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
- main
- 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
- spherical aberration: focal points do not match for axial and peripheral rays
- astigmatism: focal points do not match for parallel rays because of different curvature of lens surface
- comatic aberration: angled rays have different focal points
- distortion: magnification is different in the center and on edge, barrel and pincushion
- 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
- charge coupled device (CCD)
- 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