FreeFileSync Forum

It is very rare that files that have been modified and thus require syncing have the same size (as their previously synced version).
So, according to your algorithm, files that requiring syncing are almost always copied normally.
Therefore there is only a marginal benefit to a block wise compare ...

Here is a python script example:
https://gist.github.com/tigrouind/46edacf9b53dd34af3b01f0a94120bd1

Possible optimization: when synchronizing a file, only the delta (what has been modified) could be written to the file (instead of a normal copy of the file).

This would be useful for synchronizing large files (several GB) where only a few MB have been modified. This is the case with VM disk images ...