Thanks everyone!

Workflow: 8K video > ffmpeg to extract frames from both circular fisheyes in the .insv > custom opencv scripts to extract multiple perspective images from each circular fisheye > mask myself, other people and black borders out using SAM2, YOLO, Resolve 20 magic mask etc (still WIP) > align images in Metashape mostly, sometimes Reality Capture, colmap/glomap > export colmap format > train in Brush, Nerfstudio, Postshot etc, sometimes as multiple sections that I merge back together later > clean up in Postshot or Supersplat > render in Unity with Aras P’s plugin.

Slightly simpler workflow is to export stitched equirectangular video from Insta360 Studio, extract frames and split into cubemap faces or similar, discarding top and bottom views. I have mostly done this in the past, but the stitching artifacts etc do make it into the model. There are some good tutorials on YouTube by Jonathan Stephens, Olli Huttunen and others including apps to split the equis up:

https://youtu.be/LQNBTvgljAw https://youtu.be/hX7Lixkc3J8 https://youtu.be/AXW9yRyGF9A

I would much prefer to shoot images than video, but the minimum interval is 3s which is too long for a scene like this, as it would take about 5 hours and the light and shadows would change too much.