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Scurt Glosar de termeni MultiMedia
nota:
5.1
Surround sound using five and one additional discrete audio channels: left,
center, right, left rear/side
Surround, right rear/side Surround, and a subwoofer (the ".1" in "5.1").
AC-3
Older term for Dolby Digital, the 5.1 channel surround-sound audio standard
for ATSC digital television
and DVD video in the U.S. Achieves approximately 13:1 compression.
Aspect Ratio
The expression of the relationship of width to height for a given pixel or image,
either expressed as a ratio (example: 4:3) or as a
decimal (example: 1.33, 4 divided by 3). NTSC and PAL video are considered 4:3,
and widescreen video is typically 16:9.
AVI
Audio-Video Interleave, a media file format for storage of digital video and
audio on the Microsoft Windows platform.
Bit Rate
The speed at which digital data is streamed across a network, usually measured
in kilobits per second (Kbps) or megabits per
second (Mbps).
Cinepak
An older, widely used software codec for CD-ROM video. It was generally associated
with 320 x 240 resolution video, 15 frames
per second, at 150 Kbps. Modern codecs produce much better results.
CBR
Constant Bit Rate, the encoding or delivery of media at a specific given data
rate.
Codec
A Compressor/Decompressor is a software or hardware component used to digitally
compress video and audio data to minimize
the file size, and to decompresses media files during playback. Motion-JPEG,
DV, MPEG (and its various flavors), Indeo, and
Sorenson are all common codecs.
Composite Video
A color video signal that contains all of the color information (luminance and
chrominance) in one signal, used as a type of
analog compression. NTSC, PAL and SECAM are examples of composite video systems,
and RCA style ports on devices like a
VCR are considered composite.
Compression
The process of reducing file size for storage by finding patterns of data that
can be classified more efficiently. There are two
general categories of compression, lossless and lossy. A codec (Compressor/Decompressor)
is an algorithm or scheme used when
recording digital video or audio. For example, when video is transmitted over
the Internet, it must be compressed on the sending
end and decompressed on the receiving end. A codec can be chosen based upon
the user's audio or image quality and image size
preferences. Windows Media Technologies provides numerous codecs for streaming
media content.
Compression filter
A specialized type of transform filter. Compression filters (compressors) accept
data, use a compression scheme to transform the
data, and pass the compressed data downstream.
DivX ;-)
A set of homebrew media codecs for Windows the AVI file format. They are based
on a cracked version of Microsoft’s
"MPEG-4" codec, and named after the failed Circuit City pay-per-view
DVD scheme or 10:1 compression (depending on who
you ask). Confusingly, DivX has little to do with DVD or true MPEG-4, but nevertheless
provides excellent quality and
compression.
Deinterlace
The process of combining two interlaced field sets into a single frame, usually
to remove artifacts and scanlines to improve the
quality of video when displayed on progressive systems.
Delta Frame
Encoded video frames that contain only data of the changes from the previous
frame.
DirectDraw
DirectDraw is a Microsoft DirectX SDK component that enables direct manipulation
of display memory, the hardware blitter,
hardware overlay support, and flipping surface support. DirectDraw provides
more efficient use of system resources to create
full-screen video.
DirectShow
Successor to Microsoft's Video For Windows and ActiveMovie that supports the
capture, storage and playback of video and audio
files. At the heart of the DirectShow services is a modular system of pluggable
components called filters, arranged in a
configuration called a filter graph. A component called the filter graph manager
oversees the connection of these filters and
controls the stream's data flow. Applications control the filter graph's activities
by communicating with the filter graph manager.
Dolby Digital
Formerly Dolby AC-3, the approved 5.1 channel (surround-sound) audio standard
for ATSC digital television, achieving
approximately 13:1 compression. The system uses multiple channels and speakers
in front of and behind the listener to create the
illusion of audio depth (3 in front, 2 behind the listener and 1 sub-woofer
for low frequencies). This is also the standard that the
US uses for DVD Movies.
DVD
Digital Versatile Disc (aka Digital Video Disc), a disc format that stores 4.7
GB of data on a single sided, single layer CD size
disc (equivalent to up to 3 hours of video and multi-channel audio). DVDs can
also be double sided or dual layer-storing even
more data.
DVD-R
A recordable (write once) DVD format using dye sublimation recording technology,
capable of storing 3.95 GB on a single sided,
single layer CD size disc. Generally used for DVD pre-mastering.
