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  • Digital Video Class Spring 2006 Internet2 Member Meeting Larry Amiot Northwestern University [email_address] And Dave Devereaux-Weber University of Wisconsin at Madison [email_address]
  • Agenda
    • Analog/Digital Video
    • Digital Video ABCs
    • Digital Video Applications
    • Break
    • Digital Academic Television Network
    • Program Guide
    • Question and Answer
    • Demonstrations
  • Video – Analog and Digital
    • Analog
    • Original broadcast television was black & white
    • 262 ½ odd and 262 ½ even lines (fields) are interlaced to conserve bandwidth
    • 60 fields per second
    • 15,750 lines per second
  • National Television System Committee (NTSC)
    • A committee appointed by the Federal Communications Commission
    • Set standards for US television
  • Composite Video
    • Video and synchronizing pulses on the same wire
    • 1 volt peak-to-peak
    • 100 IRE (Institute of Radio Engineers) units of video
    • 40 IRE units of sync
  • NTSC does Color
    • Backwards compatible with B&W
    • Color information added with a subcarrier
    • Saturation represented by subcarrier amplitude
    • Hue represented by subcarrier phase
  • RGB
    • 3 connections: red, green & blue
    • Full bandwidth, full resolution, full detail
  • Digital Video
    • Over the air in the US, the standards body for digital is the Advanced Television Systems Committee http://www.atsc.org/
    • One family of digital video encoders & decoders (codecs) is MPEG
    • Named from the Moving Pictures Experts Group
    • http://www.mpeg.org/
  • Digital Video
    • DVB is a standard for digital vide broadcasting
    • Originally European, now used around the world
    • http://www.dvb.org
  • Digital Video
    • DV
    • Standard used by Sony, Avid, Apple Microsoft, others
    • (Doesn’t use MPEG)
  • IP, Codecs & Business Model
    • Codecs include Intellectual Property (IP)
    • IP often protected by patents
    • Need to license patented IP
  • IP, Codecs & Business Model
    • Windows Media (Microsoft), user cost is free, subsidized by sale of Microsoft software
    • Quicktime (Apple Computer), user cost is free, subsidized by sale of Apple Computers
    • Real Media player is free, server is paid, no hardware or software to subsidize
  • IP, Codecs & Business Model
    • License for MPEG-2 Player is $2.50 each
    • MPEG-2 codec not included with Windows Media or Quicktime
    • MPEG-4 codec included in Windows Media & Quicktime
  • IP, Codecs & Business Model
    • VideoLAN http://videolan.org/ is free, open source
    • Has codecs with IP issues (MPEG-2)
    • Does not pay a license fee for IP
    • Use of VideoLAN may carry IP risk.
  • Digital Video ABCs
  • Understanding Digital Video Quality
    • Three important factors
      • Image resolution
      • Compression
      • Bit rate of the compressed video stream
  • Image Resolution
  • Image Resolution
    • What is a pixel?
      • Tiny square or rectangular, colored picture elements on a LCD, plasma, DLP, or projection LCD monitor
      • Tiny round, color phosphor dots on a CRT
      • A value (e.g. 8 bit or 24 bit) defining color and luminescence
  • Image Resolution
    • What is resolution?
