AOMedia Video 1 (AV1) is an open, royalty-free video coding format designed for video transmissions over the Internet. It was developed by the Alliance for Open Media (AOMedia), a consortium of firms from the semiconductor industry, video on demand providers, video content producers, software development companies and web browser vendors, founded in 2015. The AV1 bitstream specification includes a reference video codec. It succeeds VP9. It can have 20% higher data compression than VP9 or HEVC/H.265 from the Moving Picture Experts Group and about 50% higher than the widely used AVC.
|Developed by||Alliance for Open Media|
|Initial release||28 March 2018|
1.0.0 Errata 1
(9 January 2019 )
|Type of format||Video compression format|
AV1 was announced with the creation of the Alliance for Open Media on 1 September 2015. Google, Mozilla and Cisco already had ongoing research projects into royalty-free video at this time, namely VP10, Daala and Thor.
AV1 is intended for use in HTML5 web video and WebRTC together with the Opus audio format. AV1-based containers have also been proposed as a replacement for JPEG, similar to Better Portable Graphics and High Efficiency Image File Format which wrap HEVC.
The official announcement of AV1 came with the press release on the formation of the Alliance for Open Media on 1 September 2015. The Alliance's seven founding members – Amazon, Cisco, Google, Intel, Microsoft, Mozilla and Netflix – announced that the initial focus of the video format would be delivery of high-quality web video. The Alliance's motivations for creating AV1 included the high cost and uncertainty involved with the patent licensing of HEVC, the MPEG-designed codec expected to succeed AVC. According to Microsoft's Ian LeGrow, an open-source, royalty-free technology was seen as the easiest way to eliminate this uncertainty around licensing.
The negative effect of patent licensing on free and open-source software has also been cited as a reason for the creation of AV1. For example, building a H.264 implementation into Firefox would prevent it from being distributed free of charge since licensing fees would have to be paid to MPEG-LA. Free Software Foundation Europe has argued that FRAND patent licensing practices make the free software implementation of standards impossible due to various incompatibilities with free software licenses.
Individual contributors started experimental technology platforms years before: Xiph's/Mozilla's Daala already published code in 2010, Google's experimental VP9 evolution project VP10 was announced on 12 September 2014, and Cisco's Thor was published on 11 August 2015. Building on the codebase of VP9, AV1 incorporates additional techniques, several of which were developed in these experimental formats. The first version 0.1.0 of the AV1 reference codec was published on 7 April 2016.
The bitstream format was projected to be frozen in January 2018; however, this was delayed due to unresolved critical bugs as well as last changes to transformations, syntax, the prediction of motion vectors, and the completion of legal analysis. The Alliance announced the release of the AV1 bitstream specification on 28 March 2018, along with a reference, software-based encoder and decoder. On 25 June 2018, a validated version 1.0.0 of the specification was released. On 8 January 2019 a validated version 1.0.0 with Errata 1 of the specification was released.
Martin Smole from AOM member Bitmovin said that the computational efficiency of the reference encoder was the greatest remaining challenge after the bitstream format freeze. While still working on the format, the encoder was not targeted for productive use and didn't receive any speed optimizations. Therefore, it worked orders of magnitude slower than e.g. existing HEVC encoders. Development was shifted its focus towards maturing the reference encoder after the freeze. In March 2019, it was reported that the speed of the reference encoder was much faster, close to or within the same order of magnitude as usual encoders for other common formats.
AV1 is a traditional block-based frequency transform format featuring new techniques. Based on Google's VP9, AV1 incorporates additional techniques that mainly give encoders more coding options to enable better adaption to different types of input.
|Developer(s)||Alliance for Open Media|
|Written in||C, assembly|
The Alliance published a reference implementation written in C and assembly language (
aomdec) as free software under the terms of the BSD 2-Clause License. Development happens in public and is open for contributions, regardless of AOM membership.
