Multimedia communications EG-371Dr Matt Roach

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Multimedia CommunicationsEG 371

• Dr Matt Roach
• Lecture 7
• Video compression standards

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Standards so far

• Video - Visual
• H.261
• H.263
• MPEG-1
• MPEG-2 (H.262)
• MPEG-4
• Image
• JPEG

• Video - Acoustic
• PCM
• MP3 (MPEG-1)
• GSM
• A-law/u-law (G.711)
• Others
• MPEG-7 meta data
• MPEG-21framework

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H. 261

• Video compression (ITU)
• Video conferencing, ISDN p x 64
• Digitisation format (divisible by macroblocks)
• CIF Y 352 x 288, 30 fps
• QCIF Y 176 x 144 15/7.5 fps
• Frame types supported
• I P only
• Enhance low quality at low bit rates leading to
  the need for H. 263
• GOP 4

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H. 261 coded

• Picture start code (each frame)
• Temporal reference (for visual and acoustic sync)
• Picture type (I or P)
• GOB (11x3) CIF 12 (2x3), QCIF 3 (1x3)
• GOB start code (resynchronisation marker)
• Group number
• Quantisation parameter (regulates the bandwidth)
• Macroblocks (MB)

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H. 261 coded cont.

• Macroblock (MB)
• Address
• Type (coding, frame)
• Quantisation value
• Motion vector
• Coded block pattern (which blocks are present)
• Block
• DC
• Skip, value
• End of block

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H.263

• Video compression ITU-T approved standard (series
  260-279)
• Video coding for low bit rate communication
• Public telephone switch networks (PSTNs) 28 kbps,
  56 kbps
• Digitisation formats
• QCIF
• S-QCIF
• Frame types supported
• I, P, B PB frame

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MPEG 1

• Video compression standard
• Adopts similar compression to H.261
• Digitisation format
• SIF (525 line, 625 line)
• Types of frames supported
• I, P, B frames

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MPEG 2

• Main profile at the main level
• Digital broadcasting
• Digitisation format
• 420
• Bite rate 5 Mbps 15Mbps
• Frame types I, P B
• IBPBPBPBPBPBPBP (I frame every 0.5 sec)
• GOP 15

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Table of standards
Standard Digitisation format Compressed rate Example applications
H. 261 CIF/ QCIF X 64 kbps Video conferencing over LANs
H. 263 S-QCIF/ QCIF lt64kbps Video conferencing over low bits rate channels
MPEG 1 SIF lt1.5Mbps VHS quality video storage
MPEG 2 Low Main High 1440 High SIF 420 422 420 422 420 420 lt4Mbps lt15Mbps lt20Mbps lt60Mbps lt80Mbps lt80Mbps lt100Mbps VHS quality video recording Digital video broadcasting High definition TV (4/3) High definition TV (16/9)
MPEG 4 Various 5kbps tens Mbps Versatile multimedia coding standard
MPEG 7 - - Content description standard
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Tutorials

• Any questions?
• My questions
• Objectives
• Remember well
• Dont remember well
• Revisit any areas of the course

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H.263 block diagram
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H.263 sampling blocks

• 420 sampling
• luminance Y to chrominance CB , CR
• Block
• 8 x 8 pixels
• Macroblock (MB)
• 4 Y CB CR blocks
• Group of blocks (GOB)
• One or more rows of MBs
• In GOB header resynchronization

Y
Y
C
Y
Y
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H.263 resolutions

• Five standardized resolutions
• CIF 352 x 288 (as in H.261)
• QCIF 176 x 144 (as in H.261)
• Sub-QCIF 128 x 96
• 4CIF 704 x 576 (little used?)
• 16CIF 1408 x 1152 (little used?)
• Custom resolutions negotiable
• multiple of 4 in both directions

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H.263 frames

• Two (six) frame types
• I-frames intra
• P-frames predictive (inter)
• B-frames (optional) bidirectional predicted
• PB-frames (optional) decoded B and P frame as
  one unit
• EI-frames (optional) enhanced I-frame
• EP-frames (optional) enhanced P-frame

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H.263 coding options (1)

• 16 modes, negotiable at session start
• Efficiency / improved picture quality (10)
• Unrestricted Motion Vector
• Syntax-Based Arithmetic Coding
• Advanced Prediction!
• Four Motion Vectors per Macroblock
• Overlapped Block Motion Compensation
• PB Frame
• Advanced Intra Coding
• Alternate Inter VLC
• Modified Quantization
• Deblocking Filter
• Improved PB Frame

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H.263 coding options (2)

• Error robustness (3) (lossy channel)
• Slice-Structured
• Reference Picture Selection
• Independent Segment Decoding
• Scalability!
• Temporal, signal-to-noise ratio (SNR), spatial
• Reference Picture Resampling
• Reduced Resolution Update

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H.263 levels

• Preferred combination of supported options
  (profiles)
• Level 1 advanced intra coding, deblocking
  filter, full-frame freeze, modified quantization
• Level 2 unrestricted motion vector,
  slice-structured, reference picture resampling
  level 1
• Level 3 advanced prediction, improved PB frames,
  independent segment decoding, alternate VLC
  level 2

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H.263 summary

• Baseline core similar to other codecs
• Flexible, many new options
• Developed for variable bit rates, low delay
• Specifies bitstream format only