VP9

Features

VP9 is customized for video resolutions beyond high-definition video (UHD) and also enables lossless compression.

The VP9 format supports the following color spaces: Rec. 601, Rec. 709, Rec. 2020, SMPTE-170, SMPTE-240, and sRGB.

VP9 supports HDR video using Hybrid Log-Gamma (HLG) and Perceptual Quantizer (PQ).

Efficiency

In Netflix's "Large-Scale Video Codec Comparison of x264, x265 and Libvpx for Practical VOD applications", libvpx came out 30% more efficient than x264 and 20% less efficient than x265 by Netflix's own VMAF metric. The comparison evaluated the slowest encoding speeds available for each encoder. The disparity between libvpx and x265 was much less on the SSIM metric (3%), which is consistent with previous findings that showed x265 to narrowly beat libvpx at the very highest quality (slowest encoding) whereas libvpx was superior at any other encoding speed, by SSIM.

In a subjective quality comparison conducted in 2014 featuring the reference encoders for HEVC (HM 15.0), MPEG-4 AVC/H.264 (JM 18.6), and VP9 (libvpx 1.2.0 with preliminary VP9 support), VP9, like H.264, required about two times the bitrate to reach video quality comparable to HEVC, while with synthetic imagery VP9 was close to HEVC. By contrast, another subjective comparison from 2014 concluded that at higher quality settings HEVC and VP9 were tied at a 40 to 45% bitrate advantage over H.264.

Performance

An encoding speed versus efficiency comparison of the reference implementation in libvpx, x264 and x265 was made by an FFmpeg developer in September 2015: By SSIM index, libvpx was mostly superior to x264 across the range of comparable encoding speeds, but the main benefit was at the slower end of x264@veryslow (reaching a sweet spot of 30–40% bitrate improvement within twice as slow as this), whereas x265 only became competitive with libvpx around 10 times as slow as x264@veryslow. It was concluded that libvpx and x265 were both capable of the claimed 50% bitrate improvement over H.264, but only at 10–20 times the encoding time of x264. Judged by the objective quality metric VQM in early 2015, the VP9 reference encoder delivered video quality on par with the best HEVC implementations.

A decoder comparison by the same developer showed 10% faster decoding for ffvp9 than ffh264 for same-quality video, or "identical" at same bitrate. It also showed that the implementation can make a difference, concluding that "ffvp9 beats libvpx consistently by 25–50%".

Another decoder comparison indicated 10–40 percent higher CPU load than H.264 (but does not say whether this was with ffvp9 or libvpx), and that on mobile, the Ittiam demo player was about 40 percent faster than the Chrome browser at playing VP9.

Profiles

There are several variants of the VP9 format, the so-called coding profiles, that successively allow more features, starting from the basic version, the profile 0 (minimum for hardware implementations), up to profile 3:

profile 0

color depth: 8 bit/sample, chroma subsampling: 4:2:0

profile 1

color depth: 8 bit, chroma subsampling: 4:2:0, 4:2:2, 4:4:4

profile 2

color depth: 10–12 bit, chroma subsampling: 4:2:0

profile 3

color depth: 10–12 bit, chroma subsampling: 4:2:0, 4:2:2, 4:4:4

Levels

VP9 offers the following 14 levels:

Technology

VP9 is a traditional block-based transform coding format. The bitstream format is relatively simple compared to formats that offer similar bitrate efficiency like HEVC.

VP9 has many design improvements compared to VP8. Its biggest improvement is support for the use of coding units of 64×64 pixels. This is especially useful with high-resolution video. Also the prediction of motion vectors was improved. In addition to the VP8's four modes (average/"DC", "true motion", horizontal, vertical), VP9 supports six oblique directions for linear extrapolation of pixels in intra-frame prediction.

