Exporting-saving video

When you try saving a project, usually it happens that it cannot be saved for an unknown motivation, maybe because starting quality is lower than final file choose. Anyway it wil be very very good to know which format file can be really saved, not to see a list and try and try until program accepts your correct format to be saved.
Another smart thing would be to know in advance the final file size, before to save project.
Program is good itself, but it misses some basic features that other smaller programs have built in