When I try to burn my movies to disc, I usually get a box that asks me 'should the existing file be used for the film'.  Also whether to 'encode' 'encode all' 'use' or 'use all', and whether to rewrite chapter and menu information.  What does all this mean?  What should I click?  I usually click on 'use all' but have juse noticed that my last film has not burnt what it should have burn onto the disc.  Can anyone explain what these options all mean so that I can make the right choices and not end up throwing away so many dvd's that either burn the wrong thing, or fail midway through the burn??!!

Thanks in advance