Digital Video Basics: Digital Video Basics CPSC 120 Principles of Computer Science December 3, 2007


Overview: Overview Digital video follows the same basic method as a motion picture. Display 24-30 still images per second, giving the impression of movement. Motion pictures use thousands of nearly identical images on celluloid/film stock 8/16/70 mm width. NTSC TV/VCR uses analog to control raster signals exciting phosphors on a video tube display. NTSC is North American, PAL is European/Asian. Modern digital displays use binary/digital data to set millions of color pixels (picture elements), making one frame, on an LCD screen. A key problem is to read the data and change the display about 30 times per second.


A Short Glossary: A Short Glossary To digitize is to encode analog/visual information into a digital/binary form. Usually saved in specific file format. Compression is a method to reduce the resulting file size for easier and/or faster copy, transfer, or streaming. To decode the file we must use the opposite method to decode the encoded binary data. Software to do this two sided-process is called a codec, for (en)coder-decoder. Many codec programs have been developed, each with advantages/disadvantages. Losses in picture quality can happen as part of the compression algorithm. True lossless compression is slower and may result in slow/jerky video effects. Compression losses cause pixelation of images, reduced color range, blurred action, and frame loss.


A Short Codec Roll Call: A Short Codec Roll Call Ogg (open source), ASF (MS), Quicktime (Apple), and MPEG-1, MPEG-2, MP-3, MP4 all are forms of MPEG (Motion Picture Experts Group) format of encoded data. Each standard is implemented in software to encode and decode video images. No single best solution here, we usually obtain some kind of plug-in to our browser or player to decode video. MPEG is a larger category of widely used technology to encode both audio and video. The common MP3 system depends on MPEG Layer 3, a lossy encoding method widely used for audio file sharing. Files are small and usually of good quality. Adobe Flash has become popular through trans-coding MPEG, ASF, etc into Flash. This is what youtube.com and others support for video sharing. Important: Not all formats allow editing. Flash does not!


Non-linear Video Editing (NLE): Non-linear Video Editing (NLE) Basic idea: Splice together video segments or clips using transitions and video effects over a sound track. Non-linear since we can jump around in the current project to edit segments. Not first to last. Editors are now very inexpensive, fast, and provide an Integrated Development Environment. Low end: WMM, iMovie, Ulead Video Studio. High end: Premiere, Final Cut Pro, Avid. Editors are visually organized as timeline or storyboard tools along with managers.


Typical Movie Making Activities: Typical Movie Making Activities First, plan then storyboard on paper what movie you want to make. Include audio plans as well. Create/gather movie clips and audio either by camera shots or existing MPEG files and audio. Use an NLE program to arrange clips into a timeline with transitions between them. You can split clips, join clips, add video effects, and intermix video-audio tracks with additional audio. Export your finished movie to a specific format by choosing the desired codec. Share your movie by uploading to a video sharing site such as Yahoo, Google, or YouTube. These sites may insist on a specific codec(s).


Apple Macintosh iMovie: Apple Macintosh iMovie


MS Windows Movie Maker: MS Windows Movie Maker


The Last Mile!: The Last Mile! Develop an idea with one partner (no more!) about what movie you want to make. Draw a basic paper storyboard. Determine what audio soundtrack you wish to use. Look for MPEG clips, MP3 audio, and audio CD resources you might use to make your movie. Use WMM to edit your clips and audio into a short 1-2 minute movie, export to a file of your desired (or required) format. Copy it to math.hws.edu and put a link to it on your home page! Get a youtube.com (yahoo,etc) account and upload your movie for the world to see.