What file format to select when recorfing from Theta to OBS Studio?

Is the video file in equirectangular or dual-fisheye? If you output from OBS, the metadata will be stripped out. You can output to equirectangular, then inject the metadata.

spatial-media/README.md at master · theta360developers/spatial-media · GitHub

You may need to set the projectiontype to equrectangular.

I did some experiments with long video below.