topical media & game development

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[] readme course(s) preface I 1 2 II 3 4 III 5 6 7 IV 8 9 10 V 11 12 afterthought(s) appendix reference(s) example(s) resource(s) _

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Codecs

compression is the key to effective information 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

Codec = (en)coder + decoder

images, video, audio are amenable to compression:

• statistical redundancy in signal
  • spatial correlation -- neighbour samples in single frame
  • spectral correlation -- between multiple sensors
  • temporal correlation -- between segments (frames)
• information that is irrelevant from perceptual point of view
• redundant features (accross space and time)

B. Vasudev & W. Li, Memory management: Codecs

Handbook of Multimedia Management, p 237-278

encoding & decoding

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
• communication delay (start coding -- end decoding)

classification of compression methods

• model-based -- LPC, polynomial fitting, object-based
• waveform-based
  lossless:
  • statistical -- gilbert, hufmann
  • universal -- arithmetic, pattern matching
  
  lossy:
  • spatial & time domain -- delta modulation
  • frequency domain
    • filter-based -- subband, wavelet
    • transform-based -- fourier, DCT

tradeoffs

• coding efficiency -- compression ratio
• coder complexity -- memory, power requirements, ops/sec
• signal quality -- bit error probability, signal/noise, ...

issues in compression selection

• resilience to transmission errors
• degradations in decoder output (lossy)
• data representation -- ( browsing & inspection )
• interplay of data modalities -- audio & video (conferencing)
• transcoding to other formats -- (interoperability)

standard-based codecs

• JPEG -- ISO/IEC 10918-1, ITU-T (T.81)
• MPEG
  • ISO 11172 (up to 1,5 Mbps) -- MPEG-1
  • ISO 13818 ITU-T H.262 -- MPEG-2
• H3.20 -- for ISDN-like environments
• ITU-T H.261 -- P x 64 standard (rate in kbs, p=1..30)
• H.324 -- video conferencing for GSTN, 26kbps/sec

pixels versus objects

pixel-based standards

• MPEG-1, MPEG-2, H3.20, H3.24

object-based codec(s)

• MPEG-4 -- segmentation-based DFD (Displaced Frame Difference)

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(C) Æliens 04/09/2009

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