DARPA Compare

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Video I
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Digital Video

• Size ltgt quality
• Broadcast quality is very different from www
• MPEG-2 is satellite dish video
• MPEG 1 is VCR quality

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Transmission Time

• Size ltgt Download speed
• 14.4k Modem, 56k Modem, ADSL, Cable Modem
• MPEG-1, 2, RealVideo
• gt Time to download a 1 minute clip (1 hour)

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Streaming

• Access disk fast enough
• RAIDs
• Dont download everything first
• Play as you start to download
• Keep a buffer for variable network speed
• equivalent to sampling a CDs faster and filling
  a buffer
• Drop frames when you fall behind (not TCP)
• Adjust the bandwidth dynamically
• need multiple encoding formats
• RTSP, QT, MS ASF, H.323 (video conferencing)

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Webcasting

• LIVE
• Encode fast enough
• Stream to multiple users connected at the same
  time
• Only time-synchronous viewing

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MPEG Motion Picture Experts Group

• MPEG-1 (1992)
• Compression for Storage
• 1.5Mbps
• Frame-based Compression
• MPEG-2 (1994)
• Digital TV
• 6.0 Mbps
• Frame-based Compression
• MPEG-4 (1998)
• Multimedia Applications
• Low bit rate
• Object based compression

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MPEG-1

• I,B,P Frames
• Choice of audio Encoding
• Picture size, bitrate is variable
• No closed-captions, etc.
• Group of Pictures
• one I frame in every group
• size 10-15
• B and P are in random within GoP

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Video I Thats all for today
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