The development process was such that coding tools were added to the reference codebase as experiments, controlled by flags that enable or disable them at build time, for review by other group members as well as specialized teams that helped with and ensured hardware friendliness and compliance with intellectual property rights (TAPAS). When the feature gained some support in the community, the experiment was enabled by default, and ultimately had its flag removed when all of the reviews were passed. Experiment names were lowercased in the configure script and uppercased in conditional compilation flags.
To better and more reliably support HDR and color spaces, corresponding metadata can now be integrated into the video bitstream instead of being signaled in the container.
Frame content is separated into adjacent same-sized blocks referred to as superblocks. Similar to the concept of a macroblock, superblocks are square-shaped and can either be of size 128×128 or 64×64 pixels. Superblocks can be divided in smaller blocks according to different partitioning patterns. The four-way split pattern is the only pattern whose partitions can be recursively subdivided. This allows superblocks to be divided into partitions as small as 4×4 pixels.
"T-shaped" partitioning patterns are introduced, a feature developed for VP10, as well as horizontal or vertical splits into four stripes of 4:1 and 1:4 aspect ratio. The available partitioning patterns vary according to the block size, both 128×128 and 8×8 blocks can't use 4:1 and 1:4 splits. Moreover, 8×8 blocks can't use "T" shaped splits.
Two separate predictions can now be used on spatially different parts of a block using a smooth, oblique transition line (wedge-partitioned prediction). This enables more accurate separation of objects without the traditional staircase lines along the boundaries of square blocks.
AV1 performs internal processing in higher precision (10 or 12 bits per sample), which leads to compression improvement due to smaller rounding errors in reference imagery.
Predictions can be combined in more advanced ways (than a uniform average) in a block (compound prediction), including smooth and sharp transition gradients in different directions (wedge-partitioned prediction) as well as implicit masks that are based on the difference between the two predictors. This allows combination of either two inter predictions or an inter and an intra prediction to be used in the same block.
The Warped Motion (
warped_motion) and Global Motion (
global_motion) tools in AV1 aim to reduce redundant information in motion vectors by recognizing patterns arising from camera motion. They implement ideas that were tried to be exploited in preceding formats like e.g. MPEG-4 ASP, albeit with a novel approach that works in three dimensions. There can be a set of warping parameters for a whole frame offered in the bitstream, or blocks can use a set of implicit local parameters that get computed based on surrounding blocks.
Switch frames (S-frame) are a new inter-frame type that can be predicted using already decoded reference frames from a higher-resolution version of the same video to allow switching to a lower resolution without the need for a full keyframe at the beginning of a video segment in the adaptive bitrate streaming use case.
Intra prediction consists of predicting the pixels of a given blocks only using information available in the current frame. Most often, intra predictions are built from the neighboring pixels above and to the left of the predicted block. The DC predictor builds a prediction by averaging the pixels above and to the left of block.
Directional predictors extrapolate these neighboring pixels according to a specified angle. In AV1, 8 main directional modes can be chosen. These modes start at an angle of 45 degrees and increase by a step size of 22.5 degrees up until 203 degrees. Furthermore, for each directional mode, six offsets of 3 degree can be signalled for bigger blocks, three above the main angle and three below it, resulting in a total of 56 angles (
The "TrueMotion" predictor got replaced with a Paeth predictor which looks at the difference from the known pixel in the above left corner to the pixel directly above and directly left of the new one and then chooses the one that lies in direction of the smaller gradient as predictor. A palette predictor is available for blocks with very few (up to 8, dominant) colors like in some computer screen content. Correlations between the luminosity and the color information can now be exploited with a predictor for chroma blocks that is based on samples from the luma plane (
cfl). In order to reduce discontinuities along borders of inter-predicted blocks, predictors can be overlapped and blended with those of neighbouring blocks (overlapped block motion compensation).
To transform the error remaining after prediction to the frequency domain, AV1 encoders can use square, 2:1/1:2, and 4:1/1:4 rectangular DCTs (
rect_tx), as well as an asymmetric DST for blocks where the top and/or left edge is expected to have lower error thanks to prediction from nearby pixels, or choose to do no transform (identity transform).