New coding tools also include:

eighth-pixel precision for motion vectors,

three different switchable 8-tap subpixel interpolation filters,

improved selection of reference motion vectors,

improved coding of offsets of motion vectors to their reference,

improved entropy coding,

improved and adapted (to new block sizes) loop filtering,

the asymmetric discrete sine transform (ADST),

larger discrete cosine transforms (DCT, 16×16 and 32×32), and

improved segmentation of frames into areas with specific similarities (e.g. fore-/background)

In order to enable some parallel processing of frames, video frames can be split along coding unit boundaries into up to four rows of 256 to 4096 pixels wide evenly spaced tiles with each tile column coded independently. This is mandatory for video resolutions in excess of 4096 pixels. A tile header contains the tile size in bytes so decoders can skip ahead and decode each tile row in a separate thread. The image is then divided into coding units called superblocks of 64×64 pixels which are adaptively subpartitioned in a quadtree coding structure. They can be subdivided either horizontally or vertically or both; square (sub)units can be subdivided recursively down to 4×4 pixel blocks. Subunits are coded in raster scan order: left to right, top to bottom.

Starting from each key frame, decoders keep 8 frames buffered to be used as reference frames or to be shown later. Transmitted frames signal which buffer to overwrite and can optionally be decoded into one of the buffers without being shown. The encoder can send a minimal frame that just triggers one of the buffers to be displayed ("skip frame"). Each inter frame can reference up to three of the buffered frames for temporal prediction. Up to two of those reference frames can be used in each coding block to calculate a sample data prediction, using spatially displaced (motion compensation) content from a reference frame or an average of content from two reference frames ("compound prediction mode"). The (ideally small) remaining difference (delta encoding) from the computed prediction to the actual image content is transformed using a DCT or ADST (for edge blocks) and quantized.

Something like a b-frame can be coded while preserving the original frame order in the bitstream using a structure named superframes. Hidden alternate reference frames can be packed together with an ordinary inter frame and a skip frame that triggers display of previous hidden altref content from its reference frame buffer right after the accompanying p-frame.

VP9 enables lossless encoding by transmitting at the lowest quantization level (q index 0) an additional 4×4-block encoded Walsh–Hadamard transformed (WHT) residue signal.

In container formats VP9 streams are marked with the FourCC VP90 (or in the future possibly VP91, ...) or VP09. In order to be searchable, raw VP9 bitstreams have to be contained either in Googles Matroska-derived WebM format (.webm) or the older minimalistic Indeo video file (IVF) format which is traditionally supported by libvpx.

Adoption

Adobe Flash, which traditionally used VPx formats up to VP7, was never upgraded to VP8 or VP9, but instead to H.264. Therefore, VP9 often penetrated corresponding web applications only with the gradual shift from Flash to HTML5 technology, which was still somewhat immature when VP9 was introduced. Trends towards UHD resolutions, higher color depth and wider gamuts are driving a shift towards new, specialized video formats. With the clear development perspective and support from the industry demonstrated by the founding of the Alliance for Open Media, as well as the pricey and complex licensing situation of HEVC it is expected that users of the hitherto leading MPEG formats will often switch to the royalty-free alternative formats of the VPx/AVx series instead of upgrading to HEVC.

A main user of VP9 is Google's popular video platform YouTube, which offers VP9 video at all resolutions along with Opus audio in the WebM file format, through DASH streaming.

Another is Wikipedia (specifically Wikimedia Commons, which hosts multimedia files across Wikipedia's subpages and languages). Wikipedia endorses open and royalty-free multimedia formats. As of 2016, the 3 accepted video formats are VP9, VP8 and Theora.

As of December 2016, Netflix is in progress of encoding their catalog to VP9, alongside AVC High, for bitrates aimed at mobile users.

VP9 is implemented in the webbrowsers

Chromium and Google Chrome (usable by default since version 29 from May and August 2013, respectively),

Opera (since version 15 from July 2013),

Mozilla Firefox (since version 28 from March 2014),

Microsoft Edge (as of summer 2016).

Internet Explorer and Apple Safari are missing VP9 support completely. In March 2016 an estimated 65 to 75% of webbrowsers in use on desktop and notebook systems were able to play VP9 videos in HTML5 webpages, based on data from StatCounter.

JW Player supports VP9 in its widely used software-as-a-service HTML5 video player.

Since 2016 a series of cloud encoding services (Amazon, Brightcove, castLabs, JW Player, Telestream, Wowza) offer VP9 encoding.

VP9 is supported in all major open source media player software, including VLC, MPlayer/MPlayer2/MPV, Kodi, MythTV and FFplay.

Android has had VP9 software decoding since version 4.4 "KitKat". For a list of consumer electronics with hardware support, including TVs, smartphones, set top boxes and game consoles, see webmproject.org's list.

