Often, a video taken with a mobile phone will be rotated in a different way than you expect. It may be taken vertically or upside-down. So you may want to correct that and get yourself a properly rotated video for viewing on computer.
All right, on Linux we use ffmpeg and there is no problem with it. The ffmpeg will happily rotate the video. What you do not expect is that the rotation information will remain in the media and then the player will try to rotate it again. What you get is a mess and you will be cursing away trying to understand why your video ends up upside down all the time although you enter the parameters to rotate it correctly.
So, the first thing you want to do is to remove the meta-information about rotation from the video. Like this:
ffmpeg -i 20160225_211430.mp4 -metadata:s:v rotate="0" -codec copy 20160225_211430_2.mp4
Once the meta-information is gone, we can check the actual rotation of the video stream and finally correct it with the ffmpeg:
ffmpeg -i 20160225_211430_2.mp4 -vf "transpose=1" 20160225_211430_3.mp4
Interestingly, the meta-information is used by some players and not used by others, so the results are unpredictable if you leave the video rotated. I prefer it to be “physically” rotated to the right direction and remove the original rotation angle – then you get reliable view on all devices. More or less :)