DVD-RAM
A recordable (write once) DVD format using phase-change recording technology,
now capable of storing 4.7 GB on a single
sided, single layer CD size disc. Generally used for archiving data on PCs,
and a more affordable option than DVD-R. Although
currently limited to drives for PCs, the backers of the format plan on releasing
DVD-Video players compatible with the
DVD-RAM format for recording and playback in the immediate future.
Encode
The conversion of data into a specified digital format for storage and retrieval,
usually involving compression and sometimes
encryption technologies.
Encrypt
In digital media, a software system used to protect sensitive data, often using
a password or code.
Filter
An effect applied to an image, video, or sound that changes its appearance or
sound quality. Also, a key component in the
Microsoft DirectShow architecture, a filter is a COM object that supports DirectShow
interfaces or base classes. It might operate
on streams of data in a variety of ways, such as reading, copying, modifying,
or writing the data to a file. Sources, transform
filters, and renderers are all particular types of filters. A filter contains
pins that it uses to connect to other filters.
Filter Graph
In DirectShow, a collection of filters that are connected to perform a particular
operation, such as playing back a media file, or
capturing to the hard disc. The Filter Graph Editor is a graphical tool included
with the Microsoft DirectX Media SDK that
creates and manages DirectShow filter graphs.
FMV
Full Motion Video, the ability to play video at the broadcast frame rate of
30 fps for NTSC signals or 25 frames per second for
PAL signals.
Frame
A single image in a video sequence containing the entire set of scanlines. NTSC
video displays at roughly 30 frames per second.
Frame Drop
Frame Drop is when a decoding or encoding system cannot keep up with the true
frame rate of the source video, resulting in
"jerky" playback.
Frame Rate
The number of frames captured or displayed in one second of a video sequence.
Frame Size
The size (resolution in pixels or lines) of the captured or displayed frame
in a video sequence.
FPS
Frames Per Second, the number of frames captured or displayed per second in
a video sequence.
HDTV
High Definition Television, any format that is at least twice the horizontal
and vertical resolution of the current standard
definition signals, displayed in a 16:9 aspect ratio.
Hue
The color of light or a pixel, the property that sets it apart from other
colors in a wavelength of light.
I-Frame
One of the three types of frames that are used in MPEG coded signals. These
contain data to represent an entire frame image
(intraframe), compressed using DCT.
Indeo
A set of video and audio codecs originally developed by Intel for PC multimedia
applications, and featuring progressive
download features for the Internet.
Interactive Television
The combination of standard television and enhancements (such as Internet access
and interactive content).
Interlace
Interlaced video uses two alternating video fields to make a single frame of
video, most commonly used in television. This
approach was originally invented as a form of compression for analog transmission,
and also provides twice the images per
second (at half the resolution) to achieve smoother fast motion. NTSC (29.97
frames per second), for example, provides a series
of 59.94 interlaced fields per second.
Interleave
A process of arranging audio and video data during compression used to obtain
smoother playback and synchronization.
Inverse Telecine
The process that reconstructs the frames that were added when 24 fps film was
converted to 29.97 fps (59.94 fields per second)
video.
Joint Stereo
A specific coding method in MPEG Layer-II audio where the upper frequencies
of the stereo signal are joined and coded as
intensity stereo in order to conserve bandwidth and improve quality.
JPEG
Named after the Joint Photographic Experts Group that created the standard,
a compression technique for images that reduces
them to a small percentage of the original file size.
Kbps
Kilobits per second, a general measurement for data transfer rate at thousands
of bits per second.
KBps
Kilobytes per second, a general measurement for data transfer rate at thousands
of bytes per second.
Keyframe
A frame of digital video that contains all the data required to reconstruct
that frame. Also, one of two or more frame in a sequence
that is used for interpolation of motion or information between frames.
Linear Editing
Traditional "cut and splice" editing done on a flatbed where the sources
are edited in the order presented. Changes to any edit
require re-recording all of the succeeding edits or using the master as the
source.
Lossless Compression
Any compression method that reduces file size without changing any data when
the file is reopened.
Lossy Compression
Any compression method that reduces file size by selectively discarding what
is determined to be nonessential data.
M-JPEG
Motion JPEG, a video compression scheme and codec that treats each field or
frame in a sequence as a separate image, and
performs separate compression on each. Popular in older digital editing systems
before the advent of DV formats.
