Transcript COM 205 Multimedia Applications St. Joseph’s College Fall 2004

COM 205
Multimedia Applications
St. Joseph’s College
Fall 2004
Chapter 8
Video
Overview
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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 imagedegrading 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)
Video Basics
How Video Works
• The video signal is magnetically
written to tape by a spinning
recording head following a helical
path
• Audio is recorded on a separate
straight track
• The control track regulates the speed
and keeps the tracks aligned as the
tape plays/records.
Video Basics
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 and broadcast 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 ( noninterlaced) 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
Computers and Video
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
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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.
Component Digital
• Component digital formats add the
advantages of component signals to
digital recording.
• D-1 component digital format is an
uncompressed format which has a very
high quality image.
• It uses a 19 mm (3/4-inch) tape in order to
save data.
• Several other digital component formats
are DCT, Digital Betacam, DV format,
DVCPRO, and DVCAM formats.
ATSC Digital TV
• These standards provide for digital
STV and HDTV recordings that can
be broadcast by digital TV
transmitters to digital TV receivers.
• ATSC standards also provide for
enhanced TV bringing the
interactivity of multimedia and the
Web to broadcast television.
Vaughn’s Law of Multimedia
Minimums
• Your goal is to produce multimedia
that is adequate and does it’s job but
doesn’t throw you into bankruptcy.
• Experiment with various levels of
consumer grade equipment
• Professional sound and video
equipment is very expensive
Recording Formats
• S-VHS and Hi-8 consumer quality
• Component (YUV) - Sony BetacamSP the
professional standard for broadcast
quality
• Component Digital- a digital version of the
Betacam- best format for
graphics > $900,000 and produces 15
minutes of video
• Composite Digital most common
>$110,000
Shooting and Editing Video
• Shooting platform
– use a steady tripod
– or a camera with an electronic image
stabilization feature to avoid “shaky
hand effect”
– or use camera moves and moving
subjects to disguise your lack of
steadiness
Shooting and Editing Video
• Lighting performance is the main
difference between professional and
consumer camcorders
• Use a simple floodlight kit or natural
daylight to improve the image
• Onboard flood lights can be used as
fill light to illumine faces
Shooting and Editing Video
Shooting and Editing Video
• Chroma Key or Blue Screen - popular
technique for making multimedia without
the use of expensive backgrounds
• In shooting against a blue screen, be sure
that the lighting is perfectly even and that
actors are not too close to the screen so
that color “spills” over on them
Shooting and Editing Video
• Composition
– Avoid wide panoramic shots
– Use close-ups, head and shoulders
– Remember the more a scene changes
the slower the playback will be
– Keep the camera still, let the subject
add the motion by walking, turning...
Using Video Tapes
• Fast forward new tapes and rewind
them so that the tension is even
(called “packing”)
• Black-stripe the tape by running it
through the recorder with the lens
cap on -eliminates “snowy noise”
• Do not reuse tapes after editing
• Remove break off tab to avoid
overwriting
Video Hardware Resolution
• Horizontal resolution -the number of lines
of detail the camera can reproduce
• Different from the vertical scan lines on TV
• The lens, and number, size and quality of
the CCDs determine the resolution
• Poor resolution = poor image
Consumer Grade Equipment
• Mass production at low cost; easier
to use
• Cameras and camcorders that use
HI-8 and S-VHS formats are superior
to 8 mm and VHS systems
• HI-8 is most widely available tape
format and best consumer grade
Making Tape Copies
• For demo or promo tapes use at least
Super VHS ( HI-8 is best and allow
unlimited copies to be made without
degradation)
• Copying ( dubbing) depends on the
tape format and the quality of the
equipment being used
• Copy in SP mode- faster writing
produces better images
Video Window Size
• Shrinking a digitized image improves
it perceived sharpness
• ( Also happens when you switch
from 19” to 13” TV)
• The image is crisper because the
scan lines are closer together
Editing with Consumer VCRs
• Editing with 2 VCRs causes
problems because the two machines
are not in sync
• Editing software, such as Premier, or
After Effects, has become more
commonly used in multimedia
P*64
• Video telephone conferencing
standard for compressing audio and
motion video images
• Encodes audio and video for
transmission over copper or fiber
optic lines
• Other compression systems are
currently being developed by Kodak,
Sony, etc.
Optimizing Video files
for CD-ROMs
• CD- ROMs are an excellent
distribution media for multimedia:
inexpensive, store great quantities of
information, with adequate video
transfer rates
• Suitable for QuickTime and AVI file
formats as well as those produced by
Director, etc.
Optimizing Video files
for CD-ROMs
• Limit the synchronization between
video and audio
– AVI interleaves them
– QuickTime files must be “flattened” - to
interleave the audio and video
• Use regularly spaced key frames (10
to 15 frames apart)
• Limit the size of the video windowthe more data the slower the
playback
Optimizing Video files
for CD-ROMs
• Choose the software compression
algorithm carefully
– Sorenson codec is optimized for CDROM playback
– Cinepack algorithm, available with AVI
and QuickTime, is also optimized for
CD-ROM playback
– Use Norton speed Disk to defragment
your files before burning the master
Summary
• Various video standards are NTSC,
PAL, SECAM, and ATSC DTV.
• Categories of video standards are
composite analog, component
analog, composite digital, and
component digital.