Encoder and method of encoding a sequence of frames

An encoder adapted to encode a sequence of frames;

• the encoder being configured to carry out the operations of:
• applying a decorrelating transform to respective frames in the sequence so as to obtain respective transformed frames having an entropy that is lower than that of the respective frames in the sequence, and
• data compressing the respective transformed frames so as to obtain respective encoded frames comprising an amount of data that is less than that of the respective transformed frames,
• wherein for each frame in at least a part of the sequence, at least one portion of the frame is encoded in an inter mode and at least one other portion of the frame is encoded in an intra mode,
• whereby, in the inter mode, a differential representation of a portion of the frame is provided, the differential representation corresponding with a difference between, on the one hand, the portion of the frame and, on the other hand, a representation of a corresponding portion of at least one other frame, the encoding being applied to the differential representation of the portion of the frame,
• whereby, in the intra mode, the encoding is directly applied to a portion of the frame, wherein the encoder is configured to frequently forcibly encode respective frame portions in the respective frames in the intra mode in a dispersed manner making that while a frame portion in one of the respective frames is forcibly encoded in the intra mode, at least one other frame portion is not forcibly encoded in the intra mode in that frame but in another one of the respective frames.