Were you doing any video uploading and downloading from youtube in the past? Youtube will convert your uploaded videos of other formats to flv for display on their site and give you and option to download an MP4 for your own keeping if you wish.
https://en.wikipedia.org/wiki/FFmpeg
This morning I found the following had printed out during the night. @echo off
echo=============================
echo Flv to Mp4 batch script using ffmpeg v1.0
echo=============================
echo.
set /p SourceDir= "Enter the source directory -> "
echo Ok, SOURCE set as %SourceDir%
set /p TargetDir= "And now the target directory ->
echo TARGET set as %TargetDir%
echo.
echo Press any key to start the batch process
pause>nul
cd /d %SourceDir%
for i in *.flv; do ffmpeg -i "$i" -qscale 0 basename "$i" .avi .mov ; done

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