Video

  1. Video
  2. Television
    1. National television system committee (NTSC)
    2. Phase altering line (PAL)
    3. Sequential color and memory (SECAM)
  3. Physics
    1. Lighting
    2. Optical lens aberrations
    3. Room design
  4. Hardware
    1. Sensors
    2. Connectors
  5. Codecs
    1. Scanning
    2. Compression
    3. H.264
    4. H.265

Video

  • floating packet size and bitrate due to compression
  • very sensitive to losses due to compression
  • elasticity: flow ability to adapt to channel state
  • QoS marking
    • bcast video: CS5 (Cisco), CS3 (RFC)
    • interactive video: CS4
  • if assigned to EF PHB, admission control is required
  • broadcast video is unidirectional ⇒ can be buffered
  • 60 FPS – max human perception

Television

  • YPbPr – analog (P ≡ primary)
  • TCbCr – digital (C ≡ code)

National television system committee (NTSC)

  • North America
  • Y = 0.299R + 0.587G + 0.114B, Y – RGB image brightness
  • 30 FPS or 60 FPS
    • depends on current frequency ≡ lamp flashing frequency
    • if frequencies of bulb flashes and video frame are not synced – horizontal inter-frame lines on the screen
  • 75 Ohm terminator
  • 525 signal lines, 480 visible lines, analog signal

Phase altering line (PAL)

  • UK, Europe, Africa, Australia
  • sends Y,R,B in lieu of R,G,B ⇒ compatible with monochrome signal
  • 25 FPS, 50 FPS
  • 75 Ohm terminator
  • 625 signal lines, 576 visible lines, analog signal

Sequential color and memory (SECAM)

  • USSR, France

Physics

Lighting

  • cold light (4500K) in room
  • types
    • main
      • upper light
      • 3200-4100K
      • diffused; if directional, then it has to be directed behind participants onto wall/floor
    • soft
      • cold light from behind the camera (e.g., LCD)
      • highlights faces: separate them from background, less contrast
    • back
      • separate from background
  • illuminance difference within frame < 100 lux
  • light brightness on shoulders should be no more than 2 times higher than brightness on face

Optical lens aberrations

  1. spherical aberration: focal points do not match for axial and peripheral rays
  2. astigmatism: focal points do not match for parallel rays because of different curvature of lens surface
  3. comatic aberration: angled rays have different focal points
  4. distortion: magnification is different in the center and on edge, barrel and pincushion
  5. chromatic aberration

Room design

  • table
    • light surface for soft light due to light reflection
    • texture is not bright: otherwise codec needs more BW
  • light reflection should not beam into camera or eyes
  • thick curtains (not window blinds)
  • no movement on background: windows, halls
  • solid wall colour without pictures ≡ less BW
  • no contrast colours

Hardware

Sensors

  • types
    • charge coupled device (CCD)
      • expensive
      • high quality
      • low noise
      • high sensitivity
      • good colour reproduction
    • complementary metal-oxide semiconductor (CMOS)
      • low power consumption
      • high speed
  • methods
    • Foveon X3: 3 layers of RGB sensors on top of each other in pixel, each layer absorbs only its own wavelength
    • 3CCD: prism separate light ray into 3 coloured rays
    • Bayer: colour filter on top of pixel, pixels are placed as mosaic

Connectors

  • composite: one signal with all components
    • Bayonet Neill-Concelman (BNC): coax
    • video graphics array (VGA)
    • RCA: yellow connector
    • S-Video: ≈ PS/2
    • DVI-A: digital visual interface – analog
  • component: colour components are transmitted separately
    • RCA: RGB connectors
    • BNC: high-definition serial digital interface (HD-SDI)
    • high-definition multimedia interface (HDMI)
    • DVI-D

Codecs

Scanning

  • progressive
    • all lines per frame, sequential
    • 1280×720p30
  • interlaced
    • odd or even lines per frame
    • 1280×720i30

Compression

  • spatial, temporal
  • macroblock: 16×16 pixels, consists of transform blocks (size depends on compression algorithm)
  • predicts block movements

H.264

  • 5 Mbps for FullHD
  • MPEG-4 AVC (advanced video coding)
  • lossy
  • compatible with HW, running H.261 and H.263
  • up to 60 FPS

H.265

  • high efficiency video codec (HEVC)
  • requires DSP ⇒ incompatible with H.264 hardware
  • UltraHD, 2K, 4K, 8K
  • up to 300 FPS