Paul Wilkins

Technical overview of VP8, an open source video codec for the web

VP8 is an open source video compression format supported by a consortium of technology companies. This paper provides a technical overview of the format, with an emphasis on its unique features. The paper also discusses how these features benefit VP8 in achieving high compression efficiency and low decoding complexity at the same time.

The latest open-source video codec VP9 - An overview and preliminary results

Google has recently finalized a next generation open-source video codec called VP9, as part of the libvpx repository of the WebM project (http://www.webmproject.org/). Starting from the VP8 video codec released by Google in 2010 as the baseline, various enhancements and new tools were added, resulting in the next-generation VP9 bit-stream. This paper provides a brief technical overview of VP9 along with comparisons with other state-of-the-art video codecs H.264/AVC and HEVC on standard test sets. Results show VP9 to be quite competitive with mainstream state-of-the-art codecs.

Towards a next generation open-source video codec

Google has recently been developing a next generation opensource video codec called VP9, as part of the experimental branch of the libvpx repository included in the WebM project (http://www.webmproject.org/). Starting from the VP8 video codec released by Google in 2010 as the baseline, a number of enhancements and new tools have been added to improve the coding efficiency. This paper provides a technical overview of the current status of this project along with comparisons and other stateoftheart video codecs H. 264/AVC and HEVC. The new tools that have been added so far include: larger prediction block sizes up to 64x64, various forms of compound INTER prediction, more modes for INTRA prediction, ⅛pel motion vectors and 8tap switchable subpel interpolation filters, improved motion reference generation and motion vector coding, improved entropy coding and framelevel entropy adaptation for various symbols, improved loop filtering, incorporation of Asymmetric Discrete Sine Transforms and larger 16x16 and 32x32 DCTs, frame level segmentation to group similar areas together, etc. Other tools and various bitstream features are being actively worked on as well. The VP9 bitstream is expected to be finalized by earlyto mid2013. Results show VP9 to be quite competitive in performance with mainstream stateoftheart codecs.

Geometry-driven quantization for omnidirectional image coding

In this paper we propose a method to adapt the quantization tables of typical block-based transform codecs when the input to the encoder is a panoramic image resulting from equirectangular projection of a spherical image. When the visual content is projected from the panorama to the viewport, a frequency shift is occurring. The quantization can be adapted accordingly: the quantization step sizes that would be optimal to quantize the transform coefficients of the viewport image block, can be used to quantize the coefficients of the panoramic block. As a proof of concept, the proposed quantization strategy has been used in JPEG compression. Results show that a rate reduction up to 2.99% can be achieved for the same perceptual quality of the spherical signal with respect to a standard quantization.

Adaptive multi-reference prediction using a symmetric framework

Google started the WebM Project in 2010 to develop open source, royalty--free video codecs designed specifically for media on the Web. Subsequently, Google jointly founded a consortium of major tech companies called the Alliance for Open Media (AOM) to develop a new codec AV1, aiming at a next edition codec that achieves at least a generational improvement in coding efficiency over VP9. This paper proposes a new coding tool as one of the many efforts devoted to AOM/AV1. In particular, we propose a second ALTREF_FRAME in the AV1 syntax, which brings the total reference frames to seven on top of the work presented in [11]. ALTREF_FRAME is a constructed, no-show reference obtained through temporal filtering of a look-ahead frame. The use of two ALTREF_FRAMEs adds further flexibility to the multilayer, multi-reference symmetric framework, and provides a great potential for the overall RateDistortion (RD) performance enhancement. The experimental results have been collected over several video test sets of various resolutions and characteristics both textureand motion-wise, which demonstrate that the proposed approach achieves a consistent coding gain, compared against the AV1 baseline as well as against the results in [11]. For instance, using overallPSNR as the distortion metric, an average bitrate saving of 5.880% in BDRate is obtained for the CIF-level resolution set, and 4.595% on average for the VGAlevel resolution set.