This project consists of two shell scrips.
One splits an adb backup into several ones by app name extracting the contents of the tars to a temporal folder and then re-taring everything to get the individual ab for each android app.
The other shell script uses Tar Binary Splitter to divide the main tar inside the adb backup without extracting anything from the tar, so is by far the best method.
Other software is needed. The bundle is included in Android Backup Extractor, with the full README...