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B-frame
In the field of video compression, a video frame is compressed using different algorithms with different advantages and disadvantages, centered mainly around amount of data compression. These different algorithms for video frames are called picture types or frame types. The three major picture types used in the different video algorithms are I, P and B. They are different in the following characteristics: * I‑frames are the least compressible but don't require other video frames to decode. * P‑frames can use data from previous frames to decompress and are more compressible than I‑frames. * B‑frames can use both previous and forward frames for data reference to get the highest amount of data compression. Summary Three types of ''pictures'' (or frames) are used in video compression: I, P, and B frames. An I‑frame ( intra-coded picture) is a complete image, like a JPG or BMP image file. A P‑frame (Predicted picture) holds only the changes in the image from a pr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Inter Frame
An inter frame is a frame in a video compression stream which is expressed in terms of one or more neighboring frames. The "inter" part of the term refers to the use of ''Inter frame prediction''. This kind of prediction tries to take advantage from temporal redundancy between neighboring frames enabling higher compression rates. Inter frame prediction An inter coded frame is divided into blocks known as macroblocks. After that, instead of directly encoding the raw pixel values for each block, the encoder will try to find a block similar to the one it is encoding on a previously encoded frame, referred to as a reference frame. This process is done by a block matching algorithm. If the encoder succeeds on its search, the block could be encoded by a vector, known as motion vector, which points to the position of the matching block at the reference frame. The process of motion vector determination is called motion estimation. In most cases the encoder will succeed, but the block ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Group Of Pictures
In video coding, a group of pictures, or GOP structure, specifies the order in which intra- and inter-frames are arranged. The GOP is a collection of successive pictures within a coded video stream. Each coded video stream consists of successive GOPs, from which the visible frames are generated. Encountering a new GOP in a compressed video stream means that the decoder doesn't need any previous frames in order to decode the next ones, and allows fast seeking through the video. Elements A GOP can contain the following picture types: * I frame (intra coded picture, also by some sources incorrectly said to always be key frame, but you cannot always start with I frame and decode next frames cleanly) – a picture that is coded independently of all other pictures, each I frame can be decoded fully on its own. Each GOP begins (in decoding order) with this type of frame. ** IDR frame (Instantaneous Decoder Refresh): I frame with a marking indicating that no subsequent P or B frame ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Macroblock
The macroblock is a processing unit in image and video compression formats based on linear block transforms, typically the discrete cosine transform (DCT). A macroblock typically consists of 16×16 samples, and is further subdivided into transform blocks, and may be further subdivided into prediction blocks. Formats which are based on macroblocks include JPEG, where they are called MCU blocks, H.261, MPEG-1 Part 2, H.262/MPEG-2 Part 2, H.263, MPEG-4 Part 2, and H.264/MPEG-4 AVC. In H.265/HEVC, the macroblock as a basic processing unit has been replaced by the coding tree unit. Technical details Transform blocks A macroblock is divided into transform blocks, which serve as input to the linear block transform, e.g. the DCT. In H.261, the first video codec to use macroblocks, transform blocks have a fixed size of 8×8 samples. In the YCbCr color space with 4:2:0 chroma subsampling, a 16×16 macroblock consists of 16×16 luma (Y) samples and 8×8 chroma (Cb and Cr) samples. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Intra-frame Coding
Intra-frame coding is a data compression technique used within a video frame, enabling smaller file sizes and lower bitrates, with little or no loss in quality. Since neighboring pixels within an image are often very similar, rather than storing each pixel independently, the frame image is divided into blocks and the typically minor difference between each pixel can be encoded using fewer bits. Intra-frame prediction exploits spatial redundancy, i.e. correlation among pixels within one frame, by calculating prediction values through extrapolation from already coded pixels for effective delta coding. It is one of the two classes of predictive coding methods in video coding. Its counterpart is inter-frame prediction which exploits temporal redundancy. Temporally independently coded so-called intra frames use only intra coding. The temporally coded predicted frames (e.g. MPEG's P- and B-frames) may use intra- as well as inter-frame prediction. Usually only few of the spatiall ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Global Motion Compensation