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. On every new superblock, the quantization parameters can be adjusted by signaling an offset.
For the in-loop filtering step, the integration of Thor's constrained low-pass filter and Daala's directional deringing filter has been fruitful: The combined Constrained Directional Enhancement Filter (
cdef) exceeds the results of using the original filters separately or together.
It is an edge-directed conditional replacement filter that smoothes blocks with configurable (signaled) strength roughly along the direction of the dominant edge to eliminate ringing artifacts.
Film grain synthesis (
film_grain) improves coding of noisy signals using a parametric video coding approach.
Due to the randomness inherent to film grain noise, this signal component is traditionally either very expensive to code or prone to get damaged or lost, possibly leaving serious coding artefacts as residue. This tool circumvents these problems using analysis and synthesis, replacing parts of the signal with a visually similar synthetic texture, based solely on subjective visual impression instead of objective similarity. It removes the grain component from the signal, analyzes its non-random characteristics, and instead transmits only descriptive parameters to the decoder, which adds back a synthetic, pseudorandom noise signal that's shaped after the original component. It is the visual equivalent of the Perceptual Noise Substitution technique used in AC3, AAC, Vorbis, and Opus audio codecs.
Daala's entropy coder (
daala_ec), a non-binary arithmetic coder, was selected for replacing VP9's binary entropy coder. The use of non-binary arithmetic coding helps evade patents, but also adds bit-level parallelism to an otherwise serial process, reducing clock rate demands on hardware implementations. This is to say that the effectiveness of modern binary arithmetic coding like CABAC is being approached using a greater alphabet than binary, hence greater speed, as in Huffman code (but not as simple and fast as Huffman code).
AV1 also gained the ability to adapt the symbol probabilities in the arithmetic coder per coded symbol instead of per frame (
Quality and efficiencyEdit
In April 2017, using the 8 enabled experimental features at the time (of 77 total), Bitmovin was able to demonstrate favorable objective metrics, as well as visual results, compared to HEVC on the Sintel and Tears of Steel animated films. A follow-up comparison by Jan Ozer of Streaming Media Magazine confirmed this, and concluded that "AV1 is at least as good as HEVC now".
Ozer noted that his and Bitmovin's results contradicted a comparison by Fraunhofer Institute for Telecommunications from late 2016 that had found AV1 38.4% less efficient than HEVC, underperforming even H.264/AVC, and justified this discrepancy by having used encoding parameters endorsed by each encoder vendor, as well as having more features in the newer AV1 encoder.
Tests from Netflix showed that, based on measurements with PSNR and VMAF at 720p, AV1 was about 25% more efficient than VP9 (libvpx). Similar conclusions with respect to quality were drawn from a test conducted by Moscow State University researchers, where VP9 was found to require 31% and HEVC 22% more bitrate than AV1 for the same level of quality. The researchers found that the used AV1 encoder was operating at a speed "2500–3500 times lower than competitors", while admitting that it has not been optimized yet.
In a comparison of AV1 against H.264 (x264) and VP9 (libvpx), Facebook showed about 45–50% bitrate savings over H.264 and about 40% over VP9 when using a constant quality encoding mode.
Decoding performance was at about half the speed of VP9 according to internal measurements from 2017.
AOMedia provides a list of test results on their website.
