I have noticed that for the same video clip the number of frames in the clip varies by a factor of 2 between Sony Vegas Pro 10 and Avidemux.

Sony Vegas counts accurately at 29.97fps for the clip whereas Avidemux is double the Sony Vegas count. Is this a known artefact with Avidemux or can Sony Vegas be configured to report the same scale of counting as Avidemux?

When exchanging files and comments with a colleague who uses Avidemux it became apparent we were talking different frame counts and I would like to get them in synchrony if that is possible?

Any advice most appreciated