title: How to "merge" 2 VR180 video files to get a 360 video (2xVR180) output with ffmpeg?
body: <p>I'm wondering how to actually use ffmpeg to create a 2xVR180 video file from 2 different VR180 videos.
  That's to say, on the front side, a stereoscopic 3D video, and on the back side, another stereoscopic 3D video.</p>
  <p>Videos are taken with an Insta360 EVO in 3D mode, so I can either deal with 4 video files (2 INSV files for the left eye and other 2 INSV files for the right eye), o directly with the 2 stitched HEVC/MP4 files.</p>
  <p>I know the result won't be a 360 3D stereoscopic video, that's why I'm talking about &quot;2xVR180&quot;.</p>
  <p>Thank you for your help</p>