If you downoload the templates for Communications Society Journals and open the README, you will find the following note
This package contains the IEEE Communications Society subset of the full
IEEEtran package and is intended for use with IEEE Communications Society
publications. The included version of the IEEEtran_HOWTO.pdf has been
specially formatted in IEEE Communications Society (comsoc) journal mode.
and the disclaimer
NOTE: Take care not to confuse the "comsoc" and "compsoc" class options/modes as they are very different:
comsoc ==> IEEE Communications Society
compsoc ==> IEEE Computer
The IEEE Transactions on Pattern Analysis and Machine Intelligence is not published by the IEEE Communications Society but by the IEEE Computer Society (compsoc). Thus, I think that for this you should use the templates for Computer Society Journals.
The IEEE Transactions on Multimedia seems to be published by both societies and by others too. The IEEE Transactions on Multimedia home page links at the information for authors page which further links to the author digital tools page, but saying (bold mine):
The style files are available on the web at the IEEE Author Digital
Toolbox (link is external) under "Template for all Transactions."
(LaTeX and MS Word).