To compress your own legal backups, use the CHDMAN utility (part of the MAME project) on a Windows PC.
Originally popular for PSP emulation, it is supported by AetherSX2 but is considered "outdated" by some enthusiasts. While it saves significant space, it can occasionally lead to longer load times or performance hiccups because the emulator has to unpack data on the fly while the game is running. GZ (Gzip): Not Recommended. aethersx2 games highly compressed
Widely considered the "Gold Standard" for AetherSX2. It provides excellent lossless compression and is faster to load than other formats. To compress your own legal backups, use the