TagRename

@echo off

rem #This stores your input to variable "tag". You must also enter the underscore
set /p tag="Enter tag: "

rem #If you want to rename files with more different file extensions, just add them after "*.mp4"
rem #For example (*.avi *.mp4 *.flv *.webm)
for %%a in (*.avi *.mp4) do ren "%%~a" "%tag%%%~na%%~xa"

rem #This batch file must be in same folder with the files you want to rename
rem #You can remove these lines beginning with "rem"