Mp4 Tags have now stabilized, they seem to be more robust and at the same time are now compatible with iTunes (all the thanks goes to menno @audiocoding.com for his hard work). A Little bit of bad news - this new method of tagging is not compatible with the older method used for beta 3, beta 4 will not read beta 3 tags.
Download:
http://www.dbpoweramp.com/beta/dBpowerAMP-...codec-mp4b4.exe
1.16MB
after installing the above (it uses fastenc AAC encoder) if you want a slightly higher quality encoder, but slower encoder then install this mp4-aacenc codec over the top:
http://www.dbpoweramp.com/beta/dBpowerAMP-...acenc-alter.exe
327KB