A prediction method, apparatus, and medium including computer readable code, for calculating an average of intra-prediction costs or an average of inter-prediction costs of macroblocks of a received picture by encoding the received picture using an intra-prediction and/or inter-prediction in consideration of a type of the received picture, calculating a threshold value using the calculated average of intra-predication costs and/or inter-predication costs, and determining whether to perform intra-prediction on a subsequent picture based on the calculated threshold value. Accordingly, it is possible to considerably reduce the amount of computation that conventionally was required to encode a picture, without any deterioration in the encoding performance, by considerably reducing the number of macroblocks that need to undergo intra-prediction.