Profiles and levelsEdit
AV1 defines three profiles for decoders which are Main, High, and Professional. The Main profile allows for a bit depth of 8- or 10-bits per sample with 4:0:0 (greyscale) and 4:2:0 chroma sampling. The High profile further adds support for 4:4:4 chroma sampling. The Professional profile extends capabilities to full support for 4:0:0, 4:2:0, 4:2:2 and 4:4:4 chroma sub-sampling with 8, 10 and 12 bit color depths.
|Main (0)||High (1)||Professional (2)|
|8 or 10-bit||8 or 10-bit||8, 10 & 12 bit|
AV1 defines levels for decoders with maximum variables for levels ranging from 2.0 to 7.3. Example resolutions would be 426×240@30 fps for level 2.0, 854×480@30 fps for level 3.0, 1920×1080@30 fps for level 4.0, 3840×2160@60 fps for level 5.1, 3840×2160@120 fps for level 5.2 and 5.3,[further explanation needed] and 7680×4320@120 fps for level 6.2. Level 7 has not been defined yet.
|Min Comp Basis||Max Tiles||Max Tile Cols||Example|
Supported container formatsEdit
- ISO Base Media File Format: The ISOBMFF containerization spec by AOMedia was the first to be finalized and the first to gain adoption. This is the format used by YouTube.
- Standards with unclear promise of finalization
- Matroska: Version 1 of the Matroska containerization spec was published in September 2018. However, arguably breaking changes continued into October, and a new version, or finalization, is yet to be announced as of December.
- Unfinished standards
- MPEG Transport Stream: 
- Not standardized
- WebM: As a matter of formality, AV1 has not been sanctioned into the subset of Matroska known as WebM as of late 2018.
- On2 IVF: This format was inherited from the first public release of VP8, where it served as a simple development container. rav1e also supports this format.
- Pre-standard WebM: Libaom featured early support for WebM, before Matroska containerization was specified, but has been changed to conform.
YouTube has begun rolling out AV1, starting with its AV1 Beta Launch Playlist. According to the description, the videos are (to begin with) encoded at high bitrate to test decoding performance, and YouTube has "ambitious goals" for rolling out AV1.
Vimeo's videos in the "Staff picks" channel are available in AV1. Vimeo is using and contributing to Mozilla's Rav1e encoder, and expects, with further encoder improvements, to eventually provide AV1 support for all videos uploaded to Vimeo as well as the company's "Live" offering.
Netflix "expects to be an early adopter of AV1".
Following very positive own test results, Facebook said to gradually roll out AV1 as soon as browser support emerges, starting with their most popular videos.
- Libaom is the reference implementation. It includes an encoder (aomenc) and a decoder (aomdec). As the former research codec, it has the advantage of being made to justifiably demonstrate efficient use of every feature, but at the general cost of encoding speed. At feature freeze, the encoder had become problematically slow, but speed optimizations with negligible efficiency impact have continued to be made also after that.
- rav1e is an encoder written in Rust and assembly. rav1e takes the opposite developmental approach to Aomenc: start out as the simplest (therefore fastest) conforming encoder, and then improve efficiency over time while remaining fast.
- SVT-AV1 includes an open-source encoder and decoder first released by Intel in February 2019 that is designed especially for usage on data center servers based on Intel Xeon processors. Netflix collaborates with Intel on SVT-AV1.
- dav1d is a decoder written in C99 and assembly focused on speed and portability. The first official version (0.1) was released in December 2018. Version 0.2 was released in March 2019, with users able to "safely use the decoder on all platforms, with excellent performance", according to the developers. Version 0.3 was announced in May 2019 with further optimizations demonstrating performance 2 to 5 times faster than aomdec. Firefox 67 switched from Libaom to dav1d as a default decoder.
- Cisco AV1 is a proprietary live encoder that Cisco developed for its Webex teleconference products. The encoder is optimized for latency and the constraint of having a "usable CPU footprint", as with a "commodity laptop". Cisco stressed that at their operating point – high speed, low latency – the large toolset of AV1 does not preclude a low encoding complexity. Rather, the availability of tools for screen content and scalability in all profiles enabled them to find good compression-to-speed tradeoffs, better even than with HEVC. Compared to their previously deployed H.264 encoder, a particular area of improvement was in high resolution screen sharing.
