Compression for the web

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Compression for the web

• The right size for the right job

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(No Transcript)
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Terms you should know

• Video Compression
• Resolution
• Interlacing vs. Progressive
• Fields vs. Frames
• Lossless vs. Lossy
• VBR vs. CBR
• Intraframe vs. Interframe

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Video Compression

• Reducing the quantity of data used to represent
  digital video images

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Resolution

• The number of pixels/lines vertically displayed
  the screen
• 320x180 (180 lines)
• 480x270 (270 lines)
• 640x360 (360 lines)
• 1280720 (720 lines)
• 19201080 (1080 lines)

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Interlaced vs. Progressive

• A FULL image for each frame

• Only HALF the lines are drawn each frame

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Fields vs. Frames

• Interlaced video is represented by either odd OR
  even fields per frame

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Lossless vs. Lossy

• Negligible file size difference from original

1/8th the file size of original with unnoticeable
quality difference to most viewers

• NOTE Lossy compression is most often noticed in
  scenes with text, transitions and/or lots of
  movement

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VBR vs. CBR

• VBR variable bit rate
• Allows for best compression size based on the
  needs of the file
• Will only use the required amount of bits to save
  frame information
• CBR constant bit rate
• Maintains the set bit rate throughout the entire
  video
• Important for streaming media

• Complex image sequence that takes advantage of
  higher bit rate as necessary

• Majority of the screen uses the same background
  from frame to frame
• File size can decrease greatly without
  significant quality loss

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Intraframe vs. Interframe

• Intraframe
• Records every pixel for every frame regardless if
  the pixel information has changed or not
• Examples
• AVC-I
• DVC-Pro HD
• Apple ProRes

• Interframe
• Records an I-Frame and then only records the
  pixels that change from one frame to the next
  depending on the GOP structure
• Examples
• HDV
• MPEG-2

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Evaluating Video for Compression
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Evaluating Video for Compression

• How was the video shot?
• Is the video image static or in motion?
• Was it shot interlaced or progressive?
• Is the video high or low contrast?

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Evaluating Video for Compression

• How was the video edited?
• Are there long or short edits?
• Are there mostly cuts or transitions?
• Are there lots of graphics?
• If so, are they static or in motion?
• Has the video been stylized in any way?

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Evaluating Video for Compression

• Who is the intended audience?
• How are the viewers watching?
• Computer, TV, Mobile, etc
• Will it be an individual or group viewing?
• How large is the screen?
• How far away are the viewers expected to be?
• Which is more important
• Quality or Speed of Delivery?

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Progressive Download vs. Streaming Video
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Progressive Download

• Allows the viewer to begin playback before the
  download is fully complete
• Use if
• Delivering short videos (less than 10min)
• Operating a small website with low traffic
• Using a higher quality video than a streaming
  connection would allow

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Streaming Video

• Allows for real time broadcasting of live
  events the ability to control playback
  on-demand
• Use if
• Delivering long videos (greater than 10min)
• Delivering to many viewers simultaneously
• Using bandwidth detection or a quality monitoring
  service
• Serving live events

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Streaming Video

• Must be played back from a separate server
  programmed for streaming
• Flash Media Server (FLV, SWF)
• Apple OS X Server (Quicktime)
• Darwin Streaming Server (Quicktime)
• Windows Media Services (WMV, Silverlight)

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Formats
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Formats

• A particular way that information is encoded for
  storage in a file
• Examples
• AVI, ASF, WMV, FLV, MOV, MPEG-2(TS), MP4, Ogg,
  RMV, 3GP

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Format vs. Codec
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Format vs. Codec

• Wrapper refers to the coding format
• Codec is an acronym for compression/decompress
  ion
• Example
• Flash Video (FLV) is a format
• H.264, On2 VP6, Sorenson Spark are codecs for
  Flash FLVs

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Current Popular Codecs
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Current Popular Codecs

• VC-1 Windows Media
• VP6 FLV
• MPEG-2 Quicktime, DVD
• MPEG-4 part 10 (AVC)

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H.264

• The most commonly used codec today

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Older Common Codecs

• MPEG-4 part 2 (DivX, Xvid, FFmpeg, 3ivx)
• H.263
• Cineform
• RealVideo
• Sorenson Spark
• Sorenson 3
• Cinepak
• MPEG-1

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Compression Software
Adobe Media Encoder CS4
Sorenson Squeeze 5
Telestream Episode 5.2
Apple Compressor 3.5
Microsoft Expression Encoder
Mac Only
Windows Only
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Adobe Media Encoder
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Adobe Media Encoder
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Apple Compressor
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Apple Compressor
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Sorenson Squeeze
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Sorenson Squeeze
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Telestream Episode
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Your Toolkit
Programs everyone should have
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Examples
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YouTubeHD

• H.264 codec
• mp4 format
• 1280 x 720
• 6Mbps - 9Mbps
• 24fps
• Audio AAC 64kbps 44.1 kHz

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iPhone

• H.264 codec
• m4v format
• 640 x 360
• 1500kbps
• Native frame rate
• Audio AAC 128kbps 44.1 kHz

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DVD-SD

• Video Settings
• MPEG-2 codec
• m2v format
• 720 x 480
• 6.2Mbps - 7.7Mbps
• 29.97fps
• Mode One Pass Best
• Motion Estimation Best

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DVD-SD

• Audio Settings
• Dialog Normalization -31 dbFS

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DVD-SD

• Audio Settings
• Compression Preset None

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Blu-Ray

• H.264 codec
• m4v format
• 1440 x 1080
• 20Mbps - 25Mbps
• 23.98fps
• Audio PCM 192kbps 48 kHz

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Questions?