Advanced Audio Coding, or AAC, is a MPEG (Motion Pictures Experts Group) audio standard first adopted as part of the MPEG-2 family of standards. Like its predecessor, MP3, AAC is a Lossy Compression format capable of delivering relatively high quality at relatively low bitrates. There are actually two AAC specifications. In addition to the MPEG-2 version of AAC, which was also referred to early on as NBC for Non Backwards Compatible, there's a newer specification developed for MPEG-4. This version is normally found in the MP4 Container, either with or without accompanying video.
Dolby Digital -(synonyms: AC3)
Dolby Digital (AC-3) is Dolby's third generation audio coding algorithm. It is a perceptual coding algorithm developed to allow the use of lower data rates with a minimum of perceived degration of sound quality.
This coder has been designed to take maximum advantage of human auditory masking in that it divides the audio spectrum of each channel into narrow frequency bands of different sizes optimized with respect to the frequency selectivity of human hearing. This makes it possible to sharply filter coding noise so that it is forced to stay very close in frequency to the frequency components of the audio signal being coded. By reducing or eliminating coding noise wherever there are no audio signals to mask it, the sound quality of the original signal can be subjectively preserved. In this key respect, a coding system like AC-3 is essentially a form of very selective and powerful noise reduction.
ASF - Advanced Streaming Format
Microsoft's new audio/video format, meant specifically for streaming purposes. It doesn't specify how the video or audio should be encoded, but instead just specifies the structure of the video/audio stream. This means that ASF files can be encoded with basically any audio/video codec and would still be in ASF format.
Many times ASF is confused with Microsoft's implementation of MPEG-4 video format, because most of the ASF streams are encoded using this technology.
AVI - which stands for Audio Video Interleave
A Container format used by Microsoft's Video for Windows multimedia framework. Since it was developed for Windows 3.1 in 1992 it lacks some features found in newer containers like MPEG or MP4, but is still widely used by consumers and even supported by some standalone DVD players. Although still supported in Windows, and suitable for certain formats like DV, it's not a good general purpose container, and even Microsoft uses other containers for their own video formats.
Bitrate - (synonyms: bps)
Bitrate refers to the size, over time, of a video or audio stream. Although most computer oriented applications measure bitrate in terms of binary kilobits and Megabits where 1kb (1 kilobit) = 1024 bits and 1Mb (1 Megabit) = 1024 kilobits, bitrate calculations use standard metric values for these prefixes, meaning 1kb = 1000b and 1Mb = 1000kb. Bitrate calculations are typically made in kilobits per second (kbps) or Megabits per second (Mbps). They can also be expressed in other units, including bits per second (bps) or even Megabytes per second (MBps). Notice the capital B denoting Bytes. You should always use a lower case b to denote bits and upper case for Bytes.
DAT can mean lots of things - often it is used to refer to a certain tape backup format. In a/v terminology it normally refers (at least most questions are focused on this one) to files that VideoCD has in its SEGMENT or MPEGAV directiories. These DAT files are basically MPEG-1 files with an additional information and certain specific file structure -- they are NOT "real" MPEG-1 files (their header data is slightly different when stored on VCD) and you need to convert them back to "real" MPEG-1 files in order to edit them even that most of the software players treat them as regular MPEG-1 files.
DRM - (synonyms: Digital Rights Management)
DRM doesn't mean just basic copy-protection of digital content (like ebooks, MP3s or DivX videos), but it basically means full protection for digital content, ranging from delivery to end user's ways to use the content.
If we speak about music DRM, companies wish to develop a product which would allow record labels to sell copy-protected audio tracks over the Internet, so that only the buyer could be allowed to listen the tracks. This is technically difficult, because traditionally, national laws require content owners like record labels, to grant "fair use" rights for products consumers buy. This means that user has to be allowed to make personal copies of the purchased music, in order to use the music in car, in portable digital audio player, in his/her laptop computer, etc.
DIVX - a new format for digital video, much like MP3 is a format for digital music. DivX is the brand name of a patent-pending video compression technology created by DivX Networks, Inc., The DivX codec is based on the MPEG-4 compression standard. This codec is so advanced that it can reduce an MPEG-2 video (the same format used for DVD or Pay-Per-View) to ten percent of its original size.
FLV (Flash Video) - "is a proprietary file format used to deliver video over the Internet using Adobe Flash Player (formerly known as Macromedia Flash Player) version 6, 7, 8, or 9. FLV content may also be embedded within SWF files. Notable users of the FLV format include YouTube, Google Video, Reuters.com, Yahoo! Video and MySpace.
Framerate - (synonyms: fps,frames per second)
Defines how many pictures eg. frames one second of video or audio contains, normally used acronym for framerate is fps - frames per second. Human eye can't see picture changes after the framerate is more than ~24fps. In American TV system NTSC the framerate is appx. 29.97fps and in European PAL system the framerate is 25fps.
4:3 - (synonyms: Full Frame,Fullscreen,Academy Ratio)
4:3 refers to an Aspect ratio (AR) with a height that's 3/4 the width. It's also commonly referred to as 1.33:1 or simply 1.33, in reference to the width being approximately 1.33 times the height. This AR is also commonly referred to as fullscreen, referring to the fact that video with this Aspect Ratio fills the full screen of an analog TV. Widescreen video, on the other hand, must be letterboxed, or vertically compressed to be viewed properly on a 4:3 TV, resulting in only part of the screen being used for the image.
H.264 - is known as MPEG4 AVC, The standard is expected to offer up to twice the compression of the current MPEG4 ASP (Advanced Simple Profile), in addition to improvements in perceptual quality. The H.264 standard can provide DVD-quality video at under 1 Mbps, and is considered promising for full-motion video over Topwireless, satellite, and ADSL Internet connections.
MOD and TOD - the informal names of tapeless video formats used by JVC (MOD and TOD), Panasonic (MOD only) and Canon (MOD only) in some models of digital camcorders. Format names correspond to extensions of video files. Neither JVC nor Panasonic, who pioneered the format, explained meaning of the file extensions. MOD is used exclusively for standard definition video files, while TOD is used for high definition files. The formats was never given an official name.
