Since Windows does not natively support 7z files in older versions, using the official 7-Zip software is the most reliable way to extract them. : Download and install the 64-bit version of 7-Zip.
: If the file was part of a larger download (like "10.mp4.001", "10.mp4.002"), you must have all parts in the same folder before you can successfully extract the final video. 10.mp4.7z
: Hover over the 7-Zip menu and select Extract Here or Extract to "10.mp4/" . Since Windows does not natively support 7z files