Multimedia Final Exam Terms

 

Active Video

The part of the video waveform that contains picture information. Most of the active video, if not all of it, is visible on the display.

Anti-Alias Filter

A lowpass filter used to bandwidth-limit a signal to less than one-half the sampling rate.

Asynchronous

Refers to circuitry without a common clock or timing signal.

Automatic Frequency Control (AFC)

A technique to lock onto and track a desired frequency.

Automatic Gain Control (AGC)

A circuit that has a constant output amplitude, regardless of the input amplitude.

Bandpass Filter

A circuit that allows only a selected range of frequencies to pass through.

Bandwidth (BW)

The range of frequencies a circuit will respond to or pass through. It may also be the difference between the highest and lowest frequencies of a signal.

BITC

Burned-In Time Code. The timecode information is displayed within a portion of the picture, and may be viewed on any monitor or TV.

Black Level

This level represents the darkest an image can get, defining what black is for a particular video system. If for some reason the video goes below this level, it is referred to as blacker-than-black. You could say that sync is blacker-than-black.

BTSC

This EIA TVSB5 standard defines a technique of implementing stereo audio for NTSC video. One FM subcarrier transmits a L+R signal, and an AM subcarrier transmits a L-R signal.

Carrier

A frequency that is modulated with data to be transmitted.

CATV

Community antenna television, now generally meaning cable TV.

Chroma Key

This is a method of combining two video images. An example of chroma keying in action is the nightly news person standing in front of a giant weather map. In actuality, the person is standing in front of a blue or green background and their image is mixed with a computer-generated weather map. This is how it works: a TV camera is pointed at the person and fed along with the image of the weather map into a box. Inside the box, a decision is made. Wherever it sees the blue or green background, it displays the weather map. Otherwise, it shows the person. So, whenever the person moves around, the box figures out where he is, and displays the appropriate image.

Closed Captioning

A service which decodes text information transmitted with the video signal and displays it on the display. For NTSC, the caption signal may be present on lines 21 and 284. For PAL, the caption signal may be present on lines 22 and 334. See the EIA-608 specification for (M) NTSC usage of closed captioning and the EIA-708 specification for DTV support.

For MPEG-2 video, including ATSC and DVB, the closed caption data are multiplexed as a separate data stream within the MPEG-2 bitstream. It may use the picture layer user_data bits as specified by EIA-708, or in PES packets (private_stream_1) as specified by ETSI EN 301 775.

For DVD, caption data may be 8-bit user_data in the group_of_pictures header (525/60 systems), a digitized caption signal (quantized to 16 levels) that is processed as normal video data (625/50 systems), or a subpicture that is simply decoded and mixed with the decoded video.

Component Video

Video using three separate color components, such as digital Y'CbCr, analog Y'PbPr, or R'G'B'.

Composite Video

A single video signal that contains brightness, color, and timing information. If a video system is to receive video correctly, it must have several pieces of the puzzle in place. It must have the picture that is to be displayed on the screen, and it must be displayed with the correct colors. This piece is called the active video. The video system also needs information that tells it where to put each pixel. This is called sync. The display needs to know when to shut off the electron beam so the viewer can't see the spot retrace across the CRT display. This piece of the video puzzle is called blanking. Now, each piece could be sent in parallel over three separate connections, and it would still be called video and would still look good on the screen. This is a waste, though, because all three pieces can be combined together so that only one connection is needed. Composite video is a video stream that combines all of the pieces required for displaying an image into one signal, thus requiring only one connection. NTSC and PAL are examples of composite video. Both are made up of active video, horizontal sync, horizontal blanking, vertical sync, vertical blanking, and color burst. RGB is not an example of composite video, even though each red, green, and blue signal may contain sync and blanking information, because all three signals are required to display the picture with the right colors.

Compression Ratio

Compression ratio is a number used to tell how much information is squeezed out of an image when it has been compressed. For example, suppose we start with a 1 MB image and compress it down to 128 KB. The compression ratio would be:

1,048,576 / 131,072 = 8

This represents a compression ratio of 8:1; 1/8 of the original amount of storage is now required. For a given compression technique - MPEG, for example - the higher the compression ratio, the worse the image looks. This has nothing to do with which compression method is better, for example JPEG vs. MPEG. Rather, it depends on the application. A video stream that is compressed using MPEG at 100:1 may look better than the same video stream compressed to 100:1 using JPEG.

Constant Bit Rate

Constant bit rate (CBR) means that a bitstream (compressed or uncompressed) has the same number of bits each second.

