Inverse Discrete Cosinus Transform IDCT is a classical mathematical algorithm to convert from a space domain to a frequency domain. In a nutshell, it codes differences instead of coding all absolute pixels. MPEG uses an 2-D IDCT in the video decoder, and a 1-D IDCT in the audio decoder.

a part of the MPEG decoding process that takes significant amount of time in the decoding process

Inverse Discrete Cosine Transform