Digital Video BasicsDigital Video Basics

CPSC 120CPSC 120

Principles of Computer SciencePrinciples of Computer Science

April 16, 2012April 16, 2012

OverviewOverview Digital video follows the same basic method as a Digital video follows the same basic method as a

motion picture. Display 24-30 still images per motion picture. Display 24-30 still images per second, giving the impression of movement.second, giving the impression of movement.

Motion pictures use thousands of nearly identical Motion pictures use thousands of nearly identical images on celluloid/film stock 8/16/70 mm width.images on celluloid/film stock 8/16/70 mm width.

NTSC TV/VCR uses analog to control NTSC TV/VCR uses analog to control rasterraster signals on a video display.signals on a video display.

NTSC is North American, PAL is European/Asian.NTSC is North American, PAL is European/Asian. Modern digital displays use binary/digital data to Modern digital displays use binary/digital data to

set millions of color set millions of color pixelspixels (picture elements), (picture elements), making one frame, on an LCD screen. A key making one frame, on an LCD screen. A key problem is to read the data and change the display problem is to read the data and change the display about 30 times per second.about 30 times per second.

A Short GlossaryA Short Glossary To To digitizedigitize is to encode analog/visual information into a is to encode analog/visual information into a

digital/binary form. Usually saved in specific file format.digital/binary form. Usually saved in specific file format. CompressionCompression is a method to reduce the resulting file size is a method to reduce the resulting file size

for easier and/or faster copy, transfer, or streaming.for easier and/or faster copy, transfer, or streaming. To To decodedecode the file we must use the opposite method to the file we must use the opposite method to

decode the encoded binary data.decode the encoded binary data. Software to do this two sided-process is called a Software to do this two sided-process is called a codeccodec, ,

for (for (en)coder-decoderen)coder-decoder.. Many codec programs have been developed, each with Many codec programs have been developed, each with

advantages/disadvantages.advantages/disadvantages. Losses in picture quality can happen as part of the Losses in picture quality can happen as part of the

compression algorithm. True compression algorithm. True losslesslossless compression is compression is slower and may result in slow/jerky video effects.slower and may result in slow/jerky video effects.

Compression losses cause Compression losses cause pixelationpixelation of images, reduced of images, reduced color range, blurred action, and frame loss.color range, blurred action, and frame loss.

A Short Codec Roll CallA Short Codec Roll Call

Flash, AVI (MS), Quicktime (Apple), and MPEG-1, Flash, AVI (MS), Quicktime (Apple), and MPEG-1, MPEG-2, MP-3, MP4, all are formats of encoded data.MPEG-2, MP-3, MP4, all are formats of encoded data.

Each standard is implemented in software to encode and Each standard is implemented in software to encode and decode video images.decode video images.

No single best solution here, we usually obtain some No single best solution here, we usually obtain some kind of plug-in to our browser or player to decode video.kind of plug-in to our browser or player to decode video.

MPEG is a larger category of widely used technology to MPEG is a larger category of widely used technology to encode both audio and video.encode both audio and video.

The common MP3 system depends on MPEG Layer 3, a The common MP3 system depends on MPEG Layer 3, a lossylossy encoding method widely used for audio file sharing. encoding method widely used for audio file sharing. Files are small and usually of good quality. Files are small and usually of good quality.

Adobe Flash has become popular through Adobe Flash has become popular through trans-codingtrans-coding MPEG, ASF, etc into Flash. This is what youtube.com MPEG, ASF, etc into Flash. This is what youtube.com and others support for video sharing.and others support for video sharing.

Important: Not all formats allow editing.Important: Not all formats allow editing.

Non-linear Video Editing (NLE)Non-linear Video Editing (NLE)

Basic scheme: Splice together video segments or Basic scheme: Splice together video segments or clipsclips using transitions and video effects over a using transitions and video effects over a sound track.sound track.

Non-linear since we can jump around in the Non-linear since we can jump around in the current project to edit segments. Not first to last.current project to edit segments. Not first to last.

Editors are now very inexpensive, fast, and Editors are now very inexpensive, fast, and provide many tools such as transitions, titles, etc. provide many tools such as transitions, titles, etc.

Low end: WLMM, iMovie. High end: Adobe Low end: WLMM, iMovie. High end: Adobe Premiere, Final Cut Pro. Web: youtube, Premiere, Final Cut Pro. Web: youtube, lightworks, vimeo.lightworks, vimeo.

Editors are visually organized as Editors are visually organized as timelinetimeline or or storyboardstoryboard tools along with managers. tools along with managers.

Typical Movie Making ActivitiesTypical Movie Making Activities

First, plan then First, plan then storyboardstoryboard on paper what movie on paper what movie you want to make. Include audio plans as well.you want to make. Include audio plans as well.

Create/gather movie clips and audio either by Create/gather movie clips and audio either by camera shots or existing MPEG files and audio.camera shots or existing MPEG files and audio.

Use an NLE program to arrange clips into a Use an NLE program to arrange clips into a timeline with transitions between them. You can timeline with transitions between them. You can split clips, join clips, add video effects, and split clips, join clips, add video effects, and intermix video-audio tracks with additional audio.intermix video-audio tracks with additional audio.

Export your finished movie to a specific format Export your finished movie to a specific format by choosing the desired codec.by choosing the desired codec.

Share your movie by uploading to a video Share your movie by uploading to a video sharing site such as YouTube. These sites may sharing site such as YouTube. These sites may insist on a specific codec(s).insist on a specific codec(s).

Apple Macintosh iMovieApple Macintosh iMovie

MS Windows Movie MakerMS Windows Movie Maker

The Last Mile!The Last Mile!

Develop an idea with one partner (no more!) Develop an idea with one partner (no more!) about what movie you want to make.about what movie you want to make.

Draw a basic paper storyboard. Determine Draw a basic paper storyboard. Determine what audio soundtrack you wish to use.what audio soundtrack you wish to use.

Look for MPEG clips, MP3 audio, and audio CD Look for MPEG clips, MP3 audio, and audio CD resources you might use to make your movie.resources you might use to make your movie.

Use WLMM, iMovie, etc to edit your clips and Use WLMM, iMovie, etc to edit your clips and audio into a short (5 minute max) movie, export audio into a short (5 minute max) movie, export to a file of your desired (or required) format.to a file of your desired (or required) format.

Optional: Copy it to math.hws.edu and put a link Optional: Copy it to math.hws.edu and put a link to it on your home page! to it on your home page!

Get a youtube.com (vimeo,etc) account and Get a youtube.com (vimeo,etc) account and upload your movie for the world to see. upload your movie for the world to see.