Since the ffmpeg is a command line tool without gui, the batch script conversion uses the .bat file that can be found easily via google, e.g. here, here and here.
for %%a in ("*.mov") do (Here, for all matches of .mov file, the batch variable %%a (double percentage sign %% for batch, % for command line) is fed into ffmpeg. The encoder for video is assigned to be 264 -c:v libx264 with audio codec -b:a aac and audio bitrate -b:a 128k of 128K. The %%~na means "Expands %%a to a file name only", which is defined in the For loop tutorial of m$ command line.
ffmpeg -i "%%a" -c:v libx264 -c:a aac -b:a 128k "output\%%~na.mp4"