MCI
Media Controller Interface, a software driver designed by Microsoft to allow
media files to be played in Windows and device
control from the PC.
Motion Compensation
In video compression, the process of analyzing previous/future frames to identify
motion vectors, and create the prediction and
the error difference signal for interframe encoding.
Motion Estimation
In video compression, the process of evaluating and describing only the differences
between adjacent frames, thus eliminating the
need to convey redundant information.
Motion Vector
Two-dimensional vector used for motion compensation and motion estimation that
provides an offset from the coordinate
position in the current picture to the coordinates in a reference picture.
MPEG
Moving Picture Experts Group, the organization involved with defining open standards
for digital media. Also used as the name
of the formats and compression methods defined by this group.
MPEG-1
A widely used set of standards for the coded representation of video and audio,
primarily for PC multimedia applications. The
basis of formats such as CD-I and VideoCD. The ISO standards are organized under
the designation ISO/IEC 11172.
MPEG-2
A widely used set of standards for the coded representation of video and audio,
primarily for digital television and digital
broadcast satellite. Intended for applications requiring support for interlaced
video, and larger frame sizes and bitrates than
supported by MPEG-1. The basis of formats such as Super VideoCD and DVD Video.
ISO standards are organized under the
designation ISO/IEC 13818.
MPEG-4
A next-generation set of standards for the coded representation of the combination
of streamed elementary audiovisual data in the
form of natural or synthetic, audio or visual, 2D and 3D objects. It is a departure
from previous MPEG standards as it
concentrates more on the architecture of a multimedia system rather than pure
compression issues. MPEG-4 provides
standardized elements enabling the integration of production, distribution and
content access, independent of the transmission
method. ISO standards are organized under the designation ISO/IEC 14496.
MPEG-J
A programmatic system that specifies an API for interoperation of MPEG-4 media
and Java applications.
MP2
A standard abbreviation or file extension for an MPEG Level II elementary audio
stream.
MP3
A standard abbreviation or file extension for an MPEG Level III elementary audio
stream.
MP4
Abbreviation used by many to describe a file containing MPEG-4 video and/or
audio information.
Multiplex
The process of combining separate elementary video and audio streams into a
single synchronized signal or stream. Also known
as "mux".
Noise
Visual or audible discrepancies that adversely affect media that has been recorded
or encoded badly.
Non-linear Editing
The method of combining multiple digital media clips to produce a finished product.
NLE offers random access at anytime to all
source material in the project until the final recording is published to tape.
NTSC
National Television Standards Committee is the standards body that defined the
commercial broadcast standards for television
used in North America (and some other parts of the world such as Canada and
Japan). It describes a system for video that is 29.97
frames (59.94 interlaced fields) per second and 525 scan lines per frame. The
standard includes the specifications for the
composite color encoding system, often considered to be difficult to work with.
Object Descriptor (OD)
In MPEG-4, a structure similar to a URL, containing pointers to elementary streams
and containing Quality of Service
parameters.
Overlay
The process of rendering part of one image transparent to allow a second image
to appear through this transparent area, used on
PC graphics systems to provide high quality video without compromising the performance.
P-Frames
In MPEG, a Predicted frame that contains only predictive information generated
by evaluating the difference between the present
frame and the previous one. They contain much less data than I-frames and help
achieve the low data rates, quality and efficiency
associated with the MPEG signal.
PAL
Phase Alternation Line is the television standard used in Europe, Africa, and
South America characterized by 25 frames (50
interlaced fields) per second and 625 scan lines per frame.
Pan-scan
DVD-Video display format in which a 16:9 video is cropped for a 4:3 display.
Parser Filter
In Microsoft's DirectShow, a filter that pulls information from a disc by using
the asynchronous file reader filter, or from the
Internet by using the URL moniker filter.
PCM
Pulse Code Modulation, a method by which analog sound is digitally sampled and
recorded. Changing the playback rate and
amplitude of the sampled digital pulses enables PCM sound to be reproduced with
a varying pitch and amplitude.
Pixel
The smallest component that makes up an image, each of which can be a different
color. Used as the unit of measurement for an
image, and derived from the shortening of the words "picture element"
or "picture cell."
Post-Production
In video and audio, the process of merging media sources from tape or film into
the finished program. Post-production includes
editing, special effects, dubbing, and titling.
