When I download one of Miro's video fles in what directory is that video file saved to?
In the menu bar choose video > options and then click to folders. With "store downloaded videos in this folder" you can change the default setting to a folder you like. But if you've already downloaded videos with the default settings and move the folder to another place I don't know if miro will switch to the new folder for these videos. Before changing the folder please wait until somebody on windows answers this question or backup your database. On linux I've moved the standard folder and and set a link, but I'm not sure if this works on windows.
If you're using Windows like I am, the options dialogue box is now under the "File" menu - select "Options", then the "Folders" tab. Under "Store downloads in this folder", press the "Change" button and select the folder you want. I'm pretty sure that videos you have already downloaded are migrated, but you would be well advised to make a backup of the old folder first.