{{refimprove, date=September 2008 ''Global motion compensation'' ''(GMC)'' is a motion compensation technique used in video compression to reduce the bitrate required to encode video. It is most commonly used in MPEG-4 ASP, such as with the DivX and Xvid codecs. Operation Global motion compensation describes the motion in a scene based on a single affine transform instruction. The reference frame is panned, rotated and zoomed in accordance to GMC warp points to create a prediction of how the following frame will look. Since this operation works on individual pixels (rather than blocks), it is capable of creating predictions that are not possible using block-based approaches. Each macroblock in such a frame can be compensated using global motion (no further motion information is then signalled) or, alternatively, local motion (as if GMC were off). This choice, while costing an additional bit per macroblock, can improve prediction quality and therefore reduce residual. B ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Digital Television
Digital television (DTV) is the transmission of television signals using Digital signal, digital encoding, in contrast to the earlier analog television technology which used analog signals. At the time of its development it was considered an innovative advancement and represented the first significant evolution in television technology since color television in the 1950s. Modern digital television is transmitted in high-definition television (HDTV) with greater resolution than analog TV. It typically uses a widescreen aspect ratio (commonly 16:9) in contrast to the narrower format (4:3) of analog TV. It makes more economical use of scarce radio spectrum space; it can transmit up to seven channels in the same Bandwidth (signal processing), bandwidth as a single analog channel, and provides many new features that analog television cannot. A digital television transition, transition from analog to digital broadcasting began around 2000. Different digital television broadcasting st ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Datamosh
A compression artifact (or artefact) is a noticeable distortion of media (including images, audio, and video) caused by the application of lossy compression. Lossy data compression involves discarding some of the media's data so that it becomes small enough to be stored within the desired disk space or transmitted (''streamed'') within the available bandwidth (known as the data rate or bit rate). If the compressor cannot store enough data in the compressed version, the result is a loss of quality, or introduction of artifacts. The compression algorithm may not be intelligent enough to discriminate between distortions of little subjective importance and those objectionable to the user. The most common digital compression artifacts are DCT blocks, caused by the discrete cosine transform (DCT) compression algorithm used in many digital media standards, such as JPEG, MP3, and MPEG video file formats. These compression artifacts appear when heavy compression is applied, and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Video Compression
In information theory, data compression, source coding, or bit-rate reduction is the process of encoding information using fewer bits than the original representation. Any particular compression is either lossy or lossless. Lossless compression reduces bits by identifying and eliminating Redundancy (information theory), statistical redundancy. No information is lost in lossless compression. Lossy compression reduces bits by removing unnecessary or less important information. Typically, a device that performs data compression is referred to as an encoder, and one that performs the reversal of the process (decompression) as a decoder. The process of reducing the size of a data file is often referred to as data compression. In the context of data transmission, it is called source coding: encoding is done at the source of the data before it is stored or transmitted. Source coding should not be confused with channel coding, for error detection and correction or line coding, the means ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Key Frame
In animation and filmmaking, a key frame (or keyframe) is a drawing or shot that defines the starting and ending points of a smooth transition. These are called ''frames'' because their position in time is measured in frames on a strip of film or on a digital video editing timeline. A sequence of key frames defines which movement the viewer will see, whereas the position of the key frames on the film, video, or animation defines the timing of the movement. Because only two or three key frames over the span of a second do not create the illusion of movement, the remaining frames are filled with " inbetweens". Use of key frames as a means to change parameters In software packages that support animation, especially 3D graphics, there are many parameters that can be changed for any one object. One example of such an object is a light. In 3D graphics, lights function similarly to real-world lights. They cause illumination, cast shadows, and create specular highlights. Lights ha ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