Contrast

A video term referring to how far the whitest whites are from the blackest blacks in a video waveform. If the peak white is far away from the peak black, the image is said to have high contrast. With high contrast, the image is very stark and very "contrasty", like a black-and-white tile floor. If the two are very close to each other, the image is said to have poor, or low, contrast. With poor contrast, an image may be referred to as being "washed out" -- you can't tell the difference between white and black, and the image looks gray.

Digital 8

Digital 8 compresses video using standard DV compression, but records it in a manner that allows it to use standard Hi-8 tape. The result is a DV "box" that can also play standard Hi-8 and 8 mm tapes. On playback, analog tapes are converted to a 25 Mbps compressed signal available via the i-Link digital output interface. Playback from analog tapes has limited video quality. New recordings are digital and identical in performance to DV; audio specs and other data also are the same.

Digital Component Video

Digital video using three separate color components, such as Y'CbCr or R'G'B'.

Digital Composite Video

Digital video that is essentially the digitized waveform of NTSC or PAL video signals, with specific digital values assigned to the sync, blank, and white levels.

Digital VCR

Digital VCRs are similar to analog VCRs in that tape is still used for storage. Instead of recording an analog audio/video signal, digital VCRs record digital signals, usually using compressed audio/video.

Digital Video Recorder

DVRs can be thought of a digital version of the VCR, with several enhancements. Instead of a tape, the DVR uses an internal hard disk to store compressed audio/video, and has the ability to record and playback at the same time. The main advantage that DVRs have over VCRs is their ability to time shift viewing the program as it is being recorded. This is accomplished by continuing to record the incoming live program, while retrieving the earlier part of the program that was just recorded. The DVR also offers pause, rewind, slow motion, and fast forward control, just as with a VCR.

Dot Pitch

The distance between screen pixels measured in millimeters. The smaller the number, the better the horizontal resolution.

DTS

DTS <http://www.dtstech.com/> stands for Digital Theater Systems. It is a multi-channel surround sound format, similar to Dolby Digital. For DVDs that use DTS audio, the DVD - Video specification still requires that PCM or Dolby Digital audio still be present. In this situation, only two channels of Dolby Digital audio may be present (due to bandwidth limitations).

DVD-Audio

DVDs that contain linear PCM audio data in any combination of 44.1, 48.0, 88.2, 96.0, 176.4, or 192 kHz sample rates, 16, 20, or 24 bits per sample, and 1 to 6 channels, subject to a maximum bit rate of 9.6 Mbps. With a 176.4 or 192 kHz sample rate, only two channels are allowed.

Meridian Lossless Packing (MLP) is a lossless compression method that has an approximate 2:1 compression ratio. The use of MLP is optional, but the decoding capability is mandatory on all DVD-Audio players.

Dolby Digital compressed audio is required for any video portion of a DVD-Audio disc.

DVD-Video

DVDs that contain about two hours of digital audio, video, and data. The video is compressed and stored using MPEG-2 MP@ML. A variable bit rate is used, with an average of about 4 Mbps (video only), and a peak of 10 Mbps (audio and video). The audio is either linear PCM or Dolby Digital compressed audio. DTS compressed audio may also be used as an option.

Linear PCM audio can be sampled at 48 or 96 kHz, 16, 20, or 24 bits per sample, and 1 to 8 channels. The maximum bitrate is 6.144 Mbps, which limits sample rates and bit sizes in some cases.

For Dolby Digital audio, the bitrate is 64 to 448 kbps, with 384 kbps being the normal rate for 5.1 channels and 192 kbps being the normal rate for stereo. The channel combinations are (front/surround): 1/0, 1+1/0 (dual mono), 2/0, 3/0, 2/1, 3/1, 2/2, and 3/2. The LFE channel (0.1) is optional with all 8 combinations.

For DTS audio, the bitrate is 64 to 1,536 kbps. The channel combinations are (front/surround): 1/0, 2/0, 3/0, 2/1, 2/2, 3/2. The LFE channel (0.1) is optional with all 6 combinations.

Columbia Tristar Home Entertainment <http://www.cthv.com/> has introduced a Superbit(TM) DVD that has an average bit rate of about 7 Mbps (video only) for improved video quality. This is achieved by having minimal "extras" on the DVD.

Field

An interlaced display is made using two fields, each one containing half of the scan lines needed to make up one frame of video. Each field is displayed in its entirety -- therefore, the odd field is displayed, then the even, then the odd, and so on. Fields only exist for interlaced scanning systems. So for (M) NTSC, which has 525 lines per frame, a field has 262.5 lines, and two fields make up a 525-line frame.

Flicker

Flicker occurs when the frame rate of the video is too low. It's the same effect produced by an old fluorescent light fixture. The two problems with flicker are that it's distracting and tiring to the eyes.

FM

See frequency modulation.

