Can't Get Playable Video From Images in FFMPEG for Oculus Go
Thanks to u/jesus_is_imba on Reddit for the following answer:

ffmpeg -r 24 -i my_images_%04d.png -c:v libx264 -crf 18 -preset slow -g 48 -pix_fmt yuv420p -movflags +faststart output.mp4



  The -g argument defines keyframe interval in frames and according to Oculus should be 2 seconds, ie. 2x your frame rate.


This command produces video that plays back perfectly both in VLC and in Oculus Gallery.