CSCI E-1 | Lecture 7 | Multimedia

Computer Science E-1: Understanding Computers and the Internet
Harvard University Extension School
Fall 2005

Lecture 7: Multimedia

Demos

Speech synthesis on a Mac
Quicktime
A brief word on file quality

Graphics

File Formats
- BMP
  - Microsoft file format
  - used for wallpaper
- GIF
  - 256 colors
  - 8-bit
  - good for non-photo graphics (e.g., icons)
  - supports animation and transparency
  - lossless compression
- JPEG
  - digital photos
  - 24-bit
  - lossy compression
- EPS
  - high resolution graphics
- PNG
  - 24-bit color
  - created in response to licensing issues with GIF
- TIFF
  - high-resolution graphics
Bitmaps v. Vectors
- What is a bitmap?
  - describes pixel properties
  - pixelated images
- Vector file formats
  - stores formulae to represent polygons
  - scales well
  - concept of displaying images via formulae often used in games
Compression
- File sizes smaller
- Eliminates redundant information
  - in GIFs, information described horizontally
  - in JPEGS, compression handled in more complex fashion
- Easier to transfer/download over a network connection
- Increased compression can result in loss of quality

Announcements

Problem Set 5 and Photoshop
Website banners
Mousepads

Audio

File Formats
- AAC
  - iPod
- CD-DA
  - Audio CDs
  - Large file sizes
- MIDI
  - Recording studios
  - Digital synthesis
  - Stores literal musical notes
  - Very small file sizes
  - Software plays back notes
- MP3
  - Compressed
  - Roughly 1/12th size of WAV files
  - MPEG-1, layer 3
- RealAudio
  - Streaming file format
  - Plays "just in time"
  - Often only watchable as stream, not download
  - Streaming media players often contain a local "buffer"
- WAV
  - Windows system sounds
  - Uncompressed
Almost all audio compression is lossy to some degree

Video

File Formats
- AVI
  - Developed by MS for video
- DivX
  - Newer
- MPEG
  - MPEG-1 - downloads
  - MPEG-2 - DVDs
  - MPEG-4 - newer, better compression and quality than MPEG-1
- QuickTime
  - Apple format
  - CSCI E-1 Podcasts
- RealVideo
  - Streaming file format
- Shockwave
  - Vector based display
  - Supports interactivity with viewer
  - TemplateMonster.com
- Windows Media Technologies
Container formats
Codec - compress/decompress
Compression
- Interframe
  - Key frame
- Intraframe
  - Similar to graphics compression
- Skipped frames
  - Less fluid motion
- Sampling rate

-- END --