COM 205Multimedia Applications St. Joseph’s College Fall 2004
Chapter 8 Video
Overview • Using video. • How video works? • Broadcast video standards. • Analog video. • Digital video. • Video recording and tape formats. • Shooting and editing video. • Optimizing video files for CD-ROM.
Video • Video is the most recent addition to the elements of multimedia • It places the greatest demands on the computer and memory (using about 108 GB per hour for full motion) • Often requires additional hardware (video compression board, audio board, RAID - Redundant Array of Independent Disks- for high speed data transfer)
Using Video • Carefully planned video can enhance a presentation (eg. film clip of JFK, better than an text box of same message) • Before adding video to a project, it is essential to understand the medium, how to integrate it, its limitations, and its costs
Using Digital Video • Digital video has replaced analog as the method of choice for making and delivering video for multimedia. • Digital video device produces excellent finished products at a fraction of the cost of analog.
Using Digital Video • Digital video eliminates the image-degrading analog-to-digital conversion. • Many digital video sources exist, but getting the rights can be difficult, time-consuming, and expensive.
Video Clips • Ways to obtain video • shoot new film clips with a digital camcorder • convert you own video clips to digital format • acquire video from an archive - often very expensive, difficult to obtain permissions or licensing rights • Be sure to obtain permission from anyone you film or for any audio you use!
How Video Works • Light passes from an object through the video camera lens and is converted into an electrical signal by a CCD (charge-coupled device). • High quality cameras have 3 CCD • Signal contains 3 channels of color information (red, green, blue) and a synchronization pulse.
How Video Works • If each channel of a color signal is separate it is called RGB ( preferred) • A single composite of the colors and sync signal is less precise • A typical video tape has separate tracks for audio, video, and control • ( See p. 180)
How Video Works • The video signal is magnetically written to tape by a spinning recording head following a helicalpath • Audio is recorded on a separate straight track • The control track regulates the speed and keeps the tracks aligned as the tape plays/records.
Broadcast Video Standards • NTSC • PAL • SECAM • HDTV • Six different formats • Aspect ratio is 16:9
Broadcast Video Standards National Television Standards Committee (NTSC): • These standards define a method for encoding information into electronic signal that creates a television picture. • It has screen resolution of 525 horizontal scan lines and a scan rate of 30 frames per second.
Broadcast Video Standards • NTSC- National Television Standards Committee - 1952, (“never the same color”) • 1 frame = 525 horizontal lines every 1/30 second • 2 passes - odd/even lines, 60/second (60 Hz) • interlacing - to reduce flicker
Broadcast Video Standards Phase Alternate Line (PAL) and Sequential Color and Memory (SECAM): • PAL has a screen resolution of 625 horizontal lines and a scan rate of 25 frames per second. • SECAM has a screen resolution of 625 horizontal lines and is a 50 Hz system. • SECAM differs from NTSC and PAL color systems in its basic technology andbroadcast method.
Broadcast Video Standards Advanced Television Systems Committee (ATSC) Digital Television (DTV): • This digital standard provides TV stations with sufficient bandwidth to present four or five Standard Television (STV) signals or one High Definition TV (HDTV) signal. • This standard allows for transmission of data to computers and for new Advanced TV (ATV) interactive services.
Broadcast Video Standards • Several incompatible standards: • NTSC (US, Japan, many other countries) • PAL - (United Kingdom, parts of Europe, Australia, South Africa) • SECAM - (France Russia, few others) • HDTV - ( US ) - newest technology
Broadcast Video Standards • HDTV- High Definition Television now available, allow viewing of Cinemascope and Panavision movies with aspect ratio 16:9 ( wider than high) (See p. 184) • Twice the resolution, interlaced format • Digitized then compressed for transmission
Broadcast Video Standards • 4: 3 Aspect Ratio
Broadcast Video Standards • 16: 9 Aspect Ratio
Integrating Computers and Television • Television video is based on analog technology and international broadcast standards • Computer video is based on digital technology and other image display standards • DVD and HDTV merges the two
Analog Video • Analog television sets remain the most widely installed platforms for delivering and viewing video. • Television sets use composite input. Hence colors are less pure and less accurate than computers using RGB component. • NTSC television uses a limited color palette and restricted luminance (brightness) levels and black levels.
Analog Video • Some colors generated by a computer that display fine on a RGB monitor may be illegal for display on a NTSC TV. • While producing a multimedia project, consider whether it will be played on a RGB monitor or a conventional television set.
Video Overlay System • To display analog video (TV) images on a computer monitor, the signal must be converted from analog to digital form ( Where else does this conversion commonly take place?) • A special digitizing video overly board is required for the conversion • Produces excellent quality, full screen, full motion video, but costly.
Video Overlay System • Many companies use computer based training (CBT) systems • These require a computer and monitor cabled to a TV and video disc player. • Overlay boards allow the video disc to be controlled by the computer and display the images on the computer screen.