Hardware encoding/decoding support

The following chips, architectures, CPUs, GPUs and SoCs provide hardware acceleration of VP9. Some of these are known to have fixed function hardware, but this list also incorporates GPU or DSP based implementations – software implementations on non-CPU hardware. The latter category also serve the purpose of offloading the CPU, but power efficiency is not as good as the fixed function hardware (more comparable to well optimized SIMD aware software).

Intel Kaby Lake CPU family, Intel Apollo Lake CPU family, Nvidia Maxwell GM206 & Pascal GPU family have full fixed function VP9 hardware decoding for highest decoding performance and power efficiency.

This is not a complete list. Further SoCs, as well as hardware IP vendors can be found at webmproject.org.

Software implementations

The reference implementation from Google is found in the free software programming library libvpx. It has a single-pass and a two-pass encoding mode, whereas the single-pass mode is considered broken and doesn't offer effective control over the target bitrate.

Encoding

libvpx

Eve – a commercial encoder

Ittiam's encoder products (OTT, broadcast, consumer)

Decoding

libvpx

ffvp9 (FFmpeg)

Ittiam's consumer decoder

FFmpeg's VP9 decoder takes advantage of a corpus of SIMD optimizations shared with other codecs to make it fast. A comparison made by an FFmpeg developer indicated that this was faster than libvpx, and compared to FFmpeg's h.264 decoder, "identical" performance for same-bitrate video, or about 10% faster for same-quality video.

History

VP9 is the last official iteration of the TrueMotion series of video formats that Google bought in 2010 for 134 million dollars together with the company On2 Technologies that created it. The development of VP9 started in the second half of 2011 under the development names of Next Gen Open Video (NGOV) and VP-Next. The design goals for VP9 included reducing the bit rate by 50% compared to VP8 while maintaining the same video quality, and aiming for better compression efficiency than the MPEG High Efficiency Video Coding (HEVC) standard. In June 2013 the "profile 0" of VP9 was finalized, and two months later Google's Chrome browser was released with support for VP9 video playback. In October of that year a native VP9 decoder was added to FFmpeg, and to Libav six weeks later. Mozilla added VP9 support to Firefox in March 2014. In 2014 Google added two high bit depth profiles: profile 2 and profile 3.

In 2013 an updated version of the WebM format was published, featuring support for VP9 together with Opus audio.

In March 2013, the MPEG Licensing Administration dropped an announced assertion of disputed patent claims against VP8 and its successors after the United States Department of Justice started to investigate whether it was acting to unfairly stifle competition.

Throughout, Google has worked with hardware vendors to get VP9 support into silicon. In January 2014, Ittiam, in collaboration with ARM and Google, demonstrated its VP9 decoder for ARM Cortex devices. Using GPGPU techniques, the decoder was capable of 1080p at 30fps on an Arndale Board. In early 2015 Nvidia announced VP9 support in its Tegra X1 SoC, and VeriSilicon announced VP9 Profile 2 support in its Hantro G2v2 decoder IP.

In April 2015 Google released a significant update to its libvpx library, with version 1.4.0 adding support for 10-bit and 12-bit bit depth, 4:2:2 and 4:4:4 chroma subsampling, and VP9 multithreaded decoding/encoding.

In December 2015, Netflix published a draft proposal for including VP9 video in an MP4 container with MPEG Common Encryption.

In January 2016, Ittiam demonstrated an OpenCL based VP9 encoder. The encoder is targeting ARM Mali mobile GPUs and was demonstrated on a Samsung Galaxy S6.

VP9 support was added to Microsoft's webbrowser Edge. It is present in development releases starting with EdgeHTML 14.14291 and due to be officially released in summer 2016.

Successor: from VP10 to AV1

On September 12, 2014, Google announced that development on VP10 had begun and that after the release of VP10 they plan to have an 18-month gap between releases of video formats. In August 2015, Google began to publish code for VP10.

However, Google decided to incorporate VP10 into AOMedia Video 1 (AV1). The AV1 codec will use elements of VP10 as well as the experimental formats Daala (Xiph/Mozilla) and Thor (Cisco). Accordingly, Google has stated that they will not deploy VP10 internally or officially release it, making VP9 the last of the VPx-based codecs to be released by Google.