How to make a reproducible iso file with mkisofs/genisoimage?

In an automated process an iso file is created with mkisofs. Even, as the original data is excactly the same, the resulting iso files are not the same (their md5sum changes). Since I rsync --checksum the result, I dislike that the "same iso" is of course retransferred every time. I expect mostly timestamps to be the main difference. Is there some libfaketime buildin switch to generate an iso via mkisofs that would indeed be the same. I do not know if only timestamps matter? I have compared the resulting iso files with their xxd isofile output like this: diff --side-by-side --suppress-common-lines <(xxd a.iso) <(xxd b.iso ) and there seem to be only 51 lines representing 16 Bytes (so roughly 800 Bytes of difference) in the else exact same file. The command used to generate this iso in question is roughly this: genisoimage -o "file.iso" -b isolinux/isolinux.bin \ -c isolinux/boot.cat -no-emul-boot \ -boot-load-size 4 -boot-info-table \ -J -R -v -T -V 'CDLABEL' "datadir/" BS: Am I missing a command line parameer switch with rsync that does checksumming for ~1MB chunks of big files, as to prevent the retransfer when as in my case only some 800 bytes differ?