Canon VIXIA HF M30 Quick Manual page 376

Select the folders to export.
Video files are exported by date folders. Date folders are created when
importing video files from the camcorder.

Video file export screen: P.40
Thumbnails are displayed only when the thumbnail file exists in the folder.
*
The thumbnail file is created from the first video file in the folder.
Even if you delete the first video file in the folder, the thumbnail file will
*
remain as the thumbnail of the folder. If there are multiple folders with
the same date, the thumbnail of the folder which was imported to the
computer first will be displayed.
If you imported several batches of video files with the same date, a suffix
*
such as "_1" and "_2" is added to the end of folder name.
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