@tokiwarthoot @eugene would know more why exactly it does not work that way.
Real benefit of fma-rep is that it works across whole data set but uses a lot less memory. For instance, if we quickly compress MS Office 2016 iso (conveniently picked to be around 2GB), we will see real benefit of fma-rep over lz coders with 64M dictionary:
Most of the difference is solely because of the fma-rep and some is due to lzmarec. So improvement in new fma-rep2 will not only help speed but also these kinds of backups.
Many popular formats (.jpg,.pdf,.docx) use outdated methods of data compression.
So it started making sense to remove that outdated compression and apply better one.
Then do it backwards to restore the file.
It usually only makes sense to do it losslessly, because it is impossible to automate otherwise -
some other file always can contain a hash of this one, or something.
And that’s what we call “recompression”, while lossy transformation would be called “re-encoding”.