      • The number of pixels on an image or on a frame of a video
      • The more pixels, the better the resolution
      • Usually expressed as the horizontal pixels times the vertical resolution
        • E.g. 720x480
  • Image Resolution
    • Interlaced Scan
      • Draw odd lines first, then the even lines
      • Full motion video requires frames every 1/60 of a second
      • The way NTSC does it
    • Progressive scan
      • Drawn top to bottom
      • Full motion video is 30 frames per second
  • Image Resolution
    • Standard Definition Television (SDTV)
      • A set of digital television standards with 480 lines of resolution
      • At least as good if not better than NTSC
      • A subset of the Digital TeleVision standards (DTV)
      • All SDTV formats are interlaced
  • Image Resolution
    • DTV standards
      • ATCS is the standard in North America
      • All use MPEG2 compression
      • 18 digital formats covering:
        • Standard definition
        • Enhanced definition
        • High definition
    • High Definition TV
    • 1. 1920 x 1080 16:9 24p Square
    • 2. 1920 x 1080 16:9 30p Square
    • 3. 1920 x 1080 16:9 30i* Square
    • 4. 1280 x 720 16:9 24p Square
    • 5. 1280 x 720 16:9 30p Square
    • 6. 1280 x 720 16:9 60p* Square
    • Enhanced Definition TV - 480p
    • 7. 704 x 480 16:9 24p Rectangle
    • 8. 704 x 480 16:9 30p Rectangle
    • 9. 704 x 480 16:9 60p* Rectangle
    • 10. 704 x 480 4:3 24p Rectangle
    • 11. 704 x 480 4:3 30p Rectangle
    • 12. 704 x 480 4:3 60p* Rectangle
    • 13. 640 x 480 4:3 24p Square
    • 14. 640 x 480 4:3 30p Square
    • 15. 640 x 480 4:3 60p Square
    • Standard Definition TV- 480i
    • 16. 704 x 480 16:9 30i Rectangle
    • 17. 704 x 480 4:3 30i*Rectangle
    • 18. 640 x 480 4:3 30i Square
    • * most popular formats
    DTV Formats
  • Image Resolution
    • CIF
      • A video format widely used in videoconferencing
      • Common Intermediate Format (CIF)
        • QCIF - Quarter CIF (resolution 176x144)
        • SQCIF - Sub quarter CIF (resolution 128x96)
        • CIF- Full CIF (resolution (352x288)
        • 4CIF - 4 x CIF (resolution 704x576)
        • 16CIF - 16 x CIF (resolution 1408x1152)
  • Compression
  • Compression
    • Spatial Redundancy
      • Takes advantage of identical picture elements within a video frame
    • Temporal Redundancy
      • Takes advantage of identical picture elements between frames
      • Takes advantage of the movement of identical picture elements between frames (motion vector)
    • Psychovisual Redundancy
      • Takes advantage of human eyes limited response to fine spatial detail
  • Compression
    • Lossless compression
      • You can take the compressed data and uncompress it to obtain an identical copy of the original uncompressed data
      • E.g. TIFF image
    • Lossy compression
      • You can not get the original data by uncompressing
      • Allows much greater compression than lossless compression
      • E.g. MPEG
  • JPEG Compression
    • A standard of the Joint Photographic Experts Group
    • A lossy compression technique
    • Handles still images
    • The degree of lossiness can be varied by adjusting compression parameters- trade quality for file size
    • You can also trade off decoding speed against image quality
  • JPEG Compression
    • A 24 bit per pixel color scheme as compared to GIF which is 8 bit
    • Can easily provide 20:1 compression of full-color data (about four times better than GIF but slower to decode)
    • Motion JPEG (M-JPEG) provides a video stream
      • but it is not a standard
      • Does not use inter frame compression
  • MPEG Compression
    • MPEG is recognized standard for motion picture compression
      • Uses many of the same techniques as JPEG, but adds inter-frame compression
      • Compresses by about a factor of 3 better than M-JPEG except at very low frame rates
      • Takes more computation than JPEG to compress
      • Difficult to edit on a frame by frame basis
  • Intra Frame Encoding- I Frames
    • Every frame is encoded separately
    • Easy to edit
    • Fast to decode
    • Lost frame produces small artifact
    I I I I I I I I
  • Inter Frame Encoding- I and P Frames
    • Forward predicted from the last I-frame or P-frame
    • Better compression
    • A little harder to decode
    • More difficult to edit
    • More artifacts if a frame is lost
    • Buffering of previous frame required
    • Frames sent in order
  • Inter Frame Encoding- I, P, and B Frames
    • B-frames are both, forward predicted and backward predicted from the last/next I-frame or P-frame
    • Best compression
    • Hardest to decode
    • Most difficult to edit
    • More artifacts with lost frames
    • More buffering required
    • Frames not sent in order
    Sent IPBBBPBBB
  • So what’s a GOP?
