Windows media video 9
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Windows Media Video 9. Tarun Bhatia [email protected] Multimedia Processing Lab University Of Texas at Arlington 11/05/04. Introduction 1. Introduction 2. Introduction 3.

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Windows media video 9

Windows Media Video 9

Tarun Bhatia

[email protected]

Multimedia Processing Lab

University Of Texas at Arlington

11/05/04


Introduction 1

Introduction 1


Introduction 2

Introduction 2


Introduction 3

Introduction 3

  • Latest video codec which gives state-of-art video quality from very low bit rates (160x120 at 10 Kbps for modem) to very high bit rates (1920x1080 for HDTV)

  • 8-bit , 4:2:0 format

  • Uses block based transform and motion compensation with quantization and entropy coding.


The block diagram

The Block Diagram :-


Block transforms integer dct

8x8 blocks can be encoded using

1_8x8 2_8x4

2_4x8 4_4x4

Frame / Macroblock/Block signaling

Block level for coarse and fine level specification

Frame level for overhead reduction

Only 8x8 used for I frames

Block Transforms(Integer DCT)


8x8 integer dct matrices

WMV 9

H.264 HP

8x8 Integer DCT Matrices


Key features of the transforms

Key features of the Transforms

  • The norms of vectors of the ratio 288:289:299

  • The variation in the norm accounted for in the encoder itself

  • At the decoder inverse transform(rows) -> rounding-> inverse transform (columns) ->rounding

    (to operate in the 16 bit range)


Quantization

Quantization

  • Same rule applied to all block sizes

  • Both types with (bit savings at low bit rates) and without dead zone ( available

  • Type used signaled at the frame level to the decoder

  • At the encoder side automatic switch from uniform quantization to dead zone quantization as Q – parameter increases

  • Other factors like noise and rate control can be used to control this switch


Loop filtering

Loop Filtering

  • Done to remove blocky artifacts and thus quality of current frame for future prediction

  • Operates on pixels on the border of blocks

  • The process involves a discontinuity measurement

  • Checks are computationally expensive so done only for one set of pixel per boundary


Motion estimation and compensation

Motion Estimation and Compensation

  • Max resolution of ¼ pixel (i.e. ¼, ½, ¾) allowed

  • 16x 16 motion vectors used by default but 8x8 allowed

  • Bicubic filter with 4 taps/ Bilinear filters with 2 taps to generate subpixel precision.

  • 4 combined modes

    1.Mixed block size (16x16 and 8x8), ¼ p ,bicubic

    2.16x16, ¼ p, bicubic

    3.16x16, ½ p, bicubic

    4.16x16, ½ p, bilinear

  • Bilinear filters for chroma components


Advanced entropy coding

Advanced entropy coding

  • Simple VLC codes

  • Multiple code tables for encoding each particular alphabet out

  • A possible set of code tables is chosen (based on frame level quantization parameter) and signaled in the bitstream

  • Additional information e.g. motion vectors resolution coded using bitplane coding


Interlaced coding

Interlaced coding

  • Supports field and frame coding


Advanced b frame coding

Advanced B frame coding

  • B frames:- employ bi-directional prediction

  • Fractional position definition with respect to the reference frames for better scaling of motion vectors

  • Intra coded B frames for scene changes

  • Allow inter field reference


Overlap smoothing

Overlap smoothing

  • The deblocking filter smoothens out the block as well as true edges and it may be disabled in less complex profiles

  • A lapped transform (input spans to pixels from other blocks as well) is used at the edges

  • Used in spatial domain as pre and post processing

  • Used only at low bit rates where blocking artifacts are higher

  • Signaled at macroblock level so can be turned off in smooth regions


Low rate tools 100 kbps

Low rate tools (<100 Kbps)

  • Code frames at multiple resolutions (both in X and Y direction)

  • A frame can be downscaled at the encoder and then upscaled at the decoder for LBR transmission

  • The downscaling factor needs to remain same from the start of 1 I frame to the start of next I frame.

  • The frame must be upscaled prior to display (upscaling out of scope of the standard).


Fading compensation

Fading compensation

  • Large amount of bits required for scenes having effects like fade-to-black ,fade-from-black

  • Not possible to predict motion using normally used techniques.

  • Effective fading detection (original refrence image- current video image>threshold=fading)

  • If detected then encoder computes fading parameters which specify a pixel-wise first order linear transform for the reference image.

  • Also signaled to the decoder


References

References

  • Windows Media Video 9: overview and applications

    Sridhar Srinivasan, Pohsiang (John) Hsu, TomHolcom b, Kunal Mukerjee, Shankar L. Regunathan, Bruce Lin, Jie Liang, Ming-Chieh Lee, Jordi Ribas-Corbera

    Windows Digital Media Division, Microsoft Corporation, Redmond, WA 98052, USA

    available online at www.sciencedirect.com


Avs china s next generation video coding standard

AVS China’s next generation video coding standard


Introduction

Introduction

  • Streamlined video coder dedicated to coding HDTV content (1920x1080 in 4:2:0 and 4:2:2)

  • 4 levels are defined

    Level 4.0 : Standard Definition 4:2:0

    Level 4.2 : Standard Definition 4:2:2

    Level 6.0 : HD 4:2:0

    Level 6.2 : HD 4:2:2 (HD: High Definition)

  • Designed to provide near optimum performance and considerable reduction in complexity (low cost implementation)

  • Applications include broadcast TV,HD-DVD and broadband video networking


Data formats

Data Formats

  • Progressive scan

    results in significantly less coding complexity

  • Interlaced scan


Structure

Structure

Have

start codes


Structure1

Structure

Slice


Structure2

Structure

4:2:0

4:2:2


Block diagram encoder

Block Diagram (Encoder)


Block diagram decoder

Block Diagram (Decoder)


Buffers

Buffers

  • The rate buffer at the encoder side helps in converting variable data rate produced by encoder to fixed data rate by controlling quantization using feedback

  • The rate buffer at the decoder side gets the fixed rate data and stores it and then passes on to the decoder at a rate demanded by decoding of each macroblock and frame.


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