Introduction

• Multimedia can be in the form of audio, image, video, ...
• Video traffic is the major consumer of internet bandwidth
• Video distributers (Netflix and YouTube) have distributed, application-level infracstructure called Content Distribution Networks (CDNs)
• How is audio recorded ?

  A) analog signal

  B) sampling rate (N samples/sec)

  C) quantization error

  D) quantized value

  
• For audio, each value is represented by 8 bits, 2^8=256 possible

  quantized values
• Receiver converts quantized audio bits back to analog signal
• example audio rates

  ▪ CD: 1.411 Mbps

  ▪ MP3: 96, 128, 160 kbps

  ▪ Internet telephony: +5.3 kbps
• Video

  sequence of images at a constant rate, coding is used within and between images to reduce the number of bits for encoding
• Encoding video techniques

  • spatial (within frame): removes redundant information to avoid repetition
  • temporal (between frames): only sends frames that changed in value
• CBR (constant bit rate)

  video encoding rate fixed
• VBR (variable bit rate)

  video encoding rate changes as amount of spatial, temporal coding changes
• Multimedia networking

  • streaming, stored audio, video
  • conversational voice/video over IP
  • streaming live audio, video
• Streaming

  play begins before full download, video is transmitted faster than audio/video is rendered (implies buffering at client), (e.g. Netflix, YouTube)
• Conversational networking

  interaction between humans, conversation needs low delay (e.g. Skype)
• Streaming live

  live sporting event
• HTTP (hypertext transfer protocol)

  client (browser) requests, receives and displays web objects from server using HTTP protocol

  A) HTTP request

  B) HTTP response