БеFrame-дер мен P-Frame-дер: Видеоқысудағы аралық кадрлардың талдауы

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.

The difference between P frames and B frames is the reference frame they are allowed to use.

P frame is the term used to define the forward Predicted pictures. The prediction is made from an earlier picture, mainly an I frame or P frame, so that require less coding data (≈50% when compared to I frame size). The amount of data needed for doing this prediction consist of motion vectors and transform coefficients describing prediction correction. It involves the use of motion compensation.

B frame is the term for bidirectionally predicted pictures. This kind of prediction method occupies less coding data than P frames generally (≈25% when compared to I frame size) because the prediction is made from either an earlier frame or a later frame or both them. (B frames can also be less efficient than P frames under certain cases, e. g.: lossless encoding)

Similar to P frames, B frames are expressed as motion vectors and transform coefficients. In order to avoid a growing propagation error, B frames are not used as a reference to make further predictions in most encoding standards. However, in newer encoding methods (such as H.264/MPEG 4 AVC and HEVC), B frames may be used as reference for better exploitation of temporal redundancy.

Luminance block partition of 16×16 (MPEG 2), 16×8, 8×16, and 8×8. The last case allows the division of the block into new blocks of 4×8, 8×4, or 4×4. The frame to be coded is divided into blocks of equal size as shown in the picture above. Each block prediction will be blocks of the same size as the reference pictures, offset by a small displacement.

Multiple references to motion estimation allows finding the best reference in 2 possible buffers (List 0 to past pictures, List 1 to future pictures) which contain up to 16 frames in total. Block prediction is done by a weighted sum of blocks from the reference picture. It allows enhanced picture quality in scenes where there are changes of plane, zoom, or when new objects are revealed.

Although the use of the term "frame" is common in informal usage, in many cases (such as in international standards for video coding by MPEG and VCEG) a more general concept is applied by using the word "picture" rather than "frame", where a picture can either be a complete frame or a single interlaced field. Video codecs such as MPEG 2, H.264 or Ogg Theora reduce the amount of data in a stream by following key frames with one or more inter frames. These frames can typically be encoded using a lower bit rate than is needed for key frames because much of the image is ordinarily similar, so only the changing parts need to be coded.