Digital Media Dr. Jim Rowan ITEC 2110 Video

Roll call Sanchez-Casas, Jon F. Simson, Davis Sinnock, Grant A. Swaim, Mark S. Tran, Dung Q. Vyas, Anand A. Woldeyohannes, Tesfamichael Barton, Paul H. Bois, Lauren C. Bonds, Allison E. Duncan, Jarred T. Lawson, Joseph I. Mulongo, Julio B. Pennison, Heather L. Reilly, Daniel J.

Roll call Jones, Crystal L. Marsh, Kerreen A. Thompson, Daniel G. Tran, Christopher V.

Video Works because of persistence of vision Fusion frequency –~ 40 frames per second –depends on the brightness of the image relative to the viewing environment Less than that –flickering –individual images appear losing the illusion of motion

Video Video vs Animation... –Video - capture of frames and then playback –Animation - create frames individually and then playback

Video Computationally demanding –Capture must be fast enough to capture sufficient frames to produce the illusion of motion –Transport (if across the web) must be fast enough to carry those captured frames at a rate fast enough to produce the illusion of motion –Playback must be fast enough to play those captured frames at a rate fast enough to produce the illusion of motion

Video If the transport and playback is not fast enough, frames will be dropped Video players make compromises differently –Some drop frames holding the last image effectively losing the illusion of motion but continuing the story as a slide show –Some play lower resolution images –Some continue to play audio

Video gets big fast NTSC –North America and Japan –640 x 480 –24 frames per second Using 3 byte color (24 bits, one byte per color) each frame ~ 1megabyte One second of video (uncompresssed) is 26 Megabytes One minute is 1.6 gigabytes

Video gets big fast PAL is even bigger –Western Europe and Australia –768x576 –25 frames per second Using 3 byte color (24 bits, one byte per color) each frame ~ 2 megabytes One second of video (uncompresssed) is 26 Megabytes One minute is 1.85 gigabytes

More on size... Uncompressed this exceeds most home computer interface standards Strains the internal speed of the home computer Strains the storage capability of home computer WAY exceeds what can be carried by the net

What to do? Apply compression On the capture side –digitization & compression needs to be carried out by the hardware to be fast enough –Can be done in the camera (VTR) –Can be done in the computer (iSight cam)

Compression in the VTR Within the camera –3 (at least) different formats internally Differing error correction and compatibitibility –Recording on different media CD tape Mini DV or DV format –Connected to computer using firewire –All 3 formats present the same stream of bits to the computer Artefacts that interfere with processing and recompression are created

Compression in the computer Analog is presented to the computer through a video capture card Compression is done (usually) in the video capture card Allows for a really small camera because the work is done elsewhere

Analog vs Digital An analog signal to the computer is susceptible to noise corruption Digital signal is not What’s the big deal? Consider compressing a video of a solid color –Analog noise will cause small fluctuations from pixel to pixel –RLE can’t compress it because each pixel is a bit different

iMovie video capture card computer miniDV compression iSight Camera analog signal digital signal 640 x 480 = 307, ,200 can be represented by < 24 bits, call it 3 bytes RLE: 307,200 (3bytes) + RGB (3 bytes) = 6 bytes Consider compressing this using RLE the scene 640 x 480 = 307,200 bytes Noise makes each pixel a little different RLE: 307,200 bytes x RGB (3bytes) = bytes !!!NOISE!!!

hardware vs software compression Hardware conversion... user has no control over it... it is hardwired –It is in the camera –It can be in the video card Software conversion... is computationally expensive... it’s a slow process –Provides for the most flexibility –Can use different software coder-decoders (codec), picking and choosing what fits your needs better

Next? Streaming video!

Questions?