When I import a clip sometimes I'm offerd a choice to convert the file into a different format so that it will run on my system. Other clips wont allow it and I'm told that I need to activate a L code as it's on my external drive. Other times it just imports without giving me the option. Then I'm stuck with trying to edit an MPEG 4 file which really slows my computer up. I think it converts it into a MPG file.
(Movie Edit Pro15)