for a project I am working on I will need to automatically decide if a video is a VR (360) video, and if so what format it is. Is there any way to tell? I was thinking the metadata but could not find any information on this.
Checking size is pointless, most properly encoded movies are using standard sizes like 1080p (1920x1080), WQHD (2560×1440) or 4K (3840×2160) because of better hardware decoding. To do that they don't have square pixels. Therefore you shouldn't guess anything by ratio.
What you should do, is check the presence of zenith and nadir. That is check for the topmost and bottommost region of image if it is the same color (assuming the most standard equirectangular projection).
This approach will need some adjusting if you have stereoscopy involved. You would have to repeat this procedure for each eye region. As a bonus, you can also deduce some stereoscopy types - for example you could differentiate top-bottom, mono and left-right. Unfortunately you couldn't guess which image is for which eye, so you would have to assume the more common situation where the left eye is usually the top or left one in the image.