26-02-2013, 03:48 PM
Multimedia
Multimedia.ppt (Size: 1.17 MB / Downloads: 238)
Classes of multimedia Applications
Streaming Stored Audio and Video
Streaming Live Audio and Video
Real-Time Interactive Audio and Video
Others
Class: Streaming Stored Audio and Video
The multimedia content has been prerecorded and stored on a server
User may pause, rewind, forward, etc…
The time between the initial request and display start can be 1 to 10 seconds
Constraint: after display start, the playout must be continuous
Class: Streaming Live Audio and Video
Similar to traditional broadcast TV/radio, but delivery on the Internet
Non-interactive just view/listen
Can not pause or rewind
Often combined with multicast
The time between the initial request and display start can be up to 10 seconds
Constraint: like stored streaming, after display start, the playout must be continuous
Class: Real-Time Interactive Audio and Video
Phone conversation/Video conferencing
Constraint: delay between initial request and display start must be small
Video: <150 ms acceptable
Audio: <150 ms not perceived, <400 ms acceptable
Constraint: after display start, the playout must be continuous
Image compression: JPEG
Divide digitized image in 8x8 pixel blocks
Pixel blocks are transformed into frequency blocks using DCT (Discrete Cosine Transform). This is similar to FFT (Fast Fourier Transform)
The quantization phase limits the precision of the frequency coefficient.
The encoding phase packs this information in a dense fashion