Sustainability of Digital Formats: Planning for Library of Congress Collections

AV1 (short for 'AOMedia Video 1') is an open, royalty-free video coding format specified in the AV1 Bitstream & Decoding Process Specification. This specification was developed as the first project of the Alliance for Open Media (AOMedia or AOM), a non-profit industry consortium that develops open, royalty-free technology for multimedia delivery. See Notes for more information about the history of AOMedia.

The formation of AOMedia and creation of AV1 are, in part, a response to complex licensing and patent issues with High Efficiency Video Coding (HEVC) (also known as H.265, MPEG-H Part 2) that inhibit use by large scale content creators of high quality web video. HEVC/H.265 is a improvement on its highly adopted predecessor Advanced Video Coding (also known as AVC or H.264) in that it supports higher bit depths and enhanced chroma formats, including the use of full-resolution chroma (4:4:4) and key innovations designed to support efficient compression such as flexible block sizes for coding and transforms efficiency. A 2020 article in IEEE Spectrum states that "HEVC was designed to have better coding efficiency over the existing Advanced Video Coding (AVC) standard, with tests showing an average of 53 percent lower bit rate than AVC while still achieving the same subjective video quality." Nonetheless, the HEVC patent situation has been an impediment to adoption despite its technological advances. As of March 2020, HEVC had approximately 17,000 registered patents with potentially more from unknown patent holders. See HEVC for more details.

AV1 is built on Google's VP9 video codec. According to A Technical Overview of AV1 published in Proceedings of the IEEE ( Volume: 109, Issue: 9, September 2021), "The AV1 bitstream is packetized into open bitstream units (OBUs). An ordered sequence of OBUs is fed into the AV1 decoding process, where each OBU comprises a variable length string of bytes. An OBU contains a header and a payload. The header identifies the OBU type and specifies the payload size." Typical OBUs include Sequence Header, Temporal Delimiter, Frame Header, Tile Group, Frame, Metadata, and Tile List. An Overview of Core Coding Tools in the AV1 Video Codec details additional structural details such as 10-way partitioning as well as increased size for superblocks (from 128×128 or 64×64 pixels to 128×128 pixels), "non-directional predictors are enriched by taking into account gradients and evolving correlations, (and) coherence of luma and chroma signals is exploited". Wikipedia notes that "AV1 has new optimized quantization matrices (aom_qm). The eight sets of quantization parameters that can be selected and signaled for each frame now have individual parameters for the two chroma planes and can use spatial prediction." In addition, there are improvements for filters and entropy encoding.

One of the main advantages of AV1, aside from being open-source and royalty free, is improved compression rates. A 2018 blog post from Engineering at Meta notes "Our testing shows AV1 surpasses its stated goal of 30% better compression than VP9, and achieves gains of 50.3%, 46.2% and 34.0%, compared to x264 main profile, x264 high profile and libvpx-vp9, respectively. The new codec requires longer encoding times vs. current alternatives, however, due to increased complexity." Bitmovin summarizes the advantages of AV1 as "interoperable and open; designed with a low computational footprint and optimized for hardware; capable of consistent, highest-quality, real-time video delivery; optimized for the Internet; scalable to any modern device at any bandwidth; and, flexible for both commercial and non-commercial content, including user-generated content." Higher compression rates mean less data use for same quality image.

The AV1 specification defines three profiles (Main, High and Professional) and various levels and clarifies that "the profile specifies the bit depth and subsampling formats supported, while the level defines resolution and performance characteristics." The seq_profile tag in the general sequence header metadata specifies the features that can be used in the coded video sequence.

• Main profile supports YUV 4:2:0 or monochrome bitstreams with bit depth equal to 8 or 10; “Main” compliant decoders must be able to decode streams with seq_profile equal to 0.
• High profile adds support for YUV 4:4:4 bitstreams (but not monochrome) with bit depth equal to 8 or 10; “High” compliant decoders must be able to decode streams with seq_profile less than or equal to 1.
• Professional profile adds support for YUV 4:2:2 video with bitstreams with bit depth equal to 12; “Professional” compliant decoders must be able to decode streams with seq_profile less than or equal to 2.

Adoption is steadily growing across a variety of domains.

In February 2020, Netflix started streaming AV1 to the Android mobile app followed by streaming to TVs in November 2021. Apple added support for the AV1 video format with the A17 Pro chip in iPhone 15 Pro in 2023.

