Wrong size in 'extract an image from a film'

[OMT]

I try to work with a film 'week-end.wmv' made with some REIMS friends the 8 may 2009.

This film as a size of 61.1 Gb on my hard-disk ( exactely 64 094 169 bytes ).

When I use the fonction 'extract an image from a video', the dialog box tells me that the film's size is 1.40 Gb non compressed.