"The sewer camera showed what appeared to be cracks in several places in the upper side of the cast iron pipe. Also perhaps some roots intruding in places and some standing water in several sections."
I Hope that you kept a tape copy for a second and possibly third opinion...
If the camera operator knew exactly what he was looking at and determined that there are cracks/defects/roots in the piping and it is holding water, the only real fix would be to replace the line. Your septic system appears to operating normally.
A licensed plumber can perform a smoke test on the interior drainage/venting system to detect any defects.