Audio Sync Issues When Creating Video

Hi,

I'm a percussionist and occasionally have to film my self playing drums and other percussion instruments for auditions and other reasons. I record with a Canon Vixia HFR20 and then import the videos to a Mac computer. Once on the PC I then convert the video files to MPG so that I can import the video to iMovie. Once I import the video to iMovie I edit the film and then export it has an .mp4. Here everything is great. However, once I put the video on a computer running Microsoft, there is immediately audio sync issues. If I do all the editing on the computer running Microsoft then I still end up with the audio sync issues.

Why is this happening and how can I fix it?

Thanks

Edit: The audio seems to get a little more out of sync as the video plays on.