yuva420P, Rgba, Rgb24.
  • Container: "webp", matches .webp by extension + RIFF/WEBP magic.

Single-image WebPs decode to one VideoFrame; animated WebPs produce N frames with PTS in milliseconds (the ANMF native unit).

For VP8+ALPH inputs the WebpDecoder defaults to Rgba output (the historical behaviour). To opt into a 4-plane Yuva420P frame straight from the VP8 + ALPH decoders — skipping the YUV→RGB conversion + alpha overlay — construct the decoder with WebpDecoder::new_yuva420p(w, h) (or set set_prefer_yuva420p(true) after construction). VP8L and animated files always go through the RGBA canvas because cross-frame disposal/blend semantics need a unified pixel format.

image crate interop

If you already have a RgbImage (image::ImageBuffer<Rgb<u8>, _>) from a JPEG decode or a PNG-without-alpha decode, you can feed its backing Vec<u8> straight to the webp_vp8l or webp_vp8 encoder with pixel_format = Some(PixelFormat::Rgb24) and a single-plane VideoFrame { stride: w * 3, data: ... } — no Rgba allocation required.

License

MIT — see LICENSE.