Some way to monitor what parts of the filesystem are already cached in a mounted remote?

I have a Shared Google Drive containing a few TB of data, consisting mainly of very large ISO or video files, mounted via rclone / WinFSP.

I have a lossless rip of a dual-layer blu-ray film on the remote and I want to play it, but playing it directly will result in lots of stuttering as my downstream connection is less than the video's bitrate, so I would need to cache part or all of the file before playing it to get seamless playback.
But the rclone mount system is a bit of a black box in this respect. How do I know for certain what parts of a file are already cached?
It would be really nice to have a way of presenting this, either in the windows shell or in a separate GUI.

If you aren't using the cache backend, then the answer is probably none of the file is cached.

Are you using the cache backend?

How did you upload the file?

There is no interface at the moment to show which files are in the cache backend.

However you can look in the vfs cache quite easily using a file explorer. Find the directory to look in with rclone help flags cache-dir.