Frame

A frame of video is essentially one picture or "still" out of a video stream. By playing these individual frames fast enough, it looks like people are "moving" on the screen. It's the same principle as flip cards, cartoons, and movies.

Frame Rate

The frame rate of a video source is how fast a new still image is available. For example, with the NTSC system, the entire display is repainted about once every 30th of a second for a frame rate of about 30 frames per second. For PAL, the frame rate is 25 frames per second. For computer displays, the frame rate is usually 70-90 frames per second.

Frame Rate Conversion

Frame rate conversion is the act of converting one frame rate to another.

Frequency Modulation (FM)

This technique sends data as frequency variations of a carrier signal.

HDTV

Short for High Definition Television. HDTV is capable of displaying at least 720 progressive or 1080 interlaced active scan lines. It must be capable of displaying a 16:9 image using at least 540 progressive or 810 interlaced active scan lines.

For the ATSC system, typical HDTV (luminance) resolutions and refresh rates are:

 

Active Resolution

Aspect Ratio

23.976p, 24p

29.97p, 30p

59.94i, 60i

59.94p, 60p

1280 x 720

16:9

x

x

 

x

1920 x 1080

16:9

x

x

x

 

 

For the DVB system, typical HDTV (luminance) resolutions and refresh rates are:

 

Active Resolution

Aspect Ratio

23.976p, 24p

25p

29.97p, 30p

50i

50p

59.94i, 60i

59.94p, 60p

1280 x 720

16:9

x

x

x

x

x

x

x

1440 x 1080

16:9

x

x

x

x

x

x

x

1920 x 1080

16:9

x

x

x

x

x

x

x

 

p = progressive; i = interlaced.

High Definition Television

See HDTV.

Hue

In technical terms, hue refers to the wavelength of the color. That means that hue is the term used for the base color -- red, green, yellow, etc. Hue is completely separate from the intensity or the saturation of the color. For example, a red hue could look brown at low saturation, bright red at a higher level of saturation, or pink at a high brightness level. All three "colors" have the same hue.

iLink

Sony's name for their IEEE 1394 interface.

Interlaced

An interlaced video system is one where two interleaved fields are used to generate one video frame. Therefore, the number of lines in a field is one-half of the number of lines in a frame. In NTSC, there are 262.5 lines per field (525 lines per frame), while there are 312.5 lines per field (625 lines per frame) in PAL. Each field is drawn on the screen consecutively -- first one field, then the other.

MPEG-1

MPEG-1 (ISO/IEC 11172) was the first MPEG standard defining the compression format for real-time audio and video. The video resolution is typically 352 x 240 or 352 x 288, although higher resolutions are supported. The maximum bitrate is about 1.5 Mbps. MPEG-1 is used for the Video CD format.

MPEG-2

MPEG-2 (ISO/IEC 13818) extends the MPEG-1 standard to cover a wider range of applications. Higher video resolutions are supported to allow for HDTV applications, both progressive and interlaced video are supported. MPEG-2 is used for the DVD - Video and SVCD formats, and also forms the basis for digital SDTV and HDTV.

Noninterlaced

This is a method of scanning out a video display that is the total opposite of interlaced. All of the lines in the frame are scanned out sequentially, one right after the other. The term "field" does not apply in a noninterlaced system. Another term for a noninterlaced system is progressive scan.

NTSC

Never Twice the Same Color, Never The Same Color, or National Television Standards Committee, depending on who you're talking to. Technically, NTSC is just a color modulation scheme. To fully specify the color video signal, it should be referred to as (M) NTSC. "NTSC" is also commonly (though incorrectly) used to refer to any 525/59.94 or 525/60 video system. See also NTSC 4.43.

Overscan

When an image is displayed, it is "overscanned" if a small portion of the image extends beyond the edges of the screen. Overscan is common in TVs that use CRTs to allow for aging and variations in components, temperature and power supply.

PAL

PAL stands for Phase Alternation Line, Picture Always Lousy, or Perfect At Last depending on your viewpoint. Technically, PAL is just a color modulation scheme. To fully specify the color video signal it should be referred to as (B, D, G, H, I, M, N, or CN) PAL. (B, D, G, H, I) PAL is the color video standard used in Europe and many other countries. (M, N, CN) PAL is also used in a few places, but is not as popular. "PAL" is also commonly (though incorrectly) used to refer to any 625/50 video system. See also PAL 60.

RGB

Abbreviation for red, green, blue.

Saturation

Saturation is the amount of color present. For example, a lightly saturated red looks pink, while a fully saturated red looks like the color of a red crayon. Saturation does not mean the brightness of the color, just how much "pigment" is used to make the color. The less "pigment", the less saturated the color is, effectively adding white to the pure color.

