Inter frame

This kind of prediction tries to take advantage from temporal redundancy between neighboring frames enabling higher compression rates.

The following image shows the whole process graphically: This kind of prediction has some pros and cons: Because of these drawbacks, a reliable and time periodic reference frame must be used for this technique to be efficient and useful.

That reference frame is known as Intra-frame, which is strictly intra coded, so it can always be decoded without additional information.

The I-frame doesn't need additional information to be decoded and it can be used as a reliable reference.

This structure also allows to achieve an I-frame periodicity, which is needed for decoder synchronization.

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.

The scheme is shown in the next picture: This structure suggests a problem because the fourth frame (a P-frame) is needed in order to predict the second and the third (B-frames).

The frame to be coded is divided into blocks of equal size as shown in the picture above.

It allows enhanced picture quality in scenes where there are changes of plane, zoom, or when new objects are revealed.

These modes are referred to when a block is coded without sending residual error or motion vectors.