Few days ago I had to rotate more then 200 videos taken on tablet. I was really surprised that there were not default easy to use tool (option) incorporated in windows explorer. So I googled and found many solutions but all required manual process for each file. Then I switched to Linux Mint (Ubuntu) and found avconv (or ffpmeg) command line tool ideal for my job. Now problem was to create script which will start avconv for each video file. This can be easily as simple bash script but I also found Winff GUI frontend for ffmpeg (avconv) so I decided to go with it (you have it in Mint Software manager).

First test failed because my Mint installation did not had all needed codecs. So I have installed libavcodec-extra package. After that all worked well.

I did not test windows version.