Equally impressive, VLC Media Player (for Windows, macOS, and Linux) can play a whole host of video formats, including MPEG-4, H.264, WMV, and MKV with no extra plug-ins. It can also convert a broad selection of different file types. Think of it as a Swiss Army knife for video conversions. With the program open on screen, choose Media, then Convert/Save. The application will ask you to pick a video file from the hard drive, and you can then choose the format you want to change it into. Rather than writing over the original file, VLC will create a separate copy of the newly-reformatted video. You can include subtitles and chapter markers in the conversion, and even convert batches of files at once.