Video Capture Boards • Video overlay boards can capture or digitize video frames and play them back as QuickTime MPEG and AVI movies. • Some also include audio input and sound management to interleave sound and images • Some also offer compression and accelerate digitizing, or support NTSC video.
Differences Between Computer and TV Video • Computer scan refresh rate = 480 lines/sec • Computer scan is progressive ( non-interlaced) at 66.67 HZ or higher • TV scans at 525 (or 625) lines/sec, with interlacing at a frame rate of 60 Hz
Interlacing Effects • The TV electron beam actually “draws all the odd line, then all the even lines, interlacing them • On a computer (RGB) monitor, lines are painted one pixel thick and are not interlaced. Displayed on a TV they “flicker” because they appear in every other field. To avoid this avoid very thin lines and elaborate serifs.
Differences Between Computer and TV Video • TV broadcasts an image larger than the screen so that the “edge” of the image is against the edge of the screen. This is called overscan • Computer images are smaller than the screen area (called underscan) and there is a border around the image
Differences Between Computer and TV Video • When a computer screen is converted to video the outer edges do not fit on the TV screen only about 360-480 lines of the computer image are visible. • Avoid using the outer 15% of the screen for graphics, or titles for use on TV • Use the safe title area ( See p. 184)
Video Color • Color reproduction and display are also different in TV and computers monitors • Computers use RBG component video and produce more pure color • NTSC TV uses a limited color palette and restricted luminance (brightness) and black levels
Working with Text and Titles for Video Productions • Use plain, bold, easily read fonts • Use light color text on a dark background • Avoid color combinations like yellow/violet, blue/orange which “vibrate” • Avoid black or colored text on white background
Working with Text and Titles for Video Productions • Make lines and graphics at least two pixels wide • Use parallel lines and boxes sparingly and draw them with thick lines • Avoid “hot” colors • Keep graphics and titles in the safe screen area
Working with Text and Titles for Video Productions • Bring titles on slowly and let them remain on the screen sufficiently long, fade out • Avoid “busy” screens- use additional pages instead
Digital Video • Digital video architecture. • Digital video compression.
Digital Video Architecture • Digital video architecture consists of a format for encoding and playing back video files by a computer. • Architecture includes a player that can recognize and play files created for that format.
Digital Video Compression • Digital video compression schemes or “codecs” ( coder/decoder) is the algorithm used to compress (code) a video for delivery. • The codec then decodes the compressed video in real-time for fast playback. • Streaming audio and video starts playback as soon as enough data has transferred to the user’s computer to sustain this playback.
Video Compression • To store even a 10 second movie clip requires the transfer of an enormous amount of data in a very short time • 30 seconds of video will fill a 1 GB hard drive • Typical hard drives transfer about 1MB/second and CD- ROMs about 600K/second
Video Compression • Full motion video requires the computer to deliver the data at 30 MB/second more than today’s PCs and MACs can handle • Solution- use video compression algorithms or codecs • Codecs compress the video for delivery and then decode it for playback at rates from 50:1 to 200:1
Video Compression & Streaming • Codecs ( such as MPEG, JPEG) use lossy compression schemes • Streaming technologies are also used to provide reasonable quality , low-bandwidth on the WEB • Playback starts as soon as enough data have been transferred to the user’s computer instead of waiting for the whole file to download • ( RealAudio and RealVideo software)
MPEG • Standard developed by the Moving PIcturesExperts Group for digital representation of moving pictures and associated audio • http://mpeg.org
Digital Video Compression • MPEG is a real-time video compression algorithm. (Moving Picture Experts Group) • MPEG-4 (1998-1999) includes numerous multimedia capabilities and is a preferred standard. • MPEG-7 (2002) (or Multimedia Content Description Interface) integrates information about motion video elements with their use. • MPEG –21 under development
Digital Video • Video clips can be shot or converted to digital format and stored on the hard drive. • They can be played back without overlay boards, second monitors or videodiscs using QuickTime or Active Movie for Windows • Analog video can be converted to digital or now created in digital form
Video Recording and Tape Formats • Composite analog video. • Component analog video. • Composite digital. • Component digital. • ATSC digital TV.
Composite Analog Video • Composite video combines the luminance and chroma information from the video signal. • Composite video produces lowest quality video and is most susceptible to generation loss. • Generation loss is the loss of quality that occurs while moving from original footage to editing master to copy.
Component Analog Video • Component video separates the luminance and chroma information. • It improves the quality of the video and decreases generation loss. • In S-video, color and luminance information are kept on two separate tracks (Y/C) to improve the picture quality. • Betacam is a new portable professional video format which lays the signal on the tape in three component channels.
Composite Digital • Composite digital recording formats combine the luminance and chroma information. • They sample the incoming waveforms and encode the information in binary (0/1) digital code. • It improves color and image resolution and eliminates generation loss.