rsinc must wait for a LONG time for rclone to hash large (severl GB) files

[ConorWilliams]

Rsinc requires an 'ID' for each file which is currently a concatenation of a files hash and its size. This must be unique for each file and independant of its name/path to allow file moves/renames to be tracked. Unfortuntly computing this hash for large files (e.g films) seems to take a huge amount of time (up to minutes per file). I welcome any suggestions to fix this problem. Ideally some way to cache the hashes and only recompute them if the file is modified?