The most common files we see are ".mp4", which you might see in export options as H.264/MPEG-4. That's the format for many digital video cameras, and it's generally an efficient format that results in smaller file sizes.
That said, we accept almost any format containing video or audio, including mp4, mov, avi, mkv, wmv, m4v, mp3, wav, and more. (If it's listed under "Supported codecs and formats" on this webpage we support it.)
Reduct does not support .exe files.
If you have a .exe file, you can double-click this file, and the video player that opens should have an option to export a video file (look for a format listed above). You can then upload this exported audio/video file to Reduct.
If you have a format that is not listed above, email firstname.lastname@example.org and we probably support it :)