@echo off
set a=1
setlocal EnableDelayedExpansion
FOR /F "delims=\" %%i IN ('dir /b *.mp3') DO (
    ren "%%i" "!a!.tmp"
    ffmpeg -i "!a!.tmp" -vn -codec copy "!a!.m4a"
    ren "!a!.m4a" "%%i.m4a"
    ren "!a!.tmp" "%%i"
:    else ( echo "ha" >> tmp.txt )
    set /A a+=1
    echo !a!
)
del *.mp3 /s /a
call remove.bat