    • A set of frames, typically between 4 and 20, is called a Group Of Pictures
    • At most one frame in the GOP can contain a reference to a frame in another GOP
    • Some GOPs do not reference any other GOP
      • E.g. IBBPBBP
  • MPEG Compression
    • Three defined standards
      • MPEG1
      • MPEG2
      • MPEG4
  • MPEG1
    • Optimized to work at video resolutions of 352x240 pixels at 30 frames/sec and 1.5 Mbps
    • May go as high as 4095x4095 at 60 frames/sec
    • Progressive scan only
  • MPEG2
    • Target bit-rate was raised to between 4 and 9 Mbps
    • Commonly used at 720x480 resolution video at 30 frames/sec, at bit-rates up to 15 Mbps
    • Also used for HDTV resolution of 1920x1080 pixels at 30 frame/sec, at a bit-rate of up to 80 Mbps
    • Can do interlaced
  • MPEG4
    • Originally optimized for very low bit rate communication at rates less than 64 Kbps
    • Currently used in videoconferencing for HD at speeds up to 4 Mbps
  • Videoconferencing Video
  • H.323-based Videoconferencing
    • An International Telecommunications Union (ITU) umbrella standard for videoconferencing across IP networks
    • Includes protocols for:
      • Video (i.e. H.261, H.263, and H.264)
      • Audio (G711, G722, etc)
      • Control (H.245, etc)
  • H.261 Compression
    • Part of the H.323 videoconferencing set of standards
    • Originally for two way communication over ISDN lines- now over the Internet
    • Supports intra and inter frame compression
    • Resolutions supported
      • QCIF(144x176 pixels)
      • CIF(288x352)
  • H.263 Compression
    • Part of the H.323 videoconferencing set of standards
    • Based on H.261 but with enhancements to improve video quality
    • Resolutions supported
      • QCIF(144x176)
      • CIF(288x352)
      • SQCIF (128x96)
      • 4CIF (704x576)
      • 16CIF(1408x1152)
  • H.264 Compression
    • Part of the H.323 videoconferencing set of standards
    • H.264, MPEG4, & AVC (Advanced Video Coding) are related codecs for achieving very high compression
    • Adds B frames to compression
    • Ultra-efficient technology that gives you excellent results across a broad range of bandwidths, from 3G for mobile devices to iChat AV for video conferencing to HD for broadcast and DVD
    • Used in QuickTime 7
  • H.264 Compression
    • H.264 delivers the same quality as MPEG-2 at a third to half the data rate
    • H.264 Part 10 delivers up to four times the frame size of MPEG-4 Part 2 at the same data rate
    • Resolutions supported
      • SQCIF (128x96)
      • 720p HD (1280x720)
      • 1080 HD (1920x1088)
  • DV and MiniDV
    • A format developed by several manufacturers for recording on cassettes
    • 500 line horizontal resolution
    • Utilizes the IEEE 1394 digital interface (Firewire)
    • Bit rate of 25 Mbps
    • The sampled video is compressed using a Discrete Cosine Transform (DCT), the same sort of compression used in motion-JPEG
    • 5:1 intraframe compression only
  • Bit Rate of Stream
  • Bit Rate
    • The quality of the video is directly related to the bit rate of the stream
    • Low compression streams require more bandwidth
    • Many codecs dynamically adjust the quality (compression) according to the amount of bits that are produced
  • Bit Rate
    • Variable bit rate
      • Number of bits produced by the codec and sent varies according to the redundancy and motion being compressed at any moment
    • Fixed bit rate
      • Bits to be transferred are buffered
      • If the codec starts producing information faster than the buffering can handle, feedback to the codec reduces the quality (compression) and thus the number of bits produced
  • Bit Rate
    • The quantization (Q) level of an MPEG stream is a measure of the amount of data the encoder throws away to bring the bit rate down
    • Higher Q values mean the encoder threw away a lot of data, implying a low bit rate, but also low visual quality
    • A low Q level implies a high bit rate, and high visual fidelity
    • You can keep a constant bit rate by varying the Q level
    • Alternatively, you can keep a constant Q level and allow the bit rate to vary
  • Compression Trade Offs
    • High Compression
    • Less video quality
    • More buffering required
    • More latency
    • Less bandwidth required
    • More complex hardware
    • Less storage required
    • More susceptible to packet loss
    • More difficult to edit
    • Low Compression
    • Better video quality
    • Less buffering required
    • Less latency
    • More bandwidth required
    • Less complex hardware
    • More storage required
    • Less susceptible to packet loss
    • Less difficult to edit
  • High Definition Video
  • Broadcast High Definition TV
    • Breathtaking quality on home monitors
      • Plasma
      • LCD and projection LCD
      • Projection DLP
    • Several carrier types
      • Through the air
      • Cable
      • Satellite dish
    • More and more HD programming becoming available
    • Downside- watch too much television!
