How to verify an ADB backup file is complete and in a good state?
If you're on Linux, Adebar contains a tiny little shell script to convert ADB Backups (.ab) to tar files, which you then easily can investigate with any archive manager. Only limitation is: it doesn't work on password protected backup files.

The basic command it runs (everything else mainly is a wrapper for command line options and syntax) is:

dd if=$1 bs=24 skip=1 | openssl zlib -d &gt;${1%%.ab}.tar &amp;&amp; gzip -9 ${1%%.ab}.tar


A command I've found here on SE some time in the past (full disclosure: I'm the author of Adebar) – see here.

As you can see in the quoted command, it requires openssl and zlib to be available.