VideoLAN launches dav2d to tackle AV2 decoding complexity

VideoLAN has announced the release of dav2d, an open-source software decoder designed for the AV2 video codec. The project, led by Jean-Baptiste Kempf, serves as the successor to dav1d, the widely deployed decoder for the AV1 standard. Developed in public and released under a BSD-style license, dav2d aims to provide a fast, portable, and correct implementation suitable for real-time applications on current hardware.

AV2, the latest royalty-free video codec from the Alliance for Open Media, represents the successor to AV1. It introduces new coding tools across prediction, transforms, entropy coding, filtering, and chroma processing. While the codec offers approximately 25% better compression efficiency than its predecessor, the decoding process is estimated to be roughly five times more complex. This increased computational demand necessitates careful, architecture-specific optimisation to ensure real-time performance on existing devices.

The decision to develop dav2d early, rather than waiting for the specification to fully stabilise, mirrors the strategy employed during the AV1 era. At that time, VideoLAN advocated for a fast software decoder, anticipating that hardware support would not materialise quickly enough for broad industry adoption. That foresight proved critical, as dav1d became the most widely deployed AV1 software decoder, integrated into major platforms including VLC, FFmpeg, Firefox, Chrome, Safari, Android, Windows, and Linux.

Current iterations of the dav2d codebase feature a feature-complete AVM v15 decoder supporting both 8-bit and 10-bit decoding. The project has already implemented architecture-specific optimisations, including AVX2 code for x86 processors and AArch64 NEON for ARM devices, with early work underway for RISC-V. This progress builds on the architectural experience gained from dav1d, allowing the team to transfer knowledge regarding threading, SIMD organisation, and API design.

To ensure accuracy and performance, dav2d utilises the 'checkasm' validation framework, originally created for dav1d. This tool allows developers to benchmark and validate optimised implementations against their C equivalents, making the optimisation process both faster and safer. As the AV2 ecosystem remains young, the project continues to focus on correctness, conformance, and further platform support, ensuring a robust foundation for future media technologies.