18. The method according to claim 17 , wherein in the step D, the constructing an SMIL file according to all the non-SMIL files obtained in step A is carried out in the following way: D1: determining a construction principle of an SMIL file, wherein the construction principle comprises: only one file of one file format can exist in a frame; a video file or an attachment file can only coexist with a text file in a frame; D2: constructing an SMIL file describing a playing layout of all the non-SMIL files according to the construction principle.
25. The method according to claim 18 , wherein the data structure describing a playing layout of MMS is a slide sequence structure.