Quantization
In the encoding of digital video, the process by which pixels from the sampled
video signal are assigned a value within a defined
range. Quantization determines the extent of frequencies to be analyzed in the
video as part of the compression process.
QuickTime
A media architecture developed by Apple Computer which allows you to compress
video files. QuickTime files are referred to as
movies and have an MOV extension.
RTSP
Real-time Streaming Protocol, a standard Internet protocol for interaction between
the server and the client for delivery of
streamed media.
RealMedia
Streaming technology architecture developed by Real Networks for delivering
live video to users over the Internet at low bit rates
to be played in RealPlayer.
Render
The process of combining source information into a single file after applying
transitions and other effects for output.
Resolution
The resolution of an image determines the size of the individual pixels in an
image, and thus the size of the whole image when
displayed or printed. Resolution is shown in pixels per inch (PPI) or dots per
inch (DPI). Common resolutions are 72 DPI for
computer video, and 600 DPI for print material.
RGB
The model used in televisions, computer monitors and image formats to display
color. It mixes varying amounts of Red, Green,
and Blue to create other colors in the spectrum
S-VHS
Super VHS, the second-generation VHS standard that improves the picture quality
by processing the brightness and the color
separately. It is unrelated to the S-Video video signal.
S-Video
A type of video signal and analog I/O system that transmits luminance and color
portions separately, using multiple wires.
S-video avoids the NTSC encoding process and the inevitable loss of picture
quality that results from it.
Saturation
The degree of a color's purity. A color that is highly saturated will be more
pure and appear stronger. Increasing a color's
saturation makes it appear quite vivid while reducing saturation makes the color
seem washed out. saturation Color purity. For
example, a color that is completely blue has a 100% saturation, while white,
which is composed of all colors, has a zero
saturation.
SECAM
System Electronic Pour Coleur Avec Mmoire, the television standard used in France,
Russia, and Africa characterized by 25
frames (50 interlaced fields) per second and 625 scan lines per frame.
SIF
Source Input Format, 352x240 at 30fps (NTSC) and 352x288 at 25fps (PAL). Commonly
used in MPEG-1 coding.
SMPTE
Society of Motion Picture and Television Engineers, an organization based in
the United States that makes recommendations for
video standards to be adopted by the industry.
Splicing
In MPEG, the ability to cut at random into a bit stream for switching and editing,
regardless of type of frames (I, B, or P).
SDTV
Standard Definition Television, an alternative to HDTV-resolution digital television.
Offers the ability to transmit four or more
standard-quality programs in the same bandwidth.
Stream
Data and associated properties transmitted across a network or system. Also,
a general term for a piece of media.
Streaming
The process of sending multimedia files in a continuous flow over networks from
server to client. Data is generally not copied to
the client for storage, and the user can start viewing the content without waiting
for the stream to be fully downloaded.
Subsampling
The process of interpreting image data by grouping and averaging color data
over a block of pixels, to enhance compression.
Subsampling reduces the number of bytes required to store a pixel’s color
information by averaging color and luminance
information.
SVCD
Super VideoCD (or Super VCD), a Compact Disc MPEG-2 video format to succeed
Video CD, and developed by the China
Recording Standards Committee. Quality is generally considered to be between
VHS and DVD, providing resolutions of 480x480
(NTSC) or 480x576 (PAL), and supporting interlaced video. Also supports variable
bitrate (VBR) MPEG-2 video at up to 2.6
Mbps, and up to two MPEG-2 Layer II stereo audio streams. A typical SVCD can
hold about 18 - 40 minutes of media, and can
be played on many set top DVD video players.
Sync Layer (SL)
In MPEG-4, the common mechanism for conveying timing information, and the wrapper
layer around elementary streams.
Synchronous
A transmission procedure by which the bit and character stream are slaved to
accurately synchronized clocks, both at the
receiving and sending end.
Telecine
The technique of converting 24 frame-per-second progressive filmed content to
interlaced 29.97 frame (59.94 fields) per second
video.
Transcode
The process of converting a file or program from one format or resolution to
another.
Transform Filter
In DirectShow, a filter that takes data, processes it, and then passes it along
to the next filter in the filter graph.
Transport Stream
A type of stream supported by MPEG-2 used for transmission applications such
as cable and satellite. TS are well suited for
delivery of multiple video and audio streams in error-prone environments.