- Firefox (since version 67.0, May 2019; enabled by default on all desktop platforms - Windows, OSX and Linux for both 32-bit and 64-bit systems)
- Google Chrome (since version 70, October 2018)
- Opera (since version 57, 28 November 2018)
- VLC media player (since version 3.0)
- GStreamer (since version 1.14)
- FFmpeg (since version 4.0)
- mpv (since version 0.29.0)
- MKVToolNix (adoption of final av1-in-mkv spec since version 28)
- MediaInfo (since version 18.03)
- Bitmovin Encoding (since version 1.50.0, July 2018)
- Microsoft Edge (since Windows 10 October 2018 Update (1809) with AV1 Video Extension beta add-on)
Operating system supportEdit
|Microsoft Windows||macOS||BSD / Linux||Chrome OS||Android OS||iOS|
|Container support||ISO base media file format (.mp4)
|TBA||ISO base media file format (.mp4)
|Notes||- Support introduced in Windows 10 October 2018 Update (1809) with AV1 Video Extension beta add-on.||Unsupported as of macOS Mojave.||supports decoding, from Chrome OS 70 onward||Supported since Android Q beta.||Unsupported as of iOS 12.|
Several Alliance members demonstrated AV1 enabled products at IBC 2018, including Socionext's hardware accelerated encoder. According to Socionext, the encoding accelerator is FPGA based and can run on an Amazon EC2 F1 cloud instance, where it runs 10 times faster than existing software encoders.
According to Mukund Srinivasan, chief business officer of AOM member Ittiam, early hardware support will be dominated by software running on non-CPU hardware (such as GPGPU, DSP or shader programs, as is the case with some VP9 hardware implementations), as fixed-function hardware will take 12–18 months after bitstream freeze until chips are available, plus 6 months for products based on those chips to hit the market. The bitstream was finally frozen on 28 March 2018, meaning chips could be available sometime between March and August 2019. According to the above forecast, products based on chips could then be on the market at the end of 2019 or the beginning of 2020.
On April 18, 2019, Allegro DVT announced its AL-E210 multi-format video encoder hardware IP, the first publicly announced hardware AV1 encoder. The AL-E210 supports, aside from VP9, H.265/HEVC, H.264/AVC and JPEG, the AV1 Main profile, with which it can encode 4:2:0 Chroma subsampling with 8 and 10 bit color depth. A single core can encode 4K with 30 fps, with multiple cores that should even be higher.
On May 9, 2019, Amphion announced their CS8000 Malone family video decoders with AV1 support of up to 8Kp60.
On June 17th 2019, Realtek announced the RTD1311 SoC for set-top boxes with an integrated AV1 decoder.
|Allegro||AL-E210||E||Main (0)||4K 30fps||?|||
D = decode, E = Encode
In March 2019, Luxembourg-based Sisvel announced the formation of patent pools for AV1 and VP9. Members of the pools included JVCKENWOOD, NTT, Orange S.A., Philips, and Toshiba, all of whom were also licensing patents to the MPEG-LA for either the AVC, DASH, or the HEVC patent pools. Sisvel announced it would demand €0.32 for display devices and €0.11 for non-display devices using AV1, but would not seek royalties for encoded content. At the time of the announcement, a list of patents owned by Sisvel was not publicly available. However, Sisvel's CEO stated in an interview that such a list would be posted on Sisvel's website before any licensing demands were sent out.
As of 8 April 2019, the Alliance for Open Media has made a press release, which reiterated the commitment to their royalty-free patent license, and made mention of their "AOMedia patent defense program to help protect AV1 ecosystem participants in the event of patent claims", but did not mention the Sisvel claim by name.
AV1 Image File Format (AVIF)Edit
The AV1 Image File Format (AVIF) is a specification for storing images or image sequences compressed with AV1 in the HEIF file format. Version 1.0.0 of the specification was finalized in February 2019 and supports features like high dynamic range and wide color gamut.
On 14 December 2018 Netflix published the first .avif sample images, and support was added in VLC. Microsoft also announced support with the Windows 10 "19h1" preview release, including File Explorer, Paint and multiple APIs, together with sample images. Mozilla and Google are also working on support for the new image format in Firefox and Chrome.
