Portrait to Landscape Video file conversion

[efiste2]

Not sure how this happened but a video taken on my phone has turned out in "portrait" mode, what software will allow me to convert it to landscape mode....Im puzzled as to how I have managed it, as i was holding the phone the correct way

[LigH.de]

Do you mean, turn by 90 degrees (counter-) clockwise?

The MP4 container may have orientation tags. Not all players will respect them, though. Recoding is safer but will reduce the quality.

[efiste2]

So how do I go about rotating it, thanks for your advice

[davejavu]

When you say it is in portrait mode do you mean that the video is taller than it is wide but with everything the right way up, or is it just being displayed with the short edge of the video at the top of the screen and the image going side to side?

If it really is in portrait mode, tall and narrow but everything the right way up, you can't just rotate it as everything will just get turned sideways and, as the image on each side of what you have is missing, recoding it to a landscape orientation will either involve stretching it and making everything squashed vertically or cropping and ending up with a tiny part of the image.

[raffriff42]

The MP4 container may have orientation tags. Not all players will respect them, though.

Sounds plausible. Yes, Google confirms it:
https://www.google.com/search?q=mp4+metadata+orientation

Which leads to:
https://forum.videohelp.com/threads/367508-MP4-orientation-issues

Which suggests:

ffmpeg -i input.mp4 -c copy -metadata:s:v:0 rotate=0 output.mp4