An SFV file is a file, video or data "checksum." It confirms the data that a file contains, allowing you to ascertain whether that file is complete. Many ripped videos come with SFVs for verification purposes. An SRT is a subtitle file that also is often included with videos, but contains different contents. If you need to convert a mistakenly-labelled SFV into an SRT file that video players can read, you can do so with Windows. Because at their core both files are plain text files, the process is simple.
Right-click the SFV file to convert.
Select "Notepad" from the "Open With" menu. This will open the text in a Notepad document. Because it is meant to be read by decoding programs, it will probably look meaningless to you.
Select "Save As" from the file menu.
Select "All extensions" from the "Format" menu.
Type a file name followed by ".srt" (no quotes) and hit "Save." Now the subtitle file will be able to be read as an SRT file by video programs.