- "Release AV1 Bitstream & Decoding Process Specification (v1.0.0-errata1)". Github.com. 9 January 2019. Retrieved 31 March 2019.
- "AV1 Bitstream & Decoding Process Specification" (PDF). The Alliance for Open Media.
- Zimmerman, Steven (15 May 2017). "Google's Royalty-Free Answer to HEVC: A Look at AV1 and the Future of Video Codecs". XDA Developers. Archived from the original on 14 June 2017. Retrieved 10 June 2017.
- How to use AV1 with open source tools, Videolan's Jean-Baptiste Kempf on using AV1 with open source tools, 2018-12-01.
- "Alliance for Open Media established to deliver next-generation open media formats" (Press release). Alliance for Open Media. 1 September 2015. Retrieved 5 September 2015.[self-published source]
- Tsahi Levent-Levi (2 April 2018). "AV1 Specification Released: Can we kiss goodbye to HEVC and royalty bearing video codecs?". BlogGeek.me. Retrieved 19 December 2018.
AV1 for video coding is what Opus is for audio coding.
- Shankland, Stephen (19 January 2018). "Photo format from Google and Mozilla could leave JPEG in the dust". CNET. CBS Interactive. Retrieved 28 January 2018.
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Because H.264 implementations are subject to a royalty bearing patent license and Mozilla is an open source project, we are unable to ship H.264 in Firefox directly. We want anyone to be able to distribute Firefox without paying the MPEG LA.
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As Free Software gives each user the freedom to redistribute the software itself, keeping track and collecting royalties based on distributed copies is also, in practice, impossible.
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What can Thor add to VP9/AV1? Since Thor aims for reasonable compression at only moderate complexity, we considered features of Thor that could increase the compression efficiency of VP9 and/or reduce the computational complexity.CS1 maint: Uses authors parameter (link)
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This version 1.0.0 with Errata 1 of the AV1 Bitstream Specification corresponds to the Git tag v1.0.0-errata1 in the AOMediaCodec/av1-spec project. Its content has been validated as consistent with the reference decoderprovided by libaom v1.0.0-errata1.
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- Jan Ozer, 26 May 2016: What Is VP9?
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Since those two experiments have been merged into the dist-8x8 experiment[self-published source]
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This experiment has been adopted[self-published source]
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The most intriguing result obtained after analysis of the data lies in the fact that the developed codec AV1 is currently equal in its performance with HEVC. The given streams are encoded with AV1 update of 2017.01.31
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The mission of the Alliance for Open Media remains the same as the mission of the WebM project that we launched back in 2010. (…) Obviously, if we have an open source codec, we need to take very strong steps, and be very diligent in making sure that we are in fact producing something that's royalty free. So we have an extensive IP diligence process which involves diligence on both the contributor level – so when Google proposes a tool, we are doing our in-house IP diligence, using our in-house patent assets and outside advisors – that is then forwarded to the group, and is then again reviewed by an outside counsel that is engaged by the alliance. So that's a step that actually slows down innovation, but is obviously necessary to produce something that is open source and royalty free.
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but we're hoping, towards 2024-2025 the AV1 ecosystem's ready, we wanna switch to AV1 a 100%. … this is our projection right now. But on the other hand, as I said, our AV1 release will be, for the head content will be a lot sooner. We are hoping 2022-2023 is we are going to release AV1 for the head content.
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We have been focusing on freezing the bitstream and getting the quality, not necessarily making things fast. This is a graph of the [encoding] speed of AV1 over its development process. You can se that as we near the end of that process, we started making things faster again, and it's now two orders of magnitude faster than it was at its slowest point. So that's going to improve. And this is a corresponding graph of the quality. (…) So you can see that even as it has continued to get much faster, the quality hasn't really gone down. (…) We wanted to approach this from the other end, so we started an encoder of our own, called rav1e, and the idea is that we would start out always being fast, and then try to make it better over time.
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