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Windows Media Video 9. Tarun Bhatia tarun79\[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 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.
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)
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

structure2
Structure

4:2:0

4:2:2

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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