However, it's not only the rotation that needs to be fixed, it's also the width and height of the video that needs to be adjusted as these can also be he wrong way round. It has 4 possible values (0, 90, 180 and 270) and it stores how the device was held when starting the recording:

In this article we'll focus on the rotation - it represents the orientation of the device. Videos and images created by mobile devices including iPhones and Android phones contain a lot of metadata like GPS position, device make and model, fps, rotation and many others. Video rotation is one tricky, but simple issue to overcome and in this guide we will show you how to fix rotated videos using FFMpeg. This might also happen if you start recording in one orientation and then rotate the smartphone before the device has a chance to update it's orientation settings. Depending on the software or app you're using to edit, preview or share, the videos might appear rotated or even upside down. Quite often, when using a smartphone, we shoot videos in portrait mode, also known as vertical video, or even rotated 180 degrees.

Ffmpeg android tutorial