You can convert media files from one format to another in the Miro interface.
Select the item you want to convert.
Right click on the item, choose Convert to, then pick a target.
The Conversions tab will show up in the sidebar. Clicking on the Conversions tab in the sidebar will bring up the Conversions view.
When the conversion is done, a new item will appear in your Video or Music tab with the same name as the item that you converted with the target tacked on to the end.
Files that are converted are stored in a Converted folder on your disk drive.
You can get to the Converted folder at any time by choosing Convert in the menu, then choosing Show Conversion Folder.
See Converting media files for help on trouble-shooting conversions.