1. A method of classifying a current coding frame in a sequence of audio data frames in real-time for switching a multi-mode audio coding system operated in a current coding mode between different modes, the method comprising: recording the sequence of audio data frames; extracting at least one long-term feature and at least one short-term feature relative to each audio data frame, wherein the features substantially exhibit distinct values for different signal types; detecting a potential switch point according to the at least one short-term feature of the current frame and the current coding mode; and determining whether to switch the current coding mode of the coding system at the potential switch point based on the at least one long-term feature.