Multimedia Study Notes

  • Audio/video files can be downloaded for future use (streaming stored audio/video) or broadcast to clients over the Internet (streaming live audio/video). The Internet can also be used for live audio/video interaction.
  • Audio and video need to be digitized before being sent over the Internet.
  • Audio files are compressed through predictive encoding or perceptual encoding.
  • Joint Photographic Experts Group (JPEG) is a method to compress pictures and graphics.
  • The JPEG process involves blocking, the discrete cosine transform, quantization, and lossless compression.
  • Moving Pictures Experts Group (MPEG) is a method to compress video.
  • MPEG involves both spatial compression and temporal compression. The former is similar to JPEG, and the latter removes redundant frames.
  • We can use a Web server, or a Web server with a metafile, or a media server, or a media server and RTSP to download a streaming audio/video file.
  • Real-time data on a packet-switched network require the preservation of the time relationship between packets of a session.
  • Gaps between consecutive packets at the receiver cause a phenomenon called jitter.
  • Jitter can be controlled through the use of timestamps and a judicious choice of the playback time.
  • A playback buffer holds data until they can be played back.
  • A receiver delays playing back real-time data held in the playback buffer until a threshold level is reached.
  • Sequence numbers on real-time data packets provide a form of error control.
  • Real-time data are multicast to receivers.
  • Real-time traffic sometimes requires a translator to change a high-bandwidth signal
    to a lower-quality narrow-bandwidth signal.
  • A mixer combines signals from different sources into one signal.
  • Real-time multimedia traffic requires both UDP and Real-time Transport Protocol
  • RTP handles time-stamping, sequencing, and mixing.
  • Real-time Transport Control Protocol (RTCP) provides flow control, quality of data
    control, and feedback to the sources.
  • Voice over IP is a real-time interactive audio/video application.
  • The Session Initiation Protocol (SIP) is an application layer protocol that establishes,
    manages, and terminates multimedia sessions.
  • H.323 is an ITU standard that allows a telephone connected to a public telephone
    network to talk to a computer connected to the Internet.


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