If the same molecules (same region on sample) have been recorded over multiple movie files, you can merge them within iSMS.
Load the two files to be merged.
Select 'Edit->Merge timed movies of same molecules'.
In the dialog, select the first movie in the left listbox and the consecutive movie in the right listbox. Tick the checkbox if you don't need the two original files. Press OK.
The files have now been merged into one single file with the second movie being in continuation of the first.