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Digital Video: Basic Concepts
http://www.arhu.umd.edu/technology/workshops/mmpublishing/dvconcepts.html
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Video
• Frames: individual image
• Frame Rate: number of images per second- frames per second (fps)
  • NTSC: National Television Standards Committee: 29.97 frames per second
  • PAL: Phase Alternating Line: 25 frames per second




Time codes

• Duration of a video clip and its starting and ending frames
• SMPTE: Society of Motion Picture and Television Engineers
• hours: minutes: seconds: frames

3:34:30:10 would be 3 hours, 34 minutes, 30 seconds and 10 frames


Digital Video

• Computers display information digitally
• Analog signals must be digitized or sampled which is referred to as "capturing"
• Video Capture Card- used to digitize an analog video signal and convert it into a computer graphics signal
• Digital video cameras shoot video digitally and information is transferred to computer by Firewire

 

Issues of Capture and Playback- a balance between quality and performance

When working with video you are dealing with huge amounts of data which means you have to deal with the issues of disk storage and processing speeed.

• Disk Storage
  • Substantial amount required for capturing video
  • Example: 1 second of video at 30 fps, 640x480 pixel image, 24-bit color, = 27MB

• Process Speed for capture and playback

You are dealing with large amounts of data that must be handled quickly by computer to go from analog to digital and playback as well. Web delivery introduces additional challenges.

What do you do? Strategies for reducing data playback rates:

1. Reduce the frame rate of the digital video
   Playback rate of your movie determines how smooth and natural-looking the movie appears. At playback rates below 15 frames per second, you notice that the movie is made up of frames; the lower the playback rate, the more distinct each frame becomes.
   Sample Files comparing framerates:
   http://www.inform.umd.edu/EdRes/Colleges/ARHU/Workshops/chays/digitalvideo/dv-fps.html
   
   
2. Reduce the image dimensions or screen size of the capture video
   NTSC Video Frame is 486 horizontal lines of information; half size is 360x240.

   Sample Files comparing screen dimensions:
   http://www.inform.umd.edu/ARHU/Workshops/chays/digitalvideo/dv-sizes.html

3. Compress video data
   Compression CODECs

   Sample Files comparing compression schemes:
   http://www.inform.umd.edu/EdRes/Colleges/ARHU/Workshops/chays/digitalvideo/dv-codecs.html
   
   

4. You can specify desired data rate and let software determine fps and compression.

Each strategy compromises the quality of the digitized video; continual compromise between quality and efficiency.
If you need to capture full-frame video at 30fps, you'll need a lot of storage capacity and a fast hard drive.

 

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