Read data for molecule_number from filename of type file_type, beginning with frame nb, ending with frame ne, with a stride of ns. Return the number of frames read from this file; if the file contains more than this number, the remaining frames will be loaded during subsequent VMD display updates. By default, one frame will be loaded before the command returns. The waitfor option allows you to specify how many frames to load before returning. The waitfor parameter nw can be any integer, or all; choosing nw less than zero is the same as choosing all. If frames from other files are still being loaded when the animate command is issued, these frames will be loaded first.