Introduction to MPEG4

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Introduction toMPEG-4

• MC2008

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Outline

• Multimedia
• MPEG-4 Profiles
• Key Features of MPEG-4 Systems
• MPEG-4
• Systems
• DMIF
• Audiovisual Objects and Scene Graph
• Editing, Composition and Rendering
• Coding Basics
• Coding Techniques

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Multimedia

• What is multimedia?
• Combination of audio, video, image, graphic, and
  text.
• Coverage of all human I/Os.
• Why does multimedia need to be coded?

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Multimedia Coding for Different Applications

• Mobile devices
• Low data-rate, error resilience, scalability
• Streaming service
• Scalability, low to medium data-range,
  interactivity
• On-disk distribution (DVD)
• Interactivity
• Broadcast
• On-demand services

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Profiles in MPEG-4

• Visual Profiles
• Audio Profiles
• Graphics Profiles
• Scene Graph Profiles
• MPEG-J Profiles
• Object Descriptor Profile

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NewPred
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H.263 Baseline
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Key Features of MPEG-4 Systems

• Provides a consistent and complete architecture
  for the coded representation of the desired
  combination of streamed elementary audio-visual
  information.
• Covers a broad range of applications,
  functionality and bit rates.
• Through profile and level definitions, it
  establishes a framework that allows consistent
  progression from simple applications (e.g., an
  audio broadcast application with graphics) to
  more complex ones (e.g., a virtual reality home
  theater).

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Key Features of MPEG-4 Systems (2)

• A set of tools for the representation of the
  multimedia content
• a framework for object description (the OD
  framework),
• BIFS a binary language for the representation
  (format) of multimedia interactive 2D and 3D
  scene description,
• SDM and SyncLayer a framework for monitoring and
  synchronizing elementary data stream, and
• MPEG-J programmable extensions to access and
  monitor MPEG-4 content.

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Key Features of MPEG-4 Systems (3)

• MPEG-4 System defines an efficient mapping of the
  MPEG-4 content on existing delivery
  infrastructures.
• FlexMux an efficient and simple multiplexing
  tool to optimize the carriage of MPEG-4 data
  (into different QoS channels),
• Extensions allowing the carriage of MPEG-4
  content on MPEG-2 and IP systems, and a flexible
  file format for authoring, streaming and
  exchanging MPEG-4 data.

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MPEG-4IS0/IEC 14496 Terminal Architecture
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Systems

• Timing Model
• Buffer Model
• Multiplexing of Streams
• Synchronization of Streams
• The Compression Layer
• Object Description Framework
• Scene Description Streams
• Audio-visual Streams
• Upchannel Streams

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Systems Decoder Model
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IS0/IEC 14496 Terminal Architecture
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Network-based Multimedia System
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The Objectives of DMIF
Delivery Multimedia Integration Framework

• to hide the delivery technology details from the
  DMIF User
• to manage real time, QoS sensitive channels
• to allow service providers to log resources per
  session for usage accounting
• to ensure interoperability between end-systems

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DMIF Communication Architecture
signaling
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High View of a Service Activation
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Audiovisual Objects

• Audiovisual scene is with objects
• Mixed different objects on the screen
• Visual
• Video
• Animated face body
• 2D and 3D animated meshes
• Text and Graphics
• Audio
• General audio mono, stereo, and multichannel
• Speech
• Synthetic sounds (Structured audio)
• Environmental spatialization

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Example of MPEG-4 Video Objects
From Olivier Avaro
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The Scene Graph
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• Composition
• Description Synchronization
• Delivery of streaming data
• Interaction with media objects
• Management and identification of intellectual
  property

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Major Components
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Composition Rendering
Media Objects
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Adding or Removing Objects (1)



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Adding or Removing Objects (2)
From Igor S. Pandic
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Adding or Removing Objects (3)

• Applications
• Video conferencing
• Real-time, automatic
• Separate foreground (communication partner) from
  background
• Object tracking in video
• May allow off-line and semi-automatic
• Separate moving object from others

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MPEG-4 Coding Basics
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Toolbox Approach
tools for synthetic scenes
tools for natural scenes
TOOLS
ALGORITHMS
PROFILES
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Coding Techniques

• Video objects
• Shape
• Motion vectors
• texture
• Audio objects
• MPEG
• AAC (Advanced Audio Coder)
• TTS (Text-To-Speech)
• Face and Body
• Animation parameters
• 2D Mesh
• Triangular patches
• Motion vector

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Content-based Audio-Visual Representation

• Audio-Visual Object (AVO)
• Video object component (video object plane, VOP)
• natural or synthetic
• 2D or 3D
• Audio object component
• mono, stereo or multi-channel

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Video Object Planes (VOP)

• Characteristics of VOP
• may have different spatial temporal resolutions
• may be associated with different degrees of
  accessibility ? sub-VOPs
• may be separated or overlapping
• VOP type
• Traditional I, P, B type
• S-VOP (Sprite) for background

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Video Object Plane Type
S-VOP
Time
S-VOP
B-VOP
B-VOP
B-VOP
B-VOP
B-VOP
B-VOP
I-VOP
P-VOP
P-VOP
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Content-based Object Manipulation

• Object manipulation
• change of the spatial position of a VOP
• application of a spatial scaling factor to a VOP
• change of the speed with which an VOP moves
• insertion of new VOPs
• deletion of an object in the scene
• change of the scene area

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Segmentation Process

• Depending on applications, segmentation can be
  perform
• Online (real-time) or offline (non-real-time)
• Automatic or semi-automatic
• Examples
• Video conferencing
• real-time, automatic
• separate foreground (communication partner) from
  background
• Object Tracking in Video
• May allow off-line and semi-automatic
• separate moving object from others