Scan Line

A scan line is an individual line across the display. It takes 525 of these scan lines to make up a NTSC TV picture and 625 scan lines to make up a PAL TV picture.

Streaming Video

Compressed audio and video that is transmitted over the Internet or other network in real time. Typical compression techniques are MPEG-2, MPEG-4, Microsoft WMT, RealNetworks, and Apple's QuickTime. It usually offers "VCR-style" remote control capabilities such as play, pause, fast forward, and reverse.

Subcarrier

A secondary signal containing additional information that is added to a main signal.

Super VideoCD (Super VCD, SVCD)

Next generation VideoCD, defined by the China National Technical Committee of Standards on Recording, that hold 35-70 minutes of digital audio and video information. MPEG-2 video is used, with a resolution of 480 x 480 (29.97 Hz frame rate) or 480 x 576 (25 Hz frame rate). Audio uses MPEG-1 layer 2 or MPEG-2 at a bit rate of 32-384 kbps, and supports four mono, two stereo, or 5.1 channels. Subtitles use overlays rather than subpictures (DVD-Video) or being encoded as video (VideoCD). Variable bit-rate encoding is used, with a maximum bit rate of 2.6 Mbps. IEC 62107 defines the Super VideoCD standard.

XSVCD, although not an industry standard, increases the video resolution and bit rate to improve the video quality over SVCD. MPEG-2 video is still used, with a resolution of 720 x 480 (29.97 Hz frame rate) or 720 x 576 (25 Hz frame rate). Variable bit-rate encoding is still used, with a maximum bit rate of 9.8 Mbps.

S-VHS

S-VHS is an enhancement to regular VHS video tape decks. S-VHS provides better resolution and less noise than VHS. S-VHS video tape decks support s-video inputs and outputs, although this is not required. It does, however, improve the quality by not having to separate and then merge the luma and chroma signals.

S-Video

Separate video, also called Y/C video. Separate luma (Y') and chroma (C) video signals are used, rather than a single composite video signal. By simply adding together the Y' and C signals, you generate a composite video signal.

A DC offset of +2.3v may be present on the C signal when a letterbox picture format is present. A DC offset of +5v may be present to indicate when a 16:9 anamorphic picture format is present. A standard 4:3 receiver ignores all DC offsets, thus displaying a typical letterboxed picture.

Sync

Sync is a fundamental, you gotta have it, piece of information for displaying any type of video. Essentially, the sync signal tells the display where to put the picture. The horizontal sync, or HSYNC for short, tells the display where to put the picture in the left-to-right dimension. The vertical sync, or VSYNC for short tells the display where to put the picture from top-to-bottom.

Analog SDTV and EDTV signals use a bi-level sync, where the sync level is a known value below the blanking level. Analog HDTV signals use a tri-level sync, where the sync levels are known values above and below the blanking level.

The reason analog HDTV signals use a tri-level sync signal is timing accu­racy. The horizontal timing reference point for a bi-level sync signal is defined as the 50% point of the leading edge of the horizontal sync pulse. In order to ascertain this point precisely, it is necessary to determine both the blanking level and sync-tip level and determine the mid-point value. If the signal is in any way distorted, this will reduce the timing accuracy.

With a tri-level sync signal, the timing reference point is the rising edge of the sync signal as it passes through the blacking level. This point is much eas­ier to accurately determine, and can be implemented relatively easily. It is also more immune to signal distortion.

Uplink

The carrier used by Earth stations to transmit information to a satellite.

Variable Bit Rate

Variable bit rate (VBR) means that a bitstream (compressed or uncompressed) has a changing number of bits each second. Simple scenes can be assigned a low bit rate, with complex scenes using a higher bit rate. This enables maintaining the audio and video quality at a more consistent level.

VideoCD

Compact discs that hold up to about an hour of digital audio and video information. MPEG-1 video is used, with a resolution of 352 x 240 (29.97 Hz frame rate) or 352 x 288 (25 Hz frame rate). Audio uses MPEG-1 layer 2 at a fixed bit rate of 224 kbps, and supports two mono or one stereo channels (with optional Dolby pro-logic). Fixed bit-rate encoding is used, with a bit rate of 1.15 Mbps. The next generation, defined for the Chinese market, is Super VideoCD.

XVCD, although not an industry standard, increases the video resolution and bit rate to improve the video quality over VCD. MPEG-1 video is still used, with a resolution of up to 720 x 480 (29.97 Hz frame rate) or 720 x 576 (25 Hz frame rate). Fixed

Zoom

Zoom is a type of image scaling. Zooming is making the picture larger so that you can see more detail. The examples described in the definition of scaling are also examples that could be used here.