Abstract: The present invention discloses a media file on-demand method, comprising: the server, upon receiving the media on-demand request from the client, provides the index information in the self-defining media file to the client; the server, upon receiving the playing progress request from said client, according to the requested time in the playing progress request, searches for the starting offset position of the media data corresponding to the requested time in the index information; the server, according to the starting offset position of the media data, reads out the media data corresponding to the requested time in the self-defining media file, and provides the media data to the client.