compression is the key to effective delivery
| media | uncompressed | compressed |
|---|
| voice 8k samples/sec, 8 bits/sample | 64 kbps | 2-4 kbps |
| slow motion video 10fps 176x120 8 bits | 5.07 Mbps | 8-16 kbps |
| audio conference 8k samples/sec 8bits | 64 kbps | 16-64 kbps |
| video conference 15 fps 352x240 8bits | 30.4 Mbps | 64-768 kbps |
| audio (stereo) 44.1 k samples/s 16 bits | 1.5 Mbps | 128k-1.5Mbps |
| video 15 fps 352x240 15 fps 8 bits | 30.4 Mbps | 384 kbps |
| video (CDROM) 30 fps 352x240 8 bits | 60.8 Mbps | 1.5-4 Mbps |
| video (broadcast) 30 fps 720x480 8 bits | 248.8 Mbps | 3-8 Mbps |
| HDTV 59.9 fps 1280x720 8 bits | 1.3 Gbps | 20 Mbps |
(phone: 56 Kb/s, ISDN: 64-128 Kb/s, cable: 0.5-1 Mb/s, DSL: 0.5-2 Mb/s)
images, video and audio are amenable to compression
statistical redundancy in signal
- spatial correlation -- neighbour samples in single frame
- temporal correlation -- between segments (frames)
irrelevant information
- from perceptual point of view
B. Vasudev & W. Li, Memory management: Codecs
codec = (en)coder + decoder
signal -> source coder -> channel coder (encoding)
signal <- source decoder <- channel decoder (decoding)
|
codec design problem
From a systems design viewpoint, one can restate
the codec design problem as a bit rate minimization problem,
meeting (among others) constraints concerning:
- specified levels of signal quality,
- implementation complexity, and
- communication delay (start coding -- end decoding).
tradeoffs
- resilience to transmission errors
- degradations in decoder output -- lossless or lossy
- data representation -- browsing & inspection
- data modalities -- audio & video.
- transcoding to other formats -- interoperability
- coding efficiency -- compression ratio
- coder complexity -- processor and memory requirements
- signal quality -- bit error probability, signal/noise ratio
- pixel-based -- MPEG-1, MPEG-2, H3.20, H3.24
- object-based -- MPEG-4
MPEG-1 video compression uses both intra-frame analysis, for the compression of individual frames (which are like images), as well as. inter-frame analysis, to detect redundant blocks or invariants between frames.
frames
- I: intra-frames -- independent images
- P: computed from closest frame using DCT (or from P frame)
- B: computed from two closest P or I frames
GigaPort
- optical network technologies - models for network architecture, optical network components and light path provisioning.
- high performance routing and switching - new routing technologies and transport protocols, with a focus on scalability and stability robustness when using data-intensive applications with a high bandwidth demand.
- management and monitoring - incident response in hybrid networks (IP and optical combined) and technologies for network performance monitoring, measuring and reporting.
- grids and access - models, interfaces and protocols for user access to network and grid facilities.
- test methodology - effective testing methods and designing tests for new technologies and network components.
| system |
spatial resolution |
frame rate |
mbps |
| NTSC | 704 x 480 |
30 |
243 mbps |
| PAL/SECAM |
720 x 576 |
25 |
249 mbps |
| item |
streaming |
downloaded |
| bandwidth |
equal to the display rate |
may be arbitrarily small |
| disk storage |
none |
the entire file must be stored |
| startup delay |
almost none |
equal to the download time |
| resolution |
depends on available bandwidth |
depends on available disk storage |
formats
Quicktime, introduced by Apple, early 1990s, for local viewing;
RealVideo, streaming video from RealNetworks; and
Windows Media, a proprietary encoding scheme fromMicrosoft.
Examples of these formats, encoded for various bitrates
are available at Video at VU.
