Hi nousome,
this could be done by setting in the "VI Properties"- dialog the options "Show Front Panel when called" & "Close afterwards..." in the section "window appearance". Then let the video play for 20 seconds, when the VI finishes it closes by itself. After this, all local variables (controls & indicators) which are not connected to the connector pane keep their state until you unload them from memory (close LabView). So you can store the current video position inside the VI and start the video at this point with the next VI- call.
Another good solution to save values inside a sub-VI between VI- calls is an uninitialized shift register. If you have difficulties implementing this lok at the example "Single Execution Uninitialized Shift Registers.vi". I found this in my LV 7.1 but older versions should have this example too.
Hope this helps,
Dave
Greets, Dave