Digital Video Basics CPSC 120 Principles of Computer Science April 16, 2012

Overview  Digital video follows the same basic method as a motion picture. Display 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 on a video 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  Flash, AVI (MS), Quicktime (Apple), and MPEG-1, MPEG-2, MP-3, MP4, all are formats 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.

Non-linear Video Editing (NLE)  Basic scheme: 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 many tools such as transitions, titles, etc.  Low end: WLMM, iMovie. High end: Adobe Premiere, Final Cut Pro. Web: youtube, lightworks, vimeo.  Editors are visually organized as timeline or storyboard tools along with managers.

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 YouTube. These sites may insist on a specific codec(s).

Apple Macintosh iMovie

MS Windows Movie Maker

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 WLMM, iMovie, etc to edit your clips and audio into a short (5 minute max) movie, export to a file of your desired (or required) format.  Optional: Copy it to math.hws.edu and put a link to it on your home page!  Get a youtube.com (vimeo,etc) account and upload your movie for the world to see.