VP8开源视频编解码器技术概述

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VP8技术概述 VP8是一个开源视频编解码器，旨在为Web提供高质量的视频压缩格式。该格式由Google领导的WebM项目开发，是一个免费、开放的媒体格式，旨在为Web提供高质量的视频体验。 VP8技术特点 VP8具有许多独特的技术特点，这些特点使其在压缩效率和解码复杂度方面具有优势。以下是VP8的一些关键技术特点： 1. 基于帧内预测的编码：VP8使用基于帧内预测的编码方法，通过预测当前帧来减少压缩后的数据量。这使得VP8在压缩效率方面具有优势。 2. 变换编码：VP8使用变换编码来将图像信号转换为频域信号，从而实现更高的压缩率。 3. 熵编码：VP8使用熵编码来对变换后的信号进行编码，进一步减少数据量。 4. 运动补偿：VP8使用运动补偿来预测当前帧中的运动信息，减少压缩后的数据量。 5. 多帧 référence：VP8支持多帧référence，允许解码器使用多个参考帧来进行解码，提高解码效率。 VP8的优点 VP8具有许多优点，以下是一些关键的优点： 1. 高压缩效率：VP8具有高压缩效率，可以将视频数据压缩到非常小的尺寸，适合Web应用。 2. 低解码复杂度：VP8的解码复杂度较低，适合在各种设备上播放视频。 3. 免费和开放：VP8是一个免费和开放的媒体格式，任何人都可以使用和修改。 4. 广泛支持：VP8受到许多技术公司的支持，包括Google、Mozilla、Opera等。 VP8在Web应用中的应用 VP8在Web应用中的应用非常广泛，以下是一些关键的应用场景： 1. 在线视频：VP8可以用于在线视频应用，例如YouTube、Vimeo等。 2. WebRTC：VP8可以用于WebRTC（Web Real-Time Communication）应用，例如视频会议、屏幕分享等。 3. 流媒体：VP8可以用于流媒体应用，例如直播、点播等。 VP8是一个功能强大且高效的视频编解码器，非常适合Web应用。其独特的技术特点和优点使其在压缩效率和解码复杂度方面具有优势，广泛应用于在线视频、WebRTC、流媒体等领域。

TECHNICAL OVERVIEW OF VP8, AN OPEN SOURCE VIDEO CODEC FOR THE WEB

Jim Bankoski, Paul Wilkins, Yaowu Xu

Google Inc. 1600 Amphitheatre Parkway, Mountain View, CA, USA

{jimbankoski, paulwilkins, yaowu}@google.com

ABSTRACT

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.

Index Terms—VP8, WebM, Video Codec, Web Video

1. INTRODUCTION

In May 2010, Google announced the start of a new open media

project “WebM”, which is dedicated to developing a high-quality,

open media format for the web that is freely available to everyone.

At the core of the project is a new open source video compression

format, VP8. The VP8 format was originally developed by a small

research team at On2 Technologies, Inc. as a successor of its VPx

family of video codecs. Compared to other video coding formats,

VP8 has many distinctive technical features that help it to achieve

high compression efficiency and low computational complexity for

decoding at the same time. Since the WebM announcement, not

only has VP8 gained strong support from a long list of major

industry players, but it has also started to attract broad interest in

the video coding research community from both industry and

academia.

This paper aims to provide a technical overview of the VP8

compression format, with an emphasis on VP8’s unique features.

Section 2 briefly reviews VP8’s design assumptions and overall

architecture; section 3 to section 7 describes VP8’s key technical

features: transform and quantization scheme, reference frame

types, prediction techniques, adaptive loop filtering, entropy

coding and parallel processing friendly data partitioning; section 8

provides a short summary with experimental results and some

thoughts on future work.

2. DESIGN ASSUMPTIONS AND FEATURE HIGHLIGHTS

From the very beginning of VP8’s development, the developers

were focused on Internet/web-based video applications. This focus

has led to a number of basic assumptions in VP8’s overall design:

Low bandwidth requirement: One of the basic design

assumptions is that for the foreseeable future, available network

bandwidth will be limited. With this assumption, VP8 was

specifically designed to operate mainly in a quality range from

“watchable video” (~30dB in the PSNR metric) to “visually

lossless” (~45dB).

Heterogeneous client hardware: There is a broad spectrum of

client hardware connected to the web, ranging from low power

mobile and embedded devices to the most advanced desktop

computers with many processor cores. It must, therefore, be

possible to create efficient implementations for a wide range of

client devices.

Web video format: VP8 was designed to handle the image

format used by the vast majority of web videos: 420 color

sampling, 8 bit per channel color depth, progressive scan (not

interlaced), and image dimensions up to a maximum of

16383x16383 pixels.

The push for compression efficiency and decoder simplicity

under these design assumptions led to a number of distinctive

technical features in VP8 [1], relative to other known video

compression formats, such as MPEG-2 [2], H.263 [3] and

H.264/AVC [4]. The following list highlights the technical

innovations in VP8:

Hybrid transform with adaptive quantization: VP8 uses 4x4

block-based discrete cosine transform (DCT) for all luma and

chroma residual signal. Depending on the prediction mode, the DC

coefficients from a 16x16 macroblock may then undergo a 4x4

Walsh-Hadamard transform.

Flexible reference frames: VP8 uses three reference frames

for inter prediction, but the scheme is somewhat different from the

multiple reference motion compensation scheme seen in other

formats. VP8’s design limits the buffer size requirement to three

reference frame buffers and still achieves effective de-correlation

in motion compensation.

Efficient intra prediction and inter prediction: VP8 makes

extensive uses of intra and inter prediction. VP8’s intra prediction

features a new “TM_PRED” mode as one of the many simple and

effective intra prediction methods. For inter prediction, VP8

features a flexible “SPLITMV” mode capable of coding arbitrary

block patterns within a macroblock.

High performance sub-pixel interpolation: VP8’s motion

compensation uses quarter-pixel accurate motion vectors for luma

pixels and up to one-eighth pixel accurate motion vectors for

chroma pixels. The sub-pixel interpolation of VP8 features a single

stage interpolation process and a set of high performance six-tap

interpolation filters.

Adaptive in-loop deblocking filtering: VP8 has a highly

adaptive in-loop deblocking filter. The type and strength of the

filtering can be adjusted for different prediction modes and

reference frame types.

Frame level adaptive entropy coding: VP8 uses binary

arithmetic coding extensively for almost all data values except a

few header bits. Entropy contexts are adaptive at the frame level,

striking a balance between compression efficiency and

computational complexity.

Parallel processing friendly data partitioning: VP8 can pack

entropy coded transform coefficients into multiple partitions, to

facilitate parallel processing in decoders. This design improves

decoder performance on multi-core processors, with close to zero

impact to compression efficiency and no impact to decoding

performance on single core processors.

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