Multimdeia Terms
Aspect Ratio
The width/heigh ratio of a television set or movie screen. Most television sets have a 4:3 aspect ratio. Wide screen television sets have a 16:9 aspect ratio.
Bidirectional (B) Frame
One of the three picture types in MPEG compression. B frames are coded in relation to previous or subsequent I or P frames. B frames do not serve as a reference for other frames
Data Rate
The speed of the data stored on a type of media, usually expressed in bits per second or bytes per second
Data Transfer Rate
The transfer rate of the storeage media itself. VCD transfer rate is 1.2MB.
Downmix
The process of converting a multi-channel audio track to two- or one- channel track
Dolby Digital
Also known as AC-3. A high-quality, bandwidth efficient perceptual audio coding system originally developed by Dolby Laboratories for multi-channel digital sound in the cinema. It can be used in broadcast, cable, film and recorded media in both professional and consumer applications. Dolby Digital is one of the main audio formats used in DVD
Dolby Surround
The consumer version of the original analog Dolby multi-channel film sound format
Drop Frame Time Code
A mode of operation when playing back NTSC video. In NTSC, the actual frame rate is roughly 29.97 fps. When the time code indicates 1 hour of film, 1 hour, 3 seconds and 18 frames worth of actual time has elapsed, or a descrepancy of 108 frames. Some encoder resolves the time code discrepancy by dropping two frame numbers every minute, on the minute, except the tenth minutes.
DTS (Digital Theater Sound)
An audio encoding technology developed for theaters. DTS was developed to compete with Dolby Digital and is an additional audio format for DVD
GOP (Group of Pictures)
A GOP is a single MPEG video random access unit
Intra (I) Frame
A key reference frame in the MPEG compression algorithmn. I Frames are one of the three types of frames used in MPEG compression. They contain all the data needed to represent an entire frame, hence are referred to as key reference frames
Linear PCM
A non-compressed digital audio format. The DVD specification allows for 16 to 24 bit Linear PCM audio sampled at 48 or 96 kHz
MP3
MP3 is the MPEG audio layer 3 standard. Layer 3 is one of three coding schemes (layer 1, 2 and 3) for the compression of audio signals defined by the MPEG committee. Layer 3 uses perceptual audio coding and psychoacoustic compression to remove the redundant parts of a sound signal. It also adds a MDCT (Modified Discrete Cosine Transform) that implements a filter bank, increasing the frequency resolution 18 times higher than that of MPEG audio layer 2
MPEG-1
ISO/IEC standard designed for low bandwidth of compressed digital video and audio. VCD uses this format with resolution of 352x288@25fps (PAL) or 352x240@29.97fps (NTSC)
MPEG-2
ISO/IEC standard designed for transmission of high bandwidth compressed digital video and audio such as that used by broadcast televsion. DVD uses this format with resolution of 720x576@25fps (PAL) or 720x480@29.97fps (NSTC)
MPEG-4
ISO 14496 is an ISO/IEC standard developed by MPEG (Moving Picture Experts Group). Although defined as one standard, MPEG-4 is actually a set of compression/decompression formats and streaming technologies that address the need for distributing rich interactive media over narrow and broadband networks
MPEG Audio
Multi-channel digital audio defined by the MPEG specification. MPEG-1 Layer 2 is compressed using perceptual coding. It has a sample rate of 32, 44.1 and 48 kHz at 16 bits and can contain mono or stereo streams. MPEG-1 Layer 3 supports variable sample rate. MPEG-2 audio is an extension of MPEG-1 audio. It supports low bit rates and upto 7.1 audio channels
Multiplexing
Combining two or more data streams together into a single stream
Predicted (P) Frame
Frames used in MPEG compression which are coded in relation to the nearest previous I or P frame. P frames serve as a prediction reference for B frames and future P frames
SDDS (Sony Dynamic Digital Sound)
An audio encoding technology developed by Sony for multi-channel audio in cinemas and theaters. SDDS was developed to compete with Dolby Digital and is an optional audio format for
DVD
S-Video
A video signal that carries seprate luminance and chrominance signals
SMPTE EBU Time Code
A standard for a signal recorded on video tape to uniquely identify each frame of the video signal. It is used to control editing operations. (SMPTE stands for Society of Motion Picture and Television Engineering)