Type-1 DV AVI
In Microsoft Windows, OpenDML AVI files using a DV codec where the video and
audio are stored in their native, interleaved
format. As they are based on OpenDML, they are limited in length only by the
file systems used by the operating system. The
NTFS file system supported on Windows NT and 2000 can store Type-1 files of
almost unlimited length. The FAT32 file system
supported on Windows 98 only supports files up to 4 GB. However, because the
Type-1 format stores data as a single AVI
stream, Type-1 DV AVI files are not compatible with Video for Windows. These
files are currently only compatible with
applications and IEEE-1394 cards that use the DirectShow media system. Type-1
DV files are typically created by
DirectShow-compatible OHCI IEEE-1394 PCI cards.
Type-2 DV AVI
In Microsoft Windows, AVI files using a DV codec where the video and audio are
not stored in their native, interleaved format,
but rather split into a single video stream and one to four audio streams within
the file. Type-2 DV AVIs have the advantage of
being backward compatible with Video for Windows. However, this format requires
a small amount of redundant size, and
additional processing to split/multiplex the DV stream during the functions
of capture/transmit to IEEE 1394 devices. In addition,
they are limited by the same restrictions in file size associated with the non-OpenDML
AVI file format.
VBI
The Vertical Blanking Interval is a synchronizing period in the broadcast video
signal when no active picture information is
transmitted, and often used to carry data.
VBR
Variable Bit Rate encoding is a method that ensures consistent high video and
audio quality throughout an encoded stream by
allocating extra bits to more complex sections. VBR generally produces an overall
higher and more consistent quality level than
Constant Bit Rate (CBR) encoding.
VCD
VideoCD is a Compact Disc MPEG-1 format that was defined by Philips and JVC,
and is also known as 'White Book'. VideoCD
can store about an hour of video sequences and sound in up to 98 A/V tracks.
It is generally playable on all CD-ROM players and
the most recent generation of DVD (Digital Versatile Disc) players. Frame size
and rate must conform to must be either 352x240
29.97 fps (NTSC) or 352x288 25 fps (PAL), with audio (mono or stereo) at a sampling
frequency of 11, 22, or 44 kHz. Quality of
video is generally considered to be less than VHS due to the low bit rate restrictions
(@1100 kbps).
VHS
Video Home System, the most widely used video recording format for consumers.
Video 1
Video 1 is an early Microsoft Video for Windows software codec originally developed
by MediaVision.
Video for Windows
Video for Windows was the first multimedia architecture developed by Microsoft.
It is one of the most common formats (through
the AVI file format) for playing video files on the PC.
VO
In MPEG-4, a scalable Video Object that correpsonds to a particular 2D object
in a scene, made up of one or more Video Object
Layers (VOL).
VOD
In broadcast, Video-On-Demand is a program sent immediately and independently
to a customer in response to his individual
request. This contrasts with scheduled broadcast television (and even Pay Per
View), which is made available simultaneously to
all customers able to receive it.
VOP
In MPEG-4, a Video Object Plane is a time sample of a video object that may
contain shape information, texture data and motion
parameters. VOPs may be encoded independently of each other, or dependant on
each other using motion compensation. Similar
to MPEG-2 syntax, these are known as I-VOPs, P-VOPs, and B-VOPs. VOPs are grouped
together in GOVs, Groups of VOPs
VTR
A Video Tape Recorder is the general term for any device capable of recording
visual information onto magnetic tape so that it
can be played back and shown on a television display.
Waveform
A visual representation of sound, often used in the process of sound editing.
Wavelet Compression
An asymmetrical image compression method that is scalable and provides high
quality. Wavelet compression assumes that an
image contains "trends" and "outliers". Trends have large
areas of slowly varying gradation, and outliers are areas of highly
concentrated changes. The wavelet transform encodes the trends at low resolution,
and the outliers at high resolution. Wavelet
compression then quantizes the transformed image so that redundant information
is mapped to zero, and then efficiently encodes
the zeros.
Weave
A method of displaying interlaced video fields on a progressive monitor by blending
two interlaced images into a frame.
Windows Media Technologies
The family of interoperable Windows streaming media applications. Windows Media
Tools create Windows Media content that
can be served by Windows Media Services and played by a Windows Media Player
client.
YUV
A color model that describes color information in terms of luminance (Y) and
chrominance, as defined as the difference between
a color and reference white at the same luminance (represented by U and V, where
U=B-Y, and V=R-Y). YUV uses properties of
the human eye to prioritize information.
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