a p u2212 frame when the upper limit for the value of n is 99 it means that one i frame is coded after 99 p frames p frames or p u2212 frames are coded by always inserting one i frame in a certain number of coded frames the following benefits can be obtained a error accumulation due to a mismatch between encoder and decoder processing can be prevented for instance a mismatch in the computation of dct and b the processing load for acquiring the reproduced image of the target frame from the coded data random access is reduced the optimal n value varies when the encoder performance or the environment where the encoder is used are changed it does not mean therefore that the value of n must always be 100 the process for determining the rounding method and coding mode for each frame is performed in 805 and the flowchart with details of this operation is shown in fig9 first of all whether n is a zero 0 or not is checked in 901 if n is 0 then u2018 i u2019 is output as distinction information of the prediction mode to the output buffer in 902 this means that the image to be coded is will be coded as an i frame here u201c output to the output buffer u201d means that after being stored in the output buffer the information is output to an external device as a portion of the coded bit stream when n is not 0 then whether n is an odd or even number is identified in 904 when n is an odd number.