Draft:Dav1d

dav1d is a free and open-source software library and a command-line utility to decode video streams in the AV1 video coding format. It is developed by the VideoLAN and FFmpeg communities and sponsored by the Alliance for Open Media. It is designed to be fast, small, cross-platform and multithreaded.

The name dav1d is derived from a combination of factors. Pronounced "David", it merges the recursive acronym "dav1d is an AV1 decoder" with the leetspeak transformation of the name David, where the "i" is replaced by a "1" due to the visual similarity of their glyphs. This playful adaptation captures both the essence of the project as an AV1 decoder and pays homage to the hacker culture, where recursive acronyms and leetspeak are common occurrences.

dav1d is released under the BSD 2-clause "Simplified" License, a distinction from the Copyleft licensing favored by projects like FFmpeg and VideoLAN. This strategic choice of a more permissive license was made to encourage wider adoption of AV1. The decision to adopt a permissive license model for dav1d finds its roots in the Vorbis project, where similar licensing strategies were employed to promote adoption and prevent the entrenchment of proprietary formats.

History
The Alliance for Open Media released AV1 in March 2018 with a production grade and SIMD optimized software decoder called aomdec as part of libaom. A widespread opinion was that the libaom software implementation was slow both in terms of encoding and decoding speeds. The VideoLAN and FFmpeg communities, who had previously written faster software decoders for both VP8 and VP9 video formats, saw this as a barrier to entry for AV1 and decided to resolve this by writing a faster software decoder.

In October 2018, Ronald Bultje and Jean-Baptiste Kempf announced dav1d at the VideoLAN Developer Days 2018 conference. The goal of the project being to develop a fast AV1 software decoder to jumpstart the AV1 ecosystem and act as a stopgap solution until AV1 hardware decoders are common place.

The first usable version of dav1d, called 0.1.0 Gazelle, was released in December 2018. Releases 0.1.0 to 0.7.1 were primarily dedicated to low-bitdepth SIMD optimizations, aimed at enhancing decoding efficiency on x86 and ARM. Subsequent releases, from 0.7.1 to 1.0, shifted focus to high-bitdepth SIMD optimizations. In 2022, benchmarks were published showing that real-time AV1 playback of 720p 30fps at 2 Mbps was possible for low-end android devices and 1080p 30 fps at 4 Mbps was possible mid-range and high-end android devices.

From the beginning, dav1d was designed to be multithreaded, allowing for a combination of both frame-level parallelism and tile-level parallelism. The 1.0.0 release introduced a thread pool design, where each component in the decoding loop runs as a generic task with a simple dependency management mechanism. In this design, worker threads iterate over a list of available tasks, allowing for a more resource-efficient parallel decoding scheme that is independent of bitstream features like tiles.

In February 2024, researchers showed that when compared to other optimized software decoders AV1 thanks to dav1d is optimal from a Bjøntegaard-Delta bit-rate (BD-Rate) vs energy point of view.

Software that uses dav1d
In December 2018, the 3.0.5 release of the VLC media player switched from aomdec to dav1d as the default AV1 decoder.

In March 2019, Chromium, the open-source project behind Google Chrome and also Microsoft Edge, disabled libaom in favor of dav1d as the default AV1 decoder. This change was subsequently released in April 2019 as part of Chrome 74.

In May 2019, Mozilla announced that Firefox switched from libaom to dav1d as the default AV1 decoder on all desktop platforms (Windows, OSX and Linux) for both 32-bit and 64-bit systems.

In June 2019, Cisco demonstrated a live video conferencing call in Webex that relied on dav1d for AV1 decoding. This was the first demonstration of AV1 and dav1d for real time applications.

Support for dav1d in FFmpeg as been available since the release of version 4.2 "Ada", in August 2019.

In February 2020, Netflix stated that their Android app relied on dav1d to decode 10-bit AV1 content.

In February 2023, Meta reported using dav1d to decode AV1 content for Facebook Reels and Instagram Reels in their iOS app.

In April 2024, Google announced that Android switched from gav1 to dav1d for software decoder to allow AV1 on all devices running Android 12 or higher via a software update. Prior to this, Android developers had to incorporate dav1d into their apps and patch ExoPlayer in order to use dav1d to decode AV1 in their apps.

A reverse engineering report from April 2024 indicates that the Safari web browser uses dav1d to decode AV1.

As for source code reuse, the ARM and x86 optimized SIMD functions from dav1d have been imported into rav1e, an AV1 encoder by Xiph.Org Foundation. Optimized SIMD functions from dav1d have also been imported into SVT-AV1. Additionally, the dav1d source code was transpilled to the Rust programming language, which served as the starting point for the rav1d project, an AV1 decoder by the Internet Security Research Group.