The Scalable Video Technology for AV1 (SVT-AV1 Encoder and Decoder) project, started in 2020 with support from Netflix but now run by the Alliance of Open Media (AOM) Software Implementation Working Group (SIWG), is an AV1-compliant software encoder/decoder library which "targets the development of a production-quality AV1-encoder with performance levels applicable to a wide range of applications, from premium VOD to real-time and live encoding/transcoding."

Another option is open source cross platform decoder dav1d built by the VideoLAN, VLC, and FFmpeg communities and sponsored by AOMedia (as described in a 2021 blog post Bringing AV1 Streaming to Netflix Members’ TVs).

Other indications of growing influence and adoption include: select Samsung TVs support AV1; YouTube added AV1 support in 2023; Discord,

There have been some notable issues however. For a time in 2021, Roku pulled YouTube TV from the Roku Channel Store because, in part (according to Protocol) "Google is requiring makers of Android TV devices to support AV1 starting this month [April 2021]. Additionally, Google also seems to push makers of smart TVs and streaming devices not based on Android TV to use AV1 for YouTube." Roku's response was that this would be an unfair burden on consumers to accept costs for new hardware requirements. Google disputed this claim, stating "Roku requested exceptions that would break the YouTube experience and limit our ability to update YouTube in order to fix issues or add new features." The issue was later resolved and now Roku supports AV1 but DASH (Dynamic Adaptive Streaming over HTTP) only.

As of January 2024, popular live-streaming service especially for gamers, Twitch has not yet implemented AV1.

avif.io notes that AV1 is also integrating into video conferencing thanks to its SVC (Scalable Video Coding) which allows for adaptable framerate and resolution that can be used to define a lower bitrate substream resulting in more consistent quality levels, especially over high volume calls.

Can I Use: AV1 video format lists browser support for AV1 but it is unclear how recent the information is. Comments welcome.

There's intermittent mention about developing AV2 as a successor to AV1 to correct issues and approaches (see for example, Nathan Egge's presentation at AOMedia Research Symposium 2019 and selected issues on the AOMedia GitHub Issue tracker) but there's no concrete work on AV2 as of this writing in February 2022. Egge explains that the compressed timeline of AV1's standards development has downstream implications including limited test conditions, less relevant evaluation criteria with a lack of quality implementation, integration with other tools and peer review, and because of rapidly changing code, no incentive to fix or simplify implementation. As AV1 grew in adoption, implementers served as the more in depth peer review group which surfaced bugs and code base issues. Comments welcome.

Leo Barnes notes in the GitHub issue tracker that adding a magic number to the eventual AV2 would be beneficial because an "AV1 bitstream is not easily identifiable as such [because it lacks a magic number]... Almost all image codecs start with some kind of magic number (JPEG 0xFF 0xD8, PNG .PNG, BMP BM). This makes it easy to embed these codecs inside other container formats without explicitly specifying the codec since a parser can easily identify the codec directly from the first N bytes."

According to Wikipedia, "the lack of a suitable video format for inclusion in the World Wide Web Consortium (W3C)'s HTML5 specification and the failed negotiations for one mandatory video format for WebRTC showed the need for a competitive, open video standard. The emergence of a second patent pool for HEVC (HEVC Advance) in spring 2015 provided motivation for investments in an alternative video format and grew support for the Alliance, mainly due to the uncertainty regarding royalties for MPEG's next-generation video format, HEVC." Several earlier projects influenced or contributed to the development of AV1 including Xiph's/Mozilla's Daala with published code in 2010, Google's experimental VP9 evolution project VP10 from on 12 September 2014, and Cisco's Thor first published in August 2015.

AV1 was the first effort of the Alliance for Open Media (AOMedia) with the project moving quickly from the founding of the AOMedia organization on September 1, 2015 to first publication of the AV1 draft specification on March 28, 2018. Recent press releases include language that AOMedia was formed "to define and develop media technologies to address marketplace demand for an open standard for video compression and delivery over the web. Board-level, Founding Members include Amazon, Apple, Arm, Cisco, Facebook, Google, Huawei, Intel, Microsoft, Mozilla, Netflix, NVIDIA, Samsung Electronics and Tencent." A full list of current members who "contributed to the creation of AV1, and license their patents essential to the codec on a royalty-free basis to create an enduring ecosystem" is available at AOMedia Members.