Hi, I have a Canon Vixia HF20 and the file format it exports from the camera is an .mts file format. Importing into the timeline is no problem, but editing isn't so easy in this format, rendering takes over an hour for an hour long clip and outputing to a different format takes just as long. Any other methods I could try without dramatically losing video quality.
This looks as though it may be of help for you: Premiere Elements 7: problems playing mts format video
There are a lot more posts re .mts files.
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As Neale says, these are AVCHD file -- the most difficult files to edit. Most people who are successfully editing it have at least a quad core processor and 4 gigs of RAM on their computers.
Does your computer have these specs?
If so, ensure that you're using the AVCHD presets wheneve you start a project and render often (by pressing the Enter key on your keyboard).