wav1c - Wondrous AV1 Encoder

An AV1 video encoder written from scratch in safe Rust with zero dependencies. Produces IVF files decodable by dav1d.

Features

• YUV 4:2:0 encoding (8-bit)
• Intra prediction (DC, V, H, Smooth, Paeth) with RD-cost mode selection
• Inter prediction (GLOBALMV with LAST_FRAME reference)
• Forward DCT/ADST transforms with RD-cost type selection (4x4 chroma, 8x8/16x16 luma)
• MSAC arithmetic coding with full coefficient encoding
• GoP structure (keyframe + inter frames)
• Arbitrary frame dimensions up to 4096x2304
• Y4M input, IVF output
• Streaming encoder API (frame-by-frame encoding)
• C FFI shared library for embedding in non-Rust applications

Workspace Structure

wav1c/          Core library with batch and streaming APIs
wav1c-cli/      Command-line encoder
wav1c-ffi/      C FFI shared library (cdylib + staticlib)
wav1c-wasm/     WebAssembly bindings (wasm-bindgen)

Build

cargo build --workspace --release

CLI Usage

Encode a Y4M video:

wav1c input.y4m -o output.ivf

Encode a solid color frame:

wav1c 320 240 128 128 128 -o gray.ivf

With options:

wav1c input.y4m -o output.ivf -q 100 --keyint 10 --bitrate 500k

Decode with dav1d:

dav1d -i output.ivf -o decoded.y4m

Generate test input with ffmpeg:

ffmpeg -f lavfi -i testsrc=duration=2:size=320x240:rate=25 -pix_fmt yuv420p input.y4m

Rust Streaming API

use wav1c::{Encoder, EncoderConfig, FrameType};
use wav1c::y4m::FramePixels;

let config = EncoderConfig {
    base_q_idx: 128,
    keyint: 25,
    target_bitrate: None,
    fps: 25.0,
};

let mut encoder = Encoder::new(320, 240, config).unwrap();
let frame = FramePixels::solid(320, 240, 128, 128, 128);

encoder.send_frame(&frame).unwrap();
let packet = encoder.receive_packet().unwrap();

assert_eq!(packet.frame_type, FrameType::Key);
// packet.data contains raw AV1 OBUs (TD + SequenceHeader + Frame)

C FFI

The wav1c-ffi crate produces libwav1c_ffi.dylib (macOS) / libwav1c_ffi.so (Linux) and libwav1c_ffi.a.

#include "wav1c.h"

Wav1cConfig cfg = { .base_q_idx = 128, .keyint = 25, .fps = 25.0 };
Wav1cEncoder *enc = wav1c_encoder_new(320, 240, &cfg);

wav1c_encoder_send_frame(enc, y, y_len, u, u_len, v, v_len, width, width / 2);
Wav1cPacket *pkt = wav1c_encoder_receive_packet(enc);
// pkt->data, pkt->size contain raw AV1 OBUs

wav1c_packet_free(pkt);
wav1c_encoder_free(enc);

Build the C example:

cargo build -p wav1c-ffi --release
cc -o encode -I wav1c-ffi/include wav1c-ffi/examples/encode.c \
   -L target/release -lwav1c_ffi

FFmpeg Integration

A patch is included to add wav1c as an FFmpeg external encoder (-c:v libwav1c).

# Build the wav1c static library
cargo build -p wav1c-ffi --release

# Clone and patch FFmpeg
git clone https://git.ffmpeg.org/ffmpeg.git
cd ffmpeg
git apply /path/to/wav1c/ffmpeg-libwav1c.patch

# Configure with libwav1c (adjust library path as needed)
./configure --enable-libwav1c \
  --extra-cflags="-I/path/to/wav1c/wav1c-ffi/include" \
  --extra-ldflags="-L/path/to/wav1c/target/release"

make -j$(sysctl -n hw.ncpu 2>/dev/null || nproc)

# Encode
./ffmpeg -i input.y4m -c:v libwav1c -wav1c-q 128 output.mp4

Test

cargo test --workspace

Integration tests decode output with dav1d and verify pixel accuracy. Install dav1d and ensure it is available in your PATH, or set the DAV1D environment variable to point to the binary. Tests will skip gracefully if dav1d is not found.

License

This project is licensed under the Mozilla Public License 2.0. See LICENSE for details.