This article explains the two most common formats of an XV file. It also explains how to open both formats and what options you have for converting an XV file.
How to open a djvu file on Windows
A file with the file extension XV is most likely a Khoros Visualization Image, also known as Khoros VIFF (Visualization Image File Format).
Other XV files are used as a container format by the Xunlei (also called Thunder) download manager software to store video content. These files are generally protected in such a way that you cannot open or convert them with a computer other than the one they were created on.
Khoros visualization images can be opened with the free XnView program. It was originally used by the Khoros software suite, but we can't find a download link.