  • High Definition Video
    • Two High Definition Formats
      • 720p
        • 1280x720
        • Progressive scan
        • Equivalent to 9CIF
      • 1080i
        • 1920x1080
        • Interlaced scan
      • Both 16x9 aspect ration compared to 4x3 of SDTV
  • High Definition Video
    • Uncompressed 1080i HD
    • 1920x1080x24x30 ~ 1.5 Gbps
    • HDV
      • Defined by four companies, Canon Inc., Sharp Corporation, Sony Corporation, and Victor Company of Japan, Limited (JVC)
      • Idea is to store high-def MPEG-2 video on standard DV media (DV or Mini DV cassette tape), and stream it across standard FireWire / IEEE 1394 interfaces
  • High Definition Video
    • HDV
      • The format supports MPEG-2 compressed video at two 16:9 resolutions:
        • 720p (1280 x 720, progressive), at approximately 19 Mbps data rate
        • 1080i (1440 x 1080, interlaced), at approximately 25 Mbps data rate- assumes a pixel aspect ratio of 1.33
  • High Definition Videoconferencing
  • H.323-based Videoconferencing
    • Compression/decompression architectures
      • Initially blurred and murky H.261 codecs
      • Major use today is H.263
      • Beginning to see H.264 (MPEG4)
    • Bandwidth requirements have been low (typically 1 Mbps or less)
  • H.323-based Videoconferencing
    • Resolutions have been limited
      • Typically CIF (352x288)
      • Recent use of 4CIF ( 704x576 )- e.g. the Gigaconference requiring bandwidths of 1 to 4 Mbps
    • Aspect ratio of 4x3
    • Several audio algorithms, but typically low quality at 64 Kbps
  • High Definition H.323-based Videoconferencing
    • High definition videoconferencing is becoming available
    • H.323-based high definition video and audio provides the quality necessary for media rich collaboration
    • Being standards-based, it offers
      • User simplicity
      • Promise of interoperability with other non-high definition H.323 systems
  • LifeSize H.323-Based Room Unit
    • Produces 720p high definition video
    • Utilizing H.264 codec
    • 16x9 aspect ratio
    • 9CIF quality
    • 1 Mbps bandwidth (can go at 2 Mbps point to point)
  • LifeSize H.323-Based Room Unit
    • Built-in 4 port MCU
    • Good acoustical quality
      • omni-directional architecture
      • circular array of 16 microphones
      • 100 Hz up to 22 kHz bandwidth
    • High definition camera with 70 degree field of view
  • What Are The HD Driving Forces?
    • Do you need high definition resolution?
    • How important is audio quality?
    • Is aspect ratio important
    • Do you have sufficient bandwidth?
    • Do you need two way interaction (conferencing)?
    • Is H.323 interoperability important?
    • What can you afford?
  • Other High Quality Video Options
    • MPEG2
      • VBrick, StarValley, etc
      • High quality video in the 7 to 16 Mbps range
      • Used at Northwestern for remote venues
    • DVTS
      • Lot of work being done in the Big Video project
      • Transports digital video over IP at 30 Mbps
      • HDV over DVTS becoming available
  • Other High Quality Video Options
    • Access Grid high definition experiments
    • Microsoft ConferenceXP
      • MPEG4 compressed high definition
  • DV Guide
  • Demonstrations
  • Display VideoLAN Client MPEG2 stream VideoLAN MPEG2 Stream Speaker VideoLAN Client Capture Card Composite Video DVD Player
  • Display VideoLAN Client MPEG2 stream VideoLAN MPEG2 Stream Speaker VideoLAN Client DVD
  • DVD Player Display VideoLAN Client StarValley Encoder Composite Video/Audio 7 Mbps (max) MPEG2 stream StarValley MPEG2 Stream Speaker
  • DV Camera Display DVTS Client (decode) Firewire Stream 30 Mbps DVTS stream DVTS Stream Speaker DVTS Client (encode)
  • Camera Display DVTS Client (decode) Composite Video 30 Mbps DVTS stream DVTS Stream Speaker DVTS Client (encode) Firewire Canopus A/D
  • HDV Camera Display VideoLAN Client Firewire Audio/video MPEG2 stream VideoLAN MPEG2 Stream Speaker VideoLAN Client
  • URLs
    • DV Guide
    • http://db.arts.usf.edu/dvguide/default.asp
    • VideoLAN
    • http://www.videolan.org/
    • DVTS
    • http://www.sfc.wide.ad.jp/DVTS/