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Compression

• Improved coding efficiency
• 5-64 kbps for mobile applications
• up to 20Mbps for TV/film applications
• subjectively better quality compared to existing
  standard
• Coding of multiple concurrent data streams
• can code multiple views of a scene
  efficiently,e.g. stereo video

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Coding VO in MPEG-4

• Reduce temporal redundancy
• Motion estimation for arbitrary shaped VOPs
• padding and modified block (polygon) matching
  motion estimation

P-VOP
B-VOP
time
I-VOP
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Encoding of Visual Objects

• Binary alpha block
• Motion vector
• Context-based arithmetic encoding
• Texture
• Motion vector
• DCT

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New Coding Features

• For each macroblock, the motion vectors can be
  computed on a 16 ? 16 or 8 ? 8 block basis
• Unrestricted motion estimation prediction can
  extend over image boundary
• Overlapped block motion compensation
• Each component of texture can range from 1 to 12
  bits
• More robust coding

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Robust Video Coding

• Resynchronization
• Allow insertion of resync marker within each VOP
• Video packet header include macroblock number,
  qunatizer value and timing information
• Data partition
• Allow shape, motion and texture data to be
  separated within a packet
• Reversible VLC
• Offer partial recovery from errors.

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Sprite VOP

• Represent background image
• Can be used for very efficient coding of scenes
  involving camera pan and zoom
• Much larger than the size of image and thus
  require more memory

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Example of Sprite VOP
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Object Mesh

• Useful for animation, content manipulation,
  content overlay, merging natural and synthetic
  video and others
• Tesselate with triangular patches
• Define motion vector for each node
• 2D motion of video objects are represented by the
  motion vectors of the node points
• Motion compensation is achieved by warping of
  texture map corresponding to patches by affine
  transform

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Example of Object Mesh
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Face Animation

• Face model
• Default face model
• Download from the encoder
• Low-level facial animation
• A set of 66 facial animation parameters
• High-level facial animation
• A set of primary facial expression like joy,
  sadness, surprise and disgust
• Speech animation
• 14 visemes for mouth shape
• Text-to-speech synthesizer

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Facial Animation
From Eine Übersicht
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Still Texture Coding

• Discrete Wavelet Transform (DWT)
• Spatial and quality scalability
• Use 2D Daubechies (9, 3)-tap biorthogonal filter
• Lowest band is lossless coded by arithmetic
  coding
• Higher bands are coded by multilevel
  quantization, zero-tree scanning and arithmetic
  coding

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Audio Coding

• Different bit-rates, different types of source
  material and different algorithms
• Combination of parameter based coding, LPC-based
  coding, time/frequency based coding
• High quality speech with 2 kbps Harmonic Vector
  eXcitation Coding (HVXC)
• Text-to-Speech (TTS)

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Natural Audio Coder
Telephone
From Olivier Dechazal
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Multiview Video
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Stereo Sequence Coding

• Multiview profile of MPEG-2
• Coding left view seqence Sl, first, for the right
  view sequence, each frame is predicated from the
  corresponding frame in Sl, based on an estimated
  disparity field and the prediction error image
  are coded.

P
B
B
B
Right view
I
B
B
P
Left view
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Intermediate View Synthesis
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Original left
Original right
Regular mesh on the left image
Corresponding mesh on the right image
Predictive right image by mesh (27.48 dB)
Predictive right image by BMA (32.03 dB)
The mesh-based scheme yields a visually more
accurate prediction
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MPEG-4 Coding Techniques
Shape Coding Shape-adaptive DCT Object-based
Inter-frame Coding Overlapped Motion
Estimation Bit-plane Coding and FGS
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Object-Based Coding
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Shape Coding

• Bitmap Coding
• Context-Based Arithmetic Encoding (CAE)
• Contour Coding
• Chain Coding
• Baseline Shape Coding
• Polygon Approximation
• Skeleton-Based Shape Coding
• Quadtree Coding

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Context-Based Arithmetic Encoding
16
16
Transparent block
Boundary blocks
Opaque block
BOUNDING BOX
Conditional entropy coding
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Context-Based Arithmetic Encoding
16
16
Transparent block
Boundary blocks
Conditional entropy coding
Opaque block
BOUNDING BOX
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Chain Coding
0
0
3
0
0
3
3
3
2
3
3
2
2
2
1
2
2
1
1
1
0
0
1
1
starting points
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4 - connected
8 - connected
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Chain Coding
starting points
4
4 - connected
8 - connected
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Differential Chain Code

• DCC records the move (forward, leftward or
  rightward) regarding two consecutive directional
  links.

F
F
F
R
L
F
R
L
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Baseline Shape Coding
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Polygon Approximation
d2
d1
d3

• Select vertices that are optimal in the
  rate-distortion sense.
• Splines are adopted to approximate the contour.

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Skeleton-Based Shape Coding
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Quadtree Coding
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Shape-adaptive DCT
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Inter-frame Coding Reconstruction of Object
Shape
MVS MVPS MVDS MVS MV for shape MVPS
predication MVDS difference (BAC)
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The context for Inter-frame Coding
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Overlapped Motion Estimation
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Weighting Coefficients in Overlapped Motion
Estimation
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Fine Granularity Scalable
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FGS Video Encoder Structure
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Bit-plane Coding
quantized residual
binary transfer
MSB
LSB
reordering
00100000010000001101100100000001010111001001101011
01000010101011
00100000010000001101100100000001010111001001101011
01000010101011
run-length coding
Enhancement layer bitstream
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FGS Video Decoder Structure
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Binary Shape Encoder
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Padding